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Let’s talk about barrier processes, now we’ve discussed barriers in the past in numerous videos but I want to give you an idea about the process that we go through as engineers when we design a barrier. Let’s start with the definition. What is a barrier? A barrier is a partition that’s between us and the noise source, it can be anything – the noise source can be anything. It can be someone playing their stereo loud and you’re in the next apartment, so the barrier is the existing wall. Now it may not be a very good barrier because you’re not very happy with the noise level, well okay, so how do we work with that.

So it is a structure that we place between a source and a receiver. Here’s the key we have to keep in mind, here’s why people get all mixed up on this, there is no one structure that works for every situation, there are types and there are certain construction methods that you use for certain frequencies but it is always dependent on what frequencies you’re trying to isolate from. If a person is singing in a room or a garbage truck is driving by, completely different amplitudes, and completely different frequencies. A singer would never be able to get down to 40 Hz but a garbage truck does and you can tell that by all the car alarms that go off when they drive down the street. That’s a huge wave of energy and the car alarms are sensitive to vibration so this huge 40 cycle wave strikes the car when the garbage truck goes by and off goes the alarms. In Los Angeles, in our studio there we don’t do anything from a recording standpoint on Thursday morning because the area’s full of garbage trucks, we just minimize that kind of energy and stuff for videos and things like that because it’s just too much, it’s too much energy to have to deal with and it doesn’t happen that often so we don’t want to build barriers to deal with a couple hours of one day’s activity so it’s always a cost thing.

So what are we trying to do with our barriers? We have to realize that three things happen, we have reflected energy transmission and absorption so some of the energy that strikes our barrier is reflected back, some of it goes through, through a process called transmission and then some of it is absorbed. So we have three things that the barrier must do: reflection transmission and absorption. Let’s try to get a feel through example of what some of this barrier technology is up to, let’s take a granite slab, a granite slab will reflect 99% of the energy that strikes it that’s why your barriers that must stop low frequency energies have huge mass and huge densities and granite is very very heavy. So a granite slab will reflect 99% of the energy going against it. What are the characteristics that we look for in our barriers? Stiffness and density, those are the two variables that we have to deal with especially when we’re dealing with low frequencies, frequencies below 125, remember from past videos, those are the hardest, that is the thickest barrier, the most expensive barrier, multiple layers, different densities, different construction methodologies so a lot of things have to go on below 125 cycles. Above 125 cycles the common one you see in all the literature is the double two-by-four drywall with a little air space. There’s much better ways to do it these days but that’s the most common that we see in the literature here’s another example, sand, lots of mass but not stiff so we need stiffness and density.

We have a formula we use in all our studio build it’s called rigidity flexibility so the shell of our rooms, the outside wall, and then we have the inside treatment room so we really have the two rooms, this is our shell and we go even farther in this relationship. We take the interior treatment room and we make sure that the stiffness of the shell and the flexibility of the treatment follow a ratio. It’s a ratio we’ve developed that’s really compatible with music and voice and like all our technologies they’re all designed around music and voice, nothing else, that’s exactly what they’re designed to do. So we even carry this one step farther and match the shell, if your shell is poured concrete, that’s very rigid, very stiff, and very dense so we must have a treatment room inside of it that moves, that’s flexible. I mean it doesn’t physically move but it gives and takes and gets back into its original form quickly because that’s important to music. It’s important to time signature on the reflections, it’s important to remodel structure, there’s a whole host of variables that’s important to. So what are we doing with this? We’re maximizing absorption and reflection with our barrier and then here’s a term that you see a lot, sound insulation. When you see this term it usually relates to variables but its material that stops the actual transmission through the structure okay, through the materials. So keep this in mind, stiffness, rigidity are your key factors in any barrier, quantifying and qualifying the frequencies and amplitudes that you’re dealing with and the only way to do this is to measure it over seven days. Three measurements a day over seven days then we get an average of what we’re up against and then we build the barrier to suit the numbers not the other way around.

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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