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¿Que es mas macho - Bass Traps o EQ? - Page 14  

post #391 of 564
Quote:
Originally Posted by Ethan Winer
Yes, this is exactly what I've been saying. Not whether this or that is theoretically possible, but rather if Joe Schmoe can use EQ to get the same or similar results as from bass traps.
I think this is an important distinction. If its theoretically possible but it seems even Terry was not able to demonstrate this with even a single mode on that graph (I dont see the slope of 39Hz and 69Hz much different either), then what chance do the rest of us have :)

Andy K.
post #392 of 564
Guys
Let's add two more factors to this discussion. Cost effectiveness and practicality. 8, 17 or more traps? How much do they cost each? Who can put more than 2 traps in a room let alone 17 or more?

Doesn't the PEQ give one excellent flexibility and performance (while not solving everything) for a very low cost? (I paid under $200 for the 2496)

Seems to me there is a cost/practicality breaking point with trap. If one doesn't spend enough or clutter up a room enough the real effect of traps isn't realized?
post #393 of 564
IMO practicality is what this is all about. I have no doubt that at a single seat and for a single simple mode and it's harmonics an EQ might effectively deal with ringing somewhat. Unfortunately, we don't deal with rooms that have one seat, or one dimension, or simple modes. We deal in a world that has lots of seats and lots of interactions between different modes and dimensions.

I'm ignoring (sorry) the part about 17 traps because we've already established that they weren't set up in an optimal fashion. Realistically, 4 or 8 absorbers capable of something on the order of .5 at 50Hz and 1 at 125Hz PROPERLY PLACED would show a reasonable improvement in terms of frequency response smoothing and decay time improvement across the spectrum and at multiple positions. This can be done at minimal cost and with minimal effort.

To get the same improvement (or even similar) via EQ alone would take a SERIOUS EQ and a LOT of effort via trial and error. Terry himself even said that they didn't redo the EQ in this very simple test because it took several hours to get it this good, for one seat. How long would it take (if ever) and how much money on EQ (and potential degradation of sound quality assuming that you'd also EQ all the way up in the spectrum since EQ can do the same things that absorbtion can...) to get a room within say a +/- 4db swing AND get the decay times EVEN across the spectrum AT THE TARGET RT60?

Practically? Too much and too long. AND, what if via careful planning, appropriate seating positions, speaker positioning, and sub positioning, we could already have a frequency response that is say within +/-3 to 4db. Then how are we going to use EQ to deal with the decay times? If it was the opposite and we had decay times under control and within target ranges, we could certainly add EQ to help tame frequency related peaks...

It's unfortunate that this has degraded. There was some good discussion happening.
post #394 of 564
bpape,
Quote:
Realistically, 4 or 8 absorbers capable of something on the order of .5 at 50Hz and 1 at 125Hz PROPERLY PLACED
Can I infer that you believe 4" of fiberglass (the typical corner recommendation) is capable of .5 at 50Hz? Thats better than I expected. Do you know how much fiberglass is needed to get 1.0 absorption coefficient at 50Hz?

Also, I dont think the discussion has degraded (well, Ethan has gotten a little testy :D) that much, considering we all knew at the beginning it was going to get somewhat heated. I think its still pretty much on track.

Andy K.
post #395 of 564
Thread Starter 
Noah,

> So no response to the following? I guess that means you concede the point. <

I concede nothing. :D I understand the relation between modes and flutter echo perfectly well. But I'll continue to try to explain it so you and the others can understand it too.

> "What he [Stranger] said is consistent with my assertion that flutter echo is mostly just that, echoes, and has only a small modal component. <

There are multiple modes for any given wall-wall spacing. The very fact that flutter echo repeats at a rate determined by the wall spacing proves my point. Obviously hand claps have little energy at 50 Hz, but that's still the fundamental frequency! This is like the people who say it's important for a stereo system to reproduce down to 27.5 Hz because a piano goes that low. The fundamental pitch for that low A note may be at 27.5, but there is close to zero energy at that frequency. I agree that flutter echo "has only a small modal component" but that's not the point. The basic principle is resonance at a fundamental frequency determined by the spacing.

> if you did have a supercomputer equalizer that could neutralize modes at a single mike position, and you recorded a flutter echo, you'd barely notice the missing modal energy." <

You don't need to neutralize anything because flutter echo created by hand claps has little energy that low to begin with. But instead of using hand claps, instead use a burst of filtered pink noise. Now you can control the exciting frequencies to span any range you want.

Now do you see what I'm getting at?

