Absorption Coefficient
The absorption coefficient is a measure of the efficiency of a material in absorbing sound. The absorption coefficient varies with frequency. Coefficients are published at the six standard frequencies centered at: 125, 250, 500, 1kHz, 2,000 and 4,000 Hz.
Active or Powered Monitors
These are self-powered monitor speakers with built-in crossovers, separate power amplifiers for each driver. They do not need an external power amplifier. They are connected directly to a line level output from an audio source such as a mixer or monitor controller.
Acoustic Foam
Open-cell porous polyurethane that absorbs high frequencies.
B
Backing Board
Backing Board is sold in similar sizes as sheets of plywood but is instead made of cement and used as waterproof backing walls for showers and bathrooms--it's denser and heavier than plywood, MDF, gypsum board or drywall.
Bass Traps
A low frequency absorber that works below about 300Hz.
Bass Reflex Speaker
A bass reflex speaker uses a vent hole, or port tube, which enables sound from the rear side of the woofer to exit the cabinet. A ported speaker cabinet increases, or extends the low frequency response of the speaker over a sealed cabinet. Additionally, a properly tuned port limits the speaker's movement at certain low frequencies, which may lower distortion at low frequencies.
Batt
A fluffy and smaller piece of fiberglass used for insulation and/or absorption.
Boundaries
In acoustic design, walls, floors, and ceilings are called boundaries where sound waves hit and are absorbed and/or reflected.
C
CAT 5, CAT 5E, CAT 6
Category (5 or 6) cable that uses twisted pairs of wires for noise rejection and primarily used for Ethernet connections between computers, routers, servers, and modern networked digital audio and video systems.
Cloud
Cloud or Ceiling Clouds: An acoustic treatment panel mounted slightly off the ceiling. A ceiling cloud is hung over the listening position and can consist of a diffuser and absorber combination.
Contractor
Sometimes known as a general contractor, a person or company in charge of executing the construction plans as drawn by an architect or architectural acoustic designer.
Crossover
An electronic circuit that splits an audio signal into separate frequency ranges which the woofer, midrange or tweeter independently reproduce. Crossovers may be passive or active circuits and may be internal to a speaker or may be an external component in a large speaker system.
D
Damped
(As used in the study of acoustics): A restraining or discouraging force. A highly damped structure would be resistant to vibration or movement by external forces such as loud sound sources either inside or outside of the studio.
Diffraction
Diffraction describes how waves bend, or change direction, as they travel around the sharp edges of obstacles. For instance, high frequencies emanating from a tweeter will bend around the edges of a small loudspeaker's faceplate and radiate outward in a way that creates comb-filtering interference with the direct signal. Good loudspeaker design minimizes diffraction effects of a speaker's faceplate (baffle).
Diffuse Sound
A sound that no longer carries the coherency of reflected sound as the different wavelengths of sound exit a diffuser with different angles of reflection and at different times.
Diffusion
The scattering of sound waves. Diffusors randomize reflections and reduce flutter echoes and the sense of localization. Diffusors are used on ceilings, rear walls behind the listening position and sometimes are preferred at the first reflection points or either side of the listening position.
Diffuser
Diffusers (also spelled Diffusor) scatters sound arriving from any direction to reduce the problem of direct reflections. Diffusers create a more even musical sound without reducing reverb time (RT60) significantly and can make a room feel larger than it actually is. Diffusers reflect and redirect incoming sound at different angles in single and/or multiple planes.
1D diffusers spread the sound out on a single plane.
2D diffusers spread the sound out on two or multiple planes.
Direct Sound
A sound that arrives at the listener directly from the speakers as opposed to a reflected sound that has bounced off at least one hard surface before it is heard.
Discrete Absorber
A Discrete Absorber can be anything in a room's space. The two most ubiquitous discrete absorbers in a room are people and furniture.
Drywall
A type of board made from plaster, wood, pulp, or other material used to form home/office interior walls. Comes in 4-ft by 8-ft sheets and in different thicknesses starting from 1/4-inch.
D-Sub
A compact, "D" shaped multi-pin connector used by analog and digital outboard equipment. A DB25 connector would have 25-pins available while a DB9 has 9-pins.
E
Electronic Room Correction
Electronic Room Correction is a software and/or hardware system that measures the monitoring system's performance at the listening position and electronically corrects it. Electronic room correction can compensate for the effects of the room's poor acoustics and its intrinsic modal issues but only at the listening position. However there is no real substitute for fixing acoustic problems of the entire room with the proper application of acoustic treatments.
F
Fletcher Munson Loudness Curve
Human hearing is increasingly sensitive to both bass and treble frequencies as volume increases to about 85 dB SPL. Two scientists, Fletcher and Munson defined and graphed this phenomenon with the Fletcher-Munson Equal Loudness Curve. Mixing and mastering engineers typically set studio monitors to a nominal volume level to take into account this loudness curve.
