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post #1 of 55 Old 11-19-2012, 02:51 PM - Thread Starter
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This thread is not intended for the Pros/Cons of bass management.  I understand those pretty well.   What I'd like to do in this thread is better understand the "inner workings" of bass management.  There are many people on this forum smarter than me that probably have the answers to my questions.  So here goes....

I've always sort of felt a bit of "bass buildup" or the soundstage moved forward to the front of the room (where my two subs are) when running my system with all speakers small and an 80hz crossover.  Setting the crossovers lower and/or running some (fronts) full range removes this apparent "bass buildup" and the soundstage appears more enveloping if you will.  Now maybe that is because I'm starting to lose some bass since my speakers can't produce it and that just sounds better to me.  But to date my measurements don't really tell me that and so let's assume that is not the case for now.

I've been doing some reading about differences in an acoustical sum (think full range speakers) vs electrical sum (think bass management).  And along with that the term coherent bass comes up, at least I think that is the correct term but others can help me here.  So coherent bass would be the same bass signal coming from say the front left, front right and center speaker all at the same time, right?  So I'm wondering how bass management deals with this summation.  And how big of a difference could this "perfect" electrical sum be than the acoustical sum in the room?  Is it enough to make a difference, say 1-2db?  And could that be what I am hearing (or imagining)?

So along those lines I took some measurements using Omnimic, and then I imported them into REW since there are more tools to use there.  The legend for both charts is:

Purple = Left speaker
Red = right speaker
Green = both left and right speaker
Magenta (or light purple) = REQ sum (A+B) of Purple and Red

charts are 1/6 octave smoothing

My goal is this would compare the acoustical sum (measured green trace) with the electrical sum (magenta trace).  I was hoping, at least from an answering my question standpoint, I'd see a 3db difference in bass between the two.  Well, I didn't.  Charts are below.

This is with fronts set to full range


This is will fronts 80hz crossover


Acoustical vs Electrical sum appear pretty similar in the bass range but not at high freq?  Is this just because of all the comb filtering going on up there?

So a lot of questions buried in there and hoping people can shed some light.  My suggestion being that bass management induces some error in the bass level because acoustical sum vs electrical sum is not the same. How does bass management deal with a signal being sent to left, right and center channel together? If is sums them to a speaker in one location wouldn't that yield a level increase of 6db since you are co-locating 3 signals? How does it compensate or even know it needs to?
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post #2 of 55 Old 11-20-2012, 05:37 AM - Thread Starter
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Some more digging and I haven't been able to turn up anything relating to increased output by summing the signal from two speakers into one.  So maybe I have something wrong in my theory there.

 

There are quite a few links about phase issues when using bass management and a couple are below.  But assuming most movies are at least checked using bass management before release that shouldn't be too big of an issue.

 

http://www.tmhlabs.com/products/bassmanager.pdf

 

"Bass management electrically combines the bass from all of the channels

together.  Even if you had full range monitors, with say a subwoofer spliced to
each of the five or more main channels, you would then be hearing an
acoustical summation of the multichannel bass in your room.  The two
levels, acoustically summed or electrically summed, could be very different.
Let's say front and surround channels are out-of-phase with each other.  Then
electrically they will cancel, but acoustically, depending on where you are
standing, you may hear them sum (the room standing wave adds its own
phase shifts!).  Thus you might hear bass in your studio that would be
completely canceled out at home (happened to a famous DVD-V production
that had to be recalled)."
 
 
"Further, if bass management and a subwoofer is not used to monitor the program during production, particularly in studios where multi-channel and/or video type production is being done, electrical summation of the channels may result in phase cancellation when played back on a bass managed system at home. This phase cancellation might not be noticed under the original monitor conditions, even if five true full-range monitors are used during the production process. This is because acoustic summation in the studio space and electrical summation may well yield different results because acoustic summation and cancellation effects would have many other variables, not the least of which is the acoustic properties of the space, speaker placement, etc., that would result in a different sound than if all those signals were electrically summed together before reaching the loudspeakers."
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post #3 of 55 Old 11-20-2012, 06:08 AM
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Not sure I understand what you're trying to do, but this is where I go for audio info. This link is for subs, but gets into detail of why full range or small crossover. Big Daddy is very knowledgable and can answer any questions you have. http://forum.blu-ray.com/forumdisplay.php?f=80

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post #4 of 55 Old 11-20-2012, 06:31 AM
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Quote:
Originally Posted by primetimeguy View Post

This thread is not intended for the Pros/Cons of bass management.  I understand those pretty well.   What I'd like to do in this thread is better understand the "inner workings" of bass management.  There are many people on this forum smarter than me that probably have the answers to my questions.  So here goes....