--Ethan
post #396 of 564
Thread Starter 
Imi,

> Cost effectiveness and practicality. 8, 17 or more traps? How much do they cost each? Who can put more than 2 traps in a room let alone 17 or more? <

I have no sympathy for people who've spent $25,000 on their system, then balk at spending another $2,000 for room treatment. Now, size and appearance is another matter, and I'm working on that. But as Bryan said, you don't need 17 traps - even four 2 by 4 foot traps will make a very noticeable improvement, and eight is night and day.

Personally, I'd rather look at a room full of treatment and enjoy fabulous sound, than have a pretty room that sounds bad.

--Ethan
post #397 of 564
Quote:
Originally Posted by Ethan Winer
Imi,

> Cost effectiveness and practicality. 8, 17 or more traps? How much do they cost each? Who can put more than 2 traps in a room let alone 17 or more? <

I have no sympathy for people who've spent $25,000 on their system, then balk at spending another $2,000 for room treatment. Now, size and appearance is another matter, and I'm working on that. But as Bryan said, you don't need 17 traps - even four 2 by 4 foot traps will make a very noticeable improvement, and eight is night and day.

Personally, I'd rather look at a room full of treatment and enjoy fabulous sound, than have a pretty room that sounds bad.

--Ethan
Besides which - if anyone is paying attention during the design phase of the project, they can work the treatments in, in such a manner, as to be invisible.......... with little or no trouble -

As far as I'm concerned this shouldn't even be on the table as a part of the discussion.

Rod
post #398 of 564
Thread Starter 
Andy,

> Ethan has gotten a little testy <

Yeah, sorry about that folks. Maybe I overreacted a bit. But I've been the target of unfair abuse for three years now. I've been right on every one of these issues, and the "guys who went to school for this" have been wrong. Not once has anyone acknowledged that I've been right all along, even though it's now obvious that I am.

This started three years ago with non-modal peaks and nulls (basic comb filtering) that a bunch of ivory tower types insisted cannot exist at low frequencies. Then it was the density of rigid fiberglass versus its performance at very low frequencies. Next it was loudspeaker radiation versus frequency as relates to treating the entire front wall with thin absorption. So I made a video proving that non-modal peaks and nulls exist, and I spent an entire day comparing rigid fiberglass densities to prove the relationship, and I rounded up polar plots for ten speaker models and wrote an article showing that little energy is radiated toward the front wall at mid and higher frequencies. Now these "trained acousticians" claimed EQ can cancel modal ringing, and I proved that wrong too.

So I'm sorry if I get a little mad sometimes, but I think I'm entitled given the years these insults have been going on for, with no apology after I have proven the insulters wrong time and time again.

--Ethan
post #399 of 564
Thread Starter 
Rod,

> As far as I'm concerned this shouldn't even be on the table as a part of the discussion. <

I agree. If someone wants a room that sounds great and looks great, the only solution is to treat the room adequately then cover the treatment with faux fabric walls or whatever.

--Ethan
post #400 of 564
Thread Starter 
Andy,

> Can I infer that you believe 4" of fiberglass (the typical corner recommendation) is capable of .5 at 50Hz? <

This brings up a great point. A large improvement in frequency response (if not ringing) can be achieved with less absorption than might seem obvious. Let's take the simple case of a deep null created by a single reflection off the rear wall.

If the wall reflects 100 percent then the null will be infinitely deep. If you put "inadequate" absorption on the wall that reduces the reflection by only 1 dB, that infinitely deep null is now only 19 dB deep. Reduce it another dB and now the null is only 14 dB deep. Reduce it again to -3 dB and now the null is only 11 dB deep. If you reduce it to -6 dB the null is now only 6 dB deep. So even 50 percent absorption is enough to make a very large improvement in frequency response. Even 25 percent absorption will help quite a lot.

--Ethan
post #401 of 564
What does .5 at 50 Hz mean? Reduction by 50%??
post #402 of 564
Quote:
Originally Posted by JimP
What does .5 at 50 Hz mean? Reduction by 50%??
Jim,

Absorption rates (measured in sabins) are based on the energy striking a 1' square surface - with 0.0= 100% reflection - and 1.0 = 100% absorption.

So a .50 would mean a reduction of 50% per square foot (of installed absorption) in a particular frequency, as a percentage of the total surface area of the room.


Rod
post #403 of 564
Quote:
Originally Posted by Ethan Winer

So I'm sorry if I get a little mad sometimes, but I think I'm entitled given the years these insults have been going on for, with no apology after I have proven the insulters wrong time and time again.

