Side Wall, Floor and Ceiling Reflections - Page 3

+1; many of hours (days) could have been saved in my undergrad years if only i had been made aware earlier...

i did that purposely because i know you search everything i say on google. it was a trap.
what you didn't realize is that blackbird C is toole's "reflection-rich" environment on steroids.
you basically argued against yourself by presenting the Fact that the sidewall reflection-rich diffusers were rendered absorbers based on the "preferences" of the "professionals"

you walked right into the trap and invalidated your own commentary. the "professionals" "preferred" sidewall absorption when doing critical mixing/mastering of which accurate localization and imaging is imperative.




i know Jens, btw - he has never been in Blackbird C. try not to produce random internet commentary with regards to the acoustical space from people who have never been in the room.

I could have sworn this was a different thread and that the op was trying to avoid dragging that argument here. Oh well... missionaries have a calling to spread the Gospel I suppose.

I said nothing about talent. Did you follow my example regarding audio compression? I was in UK once and the driver had a diesel Mercedes. I asked him why. He siad he had studied them and loved the way they worked so forever he will only buy diesel cars. That preference is different than what you are thinking as in sign of something necessarily being better. To be fair, Kevin may like it that way too. I am just saying take in he full context here.
There is such a tempation to keep cutting off this quote. Why did you take out the part that says, "....the overall illusion is altogether more spacious and open, to many listeners, more realistic." Does it make you uncomfortable to read the part that many consider that a more realistic way to enjoy the sound? I often see people leave that part out. Strange.

This is what you asked: "do you have documentation on how they are able to simulate diffused reflections from a single source (loudspeaker) like they have with respect to sparse reflections in the anechoic chamber? eg, dense diffused Broadband reflections like that of Blackbird C?" You seem to be seaking perceptual data on the specific products used in that room. I answered that they were doing that testing themselves but have not published it. If you wanted generic information on diffusers, you shouldn't have asked about that. But no, I don't know anyone who is testing what happens when you have 48 inch diffusers on the walls. Please ask the manufacturer of such products for the answer.
Nothing special? They are 48 inches deep. If you put them on each wall, they will span 8 feet. So if you have a 10 foot wide room, it leaves you 2 foot in the middle! They are not examples of any practical treatment method for home use. So any curiousity you have in their use and performance is just yours.

You knew I would find out you had left important part of that quote and still did it? That is like shoplifting in front of the security gaurd in a store and when caught saying, "I did it on purpose. I knew you would catch me! Please let me go!" Oh really?
There is no such view from Dr. Toole. For front and rear walls for example, he recommends absorbers (if you need them) since no positive perceptual effects come from enhancing them with diffusers. Our sense of spaciousness comes from the sides. Just because he advocates reflections in one context, doesn't mean it is for other.
The "professionals" preferred nothing, seeing how they apparently put curtains in front of those diffusers. Oh, that was another trap. Yes?

That said I certainly expect some to follow the teachings of Dr. Toole and other researchers and move away from too much absorption.
He didn't say he was. He said he knew oher people who have. Seeing how Dragon posts under an alias and he does not, I put more weight on what Jens has to say. Hope you understand.

Personally I dont think that helps the point your trying to make. "Many" to me would seem to indicate less than most.

There were two parts to it: one you mention, i.e. that many people prefer it that way. My read of it is that it is not stated as, "it could be either way." Second, it gives a reason why: because "to many listeners, more realistic." Why wouldn't you think the majority of people prefer a more realistic presentation? Isn't that the goal for say, a home theater? That you get lost in the experience and forget where you are and think you are inside the movie? Why would you want a "focused image" in the middle of the screen?

Think of a center channel. How wide is it relative to the sceen? A fraction of the width in a theater. Yet, the dialog comes from the talent anywhere on the screen. If you allow side reflections, the voices will then seem to come less from that point source. The side reflections pull the image wider. To be fair, you hope that the multi-channel mix does that for you but there is certainly goodness here as far as providing more "realism" otherwise.

