Acoustic treatment: putting theory into practice

Hello all. I am so glad to have found this site. what a great place! Thanks to the mods, admins, and contributors! My question regards the application of acoustic treatment devices (bass traps, absorbtion/diffusion panels, clouds, hangers etc.) according to the specific freq. characteristics of a control room. How does one create and position the correct type of treatment according to the fundamentals, nodes, modes, eigenfreqs. etc of a room? So once one has calculated all the modes/resonances etc, say at 41-59-65-72-81hz etc., are there certain places that the treatment needs to be positioned (as per the Eigenmode Calc) in order to dampen these freqs? Or is there a general rule of thumb for this sort of things, like just putting traps in the corners?. Of course, im sure it depends heavily on the size and shape of the room. Likewise, for high freq. diffusion (or are they to be absorbed? cant remember), are there general rule-of-thumb positions for any treatment processes (like the "mirror spots" etc.)? There is much info on this on the site, but (perhaps due to shortsightedness) I have been unable to find anything answering this specific question. I am accept I may be wrong tho. Cheers Chris

Hai Chris, and welcome to JLS ! Instead of giving you the fish, I'll teach you how to catch'm yeself. Sure, there's plenty of good info on this site. (perhaps too many? who knows!) So, my advise is to take your time and read this forum. Every part matters. Learn the basic and you'll soon say "DAMN! what an Idiot I was, asking these stupid questions! It all seems so clear to me now" :mrgreen: (neh, there are no stupid questions to begin with) Read, learn and design. good luck!

The Silent Coup wrote:

So once one has calculated all the modes/resonances etc, say at 41-59-65-72-81hz etc.

You're in good hands with Ro, but I'll add two relevant points: 1) The only way to know for sure where a room has problem frequencies is to measure. I've seen mode calculations be off by as much as 20 percent from what is measured. The problem is mode calculators assume perfectly rigid walls with no losses. Real-world walls (and floors and ceilings) flex some, and so absorb some, and the very act of absorbing shifts the resonant frequencies lower. 2) For most rooms, especially smaller rooms, you can toss all those frequencies aside and just use broadband absorption. --Ethan

thanks for the info guys. @Ro - i have spent some good time at work scouring these pages (ive got to do something useful while im there!) and have indeed found lots of useful information. indeed, soon after making this post i found a thread that went someway towards an answer to my question. sometimes however, one has a certain itch only direct contact can scratch. @Ethan - I thought this may well be the case, especially considering the building I/we are occupying with our studio. In order to measure the frequency characteristics of a room, does one require a specialist measurement microphone? or would a decent quality mic suffice? and what analysis software is there for this task?

Hey Chris. Some quick answers for your questions:

In order to measure the frequency characteristics of a room, does one require a specialist measurement microphone?

A measurement mic is best, but any mic with reasonably flat response in the range 50 Hz to about 8kHz. will work. Best kept secret: Some sound level meters have direct output jacks for their mics... You can probably pick up a good one on e-bay for a few bucks or so, with any luck.

or would a decent quality mic suffice?

If the response is reasonably flat, it will work: check the manufacturer's published response curve for the mic you have in mind. As long as the curve doesn't wiggle up and down more than around 3 dB or so for the area of the spectrum you are interested in, you should be OK.

and what analysis software is there for this task?

ETF is a good one. Costs around US$ 150, I think. Room EQ Wizard is also good, and is about US$ 150 cheaper than ETF! (Yup, it's free....) - Stuart -

The Silent Coup wrote:

does one require a specialist measurement microphone? or would a decent quality mic suffice? and what analysis software is there for this task?

I use the freeware REW. As for microphones: Comparison of Ten Measuring Microphones --Ethan

cheers guys for the info. budget restrictions mean ill have to make do with my SE Electronics Z33000 mic, which only has a little boost near the top end http://www.seelectronics.com/Z3300a.html. ill post up the results once i have them. and then for the next step... chris

ill have to make do with my SE Electronics Z33000 mic

Looks like it should work. Set it to "omni", of course.

I've got the cheapest mic: behringer ECM8000 :)

As for microphones: nice one Ethan.

as for room testing protocal, are there any specific precautions that need to be take into account when doing it? mic position: listening sweetspot, or middle of the room (8m L x 4.5m W x ~3m-2.3m H (sloping ceiling))? i presume RoomEQ Wizard generates the test signal. Btw, is REW Windows XP or later, only? I use Win2K at the studio. I tried to install it at home on the same OS but it came up with some errors. I guess ill have ask the manufacturers too. Still astounded with the community and support here. Chris

The Silent Coup wrote:

mic position: listening sweetspot, or middle of the room

For a control room you measure mostly at the listening position.

is REW Windows XP or later, only?

Not sure, but REW requires the Java runtime. There should be a link to that somewhere in the docs. I'd be surprised if the runtime was not available for Windows 2000 too. --Ethan

what type of room are you trying too measure btw? tracking or control room?

Ro wrote:

what type of room are you trying too measure btw? tracking or control room?

both and neither! my mate and i have a small-ish studio facility where we produce mainly electronic-based music (jungle, breaks, hiphop etc.). we do odd bits of recording in a small booth there too. our ideal aim is to have the "control" room acoustics good enough for us to do accurate mixdowns of ours or others tracks, either via the desk or in-the-box. while the booth has been floated and treated (not great but sufficient), the control room has nothing. we are planning to build a "facade" on the opposite wall to the booth, where the window and mixer are situated - partly for extra insulation (lots of noise coming from neighbours), partly for acoustic improvement. however, before embarking on this project, we want to find out the freq. makeup of the room as it currently is, hence the need for some room EQ analysis. we have drawn up plans for this, but as neither of us use SketchUp, these havent been posted up here yet.