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anonymous 29 May 2014

This past weekend, I began fabricating some acoustic treatment for my mixing environment.
The dimensions are as follows:

14' 6" L x 12' 3" W x 7' 11" H

I am lucky that during construction of this room (back in 1944) the carpenters did not square the walls to each other. With the exception of the ceiling height, which remains constant (hence, squared with the floor) the walls on both the L and W dimensions vary from end to end by up to two inches, so the longest dimension in length is at 14'6 on one end, and 14' 4" on the other end.

In the Width dimensions, at the widest point, the measurement is 12' 3" at one end, and
12' 2 1/2" at the most narrow end.

I have absolutely no idea if this splay is enough to help, in terms of parallel surface created issues..

The treatment I chose was a combination of absorption and diffusion.

This included Roxul material for bass traps in three corners, ( the 4th corner has yet to be treated. I cannot do so at this time, as that corner is behind an entry doorway).

I also incorporated a broadband cloud, using OC 703 / 2". I was able to suspend this, leaving a 1 3/4" gap between the top of the cloud and the ceiling. During fabrication, I allowed enough wire to alter this drop height, if I find the need; as an example, if I wanted to lay insulation in that gap, or, if I wanted to lessen the gap.

I didn't have to frame the cloud; I was able to pull wire through the material at 6 points: 2 on each end, and 2 in the center, offset towards the center of the panel, and attach these wires to 6 hooks, which were attached to the ceiling using anchors. It was placed directly above my mixing position.

I then wrapped this with a dark blue muslin.

My next step is to finish up a 2x2 "Skyline" Diffuser, which I plan to hang on the on the wall directly behind my mixing position. I have the pieces cut, I just need to adhere them to a base plate from which I can hang it horizontally on the wall behind me. This is going to be tricky, because it is heavy.

I haven't actually measured the extent of the change, although I'll say with confidence that I can now hear things in my mixes that I wasn't able to hear previous to the treatment being installed.

The low end now sounds tighter and more defined than it used to be, and I can now hear details in the top end that were hidden from me before the treatment.

I mixed a song last night, played it back on 3 different systems - 1. In 2 different cars, and 2.Thru a Home Theater System. Translation to these different playback mediums was very accurate. I heard no substantial gain or attenuation of any frequencies, other than what the various playback systems - such as the hyped low-end on a home theater system with a sub - would offer inherently.

At no point was any Auralex or Sonex foam used. I still have quite a bit of reflective surface remaining. And, at this point, I'm not quite sure that I really need to treat those areas, although I have enough 703 remaining to build two 2' x 3' panels for each side wall (on either side of my mixing position) if I want, or if needed. I'm just not sure if I need them or not.

I don't want to make the room too dead.

Implementing these changes has given me more confidence in how well my mixes will now translate.

Just thought I'd share.

FWIW

d/

:)

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Comments

anonymous Thu, 06/26/2014 - 04:36

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 Thu, 06/26/2014 - 06:48

kmetal, post: 416345, member: 37533 wrote: 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

avare Thu, 06/26/2014 - 09:25

kmetal, post: 416368, member: 37533 wrote: 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

anonymous Tue, 07/15/2014 - 09:04

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 Tue, 07/15/2014 - 09:19

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 Tue, 07/15/2014 - 19:13

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 :)

anonymous Wed, 07/16/2014 - 04:40

"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".

avare, post: 417154, member: 17005 wrote:
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 Fri, 07/18/2014 - 22:05

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

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