The EM Poll

The Well-Tempered Studio

Feb 1, 1999 12:00 AM, By Geoffrey Goacher

           

Improve the sound of your personal studio in three easy steps.

This article originally appeared in the February 1999 issue of Electronic Musician.

Good acoustics are often the dividing line between professional and personal studios. After all, the gear that’s used to record and mix much of what we hear on the radio these days is quite similar to what can be found in a well-appointed personal studio. Largely, it’s those big, beautiful, acoustically accurate rooms for recording and mixing that separate the big guys from the little.

But by giving a little attention to the acoustics in your own studio, you can improve the quality of your mixes so that they compete with the best the majors have to offer.

BASIC CONSIDERATIONS

Before getting into acoustics, make sure that there are no weak links in your monitoring system. Monitoring systems for critical listening must have a fairly flat frequency response from about 60 Hz (or lower) to 16 kHz (or higher). The power amp should also have as flat a frequency response and as low a distortion spec as possible. Fortunately, most of the studio-grade near-field monitors and power amps on the market today meet these specifications. Therefore, selecting the “right” system is often just a matter of personal taste.

The monitoring system must be set up symmetrically within the room. The distance between the speakers should be the same as the distance from each speaker to your ears, thus forming an equilateral triangle with your head. For near-field monitoring, your speakers should be about two to four feet apart, depending on their size and dispersion and what is most feasible ergonomically. Also, the center of this equilateral triangle should be equidistant from the room’s side walls (see Fig. 1).

FIG.1: Studio speakers should be placed symmetrically within the room, forming an equilateral triangle with your head.

Unfortunately, falling short of sonic accuracy is common, even when high-quality gear is placed symmetrically in the room. The overall sound is often boomy and muddy, the bass is too loud or too soft, the high-end is dull or harsh sounding, and the imaging is blurry and undefined. Room acoustics can play a significant role in creating, and reducing, these problems.

In pro studios, room acoustics are considered a top priority. Typically, owners spend lots of money on professional consultation, premium construction, and first-rate sonic treatments, sparing no expense to achieve problem-free, acoustically “neutral” monitoring environments. However, overcoming acoustical problems is not outside the financial realm of the personal studio owner. You should expect to spend at least the same amount of money for acoustical treatment as you did for your monitors.

The acoustical problems that occur most commonly in small monitoring rooms are room resonances (standing waves), speaker/boundary interference, early reflections, and poorly diffused late reflections. These problems can be overcome in three easy steps.

Step 1:

Controlling Resonance and Reflections

The first step deals with low frequencies—from 20 Hz to 500 Hz. This frequency range affects the smoothness of the bass and low mids: if the room’s acoustics are balanced, the bass and low mids will be full and warm; if the room has significant frequency boosts in this range, the sound will be boomy or muddy; and if the room has significant frequency dips in in this range, the sound will be thin and hollow. The goal in Step 1 is to flatten out the room’s low-frequency response so as to avoid erroneously mixing music to compensate for the boosts or dips caused by the acoustic environment.

Resonance and standing waves. The way low frequencies behave in a room is dictated largely by the room’s dimensions. Certain frequencies, due to the lengths of their respective sound waves, are reinforced as they move between the room’s boundaries (walls, floor, and ceiling), creating resonant boosts in volume at those frequencies (see Fig. 2). These resonances are commonly referred to as standing waves.

You can estimate the most prominent resonant frequencies of a room by using the following equation:

f1 = 1,130/2L = 565/L

In this formula, f1 represents the resonant frequency, and 1,130 represents the speed of sound in air under “normal” conditions, which are defined as one atmosphere of pressure at sea level at 21 degrees Celsius. L represents the length of the room in feet. For example, if the room is ten feet long, there will be a natural resonant volume boost in the room at 56.5 Hz. In addition, natural boosts in volume will occur at multiples of this frequency: f2 = 113 Hz, f3 = 169.5 Hz, f4 = 226 Hz, and so on.

FIG. 2: When wavelengths are twice as long as the distance between the room boundaries, a “standing wave” reinforcement of the wavelength occurs at that frequency and its harmonics, causing a boost in their volume.

These resonances become more closely spaced and their volumes diminish as you move up the frequency spectrum. Therefore, in small rooms, resonances are typically not as problematic above 200 Hz.

Speaker/boundary interference. Because low frequencies are omnidirectional by nature, they reflect from all nearby room boundaries. These reflections adversely affect low-frequency response, making the bass sound as though it’s coming from different directions (see Fig. 3).

These slightly delayed reflections of the original signal cause comb-filtering peaks and dips within the range of frequencies above the modal resonance range (typically 200 Hz in a small room) to an upper limit of approximately 500 Hz. The increasingly directional nature of sound above 400 Hz makes speaker/boundary interference less of a problem for mid and high frequencies.

Standing waves and speaker/boundary interference can cause frequency-response deviations as high as 15 dB. This amount of level variation could keep you guessing about proper levels for all the bass frequencies you mix.