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7 Day Noise Time Study

Dennis Foley October 27, 2017 No Comments
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I get a lot of calls and comments and questions through our inbox about noise. People want to build a wall they think they have this noise problem, they have that noise problem, they want to build a wall they’ve been reading in the literature that this wall is good and they build it and then it didn’t stop all the noises they wanted to stop. So now we have to take the existing structure and add something to it to compensate for what was missing in the first place. Let’s back up a little bit and approach this from a more scientific perspective and not what we read in the literature, and definitely not one size fits all like this double wall two sheets of dry wall with an air space; let me tell you that’s an inefficient use of space and materials. There’s much better ways to achieve the same kind of S.T.C. levels and even higher. So let’s back up a little bit and talk about noise.

We have noise that is outside to inside of our room. You can probably hear now we’ve got a drill going on the road outside. So we have inside noise that’s going to go out of the room, so we have this to a gate, this two-way vials of noise coming in, and noise coming out. Now it might be music to us inside the room, but it is noise to others if they don’t like the music especially, it’s definitely noise if it’s too loud. What do we have to do? All noise is stopped by building a barrier between the noise and the receiver, ourselves. So if it’s a garbage truck outside we want to build a barrier between the garbage truck and our music room. If we are a practicing rock band we want to build a barrier to stop the noise from leaving out into the other world, so we don’t disturb people on the outside. Here’s the thing people don’t do, they read about this, that, or the other type of construction but they don’t quantify or qualify what they are doing. They don’t quantify the amount and the level of noise that they have to work with, and they don’t qualify what type of structure or barrier technology to use to stop it.

So all noise has frequency and amplitude. So you’ve got to know what the frequency and amplitude of the noise that you are trying to solve, you have to know that first before you even start talking about construction methodologies, barriers, materials and all of that stuff; and definitely before you start talking about that double drywall with airspace. How about double drywall, green glue, and wasted space let’s call it that! Quantify and qualify, how do we do that? Well there’s two apps that we can use. We can use some simple tools to help us and one is the RTA pro, I’m going to hold it up for you now, you can see this is an iPhone app, and then the other is a dB meter.

Both of these apps are available in the Apple store, and we are going to use both of those in this process. Now this is not an exact way to do it but it’s an easy way to give you some ideas of what you are up against, and then if the noise management becomes really critical, like in a laboratory or test facility or stuff like that then more appropriate and more accurate ways of measuring; but for most general purposes this will teach you about noise and its strength and more importantly frequency, and then we can discuss barriers after we figure out what we are up against. We have to define our problem before we come up with a solution. So we are going to use these two devices. The first thing we’re going to do we are going to use the dB meter. I call this the seven day noise time study because you really have to measure noise over a seven-day period to get a handle on it. So you are going to put yourself together a little chart, and you are going to put on Monday I measured at 10 AM, I measured in the evening at 6 PM. Try to find the days when the noise is the quietest and of the loudest, the time frames in those days Monday, Tuesday, Wednesday, and then you are going to have a series of data that you list for each day.

Now how do you measure pressure levels with your dB meter? Well it’s very easy you go outside, you stand 3 to 4 feet against the wall, face the noise source and take a measurement, and then turn around and face the wall and take a measurement and then take the average of those two numbers. That will give you a good idea of what kind of pressure you are up against at 10 AM on Monday morning. Do the same thing at 6 PM at night if those are the high and low noise levels for the day, you have to use your own judgment and experience to figure that out. So at the end of the week we are going to have this sheet that’s going to show us times during the day, if you want to put in a third measurement the more the better, the more data the better, then we are going to get some average readings of how much pressure we are up against. If you live next on airport you are next to a runaway your pressure levels are probably over 100. That’s going to be very different than a guy who lives out in the country who doesn’t have any jets landing about 400 or 500 feet from his house or farm.

Completely different extremes, completely different measurements but quantifying and qualifying both are extremely critical, more so with a jet obviously, but you still need to follow the same procedure. So once we get our seven days of noise time study then we are going to try to figure out, alright what frequencies are causing us the most difficulty within those pressure readings that we’ve taken, and here’s a the RTA pro comes in. It’s a real-time analyzer in real-time, you’re going to have to use the graph standing in the same position on the outside pointing forward and then pointing at the wall. You’re going to start to see certain frequencies, you going to first see a dividing line, you will see the frequency is above 300 there all about the same, there’s no particular frequency standing out. Now the frequencies below 200 or below 100 they are really powerful, they are even stronger than the middle and higher frequencies. You begin to kind of see a dividing line, everything below 100 Cycles Is Way up and everything passed 100 cycles is more normal; then that tells us that our barrier needs to focus on those frequencies below 100, because the barrier that we build for frequencies below 100 is very different than the frequencies we build above 100 cycles; by the way that double wall green glue one, that’s only good for above 125 cycles, it’s a waste of materials.

We’ve got these two software programs that we can use, now when you are inside the room you want to do the same thing with your measurement, you want to do a pressure level reading and a frequency; it takes some time but you start to get a picture of what you are up against, and then if you quantify now we can qualify. Here is our noise, here is the amount of noise we have, here is what frequency it is at, now what kind of barrier are we going to build to fit those frequencies and amplitudes or strengths? And we can look at our seven-day time study and we will know, maybe we don’t design it for the noisiest day, we forget about Thursday so to speak because that is a real noisy day, we have pressure levels 100+ so maybe we don’t use that as our guideline. We stay out of the room on Thursdays and build the room for the other days. And this is what quantify and qualifying will do for you, it will help you work within your budget.It’s like going to a doctor and getting a blood test. You go to the doctor and get a blood test, he says well you need more iron, you need more vitamins or whatever, you need more of this that or the other. You need more money to pay me, that’s usually what they say, but anyway. The actual measurements, the quantification qualifies the build methodology, the thickness and the materials that we use in the barrier. All this is interrelated.

First we have to identify what the problem is, then we have to assign the appropriate barrier technology to do that, and the like all the projects we need data. Alright, thank you.

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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.

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

[email protected]

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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.Connect with me on Google+

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