Studio design glossary

The past few months my friend Rob, Luke, and I are busy building our studio and lab in Long Beach, Ca. When time to design the studio we decided to use Owen Corning insulating material to save the time and control our lo-freq issues in the studio. I plan to talk about this issues due to the constant emails asking me about how to design a room or treat a room well enough for mixing.

The acoustic issues for a room is deep, really deep but you can somewhat do this yourself at home or at your project studio to minimize the problem. I visited many studios during the time working in Vietnam and one comment thing i noticed was over used of Auralex foams to the point most rooms are 'suffocate' the crap out of the acoustic, which create a sense of no air and hard to breath when you are in them.

The funniest thing I ever saw was how the engineers keep clapping his hands to show me that he can tell the RT60 rate by doing that. You don't have to do that, when you walk into a room, just listen to your conversation will be enough to tell you what is going on with the room acoustic, or better play a cd.

Most professional studios in the world have a ratio of 3:1 with the cost of designing the acoustic verse the cost of the audio gears. So first, before I start here is what need to know.

Absorber: a class of acoustical materials that eliminate reflections and reverberation. Common examples of absorbers include foams, fabric-covered Fiberglas batts, carpet and upholstered furniture. A common misconception is that soundproofing can be achieved by treating walls with absorptive materials. An absorber's effectiveness is frequency-related, and most common absorption materials only affect mid- and high frequencies, leaving low frequencies (bass) unaffected.

Active Crossover: a dividing network that splits a full-range signal into two or more frequency groups and routes them to feed the various components (e.g., woofers and tweeters) in a speaker system. Active crossovers divide a line-level output signal from a mixer or other sound source and route the resulting signals to individual amplifiers that drive different speaker components. Passive crossovers usually are built inside speaker cabinets, where they divide an amplifier's output signal for routing to different speaker combinations. See Bi-Amp.

Amplifier: a device that tracks the amplitude of an incoming signal and proportionally increases the voltage, current or power of the signal by adding power from another source.

Amplitude: the magnitude, or level, of an electrical signal (voltage) or acoustical signal (volume).

Attenuation: the process of decreasing a signal’s amplitude as it passes from one point to another. Analog attenuation circuits typically use resistors to reduce the voltage of a signal. In audio, the effect of such attenuators is usually expressed in decibels. See decibel, resistor.

Baffle: typically, a term referring to the board on which a speakers are mounted. Due to weakening of the board caused by mounting holes cut into it for speakers, ports, vents, etc., the cabinet's front baffle is sometimes thicker than the other sides of an enclosure.

Bass Reflex: a popular enclosure design that uses a tuned port to extend a loudspeaker's bass response by allowing some of the air movement from a woofer cone's rear motion to combine with the bass frequencies from the cone's front movement. However, to avoid phase cancellation from occurring when these signals are combined, the port length and diameter must be carefully matched (tuned) to the speaker's free-air resonance and the enclosure volume.

Bi-Amp: short for bi-amplification. A two-way audio system in which the signal is divided by frequency into two signals that are independently amplified and fed to separate speaker system components (e.g., woofers and tweeters). In a "tri-amped" system, signals are divided by frequency into three individually amplified groups. See crossover.

Crossover: a dividing network that splits a full-range signal into two or more frequency groups and routes them to feed the various components (e.g., woofers and tweeters) in a speaker system. Passive crossovers are usually built inside speaker cabinets where they divide an amplifier's output signal for routing to different speaker combinations. Active crossovers divide a line-level output signal from a mixer or other sound source and route the resulting signals to individual amplifiers that drive different speaker components. See bi-amp.

dB: abbreviation for "decibel." See decibel.

dBm: a term expressing an electrical power level, referenced to 1 milliwatt (i.e., 0 dBm = 1 mW). Originally, dBm was used to express the power dissipated in telephone applications with 600-ohm impedances, but it is not necessarily referenced to a particular impedance.

dBu: a means of expressing voltage, referenced so that 0 dBu equals 0.775 volts, regardless of impedance. One mW of power is dissipated if 0.775 volts is applied to a 600-ohm load, so when the load impedance is 600 ohms, 0 dBu = 0 dBm.

dBV: a means of expressing voltage, referenced so that 0 dBV equals 1-volt RMS, regardless of impedance.

dBv: synonymous with dBu but rarely used due to confusion with dBV. See dBu.