Isn't it fascinating that the entire case from folks hinges on this one pargraph from Dr. Toole? Hundreds of pages of research papers and books are not believed or want to be followed. But this bit is? Why? If folks believe we should follow the man, then why not listen to everything he has to say? It makes no sense to me other than protecting one's previous beliefs. Let it go. I did it. It is good. Trust me. It is.

the blackbird C primitive root diffusers are not "products". you would know this if you had any sort of experience as to how reflection phase grating diffusers (based on primitive root number sequence) are "designed". some of us here can actually design and construct such custom treatments to match the particular design requirements and constraints of the acoustical space as needed --- unlike your company's listening room who has merely purchased an array of different "non-broadband" (shallow) diffusers and scatterers and hap-haphazardly applied them to the boundary surfaces within your room.

these are the "purchased products" that are randomly applied in your company's showroom - they are not custom designed (calculated) diffusers based on any sort of design requirements. they were applied after the fact - the treatments were not integral to your room's design from conception. that's the difference.


and im merely looking for how toole (in his anechoic chamber studying the perceptual characteristics of "reflections") was able to simulate diffused reflections from his loudspeaker(s). simulating sparse reflections with a single loudspeaker is easy to understand - the process is pretty simple and straight-forward - and his data has been presented. what im curious about, is whether toole has done any anechoic sidewall reflection testings with diffused (specifically, Broadband diffused - NOT colored) reflections --- and how this was accomplished.

i figured i'd ask you first since you would likely be most aware of such testing. is there any data on this aspect? or is his testing entirely limited to sparse simulated reflections via the single loudspeaker.



im asking about diffused reflections via the anechoic chamber -


no - the blackbird C primitive root diffusers are NOT "special" in any sense of the word other than their size and thus effective bandwidth. due to basic physics, this means the treatment (diffuser) must be LARGE with respect to wavelength in order to be effective for said wavelength. much to the same way we require sufficiently LARGE (and thick) porous absorbers to absorb lower frequencies with longer wavelengths. the same is true for diffusers/scatterers. sound has size; surely this is being taught in CEDIA courses?
Edited by localhost127 - 7/2/12 at 2:17pm

sidewall reflections, amir - not "front" or "back" wall, but sidewall. blackbird C is the most reflection-rich room that anyone here has presented. period. do you disagree with this statement?

and you claim no "positive perceptual effect" from front/sidewall diffusers? oh, dear - what do you think 1D reflection phase grating diffusers installed on the rear wall/rear side-walls do? hint: they diffuse energy in the horizontal plane to return energy to the listening position laterally. (read: from the "sides").


yep, the "professionals" "prefer" absorption at the sidewalls for critical mixing decisions where accurate imaging and localization is imperative over the reflection-rich sidewall diffusers. professionals. whose job it is to produce and make critical mixing/mastering decisions of which accuracy of the direct signal is to be maintained.


lol ignorance preserved --- you put more weight on Jens' commentary than dragon's? you may want to ask Jens himself just how imperative dragonfyr (read: SAC) has been to Jens' learning and understanding of acoustics.

what's fascinating is how many users of this forum absorb sidewall first-order reflections - and the lack of users ripping down the sidewall treatments after testing in their own personal reproduction room. care to do a poll of AVS forum users?

You're needlessly parsing words. You claimed that, as a result of special training and of his profession as speaker deisgner, Kevin posseses a unique ability to discriminate between the two approaches: "He is indeed special". The response is the same: No special training/vocation is needed in order to hear the very obvious differences between the two approaches. I was actually helping you out, Amir. The key omitted word is "many". It is not "all".

what's comical is you seem oblivious to the fact that diffusers are absorbers -

Sorry but what are you guys doing by quoting that one paragraph every which way??? That is not parsing? What were you doing then in your posts?
No I didn't tell you that at all. I said that he does this for a living. His job requires analysis of speakers. As was mine to help design compression systems. Our ears become analytical that way and in everyday life we may prefer other things than the population at large. The people in professional space tend to like mostly "dead" rooms because they also want to be analytical with what they are trying to do. If this distinction is still not understood, let's move on.
Well, thank you. I think . And oh, never said all. What Sanjay said originally was right on the mark as far as preferernce of large percentage of the population. You job is to then determine why you don't fall in that category. I am saying that if you use your intuition and marketing of companies building these acoustic products, likely you will be picking the wrong thing. Because the psychoacoustics here is highly non-intuitive.

Anyway, this is all argumentative so let's move on.

Not with respect to their pschoacoustics effect. Yeh, that science.....

and what is their "psychoacoustic effect", exactly? care to elaborate?

and what's wrong with utilizing horizontal dispersion diffusers on the front and rear walls to return energy to the listening position laterally? (read: from the sides)? i thought the side returns were good for spaciousness - especially if the energy is well mixed like that of from diffusers (vs sparse reflections)?

i hope you're learning something!