--Ethan
:rolleyes:
post #404 of 564
Thread Starter 
jim,

> What does .5 at 50 Hz mean? Reduction by 50%? <

Yes, and in terms of how much sound is reflected (at a given frequency) using my example above, with 50 percent absorption the reflections will be reduced by 6 dB.

--Ethan
post #405 of 564
Hello Ethan,

I'm afraid you are coming to a wrong conclusion based on the plots you showed in post #352. These don't show that EQ cannot reduce ringing (they successfully illustrate EQ doing just this at one frequency), unfortunately they show what happens when the EQ settings are incorrect. Perhaps this reinforces your point that it is far from easy to apply EQ correctly, though I am surprised that Terry used Smaart to adjust his EQ as from the typical plot he posted I've no idea how he could even get close.

As the ETF measurements are full range the impulse responses can be exported as pcm files and imported to my EQ app, with which it is a little easier to make measurements. Here is a plot showing the empty front center measurement, with the EQ filter response overlaid plus the predicted effect of the EQ (the lighter red trace). The EQ response is drawn inverted to make it easier to match the EQ to the peaks it should correct.

http://homepage.ntlworld.com/john.mu.../centre-eq.jpg

The only filter whose centre frequency closely matches a peak in the measured response is the one at 140.8Hz (filter 6), and as the plot shows it is a good match in bandwidth also. The actual frequency of this peak is approx 139.7Hz, so the filter is not an exact match, but it is within 1% so works reasonably well. The effect on decay at this frequency is shown in these spectral decay plots, the empty room is the upper plot, the response with EQ the lower:

http://homepage.ntlworld.com/john.mu...ecay-no-eq.jpg
http://homepage.ntlworld.com/john.mu...ay-with-eq.jpg

The plot with EQ is generated from the EQ-both speakers front center ETF data, which I trust is the correct file - there is an extra mode at 51Hz which was not present in the empty room response, which is a little odd.

The mismatched centre frequency of filter 6 causes a slight dip to the right of the mode's actual frequency. Despite this, the drops between the 80, 120, 160 and 200ms slices are 2.0, 3.4 and 4.7dB without EQ but 3.6, 6.7 and 11.0dB with EQ.

The plots also show why the 39Hz peak was not corrected by filter 2, as the peak is due to two modes at 37 and 40.5Hz rather than a single mode. The filter at 39.5Hz falls between the two modes and is too narrow, the 37Hz mode is unaffected though the 40.5Hz mode is partly reduced, the main effect is to introduce a dip at 39.5Hz. The 69Hz filter (#8) is 2% away from the mode's actual frequency of 70.6Hz which is too far to bring much benefit. I'm not sure what filter 7 (153Hz) is aimed at as the nearest mode is 159Hz, but I haven't looked at the other data sets so perhaps it addresses a peak elsewhere. A pity, as the 159Hz mode should respond very well to a properly matched filter. Filter 9 (205Hz) is 2% away from the 201Hz mode so again brings little benefit. It is also a little too broad, but modal resonances tend to have bandwidths of a few Hz (about 4Hz for that mode) and hence tend to be too high in Q once the frequency reaches 200Hz or more - most equalisers do not offer sufficiently narrow bandwidths to usefully treat modes beyond 150Hz or so.

I would like to point out that I am not posting this as an argument of EQ over room treatments, there is much that can be achieved with room treatment that is impossible with EQ. However your belief that EQ cannot address modal ringing is wrong, and I do not think you would wish to use incorrectly interpreted data to assert that.

Regards,
post #406 of 564
Making my point exactly John. To get the EQ EXACTLY correct - even for 1 seat, takes serious EQ and lots of setup and analysis. EQ is bandied about by some (not anyone particular or anyone in this thread) as a much 'easier' way to deal with frequency response. What shows above and before is that not done EXACTLY correct can cause as many problems as it helps. All that AND the fact that this is all for just one single location. When you move to the 2nd, 3rd, 4th, etc. seats in a real room, there is no way you can match exactly the inverse of all of the responses because the response is different at each seat.
post #407 of 564
Quote:
Originally Posted by bpape
Making my point exactly John. To get the EQ EXACTLY correct - even for 1 seat, takes serious EQ and lots of setup and analysis. EQ is bandied about by some (not anyone particular or anyone in this thread) as a much 'easier' way to deal with frequency response. What shows above and before is that not done EXACTLY correct can cause as many problems as it helps. All that AND the fact that this is all for just one single location. When you move to the 2nd, 3rd, 4th, etc. seats in a real room, there is no way you can match exactly the inverse of all of the responses because the response is different at each seat.
Not only is the response different at each seat - but for any response that's modal - it's physically impossible to chage the settings without screwing up what we already worked to achieve. In fact - even if there were problems with different frequencies than the initial center seat - any adjustments made on ANY frequency will affect that seating location as well.

