Poly Diffuser effectiveness?

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Postby Bob » Sun Jan 13, 2008 2:54 am

Is it possible to put a skyline on the left wall, and a skyline on the right wall, and maintain symmetry?
(i.e. can you rotate a skyline, and get the mirror shape)
Would you want to maintain symmetry even in diffusion? (or does that miss the point)

A QRD can be turned upside down, and would be an opposite wall mirror.
A poly doesn't even have to be turned upside down.
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Postby Rod Gervais » Sun Jan 13, 2008 3:51 am

Bob wrote:
Would you want to maintain symmetry even in diffusion? (or does that miss the point)

A QRD can be turned upside down, and would be an opposite wall mirror.
A poly doesn't even have to be turned upside down.


Bob,

I would have to believe that this was the case.......

Acoustic symmetry in a control room really is a critical item - you can't acheive proper stereo imagery without it.

There is though also a possible issue with Psycho-Acoustics here as well.

I know for a fact  that the control room in the "C" suite at Power Station New York  (now Avatar Studios) had to be modified (shortly after construction) before any of the big boys of the industry would work in it.

This was even though it could be proven through room measurements that the physical acoustics in the room were not a problem.

If you sat behind the desk (facing the tracking room) the door entering the control room was on the right wall  - up against the front wall - on the left was a wall with a wood slat finish - it was built adjacent to a brick wall.

No one (of any import) in the industry would work in the room because they swore the stereo imagery was screwed up in the room.

In order to fix the "problem" Tony Bongiovi (the designer of the room) had to install a complete matching door on the left hand side of the room...........

It was amazing how suddenly everyone loved the control room - now that it was symmetrical as it should have been from the start........

The brain can fool itself in a lot of ways -so that ultimately it perceives that which may not (or doesn't) exist..........

I won't design a control room that looses symmetry at any point in the room...........  I do false doors if I have to - windows - install matching rack bays if using the side walls - rack bays which are symmetrical from the room center when using the back wall - I do whatever it takes to maintain perfect symmetry left to right form the front to the back of the room.

I even do this with hidden treatments that no one could ever see or imagine existed...................

I leave nothing to chance in that respect.

Rod
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Postby BIG8 » Sun Jan 13, 2008 4:23 am

Bob wrote:Would you want to maintain symmetry even in diffusion? (or does that miss the point)


I also asked this  boring question  :wink:

http://forum.studiotips.com/viewtopic.php?p=43250#43250

:lol:

Cheers,
Jean
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Postby Bob » Sun Jan 13, 2008 6:27 am

Except I meant: how obsessive should one be about it.
Is it ok to have a skyline on the left wall, and another one on the right wall, even though there's no orientation of a skyline that would be symmetrical.
In other words, is it ok to use an RPG Skyline at all, ever, even in pairs.
Or do you Have To Build Your Own, if you're going to do something skyline-ish, so that you can make them symmetrically.

Rod's point, if I can paraphrase, or at least my understanding, even if it is actually acoustically perfectly symmetric, it must also look symmetric.

My question is just can one have an RPG Skyline on the left wall, and another RPG Skyline on the right wall, and achieve acoustically perfect symmetric, as far as brain/measurments are concerned.
Regards
Bob Golds
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Postby BIG8 » Sun Jan 13, 2008 8:30 am

I hear you, Bob, even though I bundled the adored Polys in the question, which kind of defeats the question as being one of the few diffusers that can be/look symmetric.

I also concur with Rod's mention of the 'possible' psycho-acoustic issue with the need for symmetry to achieve proper stereo imagery.

I ‘knew’ way before my inquest into acoustics that speakers had to be equidistant from corners, in small rooms, to achieve a balanced bass response, else you'll have a more bass rich speaker than the other.  In fact, I 'knew' without knowing, I did not verify it.   Knowing now that the human ear cannot perceive the direction of LF sounds (due to the omni-directional nature of LF sound waves?), I wonder if it really makes a difference  :roll:

About the 'real' need of perfect left/right symmetry to achieve proper stereo imagery, I cast my doubts....
-first of all, further to reading interesting topics in this forum, there is no way to define or quantify proper stereo imagery, so how good is it with perfect symmetry? how bad is it without?  :roll:
-is it that we want the same imperfections or the same perfections on both sides to achieve a balanced influence on the direct sound from the sound source (speakers)?
-If we take care and deal with all the first reflection spots, we've gotten rid of all the low-mid to high frequency interference with the direct sound from source, what do we have left to affect that stereo imagery? LF from room modes? LF being omni directional, is symmetry still important?

