How much isolation does your studio need, in decibels?

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How much isolation does your studio need, in decibels?

#1

Postby Soundman2020 » Mon, 2020-Nov-02, 02:02

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How much isolation does your studio need?
How can you figure that out?
Is it even important?


This is a question that comes up very frequently, and indeed is one of the most important questions you should ask (and answer!) about your studio, BEFORE you commence designing or building. The answer to this question will impact virtually ever aspect of your studio design, in one way or another.

To figure out how much isolation you need, it is not necessary to have access to the location where your studio will be built. What you DO need, is your "typical setup", and a sound level meter. By "typical setup", I mean the things you normally have in a typical session, similar to what you will be doing in your studio when it is finished. So, for example, if your studio is just for mixing (no tracking), then your typical setup would be the speakers you plan to use, your DAW, and some typical music tracks, playing at typical levels. If you are building a rehearsal space or tracking room, then your "typical setup" would be a group of musicians and instruments similar to what you plan to have rehearsing/tracking in your studio.

So, get your "typical setup" together, and get it to make lots of noise, similar to the noise you would have in a typical session in your future studio. You can do this in ANY location! It does not have to be done in the place where your studio will be. It could be in the studio you are using right now, or a rented studio, or your living room, garage, church, club... wherever. Any place of a similar size to what you are planning for your studio will do.

OK, so you have your typical setup making a lot of typical noise in some room that vaguely resembles what your future studio will be like. Now get out your sound level meter, and measure! That's it! That's all you need to do to determine "How Loud You Will Be". Set your SPL meter to "C" weighting and "Slow" response, and measure at several places around the room, and take notes. Try to keep the SPL meter about three feet (1 m) away from the things you are measuring. If you are just measuring your speakers for a control room (mixing room), then measure on-axis to the speaker, about 3 feet from the face of the speaker. That's your main measurement, but also measure in a few other locations around the room. If you are measuring a drum kit, then have the meter roughly where the head of the drummer is: a few inches above his head is a good spot, but make sure his head is not blocking the sound from any of the pieces in the kit. Once again, that's your main measurement, but measure other locations too.

Measure lots, make lots of notes. And you are done!

At this point, you have a piece of paper with lots of numbers on it, representing the SPL levels you measured at various points around the room. You should see a clear trend in there: Most of the numbers will be quite similar, with a few outliers. You could average them if you want, mathematically, but you'll probably see the trend right away, and be able to determine an overall number. Keep that number and also the highest "main measurement" number. These are your key numbers.

So, now you know the answer to one of the key questions: "How Loud Will You Be Inside Your Studio?". Next step is to find out "How Quiet Do You Need To Be Outside Your Studio?". There's two key issues here: 1) How quiet you need to be in order to not disturb the neighbors, and 2) How quiet you have to be LEGALLY. Those might not be the same! It is quite possible to meet the legal levels but still have annoyed neighbors, and the reverse is also true: it is possible that your neighbors are quite happy, not annoyed at all, even though your levels exceed the legal limits. So you should work from both points of view, then decide which one to set as your goal. It is probably better to use the legal level and try to get a bit better than that, to be safe.

#2 (legal limit) is easy to determine: check your local municipality (or other local authority) web site and download a copy of their noise ordinance. That will tell you what the maxim level is that you are allowed to produce, in decibels, along with the times of day: most noise regulations allow higher levels during the day, and restrict it to lower levels at night.

#1 (neighbor annoyance) is a bit harder! Different people have different thresholds for annoyance. The noise level that annoys one person a bit, might not even be noticed by another person, while a third person is extremely annoyed. This is more subjective. What you can do, is use some "rules of thumb", and maybe ask some friends and family for their help. Just play music in one room while they are in the next room with the door closed, and slowly turn the volume down until they say they are happy, and would not be annoyed by that level. Then measure the level IN THEIR LOCATION, and note it down. Do that with several people, and average the numbers. You will probably find that it is close to the "rule of thumb"m which is this: Most people would say that a level of 30 dBC is "silent", and that a level of maybe 35 dB to 40 dB is "acceptable".

So, now you know two things: How loud you are, and how quite you have to be. Next step: Subtract. The answer is "How Much Isolation Your Studio Needs".

It really is that simple.

