treating live room ceiling

[ejboom1]

Hey everyone. I have a question about ceiling sound treatments. The dimensions for my live room are about 350 sq. ft. with a 15’ ceiling height. There are no parallel walls in the live room and the walls are double layered sheetrock with green glue. Floor is currently concrete. The current plan is to place 24” by 24” clouds of 2” OC 705 across the entire ceiling, leaving 1’ gaps around the clouds. This breaks down to approximately 45 clouds in the live room alone. This gets crazy expensive, really quickly. Is there a more cost effective way to treat the ceiling?

[SAC]

Just a suggestion...one option of many depending upon your goal...

Assuming that you have already given thought to addressing LF room modes and also that you have thought about diffusion for the wall surfaces...sufficient to address fundamental issues and to achieve the response character you desire...

Given the luxury of the height of the ceiling and the title of the thread suggesting that you desired a live room - while also assuming that you desire a diffuse sound field, and not simply the potential to have an assemblage of hot specular reflections...

For the ceiling, of which you are lucky to have the height with which to work!) I would suspend collimating phase gratings (like the pArtScience SpaceCouplers) as clouds (these can be made without too much trouble or expense), and above them on the ceiling apply geometric reflectors in the form of, for example, pyramid scatterers or polycylinders (which can be made very cheaply with such materials such as 3/16" luaun plywood) to scatter and redirect the incident signal about the space above the phase gratings.

[ejboom1]

You make a couple great points. Do I really need to deaden the live room that much? I have already planned for bass trapping, absorbers, and diffusers on the walls. The big question is, how much do I gain by using OC 705 instead of 703?

[avare]

Originally Posted by ejboom1

The big question is, how much do I gain by using OC 705 instead of 703?

A slight variation. If making 2" deep absorbers, I would use 705.

Andre

[ejboom1]

Here is a gif of the layout. Thanks for your response Avare. Do you think I need as many clouds as I placed in the layout? The ceiling will be very dead, but the floor will be very reflective as it is concrete.

[avare]

Originally Posted by ejboom1

Here is a gif of the layout. Thanks for your response Avare. Do you think I need as many clouds as I placed in the layout?

With 15' ceilings you will not have problems with sound smearing from early reflections. What is your treatment for the walls? Specifics are impossible with the dearth of information. GENERALLY, I would evenly spread the acoustic around the room, except for a live area, and evenly distribute the amount of absorbent on the ceiling. Remember the ceiling will twice th density of material as the walls, because the floor is reflective.

With that size of room, I would investigate putting some form of diffuser on the non absorbent areas of the ceiling.

Andre

[SAC]

Originally Posted by ejboom1

You make a couple great points. Do I really need to deaden the live room that much?

Are we talking about the same thing?

My response did not propose additional deadening nor treatment for early reflections at all - although any early reflections would be diffused as well as any other specular reflection in the live room.

The collimating phase gratings (the commercial version of which is called a Space Coupler) would act as diffusors to allow you to take advantage of the ceiling height and to increase the diffusion.

I guess I am a bit confused at the talk of over-deadening the room that the name implies should be live - meaning the ratio of direct to later arriving energy is large.

[ejboom1]

no worries SAC. I changed gears and talked about reducing the clouds in the live room. I will look into the collimating phase gratings. Sorry for the confusion.

For the treatment of the walls. One wall shows 15 polycylindrical diffusers. The red lines are 2'x4' OC 703 acting as absorbers. Does it normally make sense to have all diffusers on one side and the absorbers on the other? From what you guys have said, I gather that is not usually the case.

[andrebrito]

Adding diffusion to the ceiling is going to make the room less live since the spreadout of the reflections is higher and the free path becomes shorther which results in higher reflections order. This is particulaly visible in large rooms but also occurs in small ones.

