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Radio Production Worktext: Studio sound considerations; studio construction materials; and studio size and shape

Radio Production Worktext: Studio and Equipment

by David E. Reese, Lynne S. Gross and Brian Gross

By special arrangement with the publisher, AudioLink is offering an excerpt from the newest edition of the standard text on studio equipment and production for the radio.

Chapter 1 is excerpted below for our AudioLink audience.

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DJ EquipmentThe radio production studio is a unique space in that the physical room will impact the sound produced in it. Because of this, several characteristics of sound need to be considered in designing the studio, including sound isolation, noise and vibration control, and room acoustics. When sound strikes a surface (such as a studio wall), some of that sound is reflected back, while some is absorbed within or transmitted through the material of the surface. Most of the sound that hits a hard, flat surface will be reflected back. However, if the surface is irregular, it will break up the sound wave and disperse the reflections—a phenomenon known as diffusion. Sound that’s absorbed into the surface is dissipated within it, but penetration occurs when sound goes through a surface and is transmitted into the space on the other side. Figure 1.6 illustrates that penetration, absorption, reflection, and diffusion are all characteristics that help determine the sound that is both produced and reproduced in the studio.

DJ Equipment
  FIGURE 1.6  Sound striking a studio wall with reflect off, penetrate through, be diffused by, or be absorbed by that surface.

When a sound (such as an announcer’s voice) is produced, the direct sound is the main sound that you hear. In a production situation, it is sound that goes from the announcer (the sound source) straight to the microphone. On the other hand, indirect or reflected sound reaches the microphone fractions of a second after the direct sound does because it has traveled a circuitous route. Reflected sound consists of echo and reverberation. This indirect sound has bounced off or been reflected from one surface (echo) or two or more surfaces (reverb) before reaching the microphone (see Figure 1.7). Since it’s an early reflection, echo provides a distinct repetition of the sound, such as “hello—hello—hello.” On the other hand, reverb’s repeated later reflections provide a continuous decay of the sound, such as “hello—oo—oo.” The components of direct and indirect sound make up what is commonly called the sound’s “life cycle.”

In designing the radio studio, the goal is to manipulate these sound characteristics to create a proper sound environment for production work. When considering reflected sound, we think in terms of reverb ring and reverb route, with the same concepts applying for echo but to a lesser extent. Reverb ring (or reverb time) is the time that it takes for a sound to die out or go from full volume to silence. Reverb route is the path that sound takes from its source to a reflective surface and back to the original source (or a microphone, if recording). Excessive reflected sound tends to accent high and midrange frequencies, which produces a “harsh” sound; to blur the stereo image, which produces a “muddy” sound; or to cause standing waves (see Section 1.7), which produces an “uneven” sound. Reflected sound can also be reinforced sound, which causes objects or surfaces within the studio to vibrate at the same frequencies as the original sound in a sympathetic fashion.

DJ Equipment
  FIGURE 1.7  Direct sound takes a straight path from the announcer to the microphone, but reflected sound is also produced in the production studio.

Both absorption and diffusion are utilized to control reflected sound. Part of the reflected sound can be absorbed within the carpeting, curtains, and walls of the studio. Absorption soaks up sound and shortens reverb time to prevent excessive reflection. Absorption provides a dead studio, which has a very short reverb ring (sound dies out quickly) and a long reverb route that produces a softer sound. Excessive absorption produces a totally dead studio, which provides a “dry” sound that is unlike any normal acoustic space and isn’t really desirable. In contrast, a live studio has a longer reverb ring and a shorter reverb route that produces a harder, or more brilliant, sound. Diffusion uses irregular room surfaces to break up sound reflections. This decreases the intensity of the reflections, making them less noticeable, but doesn’t deaden the sound as much because the sound reflections are redirected rather than soaked up. Most studio designs control reflections by a combination of absorption and diffusion techniques.

One common radio studio design is a live end/dead end (LEDE) approach. The front of the studio (where the announcer and equipment are located) is designed to absorb and diffuse sounds. This dead end quiets some of the equipment operation noise, picks up the direct sound of the announcer’s voice, and absorbs the excess reflections that pass by the microphone from the live end. The live end, or back, of the studio adds a desirable sharpness to the sound by providing some reflected sound so the studio isn’t totally dry. Other acoustic designs include early sound scattering (ESS), which uses a great deal of diffusion, and reflection free zone (RFZ), which uses a great deal of absorption to control unwanted reflected sound in the studio.


