Room Acoustics (part one)

It's said so often it’s become almost a cliche, “the most important thing you can do to improve your recordings is to treat your room.” But it is absolutely true, unless we are recording all electronic music, our productions start in a room and the sound of that room is one of the most important factors in the finished product. And obviously even if you are doing all electronic music, your end mix will sound better if the room you are mixing in sounds good.

But what does “good” even mean and more importantly, what steps can you take to get there?

The first thing we need to get out of the way, even though they get lumped into the same conversation, there’s really two very different things going on here and in many ways they are each handled with opposing techniques and solutions.

Many people are actually talking about sound deadening when they talk about treating a room. Meaning they want to stop sound from the outside coming into their room and messing with their perfect vocal take or they want to record drums at 2:00 AM without the cops showing up.

The other part of treating a room is how to get that room to sound good. Every room puts a fingerprint on the finished recording and instead of leaving a hot sauce and ranch dressing fingerprint all over our mix, we want that fingerprint to be as clean as possible…. okay, maybe that metaphor doesn’t really work, but you get the idea.

So in this post let’s talk about sound deadening (we will cover room treatments in a follow up discussion).

Sound Deadening

Whole books can and have been written on this topic so we are just going to scratch the surface here but, the most basic way to think about deadening sound comes down to two main points.

1. If you can see it, odds are you can hear it. A crack between a window frame and the wall, a hole in the ceiling like a chimney, or a bad seal around a door, these all let sound in and out of your room. Additionally, the “if you can see it you can hear it” doesn’t end with holes or gaps, it’s also true of windows. Your odds of hearing a sound through a window is much greater than a solid wall.
   

2. Mass is your friend when you are trying to stop sound. Think about it this way, how easy can you move a sheet of paper vs. a brick wall? That’s also true with sound, it’s easier to stop sound transfer with a brick wall than a sheet of paper, or even many papers because brick just has more mass.
   

So the answer to sound deadening is easy in theory, plug all the holes in your room and make sure you have a lot of heavy things between you and the outside. In practice, keeping sound from transferring between rooms or from a building and the outside world is really… REALLY… hard.

I have to say up front, unless you are willing to spend tens if not hundreds of thousands of dollars, you are never going to completely stop sound transfer in and out of your room. BUT, you can make the problem better with a few fairly inexpensive solutions, or relatively inexpensive solutions in some cases.

1. Fill cracks around windows or in walls. A simple tube of caulk from a box store is a great start and it will also help with your heating and cooling costs as well so… bonus! You don’t need to do anything fancy here, just fill any holes or gaps with caulk and you are done. Obviously if you are renting you might want to talk to your landlord first before you break out your paint covered Dave Matthews work t-shirt (guilty as charged, that’s exactly what I wear when I am painting or caulking lol).
   

2. Simple weather stripping around doors can make a fairly big difference. Over time, buildings shift a bit and doors tend to stop fitting as snug as they did when they were first installed. Weatherstripping around doors can fill these gaps and help prevent sound transfer.
   
   Another note here, just because your sound transfer problems are coming from the outside, don’t overlook the fact that these sounds are still making it into the rest of your home or apartment. If you were to fix 100% of your problems with your exterior studio window for example, you would still have sound leakage from your interior space so don’t overlook your inside studio doors!
   

3. Cover cracks under your doors by either installing a weather strip or using a heavy draft guard. In many cases a weather strip is probably the better solution, mostly because if it is installed properly there shouldn’t be any gaps but the draft guard solution can still really help. If you go with the draft guard method, just remember the rule above, mass is your friend. Meaning a sand filled draft guard is going to do a much better job than a bathroom towel.
   

4. “Sound blankets” are often not extremely helpful because they don’t have a lot of mass, and they don’t seal well.
   
   But if you are looking for a removable solution they are often your only option to help with troublesome windows etc. If you are going with the sound blanket route look for products with the most mass so look for the heaviest product you can afford and safely hang from the ceiling and/or curtain rods.
   