I will try to show in the upcoming weeks a project we are working on using CATT modelling software and showing the differences between using diffusion or not for the same absorption area in the room

[SAC]

Originally Posted by andrebrito

Adding diffusion to the ceiling is going to make the room less live since the spread out of the reflections is higher and the free path becomes shorter which results in higher reflections order. This is particularly visible in large rooms but also occurs in small ones.

I agree.

By the term "live", most folks are actually referring to ratio of the direct sound level to the first reflection level.

This also presents additional increased destructive factors in terms of intelligibility, imaging, polar lobing nulls, and issues regarding such factors as micing, etc.

Using diffusion breaks up the reflections and more evenly distributes them both temporally and spatially, which will tend to decrease the perception of 'liveness' by virtue of a more uniform distributed sound field.

Such a modification reduces the destructive anomalies in exchange for a much more uniform soundfield devoid of the gross destructive anomalies as the diffuse reflections are reduced in level relative to the direct signal (re. Henry Precedence Effect).

All of that being said, the use of diffusion in this instance would be superior to the use of absorption that simply reduces the total energy without diffusing the ambient sparse specular reflections. And we are here only suggesting its use for the vertically directed specular reflections via the use of a collimating phase grating/diffusive cloud.

It all depends upon what one desires, but for the purpose of a 'live room' I will trade a room featuring a diffuse sound field for one dominated by reduced acoustic energy and sparse specular reflections any day.

...And I wish CATT and EASE and Ulysses worked as well in small acoustical spaces as they do in large acoustical spaces...If they did, this forum would largely be a moot issue.

[DanDan]

You are very lucky to have a high 15 foot ceiling. However, even at that height, it will have flutter echoes between it and the concrete floor. So it needs treatment, as several posters have said, both absorbent and diffusive.
The Space Couplers would be brilliant, however few seem to master that DIY and the commercial product is very expensive. Go for it if you can.
An inexpensive thought- hanging panels of plywood, at angles, could be used to break the flutter, while keeping a woody liveness. Excellent for drums I reckon.

DD

[ejboom1]

Thanks for all of the input. Its all starting to make a bit more sense now. I should be more concerned of controlling reflections off the ceiling. In the process, can I reduce the number of absorbers, or will I need full coverage to adequately decrease the acoustical energy. So many choices...

[DanDan]

Those ceiling reflections are luckily quite far away. However, you may have flutter echoes, as I said. I suggest that you test this. I can't imagine that Space Couplers would kill these flutters, surely they would go straight through?, but I have an open mind on that. Perhaps the SC's could be mounted at an angle? Or they could have an absorptive panel above them. This combination is incredibly powerful in tests I have seen.
Do a search here on SC's. I seem to remember that terry? had amazingly helpful DIY construction details.
Those plywood or even hardboard panels could be allowed to sag , creating a diffusive curve. Thin cheap panels should be fine. I have seen such panels in Reverberation Chambers.
DD

[SAC]

Collimating phase gratings are used in conjunction with scattering treatment on the surface 'behind them' (as stated above) in all cases where they are used as diffusing agents. And as such there would be no flutter echo as the energy return is much lower...

[DanDan]

Some info on Space Couplers from the makers.
Note that absorption is used above for flutter control.
http://www.resolutionmag.com/pdfs/SW...dsmallroom.pdf

This is all well and good, but the original question did include the words cost-effective. Given that, and the splayed walls, perhaps a simple checkerboard of 703/5 cloud and light angled curved panels would be a good shot here.


DD

[SAC]

We are talking of several different intended uses/applications that are basically at odds with each other.

Normal (referring to near 90 degree) incident sound simply passes through he phase grating and would strike a reflective surface and reflect back through the phase grating at the same normal (90 degree) incidence angle!

