Reflections

Home Studio Considerations – Part 2: Bouncing and Reflecting

In setting up a home studio for recording voiceover projects, quality electronics are important, but the more money you spend, the more money you will be wasting if you are working in a poor acoustical environment. In Part 1 and Part 1a of this series we discussed the importance of keeping unwanted sounds and noises out of your recordings. This time we will talk about what happens to the desirable sound, your voice, between your mouth and the microphone.

Reflections

In most cases, the desirable environment for recording is acoustically “dead”, without any echoes or reflections. If a final recording needs some reverberation to suggest a specific environment, it can be easily added electronically. However, a too lively recording cannot easily be “deadened” with electronic processing.

The closest example of a good recording environment in a typical home is a walk-in closet full of clothing. In fact, some home-based voiceover talent actually record in their closets. The worst possible recording environment in a home would be a shower stall lined with tile. It may enhance a mediocre singing voice of the “showerer”, but recording a voiceover in there would be a disaster.

Echoes and reflections are the culprit. Hard surfaces act as an acoustic mirror, bouncing back any sound wave that strikes it. The reflected wave travels away from that surface until it strikes another surface and is reflected again. These repeated reflections are added to the original sound waves and create a confusing mixture of sound which is eventually picked up by the microphone.

For the purposes of this discussion, the reflecting surfaces are the walls, floor, ceilings, and windows of the room in which you are recording. In addition, the size and proportions of the room also have a significant effect on the complex interactions of sound waves.

So, the solution is simple, just soften all surfaces with curtains, carpet, and possibly an acoustic tile suspended ceiling, right? Well, that does go a long way toward taming an acoustically hostile environment, but a few other factors need to be considered.

To dig in to the theory a bit deeper, we find that these treatments are more effective on higher frequencies or pitches and much less effective in controlling reflections of lower or bass frequencies. Here the size and proportion the room becomes a bigger factor. Since you probably don’t have any control of this, the key is to chop up the reflected waves, i.e. divide and conquer. Bass reflections are not well absorbed by the soft surfaces, so the problems are created by flat, parallel, and perpendicular surfaces — exactly the makeup of the typical room.

In constructing a studio from scratch, the design often includes walls that aren’t parallel to each other and hard rounded convex surfaces in place of the corners where walls, ceiling and floors meet. The theory here is to scramble and scatter the bass reflected waves so they can’t interact additively to create what’s known as standing waves. These standing waves can act as an acoustic amplifier to accentuate certain low frequencies; the specific frequency or pitch is determined by the size and proportion of the room.

OK, enough theory. What can we do in an economical, practical way to create an acceptable recording space in our home? Well, here goes.

First, let’s determine if the space must be visually presentable. A quick check with your spouse would be in order here. If guests or clients in your home will ever see the space, a little more care will be needed in selecting acoustic treatment materials. For example, egg cartons attached to the wall are quite effective and inexpensive, but probably not a good idea unless you are going to share the space only with six geese a’laying.

My home studio can be seen from the family room if the door is left open, so we wanted to avoid creating an eyesore. The room started out with a few built-in advantages. It had carpet on the floor, a vaulted (non-parallel) ceiling, and one diagonal wall section, all of which helped to break up low frequency standing waves.

The remaining hard surface, parallel walls needed treatment for high frequencies. I was fortunate enough to acquire some commercial sound absorbing 2′ by 4′ panels from a defunct TV studio which we hung on the wall. They are covered with a gray fabric, and are reasonably attractive. I’m sure these were relatively expensive when originally purchased, but, when we needed one more panel, we determined that similar units could be constructed easily and inexpensively. A simple 2′ x 4′ frame constructed of 1″ x 2″ furring strips was filled with upholstery foam and covered with decorative upholstery material and proved to be attractive as well as functional. Filling with fiber insulating material instead of foam would probably be equally effective.

Also acquired from the closed studio were two bass traps, hard surface quarter round columns, which we placed in the two square corners of the room. These would be a bit more challenging to construct, and I found very little improvement after they were installed.

20130106-092702.jpg

The impact of the room’s environment on the recording is substantially controlled by two other factors — the directional pattern of the microphone, and the distance between your mouth and the microphone.

Most condenser microphones have a cardioid pickup pattern, accepting sound from one side and rejecting sound from the rear and sides. This gives preference to your voice and less preference to reflections from the wall you are facing. Some microphones have switchable patterns, and the omnidirectional (picking up sound equally from all sides) or bi-directional (picking up from front and back but rejecting from sides) settings should be avoided in the home studio environment. Stick with the cardioid pattern if you have a choice.

Finally, since cutting the distance between your mouth and the microphone in half increases your voice pickup by a factor of four while not affecting the pickup of the room’s reflections, you can see that being six inches instead of 12 inches from the mic can make your room sound a lot better.

So if you move in to one inch from the mic, that should negate the need for any acoustic treatment, shouldn’t it? Well, getting that close creates two other problems, bass boost and plosives. A typical cardioid mic pickup pattern exhibits an interesting property. When worked extremely close the audio signal has greatly accentuated low or bass frequencies. Occasionally this characteristic is used for special effects, but it is usually undesirable and unnatural.

The other more pesky problem is what’s known as plosives (derived from explosives, I suppose). These are the loud noises caused by the pronunciation of the letter “p” or “b”. The puff of air from the mouth distorts the diaphragm in the microphone and creates a huge pulse in the electrical signal. When the recording is played back the loud pop in the speaker is very distracting. A pop filter is a screen-like device which is placed between the mouth and the mic, and this helps, but working the mic too closely will permanently perpetuate plosive problems in particular.

We’ll have a lot more to say about microphones, equipment, and techniques in future posts.

I would welcome any comments or responses as to how you have treated your recording space.

 

 

Leave a Reply

Your email address will not be published. Required fields are marked *