I've always sort of felt a bit of "bass buildup" or the soundstage moved forward to the front of the room (where my two subs are) when running my system with all speakers small and an 80hz crossover.  Setting the crossovers lower and/or running some (fronts) full range removes this apparent "bass buildup" and the soundstage appears more enveloping if you will.  Now maybe that is because I'm starting to lose some bass since my speakers can't produce it and that just sounds better to me.  But to date my measurements don't really tell me that and so let's assume that is not the case for now.

I've been doing some reading about differences in an acoustical sum (think full range speakers) vs electrical sum (think bass management).  And along with that the term coherent bass comes up, at least I think that is the correct term but others can help me here.  So coherent bass would be the same bass signal coming from say the front left, front right and center speaker all at the same time, right?  So I'm wondering how bass management deals with this summation.  And how big of a difference could this "perfect" electrical sum be than the acoustical sum in the room?  Is it enough to make a difference, say 1-2db?  And could that be what I am hearing (or imagining)?

So along those lines I took some measurements using Omnimic, and then I imported them into REW since there are more tools to use there.  The legend for both charts is:

Purple = Left speaker
Red = right speaker
Green = both left and right speaker
Magenta (or light purple) = REQ sum (A+B) of Purple and Red

charts are 1/6 octave smoothing

My goal is this would compare the acoustical sum (measured green trace) with the electrical sum (magenta trace).  I was hoping, at least from an answering my question standpoint, I'd see a 3db difference in bass between the two.  Well, I didn't.  Charts are below.

This is with fronts set to full range


This is will fronts 80hz crossover



Acoustical vs Electrical sum appear pretty similar in the bass range but not at high freq?  Is this just because of all the comb filtering going on up there?

???????????

What I see is is a peak at 80 Hz with your fonts set to full range.

What I don't see is your opinion of the comparison between the two.

I don't see any details about how you set up the system before you took these measurements.

So, whether you like it or not, intended it or not, I see a trick question. I decline to answer.
Quote:
So a lot of questions buried in there and hoping people can shed some light.  My suggestion being that bass management induces some error in the bass level because acoustical sum vs electrical sum is not the same.

Expecting an electrical sum and an acoustical sum to be the same is a faulty expectation. They almost always aren't. If you do everything right, maybe they will be similar enough. Room acoustics and loudspeaker transmission errors preclude such a thing unless they are carefully accounted for and managed near-perfectly.
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How does bass management deal with a signal being sent to left, right and center channel together?

Bass management done right looks at the few limited basic things that you tell it about the speakers and takes an educated but somewhat simplistic shot at doing the right thing. The best thing about bass management is that it is usually (but not always) better than no management or stupid management.
Quote:
If is sums them to a speaker in one location wouldn't that yield a level increase of 6db since you are co-locating 3 signals? How does it compensate or even know it needs to?

No way does every bass management system do the same thing. So, this is an area where only demagogues and fools make very broad statements. ;-)

For example, if your front speakers are set to large, and there is no subwoofer, it would be stupid for the bass from all channels to be summed into one common signal and then split up. OTOH, it would be wise for the LFE channel to be spit up among the fronts.

If there is a subwoofer, and the fronts are set to large, then things get a little more complex. I would still expect that the bass from the front channels is kept separate and routed to the front. I would expect the LFE to be sent to the bass, and it gets to be a judgement call whether we want some of the LFE to be trickled to the fronts. Some AVRs let you do this, but they provide a control so you can keep it from happening.

And so on. There are a large number of reasonable permutations for the speaker configurations, and the bass maangement system should make good but usually different choices for each of them. The system optimization system tries to smooth out the larger of the rough edges that are left over by the bass management system.