I am even more inclined to put this symmetry need into question now that my room is 80% completed, and am working on the fine details.  It is probably the most un-symmetrical room around. I still don't have the first reflection absorption panels/clouds up.   Imaging is already stellar, better than I've heard it so far, but how do I qualify stellar imaging to you guys?
I can feel where treatment of first reflections is going to take me, there is a tad of tidying up in the upper mids that will be taken care of, but I've already done some urgent mixes in this room, and they translate very well!  I've also heard mixes I've done before, and rediscovered details I didn't know were there, sitting at a well defined position in the mix, as if I had meant it that way  8O.  I also listened to reference mixes which I use to learn the characters of 'bad' rooms before I mix in them: no unpleasant surprises, just more detail.. :D

So symmetry, ,,,,,,is it just a 'Slogan'?:twisted:

[Waiting to be put straight mode]

Cheers,
Jean
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Postby Ido » Sun Jan 13, 2008 11:41 am

diffusion:   I think this subject is getting so blown over, one should just do good rooms for the ears, not the brain.
making a good room can be simple.

symmetry:  IMO and in my experience, this one is overdone too. important? of course, always strive for it.
has to be absolute, if not you are screwed? hell no.
I know of non-perfect-symmetry rooms that sound..  perfect (well, almost)  :D (well treated rooms with window on one side wall).
phsyco-acoustics? sure, all the time, I surely don't belitle it,  this audio-phsyco is one big salad to begin with regarding all aspects,
but it doesn't mean symmetry has to be such a severe absolute, surely not for the average clever DIY studio guy (as opposed to the guys Rod mentioned).

Jean, why are you troubled with this? if it's good, it's good.
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Postby Ido » Sun Jan 13, 2008 11:48 am

Bob wrote:There are lots of great poly rooms. I bumped into this old one again this afternoon
http://www.royaldevice.com/sala%20audio ... %20up1.jpg
http://www.royaldevice.com/sala%20audio ... ct2007.jpg
from http://www.royaldevice.com/custom.htm  (the huge in-the-floor Subwoofer Horn room)


Bob, I'm really curious how it sounds there (the first pic), I wonder if it's that good and un-colored.
I don't know, just wondering...
I don't like overdone repetitive acoustics, even from just a conceptual point of view.
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Postby BIG8 » Sun Jan 13, 2008 11:57 am

Ido wrote:Jean, why are you troubled with this? if it's good, it's good.


he he he :lol:  not troubled, Ido, fascinated.  This "symmetry for better imaging" talk is exciting me so much, yet there's nothing to qualify it.  I am interested at the theory and explanations behind this, or is it just a "slogan" which Eric likes so much. :lol:

Cheers,
Jean
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Postby Terry Montlick » Sun Jan 13, 2008 12:01 pm

Eric.Desart wrote:
Terry Montlick wrote:Bob,

..... If I am designing for a tight space, I will use the former to provide what I think of as a more "spacious" sound.


Terry,

Just joking ....
:mrgreen: You preserve them for tight spaces where, due to the needed distance versus frequency, this, not to be used, proximity ranges overlap ??????
If you build them in mirrors, there are so many reflections that the space indeed becomes HUGE, but looking a bit confusing I assume.
.

I know.  :mrgreen:
It works, even though it violates the "rules" -- so I do it anyway! :mrgreen: :mrgreen: :mrgreen:
In theory, you need meters for all the different phases to sum nicely. In practice, a few feet will do. :)

Regards,
Terry
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Postby Eric.Desart » Sun Jan 13, 2008 12:26 pm

Rod, Bob

I think symmetry is important on the direct source and early reflections, meaning these sound paths which, in function of level, significantly contribute to the directivity or interference at the listening spot.

The walls in studio C of blackbird studios are NOT symmetric designs but just designed to create a chaotic diffuse field at a lower level.  In fact that's 1 super large diffuser split in parts to cover these walls.  That ceiling is a super huge skyline with skylines on top.  How can that be symmetric with the floor?  That main ceiling skyline in itself is not symmetrically build versus speaker positions. That's designed to create chaos.
That's just one huge scaled skyline mounted on the ceiling.

If you speak about diffusion on mirror points, or absorption, the idea is the decrease the impact of these sound paths and make the sound more spatial.