For example, let's say that you are just going to mix in your studio (no tracking or band rehearsal), and you want to do this for many, many years without destroying your hearing, so you have your speakers set at a sane level, and the maximum you measured is 80 dBC. You also checked with your friends, and they all agree that 40 dB is good, and your local noise regulations also say say 40 dB: Subtract: 80 - 40 = 40. So you need 40 dB isolation for your studio. Done!

At the other extreme, if you plan to track Pink Floyd live in your studio, and they are roaring out a massive 120 dB, while your noise regulations say that 35 dB is the limit for "quiet", then you would need 120 - 35 = 85 dB of isolation, in which case you should take out a very, very large loan from your bank, because it is going to cost a fortune to get that level of isolation! :ahh:

One caveat here: noise regulations often specify the levels in dBA (decibels, "A" weighted), but the correct method for measuring loud music is dBC (decibels, "C" weighted). You cannot validly compare these two, since they are different scales. It would be like comparing a fish to a bicycle: there's nothing at all in common! So, if your regulations use dBA then also take the above measurements with your meter using the "A" scale on the meter, but that is in addition to the readings using "C" scale! You need both. For the LEGAL aspects, use only the "A" numbers, but for the "annoy the neighbors" aspect, use only the "C" numbers, which will always be higher.

So, this is the basic method for figuring out how much isolation you need.

Summary: Measure the decibel levels in a typical situation that you expect to have in your studio, find out how quiet you need to be both legally and also from the point of view of being a good neighbor: the difference between those two numbers is how much isolation you need, in decibels.

Now, this does NOT necessarily mean that you need a wall that is able to provide that much! There are a couple of other factors involved, that you need to take into account. One is distance, the other is ambient level. These are both your friends here. If your studio is a hundred feet away from your property line, then that's a hundred feet of level drop, which is great! The normal rule of thumb here is that the sound level decreases at a rate of about 4 to 5 dB each time you double the distance. In theory, it is 6 dB for each distance doubling, but that's for "full space", with nothing around you in all directions, including above and below.... so you'd have to be hovering in mid air for that to be true. There's also things like walls, cars, fences, houses, trees, etc that can tend to reflect sound in certain directions more than others, so it is safer to use a rate of 4 or 5 dB per distance doubling. 4 to be safe, for loud levels.

So, if your future Pink Floyd studio only manages to produce 60 dB of isolation after it is built (because your bank manager flat refused to give you a million dollar loan to get 85 dB...), and you measure a level of 60 dB about three feet away from the wall when the band is going nuts inside at 120 dB, then that 60 dB level will probably drop to about about 56 dB at 6 feet from the wall, 52 dB at 12 feet, 48 dB at 24 feet, 44 dB at 48 feet, and 40 dB at 96 feet, which is the end of your property in this hypothetical situation. So the situation is a bit better than it seems. You 40 dB at your property line, which is only 5 dB over the hypothetical 35 dB limit in this case.

The second thing that might help, is ambient noise. If you live in an area that has high levels of background noise, such as close to a freeway, airport, shipping port, factory, train station, etc., then chances are that the background noise level will be higher than what the legal regulations say! For example, if the legal limit is 35 dB but the background level is 55 dB, then you are fine! Nobody would be able to hear your Pink Floyd studio, because the ambient noise is "masking" it, and in addition it is pretty much physically impossible to measure the level of a 40 dB sound in the presence of a 55 dB sound!

So that would be the "best case" scenario.

However, if your property line is just a 10 feet away from your studio, and you live in a very quiet area where the ambient level is 35 dB, then you are fresh out of luck! Your Pink Floyd studio is going to be very, very audible to people standing at your property line.

So, that's the situation here: first you need to measure how loud you are, and how quiet you have to be, subtract to get the magic number: "How Much Isolation You Need In Decibels". That tells you how to build your walls, doors, windows, ceiling, electrical system, HVAC system, etc. in order to get a legal level three feet from the studio wall. Then you can take into account the distance factor, and the ambient noise factor, to see if you can relax the isolation number a bit.

Once you arrive at the FINAL number for how much isolation you need for your studio, then you can start looking into different building methods, materials, and techniques that can provide that level of isolation, and choose the one that best fits your budget.

- Stuart -

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