In modern times AVR bass management and system optimization systems like YPAO, MCACC, and Audyssey work together to further enhance the fact-gathering behind what they finally implement.

The reference cited in post 2 looks overly-simplistic to me.
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post #5 of 55 Old 11-20-2012, 07:08 AM - Thread Starter
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Thanks Arny for the response.  I'll try to give you more detail and answer your questions.

 

My point about electrical sum vs acoustic sum in the charts is comparing the green trace, which is the actual measurement response of the sweep coming from both the left and right speakers vs the light purple trace which is the sum achieved by simply summing the left + right responses in REW.  I find it odd they are pretty similar in the bass region but once you get above 2k they deviate by 3-5db.  

 

Yes, there is a peak at 75hz or so, but only on the right speaker, when running full range.  Using 80hz crossover reduces this and is why I think 80hz crossover over should be better.  The reality is running fronts as large sounds better.  Movies sound too bassy with all channels crossed at 80hz.  I have tried lower crossovers for the fronts (rated down to low 30's) but reducing too low I still end up with the bump around 75-80hz and I run into phase issues because the mains are ported.

 

One thing I guess I failed to mention is I have Audyssey MultEQ enabled for all measurements.  Front speakers about 10ft apart, main listening position centered between them about 12ft away.  Two subs, one about a foot inside each of the mains which puts them at about thirds across the width of the room.  I'll try and get a picture tonight.

 

No trick questions intended, really just trying to really understand how bass management sums signals and what electrical vs acoustical differences may exist.  I do believe in the benefits of bass management but the reality is full range speakers sound different and better to me.  So trying to correlate this to measurements for better understanding.

 

 

So here is a specific question I'm looking to get answered.  Assume a signal of 75db is played from all 3 front channels, what would the in room summed response be?  Using http://www.sengpielaudio.com/calculator-spl.htm it says almost 80db.  I was assuming it would be 6db adder so 81db.  So maybe someone can explain that to me.  Is there just some built in fudge factor for room losses?  What sort of vatriability could exist from room to room?  Is it possible to have one room only see 76db output and another 81db so up to 5db difference between rooms?

 

Now take those same three speakers and signals, sum them electrically.  What is the sum?  Is it more than the acoustical sum and if so how does bass management deal with that?

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post #6 of 55 Old 11-20-2012, 07:09 AM - Thread Starter
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Not sure I understand what you're trying to do, but this is where I go for audio info. This link is for subs, but gets into detail of why full range or small crossover. Big Daddy is very knowledgable and can answer any questions you have. http://forum.blu-ray.com/forumdisplay.php?f=80

Thanks, I will read through the bass management stickies there, maybe some of my answers exist in there.

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post #7 of 55 Old 11-20-2012, 07:29 AM
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Quote:
Originally Posted by primetimeguy View Post



So here is a specific question I'm looking to get answered.  Assume a signal of 75db is played from all 3 front channels, what would the in room summed response be?  Using http://www.sengpielaudio.com/calculator-spl.htm it says almost 80db.  I was assuming it would be 6db adder so 81db.  So maybe someone can explain that to me.  Is there just some built in fudge factor for room losses?  What sort of vatriability could exist from room to room?  Is it possible to have one room only see 76db output and another 81db so up to 5db difference between rooms?

Now take those same three speakers and signals, sum them electrically.  What is the sum?  Is it more than the acoustical sum and if so how does bass management deal with that?


You will gain 9 dB with an electrical signal summation for a total output of 84 dB assuming the 75 dB input on all three channels.

The acoustic summation can vary depending on speaker spacing distances and frequency.
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post #8 of 55 Old 11-20-2012, 07:38 AM - Thread Starter
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Originally Posted by J_Palmer_Cass View Post

Quote:
Originally Posted by primetimeguy View Post



So here is a specific question I'm looking to get answered.  Assume a signal of 75db is played from all 3 front channels, what would the in room summed response be?  Using http://www.sengpielaudio.com/calculator-spl.htm it says almost 80db.  I was assuming it would be 6db adder so 81db.  So maybe someone can explain that to me.  Is there just some built in fudge factor for room losses?  What sort of vatriability could exist from room to room?  Is it possible to have one room only see 76db output and another 81db so up to 5db difference between rooms?

