Donny's Acoustics Project

DonnyThompson

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Nov 25, 2012
Location
Akron/Cleveland, OH
Interesting:

"A poly is a victim of peer pressure. By this, they will sound different depending on what the neighboring surfaces are. By itself, next to hard surfaces it can be unpleasant, creating detectable pings. But, when properly located in clusters, in relation to boundaries and/or with absorption, they truly sound totally neutral in a most cool manner. You do immediately get a bigger feel psychoacoustically."


Thanks for the link, Kurt.
 

avare

Member
Joined
Feb 12, 2004
Location
Hamilton, Ontario, Canada
My big question on this is still, would that diffusor be better than a bare flat wall? At what frequency? And is there a way ( that doesn't require an advanced math degree)to calculate this, based on the sequence of the diffusors pattern and the surrounding dimensions/materials? Or is it just kinda, put it up and see what it does?
Do you have the MHoA yet? It details the Davis frequency (3x the shortest dimension's wavelength). The Davis frequency is also detailed in the original papers regarding LEDE. I noticed refereing to LEDE.

Andre
 
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kmetal

Kyle P. Gushue
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Jul 21, 2009
Location
Boston, Massachusetts
I don't know what the mhoa was. I thought it was an article of some sort. I'll take a look at the Schroeder PDF, and see if I can start to make sense. I'm starting from scratch in my learning about diffusion. thanx.
 

avare

Member
Joined
Feb 12, 2004
Location
Hamilton, Ontario, Canada
I don't know what the mhoa was. I thought it was an article of some sort.
A somewhat, but not completely well known contraction for Master Book of Acoustics, orignially written by F. Alton Everest. The current edition is revised by Ken Pohlmann. An unusual book in that the target audience is the recording studio acoustics beginner, yet it is present in just about every serious acoustician's library. I write "just about" because it is present in every serious acoustician's library that I know, but I do not know every serious acoustician.;)

Sort of well known,
Andre
 
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DonnyThompson

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Nov 25, 2012
Location
Akron/Cleveland, OH
There maybe a bit of confusion happening here - or maybe not... Andre may have been referring to the papers he sent to me, and mistakenly responded in kind to K's post, thinking it was a quote from me.

Just sayin.
 

DonnyThompson

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Nov 25, 2012
Location
Akron/Cleveland, OH
From Acoustics and Psychoacoustics, Second Edition by David M. Howard and James Angus,© 2001, Focal Press:

"The reverberation part of the sound in a room behaves differently, compared to the direct sound and early reflections from the perspective of the listener. The direct sound and early reflections follow the inverse square law, with the addition of absorption effects in the case of early reflections, and so their amplitude varies with position.

However, the reverberant part of the sound remains constant with the position of the listener in the room. This is not due to the sound waves behaving differently from normal waves; instead it is due to the fact that the reverberant sound waves arrive at the listener from all directions. The result is that at any point in the room there are a large number of sound waves whose intensities are being added together. These sound waves have many different arrival times, directions and amplitudes because the sound waves are reflected back into the room, and so shuttle forwards, backwards and sideways around the room as they decay.

What is required is a means of making the sound from the loudspeakers appear as if it is coming from a larger space by suppressing the early reflections from the nearby walls. One way of achieving this is to use absorption. The effect can also be achieved by using angled or shaped walls. This is known as the reflection-free zone technique because it relies on the suppression of early reflections in a particular area of the room to achieve a larger initial time delay gap. This effect can only be achieved over a limited volume of the room, unless the room is made anechoic which is undesirable. The idea is that by absorbing, or reflecting away, the first reflections from all walls except the furthest one away from the speakers, the initial time delay gap is maximised. If this gap is larger than the initial time delay gap in the original recording space, the listener will hear the original space, and not the listening room. However this must be achieved while satisfying the need for even diffuse reverberation and so the rear wall in such situations must have some explicit form of diffusion structure on it to assure this.

I'm a little puzzled by this, guys... and leads me right back to my confusion regarding diffusion. I understand what absorption does - at least I understand it a lot more since reading Rod's book, past posts from Space,
and through the text(s) that Andre was so kind to send me - but, and correct me if I'm wrong here (PLEASE)... diffusion is meant to "break up" sound waves so that they are not all hitting you in one "wave" at the same time, correct?

Taking into account the difference between direct sound and reflected sound, is not the goal to disperse these reflected waves so that they aren't all bundled into one predominant frequency - or, to put it a better way, attenuate the reflected sound (in amplitude) so that the whole space is giving you as close to a direct sound as possible?

