Acoustic Treatment — Managing the Bounce

Building a Recording Studio — Part 5

In Part 4, I talked about what will need to go into the studio. Given that I’ll have both live music and recording happening in the same space, I need to design for how the acoustic treatments will work to let the room work well for both things.

As mentioned earlier, there’s a big difference between the two key aspects of recording studio design — sound isolation and acoustic treatment. Sound isolation is about keeping the sound in the studio from leaking out to the world around it (and vice versa). Acoustic treatment is about making sure that the sound coming out of the speakers is not altered by the room before it reaches your ears. When done poorly, recordings that sound good in the studio sound very different when you listen to them through someone else’s speakers, in the car or through headphones. When done well, what you hear in the studio is what you get from any other listening environment.

This is not easy and it’s not cheap.

There’s a Science

We know a lot about how sound behaves in rooms. There are vast amounts of data and studies on this area and it all informs both the most traditional of solutions and some very interesting new methods that are being used with good results. The big issues that all solutions must cover include managing bass buildup, eliminating first reflections, managing all of the subsequent reflections to make a room sound good and still being comfortable to work in for extended periods of time.

Very generally, sound bounces off of hard things. Sound is absorbed by softer things. The amount of this varies by the frequency of the sound and the materials and the amount of them used for absorption. As sound travels and bounces off of things, it loses some energy. You can control your listening environment by absorbing it or by reflecting/deflecting it in controlled ways.

First… Reflections

Let’s start with reflections. First reflections are the result of the sound leaving the speakers and bounding off of the walls, floor and ceilings to hit your ears. Because they are just the first reflections, they retain most of the energy they had when they left the speaker so they are the first things to deal with. The key here is to eliminate those first reflections as much as possible because they have a very strong tendency to either interfere with what you’re hearing directly from the speakers or to mess up any sense of stereo separation in your listening position. For example, if the sound from the left speaker bounces off the right wall and then comes to your right ear just a bit after the sound from the right speaker, you will hear less of the stereo separation than you would if you listened to the same thing in headphones. You might adjust for this in the mix, but then when you listen somewhere else that doesn’t have that issue, it will sound different from what you thought it did. This is exactly what we want to avoid.

The most common solution for first reflections is to add acoustic treatments like absorptive panels on both the walls and the ceiling between where the speakers are and where you’ll be listening. By absorbing a lot of the sound in these panels, the first reflections will be minimized and the majority of what you’ll hear will be coming from the speakers themselves. In the first image, you’ll see a set of panels on the ceiling and the blue ones on the side which will catch these first reflections. It’s OK that the wall is not covered above and below the wall panels because my head is not up that high (or down that low) so first reflections off of those walls will then hit other surfaces and become second, third, etc. reflections. Each time they bounce, they lose some energy

Less Bounce / Ounce

The next most relevant reflections will come off the back wall. This is where the size of the room really helps. At just over 25 feet long, the sound needs to go pretty far to get to that back wall, then pretty far once it reflects to get back to me. Adding some panels that will absorb some and reflect some will help reduce their energy. Here I have a bunch of diffusion panels which are actually 6 inch thick sound panels with a diffusion plate on the front so depending on how the waves hit it, some will absorb and some will reflect different frequencies will either absorb or reflect so it reduces energy of the overall sound without making the back of the room sound unnaturally dead.

While it may seem that a room with no reflection at all (also known as an anechoic chamber) would be ideal, it would also be very difficult to work in there for very long. Hearing no reflection is very unnatural and it really messes with your head. So some sound coming from back there is good.

Can’t you see this is the land of diffusion

Also note that there are some more diffusor panels on the ceiling that work a little differently but the goal is the same. Spread out those reflections so they don’t get back to your ear (or a microphone) with enough energy to alter the true sound from the source.

There are some other panels towards the back of the room that also help with both absorption and deflection of sound towards the back of the room which will be visible when you see the whole space.

Trappin’ da bass mon

The last of the big issues is with bass. Lower frequencies behave differently from mid-range to high frequencies. They can be very energetic and take a lot more mass to reduce their energy. Bass also has a tendency to collect in corners of a room so the solutions for trapping bass are different from other frequencies. We need a LOT of absorptive material in those corners. In these images, you see some tan colored corner panels but that is not quite what we’re going to do. Rather than placing some of these panels in the corner, we’re going to build bass traps into the walls themselves. Each corner will have a diagonal part of the wall that connects about 2 feet out from the natural corner of the room. The space behind the wall will be filled with dense sound-absorbing insulation. In front of that will be a panel with slots that reflect some sound, similar to the diffusion panels and then covered with the same fabric used on the other acoustic treatments. Because these bass traps are built in and extend from the floor to the ceiling, they will handle the bass energy in the most corner-y of corner spaces in the room.

There are other corners though. Looking at the two pictures above, there are also big blue panels in the “corner” that appears where the floor meets the wall. These are also bass traps that are over 7 inches thick and help trap the low frequencies right next to the speakers and at the opposite end of the room from them.

So why are there only three of them? And why aren’t they in the corner between the wall and the ceiling? This is where we get to the “expensive” aspect of acoustic treatment.

Then before and now once more, I’m bouncing round the room.

Nailing “Good Enough”

Adding acoustic treatment is about achieving balance. As I mentioned above, creating an anechoic chamber would be both very expensive and also very uncomfortable to work in for any extended period of time. Doing nothing would make it very difficult to know what is actually being recorded, mixed and mastered while I’m doing it. The trick is finding the goldilocks point between those two extremes both in terms of effectiveness and cost.

I’ve read about the acoustic treatment solutions for lots of studios from people putting mattresses and egg cartons up in a room (almost completely ineffective, but cheap) to using state-of-the-art solutions like Delta-H Designs ZR Acoustics Panels which are designed to treat all frequencies in the room, widening the listening space significantly, but at the cost of nearly $1,000 per panel. Given that my studio is mainly for my own use and not a big commercial endeavor, the designs I’m showing here are based on working with GIK Acoustics who offer a wide range of panels that are not cheap, but are very effective at handling a space this size.

GIK Acoustics offers tools for designing rooms using the Roomle 3D designer which is what I’ve been using to create the images in this post. Feel free to click in to the room planner for my current design to look around at the complete design. The folks at GIK Acoustics have been very helpful with their initial recommendations for this space. I’m waiting to place the order until we are a bit farther along in the construction, but the design discussed here is looking pretty close to the final plan.

Next up, we’ll revisit the sound tests with the build being farther along.

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Chris Evans - Audiogust

Chris Evans - Audiogust

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Engineer (Software and Audio), Musician, Producer, Island Dweller