Now take those same three speakers and signals, sum them electrically.  What is the sum?  Is it more than the acoustical sum and if so how does bass management deal with that?


You will gain 9 dB with an electrical signal summation for a total output of 84 dB assuming the 75 dB input on all three channels.

The acoustic summation can vary depending on speaker spacing distances and frequency.

Thank you!!

 

What is "typical" difference between acoustic and electrical sum?  Are we talking pretty small in most cases, say a db or less.  Or is it common for 2-3db or more differences?  Or are rooms just too different we can't even come up with a general rule?

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post #9 of 55 Old 11-20-2012, 07:52 AM
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Originally Posted by primetimeguy View Post


What is "typical" difference between acoustic and electrical sum?  Are we talking pretty small in most cases, say a db or less.  Or is it common for 2-3db or more differences?  Or are rooms just too different we can't even come up with a general rule?

Depends on how you measure it, and the system you are measuring.

With 1/12 octave bands and a typical system, over 10 dB would not surprise me. I would expect 2-3 dB differences to be very common.
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post #10 of 55 Old 11-20-2012, 08:16 AM - Thread Starter
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Depends on how you measure it, and the system you are measuring.

With 1/12 octave bands and a typical system, over 10 dB would not surprise me. I would expect 2-3 dB differences to be very common.

 

So is it then the case, assuming everything else being "equal" and "perfect", that simply switching settings from full range speakers to using an 80hz crossover could cause a 2-3db difference in the amount of bass heard in a room?  Because that is pretty much what I'm hearing.

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post #11 of 55 Old 11-20-2012, 09:03 AM
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Originally Posted by arnyk View Post

Depends on how you measure it, and the system you are measuring.


With 1/12 octave bands and a typical system, over 10 dB would not surprise me. I would expect 2-3 dB differences to be very common.

So is it then the case, assuming everything else being "equal" and "perfect", that simply switching settings from full range speakers to using an 80hz crossover could cause a 2-3db difference in the amount of bass heard in a room?  Because that is pretty much what I'm hearing.

Easily.
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post #12 of 55 Old 11-20-2012, 09:13 AM - Thread Starter
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Why don't I see this idea discussed more.  Isn't this a reason against using bass management? 

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post #13 of 55 Old 11-20-2012, 09:22 AM
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Why don't I see this idea discussed more.  Isn't this a reason against using bass management? 

No, its an argument for you to apply additional equalization to your system over and above what your Audyssey system is giving you automatically.

One approach might be to kick up the gain control on your sub a little after you run your Audyssey setup.

It is not written in any audio book that I've ever read or any stone I've ever seen that everybody's preference is or should be for dead flat response.

IME there is such a thing as human preference and in the end, its the final measure of how an audio system sounds.

Just like there is no rule that says that the latest winner of the greatest beauty contest in the world is going to strke your fancy.

I'm under the impression that even Audyssey has provided more user preference tools than basic Multieq.
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post #14 of 55 Old 11-20-2012, 09:30 AM - Thread Starter
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Originally Posted by arnyk View Post

Quote:
Originally Posted by primetimeguy View Post

Why don't I see this idea discussed more.  Isn't this a reason against using bass management? 

No, its an argument for you to apply additional equalization to your system over and above what your Audyssey system is giving you automatically.

One approach might be to kick up the gain control on your sub a little after you run your Audyssey setup.

It is not written in any audio book that I've ever read or any stone I've ever seen that everybody's preference is or should be for dead flat response.

IME there is such a thing as human preference and in the end, its the final measure of how an audio system sounds.

Just like there is no rule that says that the latest winner of the greatest beauty contest in the world is going to strke your fancy.

I'm under the impression that even Audyssey has provided more user preference tools than basic Multieq.

But I'm not talking about preference.  Sure I can boost the sub or turn on/off DynEQ and get a non-flat response.  But if there is a 2-3db difference in bass response by using bass management or not that is a problem.  From my standpoint this is what is happening....movie is mixed on full range speakers....I play that on my system using bass management and because of the electrical summing I am getting 2-3db more bass than what was intended in the studio.  Sure I can turn my sub level up or down but now I affected the re-routed bass and the LFE level both.