Decibel: a unit of measure used to logarithmically express ratios of change in power or signal levels. A decibel is equal to 1/10 of a Bel (named for Alexander Graham Bell).

Diffusor (or Diffuser): an acoustical device designed for wall or ceiling mounting that breaks sound waves that strike it into a large number of small, variable reflections, creating a widely scattered, diffuse soundfield rather than single reflection or echo.

Double-Wall: a studio construction technique that achieves sonic isolation (i.e., soundproofing) by building a "room within a room": using a second set of wall studs that are typically offset from the outer wall's studs. By carefull sealing the wallboard joints on the inner walls and leaving a few inches of air space between the two (inner and outer) sets of studs, a relatively high degree of sound isolation is possible.

Dynamic Range: a ratio (expressed in decibels) of the difference between the softest and the loudest sound that can be produced, reproduced or captured by a musical instrument or audio device.

Equalization: a circuit that allows the frequency-selective manipulation of a signal's amplitude. The simplest equalizers are shelving types, offering the ability to cut or boost gain above or below a given frequency. Examples include the treble and bass controls found in home stereo systems or guitar amps. More complex circuits that allow tonal shaping in multiple frequency bands include graphic and parametric equalizers. Abbreviated "EQ." See graphic equalizer, parametric equalizer.

Feedback: a condition in which the output of a circuit recycles through its input. Acoustic feedback is a whine or howl that occurs in live audio situations when an amplified sound re-enters a sound system through the same microphone (or guitar pickup) that reproduced the original source, creating a loop. Feedback also can be used in signal processing; for example, part of a signal routed through a digital delay can be fed back into the delay to create a more complex effect. This is also called "regeneration."

Floating: a construction technique that isolates studio floors or walls by decoupling them from each other and/or adjacent walls, slabs or surfaces. For example, floors can be "floated" by mounting the joists on large springs or rubber isolators, thus reducing the transmission of sounds or vibrations from that floor to nearly walls, ceilings below or adjoining floor surfaces.

Frequency: the number of times a periodic waveform cycles, or repeats, over a period of time. See hertz.

Fundamental Frequency: the lowest root frequency component of a periodic waveform. The fundamental frequency of a sound usually is perceived as its pitch. (Sometimes, this is true even when the fundamental's amplitude is lower than that of its harmonics.) See Harmonics.

Gain: a ratio expressing the difference between the input and output power, level or current in a circuit.

Gobo: in audio terms, a moveable barrier used in the studio to increase isolation, typically between a noisy sound source (i.e., drums or a guitar amp) and other mics or instruments in the studio. Alternatively, gobos can be used to "protect" a low-level source, such as a vocalist's mic, from nearby higher-level sounds.

Graphic Equalizer: a frequency-shaping device having multiple filter bands, each operating at a fixed frequency and bandwidth.

Hertz: a unit of measure of the frequency of a vibrating object, such as a guitar string, speaker cone or electrical signal. Equivalent to cycles per second, it is named for Heinrich Hertz and abbreviated "Hz."

LEDE: An abbreviation for Live End/Dead End, this is a studio design technique that combines a "live" (reflective or diffuse) area in the rear of the room and a "dead" (highly absorptive) area at the front of the control room, surrounding the speakers.

Millisecond: one one-thousandth of a second. Abbreviated "ms."

ms: See millisecond.

Near-Field Speaker: a compact studio monitor designed for listening at close distances, typically between three and five feet. When sitting at this near-field distance, the listener hears a greater proportion of direct sound from the monitors (compared to the reflected sound bouncing around the room) so, in theory, the effects of poor room acoustics are greatly reduced.

Parametric Equalizer: a circuit designed for frequency-selective attenuation or boosting of a signal's amplitude, with independent controls for gain, center frequency and bandwidth (including continuously adjustable Q). A quasi-parametric EQ may provide full frequency and gain adjustment, but only two or three Q settings. Sweepable EQs have an adjustable (sweepable) center frequency but operate on a fixed bandwidth.

