04-25-2006, 07:45 PM
Leyendo diferentes foros, me encontre este tema sobre la configuracion:
Subwoofer Setup Guide by Bossobass
NOTE! For easier reading, right-click the attachment and choose 'save as' to save this guide as a pdf to your computer. Change the file extention to pdf to make it readable.
A very special thanks to Dave ' Bossobass' for writing this guide!
The following has been a labor of love for me. Love of the subject (low frequency
reproduction in multi-channel audio systems in the home), and love for Mark
Schifter, his vision and watching him realize that vision from the sidelines (though anyone who meets him never feels like a mere spectator).
I've also done this because I promised I would.
Please go easy on me, as I'm not an educated person, and I'm sure I've left out
plenty. I only hope that someone who is in the shoes we all have to walk a mile in
when we're first introduced to this digital, multi-channel octopus, will benefit in
any small way by the information below.
I also would like to disclaim the facts that some of what I say is biased toward my
own thoughts and some of what I say is downright controversial.
I would like for those who read this rudimentary guide to add input, discoveries
and tweaks as they are appropriate, as well as adding to the TERMS section as
people ask about ones that aren't included. I omitted many terms for this reason.
I also have not included pictures or diagrams...maybe the graphics guys can add
that input.
Good Listening, and, by all means...Listen Accurately!
Subwoofer Setup Tips And Procedures
Tools:
1. RS SPL Meter.
2. 1/12 Octave Sine Wave Test Tone CD.
3. Tape Measure.
4. Frequency Response Graphing Software (optional).
5. A Tripod For Mounting Your RS Meter.
NOTE: All of the following information will assume that a Pre/Pro or Receiver is
being used to provide Bass Management with all satellites set to 'Small' and
subwoofer to 'Yes', using a crossover point of 80 Hz. It also assumes that your
subwoofer(s) is / are connected properly to your Pre/Pro or Receiver and your
house electrical system in strict accordance with the Owner's Manual that came
with your subwoofer. Finally, it is assumed that all 5 satellite speakers are
calibrated from the listening position to a reference level.
Terms:
1. LFE: Low Frequency Effects, AKA: Low Frequency Enhancement, AKA: The .1
channel.
2. Redirected Bass: This is all information contained in all 5 satellite channels that
is below 80 Hz., which is redirected to the SW (subwoofer) output of the Pre/Pro
or Receiver.
3. SW Output: This is the output of the Pre/Pro or Receiver that sends a
combined, single signal comprised of the LFE channel and the Redirected Bass
from all 5 satellites (or, any satellite that's set to 'small' in the speaker setup
menu) to the subwoofer(s).
4. SPL: Sound Pressure Level. This is the unit of measurement used to calibrate
the channel levels of all of the 5.1 channels. SPL is measured in Decibels, which is
abbreviated as dB.
5. Subsonic: This is the description used for any sound that is below the
threshold of human hearing, or below approximately 20 Hz.
6. Tight, fast, articulate, etc.: These are adjectives that describe a subwoofer
that is capable of delivering low frequencies on-time with the rest of the system,
without any peaks in response.
7. Boomy, muddy, slow, etc.: These adjectives describe a subwoofer that lacks
the capabilities of the subwoofer described in item #6, and/or is misplaced or
badly calibrated, resulting in peaky response.
8. Polarity: Better described as Absolute Phase. Usually, this adjustment is made
by comparing 0 degrees to 180 degrees. If 2 speakers are 180 degrees 'out of
phase', then there will be gross cancellation of sound waves in the region of
audio information that the 2 speakers share the reproduction of. In the case of
satellites and a subwoofer, this will be at and around the crossover point.
9. Relative Phase: Phase is time. It's measured in degrees. If you can visualize a
sound wave that curves upward to it's peak and then downward to it's bottom,
that is one cycle of the wave. Since degrees of angle are not curved, there are
infinite degrees along this wave.
As the frequency is lowered, the phase changes. Some subwoofer designs
change more drastically than others. Distance disparity between speakers and
subwoofer also changes the time that it takes for the shared audio information to
reach your ear.
Because these situations result in infinite phase differences between speakers
and subwoofer, there is no perfect phase setting that works for all frequencies
through the crossover region. This is why it's important to keep distance to the
listening position and infinite phase control in mind when setting up any
subwoofer.
10. Crossover Region: A typical multi-channel audio controller has crossover
options that are based on a Linkwitz/Riley 24 dB per octave network. This means
that the subwoofer is stopped from playing above the crossover point and the
satellite is stopped from playing below the crossover point.
This stoppage of the speaker's natural response is not a brick wall. It is a gradual
braking from the crossover point and then beyond that at a rate of 24 dB per
octave.
The idea is that across 2 octaves (from the crossover point to one octave below
that point the satellite has a brake applied that ends up being 24 dB lower, and
from the crossover point to one octave above that point the subwoofer has a
brake applied that ends up being 24 dB lower, a total region of 2 octaves), the
sum of the 2 signals at any point in the crossover region should sum to unity, or,
in other words, result in a frequency response curve that is a flat line.
This 2 octave area of overlap between the satellites and the subwoofer is the
crossover region.
Overview:
The goal in adding a subwoofer to any multi-channel audio system is to achieve
as flat a frequency response curve as possible, in your particular room, with your
particular system, through the crossover region and to as low as your subwoofer
will allow. This is not to say that there is no room for adjustment from this point to
allow for personal taste. Rather, it is the place to start.
The steps, in order, are:
1. Polarity Test. You never want to lug the subwoofer around the room looking
for the spot where it will sound best if the polarity is reversed.
2. First Volume Calibration. During the placement exercise (pun intended) you'll
listen for bass notes of a music program that are of the same volume (no boomy
notes or weak notes) and, if the subwoofer isn't at least closely calibrated to
begin with, that will occur at any spot the subwoofer is placed.
3. Placement. As in real estate, location, location, location.
4. Relative Phase Adjustment. One of the more important tweaks to smooth out
the frequency response.
5. Final Volume Level Adjustment. After tweaking all of the above, a final
subwoofer volume level tweak will get you there.
NOTE: I've left out the step of tweaking the crossover slopes of the satellites and
the subwoofer. Although it's a very important tweak, it's beyond the capability of
the vast majority of multi-channel systems, and is a rather involved discussion for
a more advanced setup guide than this one is intended to be.
Calibration discs (Avia, Video Essentials, etc.): I have little experience with
these setup discs so I can't offer an opinion as to which is preferred, or why. I
have Chesky's setup disc and, actually, found it annoying. If you have or have
interest in any of these setup discs, search the forum and pose the questions you
may have. I'm sure you'll get the answers you're looking for and end up with an
acceptable method for level calibration.
I use the calibration tones in my Pre/Pro in conjunction with the RS SPL meter
(digital version) set up on a tripod at the listening position, at ear height (when
seated). I have found this method of level calibration to be very acceptable.
I've recently found an easy way to verify this method, and it's described as an
option to try under LEVEL ADJUSTMENT, below.
STEP #1:
POLARITY TEST: Set your subwoofer near either the front left or the front right
satellite.
Set your RS meter at the listening position, ear high, when seated.
Set the Phase Control of your sub to 0 degrees.
Reduce the master volume on your Pre/Pro or Receiver to approximately -10 dB.
Play an 80 Hz test tone, using your test tone CD, with the FL, FR and subwoofer
on.
Note the SPL reading.
Switch the Phase Control to 180 degrees and repeat the process.