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post #15 of 55 Old 11-20-2012, 11:43 AM
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Not sure I understand what you're trying to do, but this is where I go for audio info. This link is for subs, but gets into detail of why full range or small crossover. Big Daddy is very knowledgable and can answer any questions you have. http://forum.blu-ray.com/forumdisplay.php?f=80

I don't "trust" Big Daddy at all.
There was a thread here 1 year ago, based on building riser platforms for your sub, this is Big Daddys "thing".
I was a member of the blu-ray forum also, and posted some questions asking for fact based data on performance of those there.

I got banned!
I tried to login just now, and still banned there.
Quote:
You have been banned for the following reason:
No reason was specified.

Date the ban will be lifted: Never
I am user name "mtbdudex" in many-many forums, never banned from any of them.
Later I'll find the link to the thread here on AVS and at blu-ray dot com, but I was very respectful and because I question what he did was banned.

[edit]
Here is thread http://www.avsforum.com/t/1349434/hearing-is-believing-wow

Here is post in the blu-ray thread http://forum.blu-ray.com/showthread.php?p=5008476#post5008476
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post #16 of 55 Old 11-20-2012, 05:17 PM - Thread Starter
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Can a bass management circuit differentiate between coherent and two non-coherent signals?

 

From http://www.sengpielaudio.com/calculator-coherentsources.htm

 

 


The addition of two coherent pressure or voltage level is:
Formula coherent signals
The addition of two values of the same level results in an increase in the overall level here of (+) 6 dB.
This is obtained with the equal input of two closely standing speakers.

 
The addition of two non-coherent pressure or voltage level is:
Formula non-coherent signals
The addition of two values of the same level results in an increase of the total level of (+) 3 dB.
This equation is used for both the electric non-coherent addition of signals, and for the calculation
of the energy level of two loudspeakers.

 

If not couldn't bass be off by 3db?

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post #17 of 55 Old 11-21-2012, 05:56 AM
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Quote:
Originally Posted by primetimeguy View Post

Can a bass management circuit differentiate between coherent and two non-coherent signals?

From http://www.sengpielaudio.com/calculator-coherentsources.htm





The addition of two coherent pressure or voltage level is:
AddingCoherentSignals.gif

The addition of two values of the same level results in an increase in the overall level here of (+) 6 dB.

This is obtained with the equal input of two closely standing speakers.

 
The addition of two non-coherent pressure or voltage level is:
AddingIncoherentSignals.gif

The addition of two values of the same level results in an increase of the total level of (+) 3 dB.

This equation is used for both the electric non-coherent addition of signals, and for the calculation

of the energy level of two loudspeakers.


If not couldn't bass be off by 3db?

I think you're overthinking it. Bass management simply transfers frequencies below the crossover point (on a slope, it's not a brick wall) to the sub. So let's say the crossover for speaker A is 80 Hz. Hard to imagine part of the 80 Hz signal going to speaker A is out of phase with another part of the 80 Hz signal going to that speaker. Isn't it? If there were somehow 2 separate 80 hz tones that were simultaneous but 180 degrees out of phase you would sum electrically to 0 dB and have no output at all at 80 Hz to bass manage.
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post #18 of 55 Old 11-21-2012, 06:10 AM - Thread Starter
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Quote:
Originally Posted by primetimeguy View Post

Can a bass management circuit differentiate between coherent and two non-coherent signals?

From http://www.sengpielaudio.com/calculator-coherentsources.htm





The addition of two coherent pressure or voltage level is:
AddingCoherentSignals.gif

The addition of two values of the same level results in an increase in the overall level here of (+) 6 dB.

This is obtained with the equal input of two closely standing speakers.

 
The addition of two non-coherent pressure or voltage level is:
AddingIncoherentSignals.gif

The addition of two values of the same level results in an increase of the total level of (+) 3 dB.

This equation is used for both the electric non-coherent addition of signals, and for the calculation

of the energy level of two loudspeakers.


If not couldn't bass be off by 3db?

I think you're overthinking it. Bass management simply transfers frequencies below the crossover point (on a slope, it's not a brick wall) to the sub. So let's say the crossover for speaker A is 80 Hz. Hard to imagine part of the 80 Hz signal going to speaker A is out of phase with another part of the 80 Hz signal going to that speaker. Isn't it? If there were somehow 2 separate 80 hz tones that were simultaneous but 180 degrees out of phase you would sum electrically to 0 dB and have no output at all at 80 Hz to bass manage.