The way the collimating phase grating works as a diffusor is that signal 'near' 90 degrees passes through collimating phase grating, which is then redirected by a scattering surface 'above/behind' the phase grating. This redirects and scatters the signal about the space until it is oriented such that it passes back out of the the space when it happens to be incident with the phase grating at a 'near' 90 degree angle. A scattering surface behind the phase grating separated by some distance is optimal to further scatter and subsequently diffuse the energy. A surface perpendicular to the incident admitted signal would simply reflect the signal back through eh grating and defeat its purpose in this case.

Using absorption in conjunction with the phase grating in this application is a waste of both the phase grating and the absorption, as our goal is to use the phase grating to augment the scattering surface and to further diffuse and delay the retransmission of the signal into the main room space - And our purpose here is certainly not to absorb the energy.

To absorb the signal above the phase grating does NOT augment the diffusion and later 'retransmission' of the acoustic energy back into the space.

Flutter echo is completely avoided as the energy retransmitted is much lower in energy content/gain then that of the original entering sparse specular reflection.

A collimating phase grating has been used for several hundred years in the optics realm for a great many purposes, and it can be used for a variety of applications. It is not limited in itself, but is a tool that can be used either alone or in conjunction with many configurations for quite a variety of tasks. We risk error if we try to state its 'use', as it can be used in a myriad configurations, either alone or in conjunction with other 'tools' for a myriad of uses.

And as far as being cost effective, phase gratings can be made very easily with a table saw and 3/16" 4x8foot sheets of luaun plywood used to cover interior doors that is available for less than $10 a sheet at any Home Depot or Lowes or foamcore material. And this would be cheaper and more easily accomplished for a given area than than applying absorptive clouds (which would simply deaden the space) or using more complex truly diffusive designs.

And our concern was NOT simply the existence of flutter echo, but of augmenting a more live than dead acoustical space while avoiding the problems of sparse specular reflections - as was stated in the original premise.

[DanDan]

Well well. Clearly 'scattering' elements above an SC cloud would prevent flutter and provide maximum return of diffuse sound from the overhead coupled space.
In the linked pdf Jeff Syzmanski uses absorption in the over space 'to prevent flutter'. I assume the use of absorption up there will indeed prevent flutter. However it would also bring down the overall room decay time and somewhat diminish the return of diffuse sound downward. This might be exactly what is required.
These are two different approaches, with slightly different goals. I don't think either could rightly be called 'wrong'.

The room has splayed walls, it may or may not need much or any additional absorption. So if one was to go with Space Couplers, which I would love to see done, the choice of scattering or absorptive devices over the couplers would be dependent on the desired room decay time. Many instruments won't record well in a washy room.
Given the 15 foot ceiling, and the cost requirement, the simple and cheap hanging bent panels could perhaps be the scattering elements.
IMHO, the best possible design here would be a checkerboard of scatter panels and absorptive panels. Perhaps with different concentrations of either at opposite ends of the room to give a variable acoustic to suit different instruments, vocals, etc. Space Couplers could be installed underneath, again not necessarily over the whole ceiling. Some recorded sounds do not benefit at all from the return of early reflections, even after 20mS. e.g. Vocals and perhaps drums, due to the high overhead mics and moving cymbals. Also I have not seen much testing of Space Couplers. In the pdf we see a picture of them over a drum kit. It has been suggested to me, by a practitioner who actually uses these, that they are superb under an absorptive cloud in the mix room. I have not seen tests or testimonials as to their use over drums however.

DD

[ejboom1]

Thanks for all this information. This is a great crash course in diffusers. What approximate percentage would you have of absorber verse diffuser on the ceiling, 75/25?

[SAC]

So, you do indeed have a few choices.

The usage I proposed is NOT intended to make the space dead. If you want a dead space, then I would suggest you might have entitled the thread something other than "treating a LIVE room ceiling".

Also, flutter echo is a non-starter with such a configuration - a complete red herring as the surfaces above the grating would not be appreciably parallel. Rather, the goal was to enhance the qualitative aspect of the room while reducing the specular nature of the sound field and while also significantly reducing the gain of any focused reflected energy without deadening the space.