Use the Phase Setting that yielded the highest output.
STEP #2:
FIRST LEVEL ADJUSTMENT: Set the subwoofer level in your Pre/Pro or Receiver's
channel calibration menu to -5 from 0 (reference).
Set the subwoofer(s) amplifier gain control to approximately one o'clock.
Use the Pre/Pro or Receiver calibration menu to calibrate the subwoofer level and
use the subwoofer amplifier gain control (add gain or reduce gain at the
subwoofer amplifier) to arrive at a reading on the RS meter that's the same as the
level you use to calibrate the mains.
The reason for the -5 preamp setting is to assure that the preamp doesn't send a
clipped signal the the subwoofer amplifier.
In the final subwoofer level tweaks, the preamp subwoofer channel trim can be
adjusted via the remote control.
STEP #3:
PLACEMENT: The goal here is to find the placement spot that offers the
smoothest frequency response (not necessarily the loudest) in your room.
NOTE: Placement also includes the placement of you yourself, in the room.
Avoid a primary listening position that is in the center of the room and that
is up against any wall in the room.
The conventional wisdom appears to be that the corner is the best place to start.
This is because the corner of most any room will boost low frequency output,
more as the frequency gets lower. It's also said to excite the highest number of
room modes, resulting in the smoothest overall response. I've often read the
recommendation of corner placement, then parametric EQ to flatten out peaks in
response.
I have experienced the highest output from corner loading a subwoofer, but have
personally rarely experienced the smoothest overall response with a subwoofer
placed in a corner.
I personally have found that if I hug a wall and slide the subwoofer away from the
corner (For example, assuming the sub is in the front right corner, either hug the
front wall and slide the sub toward the the left wall, or hug the right wall and
slide the sub toward the rear wall), anywhere from 2' to 4' feet out, it yields a
flatter response. You can also move the sub toward the middle of the room, away
from the wall, after you've slid it away from a corner. This will also get the
subwoofer closer to the mains in distance to the listening position, as the corner
is the farthest distance from the listening position in most rooms and cases.
The closer a subwoofer is to the distance of your mains from the listening
position, the more in phase it will be. In other words, the direct radiated sound
from both will arrive at your ears closer to the same time, which yields a less time
smeared, tighter sound.
This is the part of the setup of a subwoofer that requires the most time and
effort. You should use a source disc that has a wide range of bass lines in the
music. I use jazz that contains vocals and an upright bass (I always loved how
those guys run the neck in walking bass lines). This will give an idea how the
subwoofer is doing, overall, in any given position in the room, as opposed to a
source that drones on using only 2 or 3 notes in the bass line.
The point is that there is variety of bass notes, all the way up to the lower vocal
range. Pick a passage that seems to represent this description and loop it so it
repeats as you try different locations and fine tune a particular location.
Listen for notes that jump out (are too loud in relation to the rest of the notes) or
are too quiet and move the sub in small increments (6"-12" for the rough
placement and 1"-2" at a time to fine tune the placement) until the bass sounds
most even from note to note.
When you feel you've reached the best spot of those that are acceptable as a
final resting place for your subwoofer, then it's time to chart the response.
With your meter at the listening position and only the subwoofer playing, play the
test tone disc and record the results. Apply the correction numbers that are
available to correct the inaccuracies of the RS meter at lower frequencies and
graph the results (There are links to software that will automatically apply the
correction factors and plot your graph. A search or request for a link in the forum
will yield results, I'm sure).
You can tweak the placement from there and see if you can improve your
response graph before moving on to the next step.
NOTE: Use caution when playing sine wave test tones through your
subwoofer. They can damage your subwoofer by overheating the driver's
voice coil if the volume is too high. Set the master volume to yield average
readings of around 80 dB at 40 Hz for the sweep. If you start at 10 Hz (well
below human hearing and the capability of most subwoofers) you may feel
the need to raise the master volume, so start by playing a 40 Hz tone and
adjust the master volume to 80 dB, then proceed with the entire sweep. Set
the meter at the listening position and set it to 'C' weight and 'slow'. Start
the meter's range at it's lowest setting at the beginning of the sweep and
notch the range up as the frequency of the tones rises (the volume of the
tones will increase as the frequencies rise to the frequency range of the
capability of the subwoofer).
STEP #4:
LEVEL ADJUSTMENT: Use the calibration menu in the Pre/Pro or receiver setup
menu and use the on board calibration tones of your preamp to adjust the
subwoofer level (or a setup disc, if you prefer) and remember to set the master
volume to '0' before you begin this step.
Many people like to 'run the subwoofer hot', that is, louder than it should be. This
is a personal preference, but not an option at this point in setup. You're looking
for the reference setup for your subwoofer. You can always change the level later,
but you'll have the reference settings to fall back on if you aim for the flattest inroom
response during setup.
The goal here is to level the volume of the subwoofer to the satellites to as close
a degree as possible, given your limited measurement tool (sorry, Tandy).
Most people whose opinions I respect believe that the RS meter is approximately,
on average, 2 dB off when using the rumble tone pink noise calibration tone. This
would mean that if, for example, your satellites are calibrated using 75 dB as the
reference volume with the tones you're using to calibrate, you would calibrate
your subwoofer level to read 73 dB.
I tend to agree with this assessment as the proper method at this point in the
setup procedure.
STEP #5:
RELATIVE PHASE ADJUSTMENT: Since the polarity is already properly set from
step #1, it's time to fine-tune the relative phase between the satellites and
subwoofer.
We will assume that the phase control is set at 0 degrees for this description.
If it's set at 180 degrees, just work backward from 180 toward 0 instead of
from 0 toward 180. Also, remember to turn that master volume down to the
same, lower level that you used to make your frequency response graph in
step #3.
With the phase control set at 0 degrees, the satellites and subwoofer all on and
using the final frequency response graph from step #3 as a starting point,
advance the phase control knob to approximately 20 degrees above 0 degrees (0
+ 20 degrees) and run another sweep and chart the graph.
Advance the phase control another 20 degrees (0 + 40 degrees) and run another
sweep and chart the graph.
Advance the phase control another 20 degrees (0 + 60 degrees) and run yet
another sweep and chart the graph.
Use a different color for each graph and notate what setting of phase was used
for each color.
You now have frequency response graphs for 0 degrees, 0 + 20 degrees, 0 + 40
degrees and 0 + 60 degrees.
Look carefully at each graph to determine which graph has the overall flattest
line, using the (+/-) from the flat line method.
That would be where to set the phase control and leave it. Only if the 0 + 60
degrees setting is the best graph should you continue to run further sweeps (0 +
80 degrees, etc.) to make sure the next higher phase setting is not better than
what you have to this point.
STEP #6:
FINAL LEVEL ADJUSTMENT: One last time, adjust the subwoofer level to the
mains exactly as described in step #4 above. Now, use your Pre/Pro or Receiver
pink noise level calibration tones or one of the calibration discs, if that's what you
use, to lastly check the levels of all speakers and subwoofer.
There have been many comments about how the RS meter is not accurate in the
low frequency region, and is also said to differ from meter to meter.
Here is a possible method, using the RS meter, to adjust the subwoofer level to
that of the satellites.
Again, we're assuming that you have already calibrated your satellites to
the same level before this point in time, and we've done steps 1-5 of the
subwoofer setup.
Set your Pre/Pro or Receiver mode to 5 STEREO and shut your subwoofer off.
Set your master volume to approximately -10 dB from reference, or, so that a test
tone (from your test tone disc) will read in the neighborhood of 80-90 dB.