Phase: the relative measurement of a period of time referenced to the start point of a cycle of a periodic waveform. In one complete period, a wave's polarity fluctuates 360 degrees (180 degrees positive and 180 degrees negative). Absolute phase is a reference point in time within one cycle—e.g., halfway through one period, the waveform's phase is 180 degrees; at one-quarter of the waveform, the phase is 90 degrees. Relative phase is an instantaneous ("snapshot") measure of the difference in time between two acoustic or electronic waveforms of the same waveform and frequency. For example, if one waveform is one-quarter of the way through its cycle (90 degrees at its peak positive value) and the other is three-quarters of the way through its cycle (270 degrees at its greatest negative value), they are 180 degrees out-of-phase with respect to each other. The two signals are "in-phase" if their amplitudes are identical at the same point in their cycles.

Phase Shift: a slight time difference between two similar waveforms, which puts them out-of-phase with respect to each other.

Phase Cancellation: an attenuation of signal components resulting from combining out-of-phase waveforms. When two waveforms are mixed, their harmonics are added. If the signals are out-of-phase with each other, then the amplitudes of the harmonic components differ at various times (as determined by the phase relationship). If the added harmonics have the same polarity, then the signal is reinforced at those frequencies. If harmonics with positive values are added to harmonics with negative values, then the signal is attenuated (canceled) at those frequencies.

Resonance: the property possessed by a simple vibrating body of oscillating more strongly in sympathy with a regular oscillatory disturbance at the same frequency. When a vibrating object (such as a guitar body) is stimulated by a second oscillator (such as a vibrating string), its pattern of vibration may be altered. If the two vibrate at the same (or a harmonically related) frequency, they tend to phase-lock together in sympathetic vibration at this common resonant frequency. The amplitude of their vibration is thus greatly increased. Oscillations at nonharmonic frequencies have far less effect. The same principle holds with electrical signals.

Reverberation: the decaying residual signal that remains after a sound occurs, created by multiple reflections as the original sound wave bounces off walls, furniture and other barriers within a room or other acoustical environment. Modern reverb effects processors use digital signal processing (DSP) techniques to simulate acoustical spaces. Analog methods of simulating reverberation include spring reverbs (commonly used in guitar amps), plate reverbs (which use a mechanical transducer to vibrate a large metal plate) and reverb chambers (where signals from a speaker sounding in a room are picked up by one or more microphones).

RTA: An abbreviation for real-time analyzer, RTA is an acoustical measurement device that displays the frequency response of a signal played back through P.A. or studio speakers. RTAs typically divide the audio spectrum into 16 or 31 bands that represent individual frequencies that correspond with the frequency sliders used on graphic equalizers, allowing the user to compensate for room or system anomalies.

RT60: a means of expressing the measurement of the reverberation time in a room or acoustical space that indicates the elapsed time required for the reverbereration to decay by 60 decibels.

Sensitivity: a measure of the relative efficiency of a speaker or loudspeaker system, often expressed as the number of decibels the unit will produce fed from a 1-watt signal measured at a distance of 1 meter.

Sine Wave: a continuous periodic waveform whose amplitude varies as the sine of the linear function of time. Occasionally referred to as a sinusoidal wave, it has no harmonics except the fundamental.

Soffitt: a construction technique that incorporates inset spaces in a wall to accommodate studio monitors or video displays so that the front of the speakers are flush with the wall surface.

SPL: An abbreviation for sound pressure level, SPL is a means of expressing sound levels. SPL is frequently used as a comparative measure of speaker efficiency or maximum system output.

STC: An abbreviation for sound transmission class, STC is a rating appplied to the construction of partitions (typically walls) to describe the degree of sonic isolation provided by that construction technique.

Transducer: a device that transforms energy from one form to another. Examples of electromechanical transducers include microphones (which convert acoustic pressure into electrical voltage) and loudspeakers (which convert voltages into acoustic pressure).

Translation: the ability of mixes created on one set of monitors to consistently playback ("translate") to other systems.

Waveform: a 2-D graph of one period of a signal, showing changes in pressure (amplitude) as a function of time.

Wavelength: the distance from the beginning to the end of one cycle (or from equivalent points in two consecutive cycles) of a waveform. A wavelength is equal to the speed of sound times the frequency of the waveform.

White Noise: a test signal comprising random noise, providing constant energy at all frequencies, similar to the sound heard when an FM radio is set between stations.