My room: dimensions: 14' 6" L x 12' 3" W x 7' 11" H, with materials being predominantly 1940's gypsum-wall board (very little insulation between the walls of the room and the adjoining rooms), One 31"x36" window, and an entry with a door (wood), and hardwood floors, with the following treatment in place: (1) 2'x4' broadband (OC703 x 3" thick with a 3" air gap) (1) 2'x5" broadband (OC703 x 4" thick with a 4" air gap),
(1) "cloud" above my mixing position, 2'x4' broadband (OC703 x 3" thick with a 3" air gap), and 3 corners treated with Roxul Safe and Sound 3" thick with 3" air gap to the inside corner)

Can these reflections be managed through the implementation of absorption I've described above alone, or, is it better, as mentioned in the excerpt above, (and as Kurt has chimed in on recently) to achieve this through a combination of absorption and diffusion?

Is this making any sense at all... I fear that perhaps I may not be explaining my question(s) well ?

Testing, testing, is this thing on? LOL

d/
 

avare

Member
Joined
Feb 12, 2004
Location
Hamilton, Ontario, Canada
Long and short of it is summarized in the EBU specs. No sound above -10 dB relative to the direct sound for the first 15 ms after the direct sound arrives. You can absorb, diffuse of redirect the soundn that otherewise arrive within that window. Teh size of home control rooms mke absorptioj the most practical in most homes.

I am that you are enjoying the texts I sent you. Did I mention that when studying acoustics, aspirin is cheaper by the carton?

Nicely medicated,
Andre
 

Space

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Joined
Jun 26, 2007
Mr. Everest says a lot about diffusion in the MHBoA but never really applies it to a small room. I have read on just a few articles how if the listeners ears are somewhere within 6 feet of where the actual diffusion is taking place then it might not be the thing to do in your environment. Cannot support it one way or the other outside of that.

While it is often a sought after component to a well balanced acoustical room, it seems that volume is always the leading factor in if it should be used, since it is very frequency/math specific according to the room in question.

I would never say to not pursue an idea, ever. But I think that Rod understands the complexities of it as Andre does, and with small rooms you have issues to address that are far ahead of the want or need of this type of acoustical treatment, excluding the fact that it would have to be handled by an acoustian not a carpenter:).

Mr. Everest uses the term "commercial" in respect to the builds he took his data from and presents many commercial products, but a longer look is required to get an understanding of is this for me or not.

The gikacoustics link helps them hit the target audience but it didn't really help me except the confirmation that larger rooms can benefit from their product, and we kinda already know that :)

I think at the end of the day, it has to be something that we each spend time on and learn about but not to the point of obsessing :)
 

DonnyThompson

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Joined
Nov 25, 2012
Location
Akron/Cleveland, OH
"I think at the end of the day, it has to be something that we each spend time on and learn about but not to the point of obsessing.."

LOL... now ya tell me. It's a little late for that. LOL


Thanks guys. I would say that you confirmed my suspicions, but I really didn't have any suspicion about it either way, other than the fact that my space is indeed small - compared to most control rooms - and that the smaller the space, the more issues I face. Hehe... that's my new mantra: "the smaller the space, the more issues I face. the smaller the space, the more issues I face." ( In triplet meter.)

My mix position is 6' 8" from the wall behind me, where I was thinking about adding some diffusion. The operative word there is "thinking".

I am that you are enjoying the texts I sent you. Did I mention that when studying acoustics, aspirin is cheaper by the carton?

Nicely medicated,
Andre

The notes and texts you sent me have proven to be priceless, Andre. I can't say I understand all of it, or even most of it, and it's proven to me just how very little I know on the subject, and, not that I'll be able to apply all of it to my current room, because, as mentioned by both you and Space, the room is just too small.
But, I think that learning Not what to do is as vitally important as learning how to do something.

I've read some posts by Ethan Winer, who claims that "you can never have enough bass absorption". I know that Kurt has taken exception to this in the past - but after studying these various notes that Andre sent me, and reading Rod's take on it, it seems like it's true - within the context of my room.

I think that at the end of the day, my best bet, my ultimate goal, shouldn't be to try to equal a room like that which is found in a truly professional facility. My goal should be to make my room sound as optimum as possible, within the limitations it has. I need to be realistic and realize that there are indeed obstacles I won't be able to traverse.

Thanks guys. ;)

d/
 

MadMax

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Joined
Mar 18, 2001
Location
Sunny & warm NC
More aspirin fodder...

Sabine....

I really like the practical simplification....

What's the natural RT60 of the room at any given frequency... Add or subtract reflection and/or absorption (Sabines) to achieve the desired RT60 for that frequency...

Do that for 20Hz-40kHz... and you're prolly pretty well done with it.

o_O
 

DonnyThompson

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Joined
Nov 25, 2012
Location
Akron/Cleveland, OH
LOL... I could just open the window... which is fine right up until we see our first snow. ;)

I haven't taken any measurements sine I've added the treatment I have in place, mainly because I wasn't sure that I was done yet.

Maybe it's time to do that.
 

garysjo

Member
Joined
Jun 15, 2001
Location
Pembroke, MA
Kmetal..those photos of the former Normandy Sound bring back memories. I spent many a late night there in the 80's. Console was a 64cH SSL 4000. Your couch alcove held two Studer 800's. Place was the best around back in the day. I hope Phil is doing well.
 
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