It is the out of phase portion I'm trying to understand.  How likely, or is it even possible, that when a mixer puts a tone into all three of the front channels are all 3 not exactly if phase?

 

And the other thing I'm trying to understand is, based on sound/wave theory, is there an increase in SPL that occurs simply by summing 3 signals together and playing them from ONE source vs playing from 3 independent (front channels) sources?

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post #19 of 55 Old 11-21-2012, 06:13 AM
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Why don't I see this idea discussed more.  Isn't this a reason against using bass management? 


No, its an argument for you to apply additional equalization to your system over and above what your Audyssey system is giving you automatically.


One approach might be to kick up the gain control on your sub a little after you run your Audyssey setup.


It is not written in any audio book that I've ever read or any stone I've ever seen that everybody's preference is or should be for dead flat response.


IME there is such a thing as human preference and in the end, its the final measure of how an audio system sounds.


Just like there is no rule that says that the latest winner of the greatest beauty contest in the world is going to strke your fancy.


I'm under the impression that even Audyssey has provided more user preference tools than basic Multieq.
But I'm not talking about preference.  Sure I can boost the sub or turn on/off DynEQ and get a non-flat response.  But if there is a 2-3db difference in bass response by using bass management or not that is a problem.  

I echo the other poster who said something about "overthinking".

In fact the opposite is true. If there weren't a measurable difference for the kind of change you are making in your experiement, there would either be a problem or a coincidence possibly involving the relatively positions of Mars and Venus. ;-)
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From my standpoint this is what is happening....movie is mixed on full range speakers....

Says who?
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I play that on my system using bass management and because of the electrical summing I am getting 2-3db more bass than what was intended in the studio.

Based on what reliable scientific evidence?
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Sure I can turn my sub level up or down but now I affected the re-routed bass and the LFE level both.

And the evil in that is what?

I get this feeling that you are pursuing the myth that somehow you can duplicate the mixing environment in your listening room.

Lets say that you are able to obtain the exact speakers that the mixer used and set them up electrically identical to what he had when he mixed the movie.

Your listening room and his mixing room are not exact duplicates in terms of size, shape, and the details of construction, right?

Speakers are profoundly affected in terms of their response at your ears, by the room they are in and where you sit in the room.

Therefore, there' is not a snowball's chance in San Diego of you hearing what the mixer heard.

So then you take that BD disc off of your player and slap in another one and it was mixed by a different guy in a different room with different speakers.

What are you going to do - have hydraulic positioners that reconfigure your room for every mixing room in Los Angeles county? ;-)

Give it up!

Enjoy!
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post #20 of 55 Old 11-21-2012, 06:32 AM - Thread Starter
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Sure, I may be over thinking but I'm an engineer and that's what I do.  ;-)

 

I'm just trying to understand the details of bass management.  The two questions below some up what I'm trying to understand...

 

 

1)  How likely, or is it even possible, that when a mixer puts a tone into all three of the front channels are all 3 not exactly in phase?
 
2)  Based on sound/wave theory, is there an increase in SPL that occurs simply by summing 3 signals together and playing them from ONE source vs playing from 3 independent (front channels) sources?
 
On my system when when I set all speakers to small with 80hz crossover I get about 3db more bass than if I run speakers full range.  That 3db difference is by ear as I adjust the sub down that much to get them about the same.  But my measurements show that the bass level is very similar between the two, if not the "large" setting actually having more bass which is opposite of what I here.
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post #21 of 55 Old 11-21-2012, 07:00 AM
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Sure, I may be over thinking but I'm an engineer and that's what I do.  ;-)

I'm just trying to understand the details of bass management.  The two questions below some up what I'm trying to understand...


1)  How likely, or is it even possible, that when a mixer puts a tone into all three of the front channels are all 3 not exactly in phase?
 
2)  Based on sound/wave theory, is there an increase in SPL that occurs simply by summing 3 signals together and playing them from ONE source vs playing from 3 independent (front channels) sources?
 