A QRD makes sound chaotic, polys do that, even absorbers do that.
The idea of a diffuse field is that sound comes as much from all directions, hence getting rid of directivity.

In fact to get a spatial effect you need some controlled chaos.  What is the meaning of perfect symmetric chaos? Sounds as a contradiction isn't it?

My experience is that a lot of musicians or audio engineers are not necessary objective listeners, who can't exclude their brain from what they think they hear or ought to hear.  Psycho-acoustics is certainly huge part of that.
I've done some tests in my time to check in how far I could trust there capability to distinguish between what they heard or thought they ought to hear.
.
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Postby Terry Montlick » Sun Jan 13, 2008 1:53 pm

Eric.Desart wrote:My experience is that a lot of musicians or audio engineers are not necessary objective listeners, who can't exclude their brain from what they think they hear or ought to hear.  Psycho-acoustics is certainly huge part of that.
I've done some tests in my time to check in how far I could trust there capability to distinguish between what they heard or thought they ought to hear.
.

Sounds familiar. I have sometimes "accidentally" administered basic audiology tests to the professed golden-eared, in the process of setting up measurement equipment. The results are strictly confidential, but suffice it to say that very few people measure up to such self images.

I claim no golden ears. My hearing is rather average. Only my audio knowledge and experience count for anything!

Should also note that psychoacoustics is a bit of a misnomer in this context. It is rather something else -- self-delusion? Wishfull thinking? Of course, psychoacoustics is the science of ear/brain perception (masking, critical bands, localization, precedence, etc. etc.), something which governs us all --- great and small-eared. :)

Regards,
Terry
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Postby Eric.Desart » Sun Jan 13, 2008 2:36 pm

Terry Montlick wrote:Should also note that psychoacoustics is a bit of a misnomer in this context.


I do agree, but didn't know how to call it.
:mrgreen: I wrote/added some alternatives now here, but for self-safety reasons deleted them again.
.
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Postby Scott R. Foster » Sun Jan 13, 2008 3:06 pm

I ‘knew’ way before my inquest into acoustics that speakers had to be equidistant from corners, in small rooms, to achieve a balanced bass response, else you'll have a more bass rich speaker than the other.  In fact, I 'knew' without knowing, I did not verify it.   Knowing now that the human ear cannot perceive the direction of LF sounds (due to the omni-directional nature of LF sound waves?), I wonder if it really makes a difference  


Equal amplitude is critical to a balanced stereo image... if by moving one speaker closer to the corner you raise the loudness of the low band you have crippled the image in that frequency range... its starts out skewed per frequency band, and nothing you do will fix that.  I don't see anything subtle about the circumstances you describe.... equal perceived loudness and phase arising from equal actual signal output amplitude and phase is fundamental to the concept of what stereophonics is, and how it works.  The directionality of the propagation of low frequencies versus high frequencies won't save you.

Rod may go farther than would be practical for a mere mortal in his pursuit of pure bi-lateral symmetry, but that don't mean he aint right to do so.  His client's, in my view, are well served as a result because a finely balanced stereo image is an awesome thing - when you can turn a pan knob a couple of degrees and hear the source move it is astonishing compared to your average mix location where much larger changes are required to produce noticeable results.

This is not to say there is no self-delusion in assessing such things.  I would readily accept anecdotes of users claiming the ability to perceive imbalances beyond any actual truth... in cases where acoustic symmetry exists but such is contrary to what one sees [the layout is materially more acoustically balanced than visually so] I would not be surprised if one of the "golden eared" were to claim to hear things which simply were not there.

OMG my ears are bleeding... change the steel doorknob on the left to match the brass one on the right.   8O
SRF
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Postby Scott R. Foster » Sun Jan 13, 2008 3:27 pm

but how do I qualify stellar imaging to you guys?



With your eyes closed... and the bass guitar panned to the ceneter... how far do you have to move the pan knob before you hear the bass move from the center of the image to your own subjective assessment of the position "just left of the center"?  

Try the same test with headphones and compare your answers... if they be similar, then your image balance is stellar.

A balanced stereo image is just that... balanced... poised and counter-poised... an enormous flat rock resting on a finely wrought balance point.  A small change in pressure on one end, and the rock tilts.... because it is balanced.

If your right speaker in stuck in a room corner and you left speaker aint, you are going to be cranking hard on the pan knob to get the bass guitar to move leftwards out of the right corner... because your image aint balanced... instead it is down in a hole on the right side.