But using them in conjunction with absorption in this case, depending upon the spacing, may or may not increase their absorptive qualities, But duplicating the phase grating with absorption for the control of flutter echoes is an exercise in redundancy. And it will not augment your live room while controlling undesired focused specular reflections. It will simply render it more 'dead'.

And decay times? The purpose of the diffusion is not only to temporally diffuse the energy reflecting off the ceiling, but to significantly reduce the spatially distributed energy returned over a much larger area as well, as is a fundamental feature of diffusion.

In the situation expressed above, quality 2D diffusion on the ceiling would essentially accomplish the same goal that the use of phase gratings would. The difference is in the total cost and complexity of the build - if you buy or build them. Additionally, the phase grating an also be used to augment the aesthetics of the space by providing a porous ceiling allowing light to flow through unobstructed while still functioning to obscure an 'industrial' or otherwise unattractive ceiling space - if such be the case.

Phase gratings are very easily made if you have access to a saw. All that is necessary is to rip the panel into slats and to clamp and make spaced 90 degree slots of an appropriate depth and width at the proper spaced intervals in the clamped slats allowing for a snug compression fit. A frame is also easily fashioned of similar material or 1/4" ply - if desired.

Constant references to "tests" amuse me. I guess someone here who has lots of time and money is welcome to sponsor a myriad battery of tests after they define the myriad potential uses for such of a fundamental tool. But then they would have to define exactly what specific purpose they e are intended to prove and that presumes a knowledge of how collimating phase gratings have been used historically and in principle - which rather renders many such tests unnecessary.

Having dealt with collimating phase gratings in optics for far too many years, and by others for centuries, I have never seen a formal "test" that proves they work. But we employ them all the time in practical and theoretical applications. Instead those that employ them understand the physics involved and find myriad uses for them in all sorts of situations based upon their basic collimating behavior. This feature is then combined with other tools and materials in order to accomplish a desired goal. But I guess the difference is that some understand the basic behavior of the tools, and others demand that others prove their use as their basic behavior is not well understood by those who need the tests made by others. Thus, one should not expect to see many formal tests, as the potential uses are not standardized. And simply testing myriad combinations and permutations of possible uses is prohibitive at best. And CASI (scatterometer) tests, or ETCs, of simple fundamental collimating functions are, for all general purposes, a waste if one does not understand their applied uses! And if one already understands collimation, such are not necessary.

Thus a collimating phase grating can be used to enhance absorption or diffusion based upon their use within a complimentary system of components. And understanding the behavior of the other components, collimation simply is a behavior that serves to augment this.

And in the manner described, Russ Berger has actively employed them in conjunction with scattering surfaces for over 20 years to enhance the 'liveness' of small rooms. And that is simply one application of them. And all of his designs are verified with proof of performance metrics. The fact is, they can also be used for a variety of diffusive purposes, as well as to augment absorption. The simple understanding of the effectiveness of the collimation of incident signals is sufficient to allow one to think of MANY uses, in many situations.

They are a wonderful tool. One of many that a creative designer, cognizant of how the basic physics operate, can employ to create many tailored effects. And their effects can be varied by the spacing and orientation relative to reflective, diffusive or absorptive surfaces.

And anyone who understands the basic physics can easily configure many applications as well as measure the effectiveness of their application sufficient to provide adequate objective proof of performance without waiting for someone else to 'test' all of the myriad potential applications.

Thus, in this case it is one technique of several that can be employed. One would be wise to consider all of the possible alternatives in light of their overall goal, be it acoustics, aesthetics, cost, complexity, and any others that may bear on the situation and make a selection that best suites their criterion.

[andrebrito]

SAC

In my opinion CATT is way superior than Ulysses. Less expensive than EASE and better as well.. This is the software we use at our company, it is quite complex but very good.