On my system when when I set all speakers to small with 80hz crossover I get about 3db more bass than if I run speakers full range.  That 3db difference is by ear as I adjust the sub down that much to get them about the same.  But my measurements show that the bass level is very similar between the two, if not the "large" setting actually having more bass which is opposite of what I here.



Think of it this way (2 channel summation). Take two identical subwoofers being fed the same signal. When driven together will the total SPL level of two subwoofers gain identical SPL over either single subwoofer being driven alone no matter where each / both subwoofers are placed in the room?

Bass management electrical summation would approximate what distance between subwoofers used in an acoustic summation?
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Think of it this way (2 channel summation). Take two identical subwoofers being fed the same signal. When driven together will the total SPL level of two subwoofers gain identical SPL over either single subwoofer being driven alone no matter where each / both subwoofers are placed in the room?

Bass management electrical summation would approximate what distance between subwoofers used in an acoustic summation?

 

Thanks JPC, I think you and I are on the same page.  The SPLs will be different.  So I was wondering if the bass management circuit just uses the straight electrical sum or is there some guestimate built in to drop the sub level slightly to account for it?  My assumption is the electrical sum would always be greater than the acoustic sum so a drop in sub level is needed.  

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post #23 of 55 Old 11-21-2012, 09:51 AM
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Bass management electrical summation would approximate what distance between subwoofers used in an acoustic summation?

Electrical summation is well-approximated by two perfect subwoofers that themselves have no distortion, no frequency response variations, no room acoustics, and no time delays due to sound traveling through the air.

Since most modern bass management systems in AVRs include adjustable time delays, that is the approximation of distance.
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post #24 of 55 Old 11-21-2012, 10:06 AM - Thread Starter
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Is it fair to say that in a perfect world or room that acoustic sum would equal electrical sum, but because of room issues and losses that the acoustic sum would always be less than electrical sum for in-phase signals?

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post #25 of 55 Old 11-21-2012, 10:09 AM
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Think of it this way (2 channel summation). Take two identical subwoofers being fed the same signal. When driven together will the total SPL level of two subwoofers gain identical SPL over either single subwoofer being driven alone no matter where each / both subwoofers are placed in the room?


Bass management electrical summation would approximate what distance between subwoofers used in an acoustic summation?

Thanks JPC, I think you and I are on the same page.  The SPLs will be different.  So I was wondering if the bass management circuit just uses the straight electrical sum or is there some guestimate built in to drop the sub level slightly to account for it?  My assumption is the electrical sum would always be greater than the acoustic sum so a drop in sub level is needed.  


If you set you speakers so that you use the all small settings along with a subwoofer, a straight addition of signals is used. That would equate to all bass drivers being co-located on an acoustic basis. This also results in mono bass.

If you use other bass management settings, then a guestimate mix level may be used that is different than the 6 dB co-located bass driver mix level. You can obtain stereo bass with alternate bass management settings, meaning phase is accounted for on an acoustic basis.
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post #26 of 55 Old 11-21-2012, 10:17 AM
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I guess you have to take the question to the extreme and this may help undersatand why there may be confusion on the question and/or the rason for the question. As is taught in engineering classes, you must remove variables, many of which cannot be removed in the real world, to solve a problem "theoreticaly". Just as you assume wire has no resistance or reactance when solving simple Ohm's law equations, you need to assume the room has no affect - maybe infinite wall spacing (outside?). Assume "full range speakers" are truely full range with freq response of +- 0dB from 1-100 Khz. Speaker efficiency and sub efficiency are equal. Frequency response and gain of the Sub's amplifier is the same as the Main amps. Etc.

I think THX tries to eleiminate many of the variables by having "certified" equipment and ideal speaker placement guides. But as was mentioned above, that still does not mean the listener at home will hear/percieve what the sound engineer heard/desired.

It think the main conclusion that comes from most of these discussions is to adjust the system to what sounds best to you.

I too have wondered how the base management system deals with bass signal summation. It gets even more fun when you think about six channels all being directed to the sub. I have read this thread with interest thinking it may solve my bewlderment, but it has not. I don't mean to squech the conversation, but maybe people to ask how bass management is engineered is to ask the engineers at the manufacture of the equipment in question or learn about the various audio processor chips.
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post #27 of 55 Old 11-21-2012, 10:20 AM
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Bass management electrical summation would approximate what distance between subwoofers used in an acoustic summation?