Play an 80 Hz tone from your test tone disc (it should play through all 5 satellites
equally).
Note the reading.
Now, shut your satellites off and turn the subwoofer on and play the same tone
through your sub only.
Adjust the subwoofer level to the same reading that you got when playing just
the satellites.
A crossover only works correctly if the speakers being crossed over together play
exactly the same volume at the crossover point. In adjusting the subwoofer level
with this method, the accuracy of the RS meter becomes irrelevant because the
only thing that matters is that the subwoofer and the mains are at the same level
at 80 Hz (the crossover point).
The meter will read the same at 80 Hz every time. Whether or not it's an accurate
reading, it will level the sub to the mains at the crossover point by this method,
accurately. Since the satellites are already calibrated, the subwoofer will
automatically be exactly at that level at 80 Hz.
I have personally done this test many times and found the subwoofer level to be
within 1 dB of 75 dB (which is the level I calibrate to when using the Pre/Pro
calibration tones), and you can quickly check this method against your calibration
rumble tone method to see if it's of any value in your case. My opinion is that, if
this method is close the the rumble calibration tone, then keep the subwoofer
volume set to the level arrived at by the 80 Hz test tone method.
You can adjust the level of your subwoofer up or down for different source
playback, at will. There is no rule that dictates what level you have to play a
subwoofer at. BUT, you now have the correct settings that will tell you where your
subwoofer should be, in your room, with your associated hardware, as a
reference.
It's a good idea to write these settings down (Pre/Pro or Receiver sub level,
phase, placement position and subwoofer amplifier gain), as you'll forget them
shortly after you change any of them, and it's a good idea to reset them to these
reference settings every so often to see what havoc you may have wrought over
time.
You are now ready to play your system and evaluate the results of your setup
labors.
PARAMETRIC EQ: It is currently popular to use this tool to flatten peaks in
subwoofer response that are caused by the room's interaction with bass sound
waves. I am not a fan of this idea (nor have I ever been). I believe time will tell
the correct story on this as more people discover the problems associated with
this method through experimentation and documentation.
I do believe, however, that parametric EQ can enhance the listening experience
when used as a tool to create a frequency response that would otherwise be
beyond the ability of the subwoofer alone. This is a personal choice that you can
decide upon, if you have such a device.
Mine is a season-to-taste approach. It's not to correct a mistake in the room's
interaction with a subwoofer. It's a way to boost certain frequencies during
certain source material playback, or cut certain frequencies or change the overall
damping of your subwoofer in a way that pleases your ears with a given source in
your own room.
There are 3 basic controls in a parametric EQ circuit that change the input signal,
which, in turn, changes what the subwoofer amplifies and sends to your ears.
First, is the frequency selection control. Use this control to center the EQ's effect
at a particular frequency. You can start with 40 Hz and adjust the controls
mentioned next to get an idea of what the EQ does to the signal that's feeding
your subwoofer.
Second, is the bandwidth control, which is just what it's name implies. It controls
the width of the band of frequencies around the frequency that you centered on
with the first control. Dial it to a medium width to follow the suggestion given
above to hear the effect.
Third, is the boost/cut control. Again, it is what it's name implies. It controls the
signal strength or weakness specifically at the frequency you've selected across
the bandwidth you dialed in above and below the center frequency. Try boosting
to 4 dB, and listen to the effect.
REMEMBER: A general (and good) rule of thumb is to never add boost or cut more
than 6 dB with any parametric EQ. Also, remember to play a source that you know
contains information at the frequency band you are trying to affect with the EQ
(otherwise, you'll hear little to no effect).
Play with the EQ controls a bit from there in the way of experimentation until you
get the hang of it's effect. Like anything else that's new to you, it takes time until
you catch on...and you definitely will.
With most on board parametric EQ, simply dialing the boost/cut control to '0' will
disable it. No need to worry what the other 2 controls are set to.
DUAL SUBWOOFERS, MONO CONFIGURATION: Now it gets interesting. Dual
subwoofers affords several options that a single subwoofer can't. Let's explore
them...
NOTE: A quick word about bass in multi-channel audio systems, in general.
When your satellites are set to 'small' and subwoofer to 'yes', the Pre/Pro or
Receiver sums the LFE channel with the redirected bass from the satellites that
are set to 'small' and sends that single, summed bass signal to the subwoofer(s)
through the SW (subwoofer) output.
I personally think that this is a flawed scheme, and will expound later. You can
'trick' your system into other schemes...I'll explain that also, later...
First, is the school of thought that if you place the second subwoofer directly next
to, or on top of the first subwoofer, you'll increase the overall output by up to 6
dB vs. one subwoofer (assuming the subwoofers are exactly the same model).
This is true. It's a viable option, and an easy one to do. Simply head off the cable
to your first subwoofer with a 'Y' jack (1 male plug to 2 female jacks) by inserting
the male end into your subwoofer output, plugging the first subwoofer's cable
into 1 female end and inserting another cable into the second female end that
you'll run to the second subwoofer.
There's not much to say about this scheme, other than to make sure the phase
control is set properly and the level of gain is also set properly.
To adjust the phase, simply follow the same routine as outlined for phase
adjustment of a single subwoofer. The only difference is that you should do 1
subwoofer while the second subwoofer is off, then turn on the second subwoofer
(with all other speakers and the first subwoofer on) and adjust the phase of the
second subwoofer. The phase adjustment of the second subwoofer can be done
by playing an 80 Hz sine wave test tone and dialing the second subwoofer's
phase control until you achieve the highest reading.
Adjust the gain by notching the gain of the first subwoofer down a notch or two
and matching that setting on the second subwoofer. Then, use the calibration
method you are used to using to bring the dual subwoofers to the proper level,
using the Pre/Pro or Receiver subwoofer trim in the calibration menu.
Asymmetric Placement Of Dual Subwoofers:
Asymmetric...Not symmetric: This is another school of thought for placement of
dual subwoofers.
Picture the front wall of your multi-channel audio/visual room. Imagine that your
subwoofer is placed in the front right corner. Slide it out along the right wall
approximately 2 feet. Place the second sub against the front wall, 4 feet from the
right corner. That would be an asymmetric placement.
Or, place the second sub in the left front corner, then slide it toward the right
wall, away from the corner, 2 feet (the first subwoofer is still on the right wall, 2
feet away from the right front corner). That's another example of asymmetric
placement.
This configuration of 2 subwoofers will allow you to achieve a smoother, more
time coherent response if the same placement, phase and level tweaks as
outlined for a single subwoofer are followed.
You'll lose 3 dB or so of output vs stacked subwoofers, and possibly more overall
output vs. a corner placement as the sacrifice for better sounding bass, in my
definite opinion.
NOTE: In my opinion, whenever 2 or more subwoofers are used, regardless of
placement configuration, they should ALWAYS be placed with every effort to
achieving equidistance to the listening position with the main satellite speakers,
which is measured by using a measuring tape to measure the distance from the
SPL microphone (which, of course should be set up at the listening position, using
a tripod and at ear level, when seated) to the center of the subwoofer driver's
cone.
DUAL SUBWOOFERS, STEREO CONFIGURATION: This configuration requires an
outboard crossover network in most multi-channel audio setups. It also requires
external amplifiers (in other words, if you use a Receiver, it must be used as a
preamp and send to seperate amplifiers).