Nope. I have done enough elaborating for a day . http://www.avsforum.com/t/1413173/does-sound-sounds-better-in-a-room-full-of-furniture-and-stuff-or-without/210#post_22185014
What was wrong was you saying Dr. Toole advocates that. If you still think that, can you please point us to the page in his book that advocates 48 inch diffusers used on every wall?

And is that how you have done your room? Give us your choices of treatment for every surface and measurements of your room please. You post pictures of our set up. Now it is your turn.

so you can't back your statement with any evidence regarding psychoacoustics of absorbers vs diffusers at front/rear walls? really? or your statement that: "Not with respect to their pschoacoustics effect. Yeh, that science....."

did you only just now realize that this is specifically the reason why 1D reflection phase grating diffusers are deployed on the rear wall with the wells oriented vertically such that the spatial dispersion is in the horizontal plane? providing diffused returns laterally via the side walls? well consider yourself informed


can you quote me where ive advocated what toole has said? no?
reflection phase grating diffusers are absorbers, naturally. 1/4wave resonances, viscous losses, and edge diffraction losses. this is why the absorption coefficient (losses) are so much greater for 2dimensional RPG diffusers vs that of 1D.


sorry, amir - sound has size. this is basic physics. objects must be large with respect to wavelength --- are they truly not teaching this at CEDIA courses??

the physics of acoustical behavior isn't modified just because one has real estate constraints. although now that we're on the subject, it would be nice to hear what toole's ideal diffuser is? is it the auralex T'fusor you have deployed in your company's show room?
Edited by localhost127 - 7/2/12 at 3:27pm

I addressed most of this post earlier but forgot this bit. You talk about reading the book, Sound System Engineering. In chapter 6 (Audio and AcousticMeasurements), before he talks about measurement techniques including ETC, Don Davis has this to say:

"The finest acoustical measurement apparatus available cannot duplicate what a trained human listener can achieve. If we examine an unknown signal with all extant equipment we can’t tell if its music, noise, speech, or gibberish, but a $2 loudspeaker allows the trained human listener to tell which, and if speech, what language."

You believe this? Why do you think he is making this preface on a chapter focused on measurements?

Why would the human listener need to be trained to tell the difference between music, noise, and speech?

I would hope that Davis said this long ago, since we now have computerized speech recognition that AFAIK does all of the above.

I'm not sure why this level of complexity was required. If the chamber was big enough, you could just put a speaker where the phantom was. No need for time delays.
Of course then you would have to be careful to make sure the simulated reflection matched with the speakers dispersion pattern - maybe just mount the simulated reflection speaker upside down (to evaluate the effects of ceiling reflection)?

He makes the OBVIOUS observation apparent to everyone with the apparent exception of you, who is the only one who seems to need this pointed out.
The rest of us use measurements as diagnostic tools to examine aspects of behavior as one might use a microscope or telescope, to augment the observation and analysis of that which is beyond the solution of our senses to discreetly discern and examine.

But I feel pretty safe is assuming that there were folks like yourself around to denigrate the practical uses of the microscope and telescope as well.
Edited by dragonfyr - 7/2/12 at 4:22pm

im not arguing the complexity - i was asking if the electric delay was calibrated. eg, were measurements used to verify the electronic delay was truly producing a signal at the listening position (receiver) exactly at the time off-set configured on the electronic delay. and most importantly - what tool did they use to perform this basic level of calibration

it's a simple question; a yes or no would suffice along with the type of tool used for calibration in such a scenario. what good is an electronic delay set at 16ms if the actual signal arriving at the listening position is 15ms. this is a basic check-and-balance verification.

i also want to know how simulated diffused reflections were produced and tested in the anechoic chamber. a sparse reflection is an easy task with a single loudspeaker (delayed signal) - im looking for more information on how they simulated diffused reflections.

Localhost, have you heard the blackbird space? If so, how did it sound to you? I haven't but am curious, I and thought I saw you had (but can't find it now).

question pt 2. How does the depth of a broadband diffuser compare to the depth of a broadband absorber? I'd guess the same, but am not sure.

question pt 3. How would (did) you treat the first reflection point on the ceilings in the room you listen in?

SSSSHHHHHHH!

For those who so adamantly deny the viability and utility of measurements in the time domain, it sure seems unusual that the preponderance of their data is all dependent in one form or another precisely on the very utility that they deny.


