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We’re going to start a new series about questions I get in my inbox. Because I see a lot of the same questions all the time, and I thought if I start listing a few of them, walking through them, it will be a lot easier. It will also be a lot easier for me, rather than answering the same questions a hundred times.

So let’s work on the first question we get a lot of times: What type of material for X Y or Z usage?

It’s impossible to tell. There are general guidelines that you can use, but this is the problem in the literature today, there are too many general guidelines sacrificing too much sound quality. And this hast to stop. We have to select the material for the usage, and we have to define what kind of material we are going to use by the usage. Vocal booth is all about noise issues, right? We’ve got to have it quiet, so the barrier or the shell technology has to be related to the amount of noise that is outside of the room in order to get the inside of the room correct.

So what type of material do I need in my vocal booth? Unknown! You’ve got to tell me more. You have to tell me about your noise, we have to measure your noise, we have to know what frequencies the noise is at in and what it’s strength of amplitude is in order to design the proper barrier to keep it out, because we don’t want them in our recording. So what type of material do you use in a vocal booth? It’s too dependent on too many variables. One material may work for one situation, one material may not work for another. Inside the room in a vocal room, treatment is usually absorption, it’s usually foam. Well diffusion is a good quality treatment to use in voice also, and we’re going to do series about that. Diffusion is an amazing technology, but really misunderstood, and not widely used because it’s so misunderstood. But if you start using it, start moving your microphone around and start to make your recordings you will be like: „Oh my God, I missed so much in my recordings by not using diffusion“, especially for voice. And we’re going to do a series of videos – is microphone distance dependent from the diffuser? Is frequency response dependent from the diffuser? A lot of variables, but once you get it dialed in, it’s incredible. You don’t have to put a lot of electronics, as I call it stink, on the signal.

How do you soundproof with carbon?

Well the bottom line is: you don’t!

Carbon Technology is a sound absorption technology, not a sound proofing technology, which we all know from past videos that I do, there is no such a thing as soundproofing. Sound is not proofed, you don’t stop it a 100%, you manage it. You lower levels. Sound transmission class ratings are based on scales that use frequencies starting at 125 and going up. So you have to be very, very careful by using STC numbers sound transmission class ratings which determine noise loss of a barrier, construction methodology. So there is no such a thing as proofing, and you definitely don’t proof or isolate sound with foam. Even our carbon technology, it’s a sound absorbing technology, you will remember from past videos, we have sound absorption technology and we have barrier technology. Completely different sizes, some overlap. But you will get the idea if you look at our other videos.

What type of sound proofing, once again, for floor and ceiling?

Well, let’s get rid of the word soundproof and substitute for managing. So what type of materials do I have to use to manage the noise, it’s really what we are talking about here, in the floor and ceiling? Once again, I know, how much noise do we have to manage, how critical is it that we don’t have any noise leaving the room? How critical is it, especially in a control room, how critical is that we don’t have noise coming in? The bottom line here is there is, no such a thing as sound proofing, but sound management. And that is frequency and amplitude dependent, and floor and ceilings are once again usage dependent. What are we trying to do? With barrier technology and isolating from noise you want to measure and quantify the noise. Because the measurement and quantification of the noise determines how much you are going to spend stopping it. So there is a direct correlation between the numbers and costs. You don’t want to put any more material than you need and if you guess barrier technology you always guess wrong, because you will thing that more is better. And that’s not necessarily the case. It’s all dependent on frequency and amplitude, so we’ve got to measure twice and cut once.

How do I soundproof a control room?

The same issue here, there is no such thing as soundproofing, and control room, we have to know a lot of other barriers. That’s how I came up with the room form that we have you fill out, because that at least get’s it started. That gives a size and volume and usage. And then we have the number of energy sources in the room. So if we know the size, we know the volume, and we know what you are trying to do in the room, then we can treat accordingly, for the barrier or the treatment side of the room inside, all usage dependent. So I build the wall, a double walls like literature says, I use drywall and I use green glue, and I use my resilient clips. But my low frequency energy just goes right through. Well, that’s because the double wall with this arrangement here is really only good for frequencies above 125 Hz cycles. Low frequency energy just goes right through it. My people call me all the time: „I built my home theater using this“ – „How many subwoofers do you have in the room?“ – „Four. Four 15s.“

„How big is the room?“ „Oh, it’s average: 12X13X8 foot tall“. So it’s closet. He’s got four drivers that are fifteen inches in diameter, and to use the technology is only good for frequencies above 125 Hz, so do no harm! Remember, if you put too much energy in a too small room that violates our first acoustic rule that we have talked about in our last series. So you have to be very, very careful, and literature is full of a lot of misinformation. You have to sort through it. Step back, take a deep breath and realize that the energy within the room has to be managed within the room, but the energy outside of the room has also have to be managed, and there are to separated management technologies.

This is an unedited transcript from our video series from Acoustic Fields. There will be some errors in grammar and sentence structure that occur during this translation process.

For complete understanding and comprehension, please view the video which is included in this text. For any additional information regarding this topic or others relating to room acoustics, please contact us directly at:

P: 520 – 392 – 9486

Dennis Foley

I am an acoustic engineer with over 30 years’ experience in the business. My technology has been used in Electric Lady Land Studios, Sony Music of New York, Cello Music and Films founded by Mark Levinson, and Saltmines Studios in Mesa, Arizona, along with hundreds of others.

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