My $0.02
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Postby Zaphod » Sun Jan 13, 2008 4:52 pm

What if you seat in the listening position with a signal generator making a
sine wave, and see what happens when you move the frequency up and
down the spectrum?

I figure with perfectly balanced speakers the sound should be still in the
centre while when that's not the case anymore it could move left-right.

And you do that in a room full of polys and QRDs so it's not OT  :mrgreen:
I try never to get involved in my own life. Too much trouble. :mrgreen:
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Postby BIG8 » Sun Jan 13, 2008 5:30 pm

Thanks for taking the time and going into depth, Scott + Zaph.

Got to nap, early flight tomorrow morning, back the day after.  If I get a mom tomorrow, I will extend, else, on Tuesday.

Cheers,
Jean
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Viva checking your mixes outside the mixing room! :D
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Postby bert stoltenborg » Sun Jan 13, 2008 5:41 pm

I thought this site was about bashing the magic out of acoustics.
I seldom read something more stupid than some of the reactions here.
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Postby Rod Gervais » Sun Jan 13, 2008 5:58 pm

Eric.Desart wrote:
Terry Montlick wrote:Should also note that psychoacoustics is a bit of a misnomer in this context.


I do agree, but didn't know how to call it.
:mrgreen: I wrote/added some alternatives now here, but for self-safety reasons deleted them again.
.


I had to think about it as well............  but by this definition of Psychoacoustics I do not feel it's a misnomer at all.......

"The science pertaining to the interrelationship of psychologic phenomena and the individual's response to the physical properties of sound. "

http://cancerweb.ncl.ac.uk/cgi-bin/omd?psychoacoustics

(Above is from an online medical dictionary)

I have a great difficulty finding any other term to explain the existance of this experience with seasoned recording engineers.

This was one subject of discussion at the recent round table seminar about the legacy of  Power Station New York at the last AES in NYC  - and there was consensus of this happening from the forum participants - which included  Tony Bongiovi, Bob Clearmountain, Neil Dorfsman, and Nile Rodgers (it was a subject there specificallly becuase of the "C" control room issue - which all of the parties involved in the discussion were personally aware of.)

If anyone hasa term which would be more applicable I would be happy to use it.

Sincerely,

Rod
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Poly Diffuser effectiveness?

Postby TWDay » Sun Jan 13, 2008 6:44 pm

Last night I had a wonderful demonstration of poly effectiveness. I was recording a live large jazz orchestra in a local college auditorium for a television program. It is a religious college, so they have an infinite budget for equipment and their FOH engineer mic'd every instrument on the stage, sometimes multiply. The producer wanted me to take a feed from the FOH and use that for the show sound, but I have had poor experiences with live sound engineers and wanted a backup. I put out a trio of omni condensers along the front of the stage, used a trio of mics on the kit, pulled a DI feed from the bass, and hung one solo mic in the center of the orchestra. And crossed all of my appendeges.

As usual, the FOH sound feed sucked. The sound goof appeared to have all mics up always and the phase distortion disaster coming from the FOH console was garbage. Surprisingly, the sound from the trio of omnis was killer, except for the occasional low signal from solo instruments. This morning, the station was barraged by calls from listeners who wanted to buy a DVD of the show and the camera guys said what they heard on the playback was completely different than the disaster they heard in the auditorium.

Finally, to the point, the stage was completely surrounded with heavy lighting polys. Each poly unit was about 6' wide and 20' tall (the arc was about 2' in depth) and the ceiling was also decorated with these same units. On stage during the sound check, I was astounded at how crisp and clean the band sounded. That encouraged me to go light on the mics (and the lack of available channels in the control truck) and try the Eargle omni placement tactic. My center orchestra solo mic worked about a half dozen times and failed me about as often, but I still had a big band sound with a really diffuse sounding room reverb. The hall was another problem, but it didn't really screw up the recorded sound any worse than the usual Saturday Night Live mix.

I'm doing a string quartet in that same room in a month, I'm looking forward to being without the FOH mix and stage monitors altogether.
T.W. Day
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Postby Terry Montlick » Sun Jan 13, 2008 7:04 pm

Rod Gervais wrote:If anyone hasa term which would be more applicable I would be happy to use it.

How about "auditory suggestibility?" 8O

It is certainly more polite and accurate than, for example, "auditory dementia." :evil: :mrgreen:

Regards,
Terry
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