NOTE: My friend, whose screen name is Soundhound and who frequents the
OUTLAW SALOON forum, is an avid proponent of stereo subwoofers. If you find
this configuration to be the one you'd like to use, I highly recommend visiting that
site and asking your question, directed at Soundhound, or searching the threads
on various subwoofer connection schemes in which we've discussed them at
length.
This is the standard configuration, in my opinion, which assumes a Pre/Pro or
use of a Receiver as a Pre/pro feeding separate amplifiers to the satellite
speakers:
Set the front left and front right speakers (in your Pre/Pro or Receiver speaker
setup menu) to 'large' and your subwoofer to 'no' and your center and rears to
'small'.
You need a quality, active, 2-way-stereo crossover.
Run the interconnect cable from the Pre/pro or Receiver front left preamp output
to the left channel input of the crossover.
Connect the crossover's left channel high pass output to the front left amplifier
input.
Connect the crossover's left channel low pass output to the left subwoofer.
Repeat these steps for connection of the right front speaker and the right
subwoofer.
Set the crossover to 80 Hz.
PLACEMENT: You can try symmetric placement, keeping each subwoofer as close
to the mains as possible. In fact, I believe that best results will be realized only if
the subwoofers are the exact distance from the listening position as the main
speakers.
You can also achieve equidistance placement using an asymmetric placement of
the 2 subwoofers if you measure as outlined above, in some rooms. This requires
some planning, listening and testing, as all subwoofer placement techniques also
do.
Tweak placement from these guidelines in small increments until you feel satisfied
that you have the best of compromises for your room.
Phase adjustment is also accomplished as outlined above, one subwoofer at a
time.
The disadvantage of this configuration, in my opinion, is that, with multi-channel
audio sources that contain LFE signal, this is what happens:
The mono LFE signal will be equally distributed to the front left and front right
speakers, which means that some of it will be fed to the mains as well as the
subwoofers, resulting in a collapse of the stereo effect. I've been chided for this
(and many others) opinion, but I stand by it.
Of course, if you like stereo CD formatted, live acoustic types of music, this
configuration definitely adds to the listening experience with a sense of realism
and added space, or air. I've used this setup and found this to be the case.
DUAL SUBWOOFERS, REBASE ROUTING CONFIGURATION:
This one is my baby. I devised the scheme, reasoned the advantages and tested
the theory in my 3,000 cubic feet multi-channel audio room over the past 2 years.
Most of my comments on this routing scheme are tested facts.
The rest of my comments are pure bias...forgive me.
The idea is simple. Use one subwoofer system for discrete LFE playback, and
another subwoofer system for discrete redirected bass playback.
The execution is a PITA because, apparently, no preamp designer seems to see
the merit in adding an output jack and a switch to the output options.
YOU MUST HAVE:
A DVD player that has 6 analog outputs (in other words, a DVD-A and/or SACD
player).
5.1 analog inputs on the Pre/Pro or Receiver.
Analog bass management for the bypass mode, either built into the Pre/Pro or
Receiver, or, outboard, ala the Outlaw ICBM.
And, of course, 2 powered subwoofers.
Connections:
Set all satellites to 'large' and subwoofer to 'yes' in your player's speaker setup
menu.
Run a cable from the player's analog SW output to subwoofer #1. This is the LFE
subwoofer, so if you have 2 different kinds of subwoofers and one of them is a
bottom feeder, use it.
NOTE: If your player doesn't have enough signal output, you may have to
insert a preamp between the player and the subwoofer. You can use any
channel of an old stereo preamp or receiver that's not being used, or of an
old stereo preamp that you're not currently using, or, lastly, purchase a
mono preamp by Behringer, A.R.T., etc., on-the-cheap.
Connect the remaining 5 cables from the player to the Pre/Pro or Receiver analog
inputs (no subwoofer input), or, if the Pre/Pro or Receiver doesn't have on board
analog bass management, connect the 5 cables to the ICBM inputs and then into
the Pre/Pro or Receiver, making sure that FL, C, FR, SL and SR are followed
through the chain.
Connect a cable from the SW (subwoofer) output of the Pre/Pro or Receiver or
ICBM (whichever the case is in your setup) to subwoofer #2. This is the redirected
bass subwoofer.
This is what happens:
The player outputs only the LFE signal to the LFE subwoofer. Most players have a
global 120 Hz low pass filter on their analog SW output (check your manual). If
not, you can use the filter that's built into your powered subwoofer's plate
amplifier. You can set the filter to any point that sounds best to you, as this filter
is unrelated to the rest of your bass management in the system.
The Pre/Pro or Receiver or ICBM SW output will now only output the redirected
bass from the satellites because there is no LFE signal input into it in the first
place (remember you headed that signal off at the player and ran it directly to
subwoofer #1).
You will now be able to tweak subwoofer #2 to achieve the best blend with your
satellites, in your room. You can select any crossover point that may be available
in your setup's analog bass management configuration and not affect the LFE
signal at all.
Placement, phase and level adjustments are the same as for the setup
procedures outlined above, with 1 exception: The LFE subwoofer's level must be
set by using the player's subwoofer calibration tone. It should also be set to 73
dB (if 75 dB is the reference level used for the satellites).
Also, you should switch cables with the redirected bass subwoofer when running
a frequency sweep and charting response onto a graph because a test tone CD
won't have an LFE signal and, therefore, won't output the tones to the LFE
subwoofer.
ADVANTAGES:
You'll get more headroom from each subwoofer because now there isn't a single,
summed signal of LFE and redirected bass going into both subwoofers. Each
subwoofer only has to handle it's own, discrete signal.
You'll have control of the LFE volume independent of the redirected bass volume
during playback of any source that contains LFE signal.
During movie playback, you can switch your Pre/Pro or Receiver to digital mode
(instead of direct bypass mode). This will send the single, summed bass signal
(LFE + Redirected bass) to subwoofer #2 because the digital cable from your
player to your Pre/Pro or Receiver contains the LFE signal (this cannot be avoided,
BTW). This will usually boost the low frequency output by approximately 6 dB. You
may have to lower the gain of subwoofer #2 in this mode, depending on it's
capability.
You will reduce distortions of every kind.
You'll notice a tighter, less 'bloated' sound in the low frequency reproduction of
your system when playing any source that contains LFE information.
You'll be able to have a bottom feeding LFE monster and a tight, musical
subwoofer in the same system, as, contrary to some subwoofer manufacturer's
hype, one subwoofer design cannot do both exceptionally well.
When playing music formats, if you have a 'musical' subwoofer for redirected bass,
you can reduce the volume of the LFE subwoofer, or, in the case of the stereo CD
format, there will be no information sent to the LFE subwoofer. This will notch up
your enjoyment of music listening quite a bit, with little or no tweaking needed
when switching between different formats.
NOTE: Some Pre/Pros and Receivers don't add the 10 dB boost
(actually, it's 15 dB of boost, but that's another discussion for another time)
that's required of the LFE signal in movie watching when in bypass mode,
assuming it's being done in the player. This may mean that in direct bypass
mode, you won't have this boost added. You will then have to adjust the
level of your LFE subwoofer to compensate. Since 10 dB is a lot of boost,
you'll usually be able to tell immediately if this is the case, and add the
boost.
Well, there you have it. Though by no means the definitive multi-channel audio
subwoofer set guide, I assure you that there is enough information to get you
well on your way to understanding how to get the most benefit from the system
you've labored over to research, purchase and set up.
Please offer any input in the way of information that I've missed or omitted and
especially any tweaks or discoveries you may stumble across or otherwise
discover.