To answer your questions above:
2. The depth primarily regulates the low frequency extension. In the case of the diffusors in Blackbird that is ~120 Hz (cited from memory rather than reference docs).

The varying well depths create a wider band of tuned frequencies creating a larger effective bandwidth.

Covering it simply converts the diffusor to a broadband absorber both by virtue of the multitude of 'tuned wells and converting the diffusor into an effective tuned absorber.

3. Treating lateral first reflection points depend upon what response one desires as well as on the polar dispersion of the speakers as well as the topology of the room - as these factors determine what options of many available, are useable in a given space.

Generally speaking without regard to response model desired... Some wantonly apply absorption (either too thin that results in coloration as it is not sufficient to damp all specular frequencies) or broadband absorption. Often, if simply applied 'to control reflections', the surface may actually be overdamped with respect to the actual incident energy.

Alternatively, one can analyze the actual incident energy and identify actual high gain early reflections and their actual points of incidence and apply broadband treatment to surgically control said energy.

And depending on the room topology, the speakers' polar dispersion, the seating distance from the boundary at issue, and the degree of gain reduction desired, this can be accomplished by redirection, diffusion or absorption. Due primarily to the practical spacing requirements for diffusion, absorption is often the treatment of choice. And the manner of analysis generally determines sufficient data to determine whether the treatment is sufficient in size, placement and effective bandwidth to surgically and sufficiently control the actual anomaly and no more.
Edited by dragonfyr - 7/2/12 at 4:39pm

I can only assume the time delay was correct and verified. But I have no way to confirm this without contacting the authors.

I'm, not sure you can simulate diffused reflections in an anechoic chamber. But I could be wrong. Was such a claim made?

Dragonfyr, how did you choose to handle ceiling reflection points in your listening room?

arnyk, amirm, and others

How did you treat the ceiling first reflection points in your room?

Let me back up a bit, as what is done in one room may not be the only choices available in another. Let me try to briefly explain...

Depending upon the actual specular behavioral characteristics in the room (as one would properly deal with modal behavior earlier...), you have several potential choices.

Since we are properly dealing with an assortment of possible combinations and permutations of room topology, equipment Qs/dispersions and desired room responses, you have choices in treatment configurations.

The first two are generally reserved for larger rooms and higher ceilng surfaces.
These are redirection and diffusion.

Limitations that must be considered are spacing from the boundary, as diffusors require a minimum spacing for a sufficiently mixed diffuse field to developed lest one be exposed to slightly modified specular polar lobing replacing one problem with another.

On the other hand, if sufficient spacing is available, 2D 3space diffusors such as the 2D QRD/PRD 'RPG skyline' style of diffusor has the advantage of preserving and dispersing said energy in multiple directions, with a portion of the energy being redirected favorably to the side - lateral- surfaces.

Likewise geometric surfaces can be used to similarly redirect energy away from the listening position toward lateral surfaces where it may be further diffused and returned.

The general limitations are proximity due to room topology and cost. The advantage is that the energy is largely preserved in the space for return in a more advantageous manner.

This leaves absorption. A brute force tool that removes precious finite energy in a small space that we would prefer to retain and use in a more productive manner if such was possible. Thus absorption being a 'last resort', but commonly used treatment.

In order to use absorption optimally, you would identify the actual anomalous high gain early arriving specular behavior and resolve it to its point of incidence. (Some use the ETC response for this, others guess...) In this manner one can then apply properly broadband absorption only to the area sufficient to effectively damp the high gain arrival while minimizing its effects on additional incident energies. In other words, you surgically apply only as much broadband absorption as is necessary in order to address early high gain reflections while limiting and preserving any detrimental overdamping of the finite specular energies in small acoustical space.

Typically, if velocity based porous absorption is the means chosen, that would involve constructing a suitably sized (~4 foot for extension down to ~300 Hz) panel of 3 to (ideally) 4" thick ~3lb/ft^3 Fiberglass or ~4 lb/ft^3 mineral wool suspended an amount equal to the panel thickness from the ceiling surface, resulting in a panel that has the effective thickness of a panel as thick as the porous materiel thickness plus the spacing. This would be placed such that it intercepted only the anomalous high gain early reflections. The total planar surface area would also be moderated such that it was large enough to be broadband, but not so large as to needlessly absorb energy that does not negatively impinge upon the listening area that can otherwise be used productively.