DJ Equipment
  FIGURE 1.8  Acoustic panels and tiles help control reflected sound through both absorption (by the foam material) and diffusion (by the irregular surfaces). (Image courtesy of Auralex Acoustics, Inc. – Photo by Erikk D. Lee.)

Another design consideration involves the actual construction materials used for the studio. Ideally, you want to keep penetration to a minimum by keeping outside (unwanted) sound from entering the studio and inside sound from escaping from the studio, except via the audio console. Radio studios utilize soundproofing to accomplish this sound isolation. Doors are heavy-duty and tightly sealed; windows are often double glass with the interior pane slanted downward to minimize reflected sounds; and walls, ceiling, and flooring use special sound-treatment materials. For example, studio walls may be covered with acoustically treated and designed panels that both absorb and trap reflected sounds (see Figure 1.8). Some stations use carpeting on the studio walls, but this type of soundproofing doesn’t absorb low frequencies very well. Some production studios have actually used egg cartons on the walls as a sound treatment. If you compare the design of an egg carton with the design of the acoustic panel shown in Figure 1.8, you’ll see why some stations have gone the inexpensive egg carton route.

All materials absorb sound to some degree, but each material will have a different absorption coefficient, which is the proportion of sound that it can absorb. A coefficient of 1.00 indicates that all sound is absorbed in the material. On the other hand, a coefficient of 0.00 means no absorption occurs and that all the sound is reflected back. Hard, smooth surfaces like plaster or panel walls and hardwood floors have low absorption coefficients. Heavy, plush carpets, drape-covered windows, and specially designed acoustic tiles will have higher coefficients. For example, using a 1,000 Hz tone as the sound source, the absorption coefficient of a sheet rock wall would be .04 while a 2-inch Sonex foam tile would be .81; a glass window would be .12 while a window curtain would be .75; and a painted concrete block wall would be .07 while a carpeted concrete wall would be .37. The purpose of any soundproofing material is to help give the studio a dead sound. Soundproofing absorbs and controls excess reverb and echo and helps produce a softer sound.


The size and shape of a production studio can also determine how reflective the studio is. As noted, the radio production studio shouldn’t be overly reflective because sound produced or recorded would be too bright and even harsh. Unfortunately, standard room construction often goes counter to good broadcast studio design. For example, studios with parallel walls (the normal box-shaped room) produce more reflected sound than irregularly shaped studios. Sound waves that are reflected back and forth within a limited area, such as between studio walls that are parallel, can produce standing waves. In basic terms, a standing wave is a combination of a sound wave going in one direction and its reflected wave going in the opposite direction. If the distance between the walls is the same as the wave length (or a multiple of it), the waves interact and produce an undesirable combined sound that tends to be uneven, as previously mentioned. To help prevent standing waves, adjacent studio walls can be splayed (joined at more than a 90-degree angle) to help break up reflected sound and control excessive reverb and echo.

The actual size of the production facility is partially determined by the equipment that must be housed in it. However, in constructing the radio production room, consideration should be given to the fact that when rooms are built with height, width, and length dimensions that are equal or exact multiples of each other, certain sound frequencies tend to be boosted, and other sound frequencies tend to be canceled. Since this “peaks and valleys” sound is not desirable in the radio production room, cubic construction should be avoided when possible.

Installment 1: The audio chain
Installment 2: Studio layout
using studio furniture & racks
Installment 3: Studio sound considerations, construction materials, and size and shape

Next installment: STUDIO AESTHETICS

AUTHORS: David Reese, General Manager of KUNV radio and Affiliate Assistant Professor in the Greenspun School of Journalism and Media Studies in the College of Urban Affairs at the University of Nevada, Las Vegas (UNLV).; Lynne Gross, Professor, Communications Department, California State University, Fullerton. Independent programming consultant. President of Broadcast Education Association.; and Brian Gross, Professor in Radio, Film, and Television department at California State University at Fullerton. Published author, composer, and visual artist; video editor and writer for public television.

ISBN: 978-0-240-80690-7.