Dave
[/code]
Subwoofer Setup Guide by Bossobass
NOTE! For easier reading, right-click the attachment and choose 'save as' to save this guide as a pdf to your computer. Change the file extention to pdf to make it readable.
A very special thanks to Dave ' Bossobass' for writing this guide!
The following has been a labor of love for me. Love of the subject (low frequency
reproduction in multi-channel audio systems in the home), and love for Mark
Schifter, his vision and watching him realize that vision from the sidelines (though anyone who meets him never feels like a mere spectator).
I've also done this because I promised I would.
Please go easy on me, as I'm not an educated person, and I'm sure I've left out
plenty. I only hope that someone who is in the shoes we all have to walk a mile in
when we're first introduced to this digital, multi-channel octopus, will benefit in
any small way by the information below.
I also would like to disclaim the facts that some of what I say is biased toward my
own thoughts and some of what I say is downright controversial.
I would like for those who read this rudimentary guide to add input, discoveries
and tweaks as they are appropriate, as well as adding to the TERMS section as
people ask about ones that aren't included. I omitted many terms for this reason.
I also have not included pictures or diagrams...maybe the graphics guys can add
that input.
Good Listening, and, by all means...Listen Accurately!
Subwoofer Setup Tips And Procedures
Tools:
1. RS SPL Meter.
2. 1/12 Octave Sine Wave Test Tone CD.
3. Tape Measure.
4. Frequency Response Graphing Software (optional).
5. A Tripod For Mounting Your RS Meter.
NOTE: All of the following information will assume that a Pre/Pro or Receiver is
being used to provide Bass Management with all satellites set to 'Small' and
subwoofer to 'Yes', using a crossover point of 80 Hz. It also assumes that your
subwoofer(s) is / are connected properly to your Pre/Pro or Receiver and your
house electrical system in strict accordance with the Owner's Manual that came
with your subwoofer. Finally, it is assumed that all 5 satellite speakers are
calibrated from the listening position to a reference level.
Terms:
1. LFE: Low Frequency Effects, AKA: Low Frequency Enhancement, AKA: The .1
channel.
2. Redirected Bass: This is all information contained in all 5 satellite channels that
is below 80 Hz., which is redirected to the SW (subwoofer) output of the Pre/Pro
or Receiver.
3. SW Output: This is the output of the Pre/Pro or Receiver that sends a
combined, single signal comprised of the LFE channel and the Redirected Bass
from all 5 satellites (or, any satellite that's set to 'small' in the speaker setup
menu) to the subwoofer(s).
4. SPL: Sound Pressure Level. This is the unit of measurement used to calibrate
the channel levels of all of the 5.1 channels. SPL is measured in Decibels, which is
abbreviated as dB.
5. Subsonic: This is the description used for any sound that is below the
threshold of human hearing, or below approximately 20 Hz.
6. Tight, fast, articulate, etc.: These are adjectives that describe a subwoofer
that is capable of delivering low frequencies on-time with the rest of the system,
without any peaks in response.
7. Boomy, muddy, slow, etc.: These adjectives describe a subwoofer that lacks
the capabilities of the subwoofer described in item #6, and/or is misplaced or
badly calibrated, resulting in peaky response.
8. Polarity: Better described as Absolute Phase. Usually, this adjustment is made
by comparing 0 degrees to 180 degrees. If 2 speakers are 180 degrees 'out of
phase', then there will be gross cancellation of sound waves in the region of
audio information that the 2 speakers share the reproduction of. In the case of
satellites and a subwoofer, this will be at and around the crossover point.
9. Relative Phase: Phase is time. It's measured in degrees. If you can visualize a
sound wave that curves upward to it's peak and then downward to it's bottom,
that is one cycle of the wave. Since degrees of angle are not curved, there are
infinite degrees along this wave.
As the frequency is lowered, the phase changes. Some subwoofer designs
change more drastically than others. Distance disparity between speakers and
subwoofer also changes the time that it takes for the shared audio information to
reach your ear.
Because these situations result in infinite phase differences between speakers
and subwoofer, there is no perfect phase setting that works for all frequencies
through the crossover region. This is why it's important to keep distance to the
listening position and infinite phase control in mind when setting up any
subwoofer.
10. Crossover Region: A typical multi-channel audio controller has crossover
options that are based on a Linkwitz/Riley 24 dB per octave network. This means
that the subwoofer is stopped from playing above the crossover point and the
satellite is stopped from playing below the crossover point.
This stoppage of the speaker's natural response is not a brick wall. It is a gradual
braking from the crossover point and then beyond that at a rate of 24 dB per
octave.
The idea is that across 2 octaves (from the crossover point to one octave below
that point the satellite has a brake applied that ends up being 24 dB lower, and
from the crossover point to one octave above that point the subwoofer has a
brake applied that ends up being 24 dB lower, a total region of 2 octaves), the
sum of the 2 signals at any point in the crossover region should sum to unity, or,
in other words, result in a frequency response curve that is a flat line.
This 2 octave area of overlap between the satellites and the subwoofer is the
crossover region.
Overview:
The goal in adding a subwoofer to any multi-channel audio system is to achieve
as flat a frequency response curve as possible, in your particular room, with your
particular system, through the crossover region and to as low as your subwoofer
will allow. This is not to say that there is no room for adjustment from this point to
allow for personal taste. Rather, it is the place to start.
The steps, in order, are:
1. Polarity Test. You never want to lug the subwoofer around the room looking
for the spot where it will sound best if the polarity is reversed.
2. First Volume Calibration. During the placement exercise (pun intended) you'll
listen for bass notes of a music program that are of the same volume (no boomy
notes or weak notes) and, if the subwoofer isn't at least closely calibrated to
begin with, that will occur at any spot the subwoofer is placed.
3. Placement. As in real estate, location, location, location.
4. Relative Phase Adjustment. One of the more important tweaks to smooth out
the frequency response.
5. Final Volume Level Adjustment. After tweaking all of the above, a final
subwoofer volume level tweak will get you there.
NOTE: I've left out the step of tweaking the crossover slopes of the satellites and
the subwoofer. Although it's a very important tweak, it's beyond the capability of
the vast majority of multi-channel systems, and is a rather involved discussion for
a more advanced setup guide than this one is intended to be.
Calibration discs (Avia, Video Essentials, etc.): I have little experience with
these setup discs so I can't offer an opinion as to which is preferred, or why. I
have Chesky's setup disc and, actually, found it annoying. If you have or have
interest in any of these setup discs, search the forum and pose the questions you
may have. I'm sure you'll get the answers you're looking for and end up with an
acceptable method for level calibration.
I use the calibration tones in my Pre/Pro in conjunction with the RS SPL meter
(digital version) set up on a tripod at the listening position, at ear height (when
seated). I have found this method of level calibration to be very acceptable.
I've recently found an easy way to verify this method, and it's described as an
option to try under LEVEL ADJUSTMENT, below.
STEP #1:
POLARITY TEST: Set your subwoofer near either the front left or the front right
satellite.
Set your RS meter at the listening position, ear high, when seated.
Set the Phase Control of your sub to 0 degrees.
Reduce the master volume on your Pre/Pro or Receiver to approximately -10 dB.
Play an 80 Hz test tone, using your test tone CD, with the FL, FR and subwoofer
on.
Note the SPL reading.
Switch the Phase Control to 180 degrees and repeat the process.
Use the Phase Setting that yielded the highest output.