For small rooms it has some application in terms of time domain and mid and high frequency response of the rooms

[SAC]

All assume far field behavior as sources are assumed to be 'point' sources - unless you want to try to model sources as driver arrays - and the exact FER modeling of the acoustical impedance of surfaces is still evolving and have limitations for small spaces, especially the near field.

I prefer EASE, but then that is what I am most familiar, while friends also use CATT-A.

Both CATT-A and EASE are fine programs that provide quite a bit of functionality - albeit for a non-trivial price.

[DanDan]

Thanks for all this information. This is a great crash course in diffusers. What approximate percentage would you have of absorber verse diffuser on the ceiling, 75/25?

You are very welcome. Absorbers will decrease your decay times. Probably the best way to proceed is to install some ceiling treatment, the TEST using real instruments. Record it , tweak the treatment as you go. Do remember that different sources require radically different local acoustics to record well. Vocals and acoustic guitar fare well in dead booths, drums die.

Ceilings and floors are usually parallel in our world, presumably leading to flutter echo. Hardly a red herring. However there does appear to be another reality amongs us, unfortunately.....
As ever, SAC returns to the usual ignorant and vituperative form.
Helpful?
As ever I suggest readers do a search on posts by SAS aka the banned foxfyr. Takes a lot to get banned from GS, but we have a winner here.
Such a search will as ever, show form, nasty form. He does occasionally make a real point, sometimes overlooked and useful ones. However the litany of insult, snide remarks, apparently laughing at us and so on, and on, completely negate that. Perhaps more importantly the seemingly erudite and long winded posts are sometimes simply wrong.
DD

[SAC]

Come up with a new line.

HE is designing a LIVE ROOM. Newsflash! There is more to acoustics than simply eliminating reflections. And more to reflections than simply flutter echo!

Your one trick pony mantra of 'try a bunch of stuff' and 'use more absorption' and if in doubt, 'use more absorption' to create a dead room has grown old. The more mature world of acoustics has moved beyond this.

But you just can't stand or tolerate anyone making a suggestion for a PROVEN alternative approach, can you?

And flutter echo is perhaps the simplest issue in a room to resolve. And ironically EVERY suggestion made in this thread will treat it! But despite that it is perhaps the only reflective issue of which you are aware, which renders it a crisis in every case about which you post, that hardly makes it a critical issue - nor one that requires absorption to be used in your 1 trick pony solution!

Besides, can you produce tests utilizing the precise type of absorption in the precise pattern to be used that will specifically reduce vertical floor to ceiling flutter echo for boundaries placed precisely 15 feet apart? If not, all suggestions of such are questionable. After all, the general use of basic fundamental units arranged in predictable patterns is not sufficient, as you have repeatedly informed us regarding other Basic tools.

And as far as "return(ing) to the usual ignorant and vituperative form." Only you embody this repeatedly in your tired returning role as a fly offering nothing - as you express your derision and mistrust based upon an ignorance of proven designs - just as you have indirectly challenged their widespread objectively verified use for over 20 years by Russ Berger - someone, according to your esoteric standards, apparently well known for questionable designs and even more questionable measurements (sic!!!!) The irony is that perhaps no one in the industry uses the exact measurements you deride more thoroughly and consistently in their associated designs - as ANYONE even vaguely familiar with his history should know!

But then, listening to you, one should refrain from using 2x4's in the building of a projects, as you will not see "test data" verifying that a 2x4 can be used in every possible combination or permutation, let alone a screw driver used in the building of such projects!!! But then, anyone familiar with the basic characteristics of a 2x4 (or a screwdriver) should feel fine proceeding within the parameters of the basic 2x4. And whatever you do, DON'T use a screwdriver to pry open the lid of a can! After all, have you ever seen conclusive tests verifying that such action can be effective or safe????? Oh the horror! But you see, the REAL problem is that dd does not understand how or why they work!