And, introducing a new set of filters with a totally different set of speakers (intended for seat 2) is impossible without (again) screwing up that first seat we already adjusted for.

Guys, I have been quietly working through this in my head ever since becoming involved in the thread......... and I have to tell you - although I know in theory how this works - and I do believe that it's possible - I think from a practical point of view - it doesn't work. And from the impractical view - you aren't going to get there without a lot of equipment much more sophisticated than anything put out by Behringer for a couple of hundred bucks........

Now if you go back to computer generated solutions - you could actually analyze the signal at each listening position - compare that analysis with the original signals - generate a series of frequency pulses either in sysnc or out of sysnc in a localized manner - to affect ony what was heard in each individual seating area - correcting for any modal or non-modal phenomenon - probably including flutter echo,comb filtering, stereo imaging, etc.

However - I have to believe, seeing as I have 2 broithers who are computer scientists - one who's worked with the Cray computers inside of NSA (and was rated one of the top 100 super-computer scientists in the world by the NSA)- and having discussed this with them - that we could probably treat a room a lot cheaper than we could deal with it otherwise...........

Sincerely,

Rod
post #408 of 564
Quote:
Originally Posted by Rod Gervais
Not only is the response different at each seat - but for any response that's modal - it's physically impossible to chage the settings without screwing up what we already worked to achieve. In fact - even if there were problems with different frequencies than the initial center seat - any adjustments made on ANY frequency will affect that seating location as well.

And, introducing a new set of filters with a totally different set of speakers (intended for seat 2) is impossible without (again) screwing up that first seat we already adjusted for.

Guys, I have been quietly working through this in my head ever since becoming involved in the thread......... and I have to tell you - although I know in theory how this works - and I do believe that it's possible - I think from a practical point of view - it doesn't work. And from the impractical view - you aren't going to get there without a lot of equipment much more sophisticated than anything put out by Behringer for a couple of hundred bucks........

Now if you go back to computer generated solutions - you could actually analyze the signal at each listening position - compare that analysis with the original signals - generate a series of frequency pulses either in sysnc or out of sysnc in a localized manner - to affect ony what was heard in each individual seating area - correcting for any modal or non-modal phenomenon - probably including flutter echo,comb filtering, stereo imaging, etc.

However - I have to believe, seeing as I have 2 broithers who are computer scientists - one who's worked with the Cray computers inside of NSA (and was rated one of the top 100 super-computer scientists in the world by the NSA)- and having discussed this with them - that we could probably treat a room a lot cheaper than we could deal with it otherwise...........

Sincerely,

Rod
Rod I must say this is the best post so far on this thread... It really comes down to one thing... Enjoy the sound!!!!!!!! :D

Glenn
post #409 of 564
I've scanned this thread and, in general, I'm very glad the room treatment versus corrective EQ thing is being addressed at such length.

Having said that, I'd like to risk stirring things up in light of the last series few posts...
Quote:
Originally Posted by Ethan Winer
This started three years ago with non-modal peaks and nulls (basic comb filtering) that a bunch of ivory tower types insisted cannot exist at low frequencies.
No one ever insisted that comb-filtering could not exist at low frequencies. The argument came down to semantics. What is described by you as "non-modal peaks and nulls" is the well-documented phenomenon known as "speaker-boundary interference" (which I believe you also prefer to call "listener-boundary interference" - again, semantics).

Quote:
Then it was the density of rigid fiberglass versus its performance at very low frequencies.
This sort of performance depends on more than density. But if only density is considered, the results are well-documented elsewhere - some of it by you, if I'm not mistaken? I suppose that's kind of your point! :o

Quote:
Next it was loudspeaker radiation versus frequency as relates to treating the entire front wall with thin absorption.
This depends on what frequency (or range) is being considered and how "thin" the absorption is. I have treated a front wall null quite well in the past with 2" thick acoustical foam. Other times, 3" or thicker was necessary.

Quote:
Now these "trained acousticians" claimed EQ can cancel modal ringing, and I proved that wrong too.
The only note I would add here is that some "room correction" systems - Bag End and Meridian come to mind - are using electronic damping as opposed to EQ. The former can be quite effective. The latter is well-documented here and elsewhere as being limited in its effectiveness.

