Acoustic Fields Inbox #5

1) There is a lot of confusion between absorption and barrier technology. I don’t know why that is, but it seems to be. A barrier is just that: if you have a noise source, someone yelling on the outside of your room and you are on the inside of your room, the quickest way to stop that noise to get into the room is to construct a barrier. A barrier is a boundary surface between the noise source and a receiver. The quickest way is to build a barrier between the source and the receiver. Now, when you build your barrier between the source and the receiver, there you use sound absorption technology on the inside of the room. That is the big difference. The absorption is an inside treatment for reflections and all the issues that go on inside the room. You don’t use absorption as a barrier. And we get a lot of that: „I have got some foam and my neighbor is playing drums, so I’m going to put some foam and this will stop the drum sound from coming in“. So you have to be really careful about what you are doing here with the terms. Absorption is a technology that you use to lower reflections, minimize pressure within a room. A barrier is a technology that you use to isolate yourself and others from noise issues.

2) Here is another one I get a lot of questions about, I don’t know why, because it is not that popular anymore, it is very expensive and not really used in studios today: Angled or splayed sidewalls. We know from our two channel setup that we have a left and right speaker. The thinking is, if you angle the side walls, that you reduce the reflections at the listening position because the angles send the reflections behind the listening position. So what angle do you use? It depends, depends on usage, depends on distance from speaker to listening position, depends on listening position to the rear wall, depends on size and volume. And those of you that are in construction, building a wall that has a 6, 7, 8, 9, 10 degree angle on both sides, can be very expensive. We don’t use any of that in our construction, we stay with a rectangular room because it is predictable and consistent with it’s low frequency issues, with it’s middle and high frequency issues and, more importantly, with it’s treatment issues. So with that predictability and consistency you don’t really need this because we have the technology today to minimize reflections. We don’t have to spend the extra money. I would rather see you spend the extra money that you save by not doing angled or splayed walls on the treatment side of the room.

3) Structural versus airborne energy: Structural is energy, vibrational acoustic, airborne energy that hits a structure like a barrier. Like the example where we have a person, another person and a barrier in the middle. So when one of them is screaming the energy hits the barrier and starts to move. And this movement has a particular frequency response, and the frequency response of this noise determines how thick and what materials we use in that barrier and how quiet you want to make this. So if you really want to make it quiet maybe it has to be thicker, maybe not. It just depends on the frequency and the strength of all that energy. So, structural energy is energy that strikes a structure and gets the structure moving, like your speaker cabinet, a subwoofer for the cabinets poorly designed, the driver goes back and forth, and the cabinet makes more sound than the driver. So you have to be careful there.

Airborne energy is energy that goes through the air. So you have airborne here first, then it strikes the barrier and becomes structural. The goal is not to allow the structural to produce noise on the inside and become airborne energy on the inside. So we have two different approaches, two different ways to look at energy. Some overlap in the disciplines, but the key to the application of those is in the differences between the two. That’s how you will be successful with it.

4) Vocal room size / volume: usage. How many people we are going to put in our vocal room? How big does it have to be? There’s a big difference between one person, two people and three people in the room. So you will have to be very careful to choose the right volume depending on the number of people that you are going to put in a room. And use diffusion and absorption in your vocal rooms, that is a great way to get great sounding vocals that have lots of air, lots of liveliness, lots of separation and definition and realism and not this boxy feeling that you get in some vocal rooms where everything is just centered and close, there is no air or anything in the presentation.

5) I had a lot of calls from noise, people having noise issues. I have a client that has a machine shop fifty feet away from his house, and it is producing structural vibrations as these presses go up and down and slam. Then you have the machine shop and a house near to each other producing all this energy through the crown and traveling into the house. So what do we have to do? We are going to build a barrier between the house and the shop to block that. And the depth, thickness and size depends on the frequency and the strength of the signal. We don’t want to build any more than we have to because it is expensive, but obviously we don’t want to make it thinner than we need to, because then we still have the problem after building the barrier.

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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.

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