STEP #2:
FIRST LEVEL ADJUSTMENT: Set the subwoofer level in your Pre/Pro or Receiver's
channel calibration menu to -5 from 0 (reference).
Set the subwoofer(s) amplifier gain control to approximately one o'clock.
Use the Pre/Pro or Receiver calibration menu to calibrate the subwoofer level and
use the subwoofer amplifier gain control (add gain or reduce gain at the
subwoofer amplifier) to arrive at a reading on the RS meter that's the same as the
level you use to calibrate the mains.
The reason for the -5 preamp setting is to assure that the preamp doesn't send a
clipped signal the the subwoofer amplifier.
In the final subwoofer level tweaks, the preamp subwoofer channel trim can be
adjusted via the remote control.
STEP #3:
PLACEMENT: The goal here is to find the placement spot that offers the
smoothest frequency response (not necessarily the loudest) in your room.
NOTE: Placement also includes the placement of you yourself, in the room.
Avoid a primary listening position that is in the center of the room and that
is up against any wall in the room.
The conventional wisdom appears to be that the corner is the best place to start.
This is because the corner of most any room will boost low frequency output,
more as the frequency gets lower. It's also said to excite the highest number of
room modes, resulting in the smoothest overall response. I've often read the
recommendation of corner placement, then parametric EQ to flatten out peaks in
response.
I have experienced the highest output from corner loading a subwoofer, but have
personally rarely experienced the smoothest overall response with a subwoofer
placed in a corner.
I personally have found that if I hug a wall and slide the subwoofer away from the
corner (For example, assuming the sub is in the front right corner, either hug the
front wall and slide the sub toward the the left wall, or hug the right wall and
slide the sub toward the rear wall), anywhere from 2' to 4' feet out, it yields a
flatter response. You can also move the sub toward the middle of the room, away
from the wall, after you've slid it away from a corner. This will also get the
subwoofer closer to the mains in distance to the listening position, as the corner
is the farthest distance from the listening position in most rooms and cases.
The closer a subwoofer is to the distance of your mains from the listening
position, the more in phase it will be. In other words, the direct radiated sound
from both will arrive at your ears closer to the same time, which yields a less time
smeared, tighter sound.
This is the part of the setup of a subwoofer that requires the most time and
effort. You should use a source disc that has a wide range of bass lines in the
music. I use jazz that contains vocals and an upright bass (I always loved how
those guys run the neck in walking bass lines). This will give an idea how the
subwoofer is doing, overall, in any given position in the room, as opposed to a
source that drones on using only 2 or 3 notes in the bass line.
The point is that there is variety of bass notes, all the way up to the lower vocal
range. Pick a passage that seems to represent this description and loop it so it
repeats as you try different locations and fine tune a particular location.
Listen for notes that jump out (are too loud in relation to the rest of the notes) or
are too quiet and move the sub in small increments (6"-12" for the rough
placement and 1"-2" at a time to fine tune the placement) until the bass sounds
most even from note to note.
When you feel you've reached the best spot of those that are acceptable as a
final resting place for your subwoofer, then it's time to chart the response.
With your meter at the listening position and only the subwoofer playing, play the
test tone disc and record the results. Apply the correction numbers that are
available to correct the inaccuracies of the RS meter at lower frequencies and
graph the results (There are links to software that will automatically apply the
correction factors and plot your graph. A search or request for a link in the forum
will yield results, I'm sure).
You can tweak the placement from there and see if you can improve your
response graph before moving on to the next step.
NOTE: Use caution when playing sine wave test tones through your
subwoofer. They can damage your subwoofer by overheating the driver's
voice coil if the volume is too high. Set the master volume to yield average
readings of around 80 dB at 40 Hz for the sweep. If you start at 10 Hz (well
below human hearing and the capability of most subwoofers) you may feel
the need to raise the master volume, so start by playing a 40 Hz tone and
adjust the master volume to 80 dB, then proceed with the entire sweep. Set
the meter at the listening position and set it to 'C' weight and 'slow'. Start
the meter's range at it's lowest setting at the beginning of the sweep and
notch the range up as the frequency of the tones rises (the volume of the
tones will increase as the frequencies rise to the frequency range of the
capability of the subwoofer).
STEP #4:
LEVEL ADJUSTMENT: Use the calibration menu in the Pre/Pro or receiver setup
menu and use the on board calibration tones of your preamp to adjust the
subwoofer level (or a setup disc, if you prefer) and remember to set the master
volume to '0' before you begin this step.
Many people like to 'run the subwoofer hot', that is, louder than it should be. This
is a personal preference, but not an option at this point in setup. You're looking
for the reference setup for your subwoofer. You can always change the level later,
but you'll have the reference settings to fall back on if you aim for the flattest inroom
response during setup.
The goal here is to level the volume of the subwoofer to the satellites to as close
a degree as possible, given your limited measurement tool (sorry, Tandy).
Most people whose opinions I respect believe that the RS meter is approximately,
on average, 2 dB off when using the rumble tone pink noise calibration tone. This
would mean that if, for example, your satellites are calibrated using 75 dB as the
reference volume with the tones you're using to calibrate, you would calibrate
your subwoofer level to read 73 dB.
I tend to agree with this assessment as the proper method at this point in the
setup procedure.
STEP #5:
RELATIVE PHASE ADJUSTMENT: Since the polarity is already properly set from
step #1, it's time to fine-tune the relative phase between the satellites and
subwoofer.
We will assume that the phase control is set at 0 degrees for this description.
If it's set at 180 degrees, just work backward from 180 toward 0 instead of
from 0 toward 180. Also, remember to turn that master volume down to the
same, lower level that you used to make your frequency response graph in
step #3.
With the phase control set at 0 degrees, the satellites and subwoofer all on and
using the final frequency response graph from step #3 as a starting point,
advance the phase control knob to approximately 20 degrees above 0 degrees (0
+ 20 degrees) and run another sweep and chart the graph.
Advance the phase control another 20 degrees (0 + 40 degrees) and run another
sweep and chart the graph.
Advance the phase control another 20 degrees (0 + 60 degrees) and run yet
another sweep and chart the graph.
Use a different color for each graph and notate what setting of phase was used
for each color.
You now have frequency response graphs for 0 degrees, 0 + 20 degrees, 0 + 40
degrees and 0 + 60 degrees.
Look carefully at each graph to determine which graph has the overall flattest
line, using the (+/-) from the flat line method.
That would be where to set the phase control and leave it. Only if the 0 + 60
degrees setting is the best graph should you continue to run further sweeps (0 +
80 degrees, etc.) to make sure the next higher phase setting is not better than
what you have to this point.
STEP #6:
FINAL LEVEL ADJUSTMENT: One last time, adjust the subwoofer level to the
mains exactly as described in step #4 above. Now, use your Pre/Pro or Receiver
pink noise level calibration tones or one of the calibration discs, if that's what you
use, to lastly check the levels of all speakers and subwoofer.
There have been many comments about how the RS meter is not accurate in the
low frequency region, and is also said to differ from meter to meter.
Here is a possible method, using the RS meter, to adjust the subwoofer level to
that of the satellites.
Again, we're assuming that you have already calibrated your satellites to
the same level before this point in time, and we've done steps 1-5 of the
subwoofer setup.
Set your Pre/Pro or Receiver mode to 5 STEREO and shut your subwoofer off.
Set your master volume to approximately -10 dB from reference, or, so that a test
tone (from your test tone disc) will read in the neighborhood of 80-90 dB.