******

I'd also like to clarify some other points:

• The absorption coefficients that are typically published for acoustical materials are found using the reverberation chamber method. This method yields random incidence absorption coefficients, which are not percentages. Normal incidence absorption coefficients are percentages. The two are often confused in the literature. And, it would seem, here as well! A material that has a random incidence absorption coefficient of 1.22 is simply a better absorber relative to a material with a random incidence absorption coefficient of 0.67 for the same frequency band, all other factors being equal. The numbers should not, however, be treated as an indicator of the percentage of sound absorbed by the material.

• Along the same lines, the SPL decrease based on percentage sound absorbed for random incidence absorption coefficients is not as simple as described above. In fact, SPL reduction due to absorption cannot typically be calculated accurately in small rooms like studios since most positions in the room will be in the near-field of the loudspeaker (or other sound source). However, if the far-field can be reasonably assumed, the amount of SPL decrease can be estimated using standard formulae. In this case, the result is relative to what the initial absorption of the surface is without the absorber present. Thus, one application of a material with a 0.50 absorption coefficient could reduce SPL by less than 1 dB. Another application could yield a >10 dB decrease. In most real-world applications of absorbers, SPL is reduced by ~5-10 dB over the range of effectiveness of the absorber. For early reflection applications in studios, greater than 10 dB of reduction is not uncommon - even for absorbers with seemingly "low" absorption coefficients. However, this is beginning to mix concepts since the random incidence absorption coefficient is not at all indicative of an absorber's behavior when a single bounce from one early reflection is considered as opposed to randomly incident sound.

:) :) :)
post #410 of 564
Ethan,

"I think I'm entitled given the years these insults have been going on for, with no apology after I have proven the insulters wrong time and time again."

Curious if I count as an "insulter", as I can't recall anyone behaving that badly.

Perhaps anyone who continues to disagree with your misconceptions is in that category?

I, as well as Terry, gave several reasoned statements that illustrate that slap echo is not intrinsically a modal phenomenon.

You haven't countered any of the reasoning, you simply make further arguments, that while not false, in no way support your point.

But you'll be glad to know that I won't bother engaging you in any further discussions.
post #411 of 564
Great post Rod. Thanks for expounding further on what I was trying to say. It's just another one of those things where in theory it could work VERY well and in practice it just doesn't.

Before anybody gets their shorts in a wad here, I'm not saying that EQ doesn't work. I'm just saying that you can't get EVERYTHING with EQ only.
post #412 of 564
Would it be accurate to say that you can't get everything with EQ any more than you can with accoustical treatments? That they're problems that neither can correct. The trick to to find out before you spend any money what can and can't be done??
post #413 of 564
Jim,
Quote:
Originally Posted by JimP
Would it be accurate to say that you can't get everything with EQ any more than you can with accoustical treatments? That they're problems that neither can correct. The trick to to find out before you spend any money what can and can't be done??
From my experience, I would say that thorough acoustical treatment of a room can render something like EQ unnecessary. However, most theater rooms are not going to be able to control all the modal peaks below 50 Hz. Thus, something like electronic damping, or even a good digital EQ can help tweak the lowest octave or so.

IMO, EQ is a tweak that should only be used in rooms where the acoustical problems have been addressed as much as possible. In most of the HTs I've tuned and tweaked, it was debatable whether EQ would have helped that much for the lowest octave or so. In most, I've done without it as any attempt at implementing it would only either make the sound in general worse (subjectively), or it would fix a problem at one seat or area, but not affect anything or make things worse elsewhere in the room.

I haven't come across a room problem yet that wasn't completely treatable with well-thought-out acoustical treatments. But I can think of possible applications for systems like the Meridian and the Bag End I mentioned above.

:) :) :)
post #414 of 564
Quote:
Originally Posted by JimP
Would it be accurate to say that you can't get everything with EQ any more than you can with accoustical treatments? That they're problems that neither can correct. The trick to to find out before you spend any money what can and can't be done??
Jim,

No it would not be accurate to say that. I've built recording studios that (when completed) needed no treatments outside of what was in the original design.

A properly designed room - with treatments taken into consideration as a part of the design, can achieve everything that's needed - something that cannot be claimed with EQ. Leaving EQ to only deal with speaker issues - not room issues.

If I were to strip the walls of those studios to bare drywall - you could never replace those treatments through the use of EQ.

Thus - one approach can handle everything - and one approach cannot.