Take some of the time that you use to deride concepts that you obviously do not understand, and do a bit of familiarization with collimating phase gratings that have been well understood for several centuries. And they can be used in more ways than your overly reductionist use of augmenting ABSORPTION. And you only begrudgingly accept that, not because you have a clue as to why they work, but because the word "absorption" is used!!!

So let's review: ETC measurements - what they represent and how to interpret them, the Analytic upon which they are based, collimating phase gratings....the list grows longer...so many things that are prohibitively confusing to you - or, as you have stated, that should be left to only "pros" - which ironically explains allot!...

And please state the obvious correctly. I ONLY laugh at YOU.

[DanDan]

Someone ought to tell him that we don't read these absurd long posts.
I would like to quote this another instance of form by SAC, aka the banned foxfy.The pattern repeats over and over and over.
Here is thread where SAC proposes to diminish a 110Hz floor bounce problem using 'a simple broadband trap'. I offered to test this idea. If there was a solution to floor bounce, we should surely prove it and tell the world?
I invited SAC to specify the test, for fairness. What type of panel, where?
He went silent and left the thread.
floor reflection what to do ?


I am firmly of the opinion that SAC/foxfyr is a consistent negative here on GS.
The forum is suffering since his appearance. He comes here to start rows.
Quite a few people have PM'd me on this. I now urge them and anyone else who has had enough of this pest to directly ask Jay to ban SAC.
It is time.
DD

[SAC]

What was the point, as after 2 or 3 answers he still didn't get it. Just like he failed to understand the concept of a vertical absorber in the form of what many more knowledgeably refer to as a GOBO - although height limited in that case. (and the concept and use of an ETC, a measurement now fundamental to all full featured measurement and analytical platforms...as well as centuries old collimating phase gratings. And heaven forbid he understand or even be aware of the fundamental Analytic of which all the various measurement responses provide a perspective. The list of subjects about which he is ignorant but persists in denigrating grows longer and longer.)

Here's a suggestion sure to confuse the Luddite fly intimidated by "professional"(LOL!) tools and concepts:
You say no one reads my long posts. So how about following your own observation and simply cease reading and responding?

Follow someone else around who talks of concepts you might actually understand. I am sure most will agree to let you handle questions about bass traps affecting acoustic energy below the Schroeder critical frequency and anything that involves clapping. As you waste much of your time objecting to concepts that are not new and which are well established and have been scrutinized by many MUCH more astute than you.

Or is that too kompleekated for you?

But ole' dd likes to be the big fish in a small pond. And heaven forbid anyone dare suggest well established alternative ways of looking at concepts than those posited in his very limited world view. And note how HE follows ME around like a small bedroom slipper that barks and then consistently cries for others' help.

For above room modes and eliminating first order reflections (for reasons I suggest he has little clue) and chasing the ever elusive flutter echo, he has no idea as to what occurs above the Schroeder critical frequency - yet another concept he previously had no clue!

The real irony is that as my focus is on the analysis and behavior above the Schroeder critical frequency and modal behavior, he sure spends allot of time worrying about things he neither thinks important nor understands!

[DanDan]

I offered to perform that test in order to prove whether SAC's suggested solution to the OP's floor bounce issue, would work or not.
SAC's refusal to participate in such a test speaks volumes here.
He knows it will not work. The suggested solution was a nonsense.
SAC =Loud Confident Wrong.

DD

[DanDan]

Some context. SAC was foxfyr until a mysterious reincarnation.
A search will reveal many many examples of SAC starting rows and threads ending in disarray.
I make no apologies for quoting this one as typical. It is.

11th July 2009, 07:03 PM
foxfyr
This message has been deleted by jayfrigo. Reason: repeated insults, bickering, and unnecessary escalation.

DD

[SAC]

LOL!

Folks, here is the concept of absorber placement that is so far beyond the understanding of ol' dd that he needs to test it!




Note: The vertical use of absorption still confounds him. 'Flatlander' sorta takes on a new meaning!