Play an 80 Hz tone from your test tone disc (it should play through all 5 satellites
equally).
Note the reading.
Now, shut your satellites off and turn the subwoofer on and play the same tone
through your sub only.
Adjust the subwoofer level to the same reading that you got when playing just
the satellites.
A crossover only works correctly if the speakers being crossed over together play
exactly the same volume at the crossover point. In adjusting the subwoofer level
with this method, the accuracy of the RS meter becomes irrelevant because the
only thing that matters is that the subwoofer and the mains are at the same level
at 80 Hz (the crossover point).
The meter will read the same at 80 Hz every time. Whether or not it's an accurate
reading, it will level the sub to the mains at the crossover point by this method,
accurately. Since the satellites are already calibrated, the subwoofer will
automatically be exactly at that level at 80 Hz.
I have personally done this test many times and found the subwoofer level to be
within 1 dB of 75 dB (which is the level I calibrate to when using the Pre/Pro
calibration tones), and you can quickly check this method against your calibration
rumble tone method to see if it's of any value in your case. My opinion is that, if
this method is close the the rumble calibration tone, then keep the subwoofer
volume set to the level arrived at by the 80 Hz test tone method.
You can adjust the level of your subwoofer up or down for different source
playback, at will. There is no rule that dictates what level you have to play a
subwoofer at. BUT, you now have the correct settings that will tell you where your
subwoofer should be, in your room, with your associated hardware, as a
reference.
It's a good idea to write these settings down (Pre/Pro or Receiver sub level,
phase, placement position and subwoofer amplifier gain), as you'll forget them
shortly after you change any of them, and it's a good idea to reset them to these
reference settings every so often to see what havoc you may have wrought over
time.
You are now ready to play your system and evaluate the results of your setup
labors.
PARAMETRIC EQ: It is currently popular to use this tool to flatten peaks in
subwoofer response that are caused by the room's interaction with bass sound
waves. I am not a fan of this idea (nor have I ever been). I believe time will tell
the correct story on this as more people discover the problems associated with
this method through experimentation and documentation.
I do believe, however, that parametric EQ can enhance the listening experience
when used as a tool to create a frequency response that would otherwise be
beyond the ability of the subwoofer alone. This is a personal choice that you can
decide upon, if you have such a device.
Mine is a season-to-taste approach. It's not to correct a mistake in the room's
interaction with a subwoofer. It's a way to boost certain frequencies during
certain source material playback, or cut certain frequencies or change the overall
damping of your subwoofer in a way that pleases your ears with a given source in
your own room.
There are 3 basic controls in a parametric EQ circuit that change the input signal,
which, in turn, changes what the subwoofer amplifies and sends to your ears.
First, is the frequency selection control. Use this control to center the EQ's effect
at a particular frequency. You can start with 40 Hz and adjust the controls
mentioned next to get an idea of what the EQ does to the signal that's feeding
your subwoofer.
Second, is the bandwidth control, which is just what it's name implies. It controls
the width of the band of frequencies around the frequency that you centered on
with the first control. Dial it to a medium width to follow the suggestion given
above to hear the effect.
Third, is the boost/cut control. Again, it is what it's name implies. It controls the
signal strength or weakness specifically at the frequency you've selected across
the bandwidth you dialed in above and below the center frequency. Try boosting
to 4 dB, and listen to the effect.
REMEMBER: A general (and good) rule of thumb is to never add boost or cut more
than 6 dB with any parametric EQ. Also, remember to play a source that you know
contains information at the frequency band you are trying to affect with the EQ
(otherwise, you'll hear little to no effect).
Play with the EQ controls a bit from there in the way of experimentation until you
get the hang of it's effect. Like anything else that's new to you, it takes time until
you catch on...and you definitely will.
With most on board parametric EQ, simply dialing the boost/cut control to '0' will
disable it. No need to worry what the other 2 controls are set to.
DUAL SUBWOOFERS, MONO CONFIGURATION: Now it gets interesting. Dual
subwoofers affords several options that a single subwoofer can't. Let's explore
them...
NOTE: A quick word about bass in multi-channel audio systems, in general.
When your satellites are set to 'small' and subwoofer to 'yes', the Pre/Pro or
Receiver sums the LFE channel with the redirected bass from the satellites that
are set to 'small' and sends that single, summed bass signal to the subwoofer(s)
through the SW (subwoofer) output.
I personally think that this is a flawed scheme, and will expound later. You can
'trick' your system into other schemes...I'll explain that also, later...
First, is the school of thought that if you place the second subwoofer directly next
to, or on top of the first subwoofer, you'll increase the overall output by up to 6
dB vs. one subwoofer (assuming the subwoofers are exactly the same model).
This is true. It's a viable option, and an easy one to do. Simply head off the cable
to your first subwoofer with a 'Y' jack (1 male plug to 2 female jacks) by inserting
the male end into your subwoofer output, plugging the first subwoofer's cable
into 1 female end and inserting another cable into the second female end that
you'll run to the second subwoofer.
There's not much to say about this scheme, other than to make sure the phase
control is set properly and the level of gain is also set properly.
To adjust the phase, simply follow the same routine as outlined for phase
adjustment of a single subwoofer. The only difference is that you should do 1
subwoofer while the second subwoofer is off, then turn on the second subwoofer
(with all other speakers and the first subwoofer on) and adjust the phase of the
second subwoofer. The phase adjustment of the second subwoofer can be done
by playing an 80 Hz sine wave test tone and dialing the second subwoofer's
phase control until you achieve the highest reading.
Adjust the gain by notching the gain of the first subwoofer down a notch or two
and matching that setting on the second subwoofer. Then, use the calibration
method you are used to using to bring the dual subwoofers to the proper level,
using the Pre/Pro or Receiver subwoofer trim in the calibration menu.
Asymmetric Placement Of Dual Subwoofers:
Asymmetric...Not symmetric: This is another school of thought for placement of
dual subwoofers.
Picture the front wall of your multi-channel audio/visual room. Imagine that your
subwoofer is placed in the front right corner. Slide it out along the right wall
approximately 2 feet. Place the second sub against the front wall, 4 feet from the
right corner. That would be an asymmetric placement.
Or, place the second sub in the left front corner, then slide it toward the right
wall, away from the corner, 2 feet (the first subwoofer is still on the right wall, 2
feet away from the right front corner). That's another example of asymmetric
placement.
This configuration of 2 subwoofers will allow you to achieve a smoother, more
time coherent response if the same placement, phase and level tweaks as
outlined for a single subwoofer are followed.
You'll lose 3 dB or so of output vs stacked subwoofers, and possibly more overall
output vs. a corner placement as the sacrifice for better sounding bass, in my
definite opinion.
NOTE: In my opinion, whenever 2 or more subwoofers are used, regardless of
placement configuration, they should ALWAYS be placed with every effort to
achieving equidistance to the listening position with the main satellite speakers,
which is measured by using a measuring tape to measure the distance from the
SPL microphone (which, of course should be set up at the listening position, using
a tripod and at ear level, when seated) to the center of the subwoofer driver's
cone.
DUAL SUBWOOFERS, STEREO CONFIGURATION: This configuration requires an
outboard crossover network in most multi-channel audio setups. It also requires
external amplifiers (in other words, if you use a Receiver, it must be used as a
preamp and send to seperate amplifiers).