Electrical summation is well-approximated by two perfect subwoofers that themselves have no distortion, no frequency response variations, no room acoustics, and no time delays due to sound traveling through the air.

Since most modern bass management systems in AVRs include adjustable time delays, that is the approximation of distance.



What does time delay in an AVR have to do with the issue being discussed? The time delay that an AVR uses is the time delay between the subwoofers and the main speakers

We are talking about the difference between mutual coupling on an acoustic basis of bass from the main speakers (AKA distance between main speakers) as compared with electronic addition of bass being sent to one subwoofer at a single location.
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I too have wondered how the base management system deals with bass signal summation. It gets even more fun when you think about six channels all being directed to the sub. I have read this thread with interest thinking it may solve my bewlderment, but it has not. I don't mean to squech the conversation, but maybe people to ask how bass management is engineered is to ask the engineers at the manufacture of the equipment in question or learn about the various audio processor chips.

 

Yep, that sounds like what I am looking for.  I started with two channels to try and make it easy but my bigger concern is summing 6 channels "perfectly" to the sub not equating to the proper bass level heard on the mix stage at all.  But I do understand that me running all full range speakers like a mix stage may not be close to equating what was heard either because of room size.  What I do know is running my speakers large vs small/bass management sounds quite a bit different.  Just trying to understand what that difference is (freq response, localization, summed bass to sub, phase differences, etc).  And I can't decide which way sounds better at this point, they are just different. 

 

Was hoping people here had some answers rather than digging up how various DSPs work.  :-)

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post #29 of 55 Old 11-21-2012, 12:16 PM
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 What I do know is running my speakers large vs small/bass management sounds quite a bit different.

"I've always sort of felt a bit of "bass buildup" or the soundstage moved forward to the front of the room (where my two subs are) when running my system with all speakers small and an 80hz crossover. Setting the crossovers lower and/or running some (fronts) full range removes this apparent "bass buildup" and the soundstage appears more enveloping if you will."

What you describe here is exactly what I have experienced as well with a 80hz crossover and have brought this up before only to be pooh-poohed by the self appointed "experts" around here. (e.g.) I feel a higher crossover robs too much stereo information and turns it into mono. The left and right speakers lose too much weight and are unable to produce a dynamic soundstage. Like I suggest in that other thread.... with that 80hz crossover, turn the subs off at the power (so your AVR still thinks they are running) and listen to the speakers by themselves with that 80hz crossover. What you hear now will be as dynamic as they will ever get with that 80hz crossover. To me it makes them sound like small satellite speakers. So how are they ever going to reproduce a dynamic soundstage of say a drum riff racing across from left to right?

I have never liked an 80hz crossover for this reason. A 60hz crossover doesn't seem to have this problem as much. My system gets mostly used for music and only very little blu-ray movie use.
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I have tried lower crossovers for the fronts (rated down to low 30's) but reducing too low I still end up with the bump around 75-80hz and I run into phase issues because the mains are ported.

You could get your system to work better with a lower crossover with more fine tuning. Different sub placement, different distance settings for the sub, and even blocking the ports on the speakers. You have a real time analyzer so you are in a good position to keep experimenting until you find a setup that works with a lower crossover.

.
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post #30 of 55 Old 11-21-2012, 12:37 PM
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Bass management electrical summation would approximate what distance between subwoofers used in an acoustic summation?

Electrical summation is well-approximated by two perfect subwoofers that themselves have no distortion, no frequency response variations, no room acoustics, and no time delays due to sound traveling through the air.

Since most modern bass management systems in AVRs include adjustable time delays, that is the approximation of distance.



What does time delay in an AVR have to do with the issue being discussed? The time delay that an AVR uses is the time delay between the subwoofers and the main speakers

We are talking about the difference between mutual coupling on an acoustic basis of bass from the main speakers (AKA distance between main speakers) as compared with electronic addition of bass being sent to one subwoofer at a single location.

There are two views of that. One is that time delay whether acoustic or electrical is time delay.

The other view is that trying to guess the acoustic response of summed arbitrary speakers in arbitrary locations in an arbitrary room is pretty much like rolling dice.
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