Whatever you do, don't us the word G...O...B...O... around him!


' 'Dem specular reflections is just soooo kompleekated!'

No need to do any searches (or tests!!!)! Just look RIGHT HERE at the result of dd's erudite contributions!



Shoo fly.

Have fun, as ol' dd will be sure to try to rationalize his ignorance once again. And while he's at it, perhaps he will explain the concept of an ETC measurement once more. And please explain the Analytic of which it is one POV.

If he wants to actually accomplish something positive, he can explore why the "ignore" function only works on subsequent viewing rather than on all occurrences including the initial posting.

[DanDan]

SAC, lovely diagram. Now, would you like to post that back in the correct thread and I will do the test. I think we have already dispensed with the totally impractical notion of putting a panel on the floor, so lets just do the vertical, albeit only slightly less impractical. Is a MiniTrap OK with you?

Just to tidy up here-.
SAC is suggesting that a 'broadband' absorber in that vertical position, in front of our speaker, will diminish the level of a floor bounce which is causing a 15dB 135Hz dip in the frequency response. I am saying that a regular panel, say a MiniTrap, will do little or nothing to interfere with the floor bounce for two reasons.
One, such panels are not a barrier to LF, not a gobo either.
i.e. LF will simply pass through, only slightly diminished.
Two, LF wavefronts are not specular, 135Hz will diffract around the panel.
Test over on the other thread shortly......

DD

[SAC]

The poor guy is still distraught over a system where it was never established as to whether a null was caused by a room mode or by the superposition of a direct and a reflected signal - a reflected signal that is essentially identical to the direct signal.

Glad you liked the picture - as I know you were quite upset at our observation that your original suggestion of a horizontally placed absorber on the floor was a bit absurd. You see, words (and "higher maths", and quite a few other concepts for that matter...) confuse ol' dd.

In a system exhibiting comb filtering comb filtering caused by the superposition of broadband signals, the initial null frequency and the subsequent nulls are a result of the time differential between the superposed signals.

But that assumes that one is familiar with superposition, and he is afraid of "higher maths", as he calls them, consisting of addition, subtraction, multiplication and division. Such heady stuff!

But he thinks he is off chasing an isolated ~100Hz signal. Time confuses dd too.

Do whatever you like. You have already demonstrated your abject ignorance of the ETC - what it indicates and how it can be used, as well as the Analytic of which it is a perspective view; the collimating phase grating, and now superposition. For you see, while it is commonly addressed by many in the horizontal realm, the fact that it is addressed in the vertical realm renders it a new and mystical quantity.

And to create the controlled experiment resulting in said comb filtering by injecting a signal delayed by the proper amount to combine with the direct signal, he will test the hypothesis by blocking the arrival of the same signal that creates the anomaly!

Of course, if he understood the principle of superposition and the practical effects, all would be moot. The irony is that he is debating the very basic concept of superposition.

Everyone hold your breath. It should be interesting to see how he screws this bit of solipsism up as well as he attempts to disprove the concept of superposition. Just one more well known and well understood fundamental of physics of which he is oblivious.

You would think that he would be more than busy contacting every major manufacturer of acoustical analysis equipment to tell them of how misguided they are to include such measurements as the ETC response of which he proudly espouses his ignorance of both how the plot an be interpreted to aid in identifying path-length and route as well as to what the perspective itself represents. So - please - tell us again of how it differs from the log-squared response...

Stick to bass traps and hand clapping as you seek out the ever-elusive flutter echoes! But he is fun. ...Sorta like attending the Barnum & Bailey circus without having to leave your home.


If anyone cares, in this exercise from the Theatre of the Absurd, here is a comb filter created with an initial signal superposed with a signal delayed by 3ms, exhibiting an initial null frequency of ~160 Hz. The later the delay, the lower the frequency of the initial null frequency. You damp the reflected energy, and the comb filtering disappears! Its very kompleecatted.