NOTE: My friend, whose screen name is Soundhound and who frequents the
OUTLAW SALOON forum, is an avid proponent of stereo subwoofers. If you find
this configuration to be the one you'd like to use, I highly recommend visiting that
site and asking your question, directed at Soundhound, or searching the threads
on various subwoofer connection schemes in which we've discussed them at
length.
This is the standard configuration, in my opinion, which assumes a Pre/Pro or
use of a Receiver as a Pre/pro feeding separate amplifiers to the satellite
speakers:
Set the front left and front right speakers (in your Pre/Pro or Receiver speaker
setup menu) to 'large' and your subwoofer to 'no' and your center and rears to
'small'.
You need a quality, active, 2-way-stereo crossover.
Run the interconnect cable from the Pre/pro or Receiver front left preamp output
to the left channel input of the crossover.
Connect the crossover's left channel high pass output to the front left amplifier
input.
Connect the crossover's left channel low pass output to the left subwoofer.
Repeat these steps for connection of the right front speaker and the right
subwoofer.
Set the crossover to 80 Hz.
PLACEMENT: You can try symmetric placement, keeping each subwoofer as close
to the mains as possible. In fact, I believe that best results will be realized only if
the subwoofers are the exact distance from the listening position as the main
speakers.
You can also achieve equidistance placement using an asymmetric placement of
the 2 subwoofers if you measure as outlined above, in some rooms. This requires
some planning, listening and testing, as all subwoofer placement techniques also
do.
Tweak placement from these guidelines in small increments until you feel satisfied
that you have the best of compromises for your room.
Phase adjustment is also accomplished as outlined above, one subwoofer at a
time.
The disadvantage of this configuration, in my opinion, is that, with multi-channel
audio sources that contain LFE signal, this is what happens:
The mono LFE signal will be equally distributed to the front left and front right
speakers, which means that some of it will be fed to the mains as well as the
subwoofers, resulting in a collapse of the stereo effect. I've been chided for this
(and many others) opinion, but I stand by it.
Of course, if you like stereo CD formatted, live acoustic types of music, this
configuration definitely adds to the listening experience with a sense of realism
and added space, or air. I've used this setup and found this to be the case.
DUAL SUBWOOFERS, REBASE ROUTING CONFIGURATION:
This one is my baby. I devised the scheme, reasoned the advantages and tested
the theory in my 3,000 cubic feet multi-channel audio room over the past 2 years.
Most of my comments on this routing scheme are tested facts.
The rest of my comments are pure bias...forgive me.
The idea is simple. Use one subwoofer system for discrete LFE playback, and
another subwoofer system for discrete redirected bass playback.
The execution is a PITA because, apparently, no preamp designer seems to see
the merit in adding an output jack and a switch to the output options.
YOU MUST HAVE:
A DVD player that has 6 analog outputs (in other words, a DVD-A and/or SACD
player).
5.1 analog inputs on the Pre/Pro or Receiver.
Analog bass management for the bypass mode, either built into the Pre/Pro or
Receiver, or, outboard, ala the Outlaw ICBM.
And, of course, 2 powered subwoofers.
Connections:
Set all satellites to 'large' and subwoofer to 'yes' in your player's speaker setup
menu.
Run a cable from the player's analog SW output to subwoofer #1. This is the LFE
subwoofer, so if you have 2 different kinds of subwoofers and one of them is a
bottom feeder, use it.
NOTE: If your player doesn't have enough signal output, you may have to
insert a preamp between the player and the subwoofer. You can use any
channel of an old stereo preamp or receiver that's not being used, or of an
old stereo preamp that you're not currently using, or, lastly, purchase a
mono preamp by Behringer, A.R.T., etc., on-the-cheap.
Connect the remaining 5 cables from the player to the Pre/Pro or Receiver analog
inputs (no subwoofer input), or, if the Pre/Pro or Receiver doesn't have on board
analog bass management, connect the 5 cables to the ICBM inputs and then into
the Pre/Pro or Receiver, making sure that FL, C, FR, SL and SR are followed
through the chain.
Connect a cable from the SW (subwoofer) output of the Pre/Pro or Receiver or
ICBM (whichever the case is in your setup) to subwoofer #2. This is the redirected
bass subwoofer.
This is what happens:
The player outputs only the LFE signal to the LFE subwoofer. Most players have a
global 120 Hz low pass filter on their analog SW output (check your manual). If
not, you can use the filter that's built into your powered subwoofer's plate
amplifier. You can set the filter to any point that sounds best to you, as this filter
is unrelated to the rest of your bass management in the system.
The Pre/Pro or Receiver or ICBM SW output will now only output the redirected
bass from the satellites because there is no LFE signal input into it in the first
place (remember you headed that signal off at the player and ran it directly to
subwoofer #1).
You will now be able to tweak subwoofer #2 to achieve the best blend with your
satellites, in your room. You can select any crossover point that may be available
in your setup's analog bass management configuration and not affect the LFE
signal at all.
Placement, phase and level adjustments are the same as for the setup
procedures outlined above, with 1 exception: The LFE subwoofer's level must be
set by using the player's subwoofer calibration tone. It should also be set to 73
dB (if 75 dB is the reference level used for the satellites).
Also, you should switch cables with the redirected bass subwoofer when running
a frequency sweep and charting response onto a graph because a test tone CD
won't have an LFE signal and, therefore, won't output the tones to the LFE
subwoofer.
ADVANTAGES:
You'll get more headroom from each subwoofer because now there isn't a single,
summed signal of LFE and redirected bass going into both subwoofers. Each
subwoofer only has to handle it's own, discrete signal.
You'll have control of the LFE volume independent of the redirected bass volume
during playback of any source that contains LFE signal.
During movie playback, you can switch your Pre/Pro or Receiver to digital mode
(instead of direct bypass mode). This will send the single, summed bass signal
(LFE + Redirected bass) to subwoofer #2 because the digital cable from your
player to your Pre/Pro or Receiver contains the LFE signal (this cannot be avoided,
BTW). This will usually boost the low frequency output by approximately 6 dB. You
may have to lower the gain of subwoofer #2 in this mode, depending on it's
capability.
You will reduce distortions of every kind.
You'll notice a tighter, less 'bloated' sound in the low frequency reproduction of
your system when playing any source that contains LFE information.
You'll be able to have a bottom feeding LFE monster and a tight, musical
subwoofer in the same system, as, contrary to some subwoofer manufacturer's
hype, one subwoofer design cannot do both exceptionally well.
When playing music formats, if you have a 'musical' subwoofer for redirected bass,
you can reduce the volume of the LFE subwoofer, or, in the case of the stereo CD
format, there will be no information sent to the LFE subwoofer. This will notch up
your enjoyment of music listening quite a bit, with little or no tweaking needed
when switching between different formats.
NOTE: Some Pre/Pros and Receivers don't add the 10 dB boost
(actually, it's 15 dB of boost, but that's another discussion for another time)
that's required of the LFE signal in movie watching when in bypass mode,
assuming it's being done in the player. This may mean that in direct bypass
mode, you won't have this boost added. You will then have to adjust the
level of your LFE subwoofer to compensate. Since 10 dB is a lot of boost,
you'll usually be able to tell immediately if this is the case, and add the
boost.
Well, there you have it. Though by no means the definitive multi-channel audio
subwoofer set guide, I assure you that there is enough information to get you
well on your way to understanding how to get the most benefit from the system
you've labored over to research, purchase and set up.
Please offer any input in the way of information that I've missed or omitted and
especially any tweaks or discoveries you may stumble across or otherwise
discover.
Dave
[/code]