   Another thing to think about is that sound waves will dissipate as they move through different materials. Two medium heavy blankets are better than a single really heavy one, even if the total mass is the same between the two options. As the sound transfers from the air into the blanket (or any solid object) some of the sound’s energy is absorbed. This happens again when the sound moves out of that object back into the air. If you make the sound wave do that multiple times you will knock down more energy and multiple layers of heavy blankets or fabric can work to minimize sound transfer (to a degree).
   

5. If your goal is to stop sound from entering your room and messing with your recordings you can pull your sound deadening closer to your recording.
   
   You should look for a microphone like a Beyer M88 or a Shure SM7b. These are just two options, but really, any microphone with good rear rejection will help keep bad sounds out of your recordings and there are a number of mics out there that can help.
   
   That solution isn’t going to fix all your problems, and it’s not going to do anything to keep the cops from knocking on your door at 2:00 during the middle of your 10th thrash metal guitar take. But taken together with the other solutions above, the proper microphone can make a big difference in your final recording.
   

6. Keeping with the idea that you can move your sound deadening closer to your microphone, you can try using a small sound screen that goes behind or even partly around your microphone.
   
   This solution really isn’t always the best option and if done the wrong way it can actually cause negative effects with your recordings due to reflection issues. But, if you can get a heavy (again, mass is your friend) screen between your microphone and the main transmission vector, like a window or door to the outside, it can help.

   
   Something to keep in mind with many of the “microphone sound screen” solutions available on the market, these are often geared more toward helping remove reflections from your room, meaning they are designed to help make your recording sound more even, but they are not really intended to help with sound transfer into or out of your space.

   Don’t assume a simple foam sound screen is going to do much because in reality… it isn’t going to do much. Products like this just doesn’t have enough mass to absorb the rumble of a truck passing by outside your window. Another obvious problem with this solution is that it has “gaps” around it so it’s not going to fix all problems. But again, used with other options, this solution can be marginally helpful.
   

7. Low end sounds have more energy and energy is the reason you need as much mass as possible between you and sounds you are trying to keep out of your recordings. This means in most cases low end sounds are the things you need to be most concerned about.
   
   You can use the low cut filter on your microphone or a low cut EQ in your DAW to cut back a lot of outside sounds from your vocal or even some soprano / alto range instrument recordings. Again, this isn’t a fix for every problem, but it can help. And, if you use a low cut filter with techniques and solutions from #4, 5 and 6 above you will probably get beyond all but the worst offending sounds from messing with your recordings.
   

8. If you have the ability to make more permanent changes to your room, replace any doors in your space with solid core options. Most interior doors are hollow and they have very low mass. A solid core door has a lot more mass and a well fitted solid core door will do a lot better job of rejecting outside sounds. Additionally, as mentioned above many older buildings will have shifted over time so a new door can be fitted to the frame a little tighter… but don’t forget you can and should still use weatherstripping on a new door as mentioned in #2 above.
   

9. Again, if you have the ability to make more permanent changes, replacing older single pane windows with double pane options can really help with sound transfer. Just keep in mind, as I mentioned above, if you can see it you can hear it so most traditional windows are never going to stop sound very well. But a double pane window will do a lot better than a single pane when it comes to sound transfer.
   
   Small note on this, there are a lot of physics that go into sound rejection but generally speaking, a double pane window in most cases will do a better job of sound deadening than a triple pane window (because the triple pane window starts acting like a single unit due to air pressure trapped between the panes). Do your homework, and don’t do that homework based on manufacturer marketing and hype. I have seen really bad specs on products that claim to be “high noise rejection windows,” make sure you check the SPL ratings between different products.
   

One last point, there isn’t a “one size fits all” solution to stopping sound transfer out of a structure. It’s all a game of inches so multiple techniques will add up.

There are a lot of things to keep in mind with sound transfer, the ideas above are just a starting point but I hope they give you some things to think about.

If you have any questions please hit the contact link here on my site, I am happy to help if I can.

Stay tuned for post number two where we will talk about room treatments!