That having been said, I will grant you that there are rooms that exist that cannot be turned into a home theaters, with perfect sound, through the use of treatments - some rooms are just impossible from that point of view. But, even in those rooms, treatments alone will get you to places you never could with EQ alone.

Rod
post #415 of 564
Can anyone come up with evidence demonstrating a response trough / peak and ringing that was left AFTER corner treatments, that was fixed with EQ? Especially EQ that fixed it for multiple seats?

If one has as the primary seating 3 seats next to eachother in a row, a length mode would affect each seat the same, wouldn't it? So EQing that problem would fix it for those 3 seats, which might be "good enough".
post #416 of 564
"The only note I would add here is that some "room correction" systems - Bag End and Meridian come to mind - are using electronic damping as opposed to EQ. The former can be quite effective. The latter is well-documented here and elsewhere as being limited in its effectiveness"

Could someone please explain what "electronic damping" is? Thank you.
post #417 of 564
Eyleron.

Your thinking is correct. Unfortunately, it's rarely that cut and dried that all of the issues are purely length related. If it was then that might work. Also, in many theaters there are more than one row in which case even that can't do everything.

The idea, as Rod pointed out, is to deal with the overall issues via appropriate placement of seating, speakers, sub, etc. first. Then deal with the room as much as possible via treatment. After that, if you still have issues that can't be resolved for whatever reason (spousal approval, lack of appropriate mounting positions, budget, whatever) via treatment - then you can look at the response at all of the seats and see where you can make changes that will help all of them.
post #418 of 564
Quote:
Originally Posted by Eyleron
If one has as the primary seating 3 seats next to eachother in a row, a length mode would affect each seat the same, wouldn't it? So EQing that problem would fix it for those 3 seats, which might be "good enough".
Eyleron,

Picture, you have length - height, width - for axial modes - then any combined 4 surfaces for tangential modes, combined 6 surfaces for oblique modes - and we haven't even begun speaking to back wall interference, first reflections, etc.

So even if you could cure for one condition at a seating position as you suggest - it wouldn't be (i.e.: couldn't be) "good enough" if one is looking for anywhere near accurate sound reporduction.

Then again - "good enough" is a subjective term - as I mentioned very early on in the thread.......... for some people no treatments or eq is "good enough" - but for anyone with a discerning ear - it just doesn't work.

Rod
post #419 of 564
Thread Starter 
John,

Thanks for your truly fabulous post. I do not disagree with any of it. Just to be clear, I am not arguing that an EQ could not be designed to counter ringing for one location in the room. I understand that in theory this is possible. But if an expert like Terry is unable to make it happen with a sophisticated EQ like the one he used, then it's just not practical as a solution for us mere mortals. More to the point, the precision counter-EQ needed to reduce ringing (not just help the raw LF response) will be valid for only one very tiny place in the room. Move even a few inches, or just turn your head, and I'm pretty sure all of the ringing will return. So even if there were such a thing as an auto-adjusting EQ that dials in the exact inverse response, it will help too small of an area to be useful for reducing ringing.

--Ethan
post #420 of 564
Thread Starter 
Jeff,

> No one ever insisted that comb-filtering could not exist at low frequencies. <

I don't think we need to revisit that can of worms, and certainly not in this thread. But I still have the dozens of posts from Yahoo and AVS where a number of "trained acousticians" and their friends insisted for many months that 1/4 wavelength-related comb filtering was a figment of my imagination. If you're intent on starting this all over again, don't let me stop you. But please do it in a new thread, okay?

> This sort of performance depends on more than density. But if only density is considered, the results are well-documented elsewhere - some of it by you, if I'm not mistaken? I suppose that's kind of your point! :o <

Yes, and I agree that density is only part of the story. But I'm sure you recall how I was called wrong repeatedly and, worse, insulted repeatedly, yet eventually I prevailed with the results of my Density Report.

> electronic damping <

I haven't actually tried a Bag End bass trap, but from the test results I saw at AES I'm pretty sure it suffers from the same fundamental flaw as EQ. As soon as you "turn up the volume" enough to get more absorption than 1.0, the improvement becomes localized. As opposed to passive bass traps that always help at all locations. One feature of an active bass trap is high absorption at very low frequencies. But I don't see how that can be done effectively with a relatively small device without the improved area becoming more and more localized.

> SPL reduction due to absorption cannot typically be calculated accurately in small rooms <

I agree with all of those points. My simplisitic example was for a single bounce off a single surface, ignoring any other reflections that will of course also be present.

--Ethan
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