Frequency Response Curve
A measurement, in Hertz, of an amplifier circuit or a monitor's ability to produce sound from low bass to high treble. This measurement includes a range of an acceptable tolerance stated in decibels, For example frequency response of a device would be expressed as: 20 Hz to 20 kHz (+/- 3 dB). Human hearing covers a range from 20 Hz to 20 kHz.
Flanking Transmission
Air leakage around ("out-flanks") doors, windows and gaps in a room that will defeat isolation.
Floating Floor
A floor that is detached from the underlying subfloor or concrete foundation slab in order to increase the isolation from external vibration or acoustic sources.
Flutter Echoes
Flutter Echoes result when a sharp, transient sound is produced between parallel reflective surfaces that are separated by more than about eight meters. With surfaces separated by less distance, the result is a metallic ringing, "Boing" sound. Flutter echo, when made loud enough, can interfere with sonic intelligibility.
G
Ground
The chosen common return point for all power supplies and circuits. It is also the braided-shield connection for analog and digital input and output connections.
Ground Loop(s)
Unwanted signals, radio frequency, buzzes and noises injected into the audio. It happens whenever sensitive audio equipment detects two or more different paths to ground.
Gypsum Board
It is drywall made from plaster sandwiched between two sheets of heavy paper.
H
Harman Room Mode Calculator
An Excel spread sheet (.xls file) analysis that will output the frequencies of the 1st, 2nd, 3rd, and 4th axial room modes just by typing in the room's H, W, L dimensions in feet. The default value for the speed of sound is 1,130 feet/second.
Download Your Free Copy Of The Harman Room Mode Calculator: Here
Helmholtz Resonator
A tuned, narrow band resonant cavity bass trap used in architectural acoustics to reduce undesirable low frequency room modes and standing waves.
HVAC
HVAC or Heating Ventilation Air Conditioning: A single built-in system that does heating, ventilation, and air-conditioning.
I
Impedance
A measurement of electrical resistance in ohms for AC electrical circuits such as in audio. For headphones, low impedance phones (30 ohms) will play loudly with a portable music player, like a phone. Higher impedance headphones (250 ohm) are more appropriate with professional headphone amplifiers and studio equipment. Passive speakers typically are typically rated at 8-ohms and should be powered by an amplifier that matches the speaker's impedance.
IEC Cables
International Electro-technical Commission standardized AC power connection cables are used for electronic gear throughout the world for AC line voltages ranging anywhere from 100 to 250-volts. All modern electronic equipment uses a single standardized "IEC" socket mounted on their chassis. The standardized mating IEC power cable has the proper plug on its end to connect to the particular country's wall socket type.
Inverter
A device that converts DC voltage (usually from a battery or rooftop solar panels) into 120-volt AC to power small household appliances.
Indirect Sound
A sound that arrives at the listener's ears by some path(es) other than directly from the speakers.
J
Joist
A joist is framing member used to support a floor called a "floor joist" or a ceiling called a "ceiling joist".
K
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L
Loudness
The subjective perception of a sound's intensity or volume. Human hearing is sensitive to different frequencies at different SPL levels (see Fletcher-Munson) so loudness needs to be measured with a frequency-weighted meter. LKFS/LUFS and weighted SPL meters may be used to measure loudness.
Listening Position
The listening position: is equidistant between the left and right monitor speakers for a balanced stereo image and a stable frequency response from the monitors.
Live End/Dead End
In a LEDE Control room design, the front or dead end of the room uses more absorption to control unwanted reflections and increase intelligibility around the listening position. The rear or live end of the control room behind the listening position is kept more live and reflective. The live end can be used for recording in "all-in-one" room Project Studio Designs.
M
Magic Triangle Method
This is an equilateral triangle at which the positions of the left speaker, right speaker, and the optimal listening position are located at the triangle's three corners. At the optimal listening position, the listener's head is located just inside that corner. The optimal listening position corner should be just located just behind the listener's head.
Mass Law
The Mass Law says that if you double the mass of the wall, you get 6 dB more isolation. It takes four times the mass to get 10 dB more isolation--or about twice as much isolation.
Mass Loaded Vinyl
A limp-mass material made of vinyl that is infused with heavy Barium (atomic number 56). It is 6dB more effective than solid lead at stopping the transmission of sound when used in multi-layer construction techniques.
MDF
Medium Density Fiberboard. Engineered wood made of compressed wood fibers used in the construction of walls, floors and roofs.
Mineral Wool
A substance resembling matted wool that's made from Basalt (rock) and spun into fibers for both insulation and sound isolation.
Mini-Split
A two-piece air conditioner system where the noisy compressor machinery (located outside) is separated from the head unit placed high on the room's wall. Popular in Europe and Asia, they do not require extensive ducting work or extensive wiring. In the US, there is no need for 220-240 VAC and can run on 110-120 VAC with no special wiring needed to be installed. Mini-Splits are an ideal solution for project studios located in garages, basements--anywhere without HVAC.
MSM Wall System
Mass-Spring-Mass is a massive wall with an air gap acting as Spring and then another Massive wall. This is a proven wall design for sound isolation.
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O
OSB
Oriented Strand Board is engineered wood formed by gluing and layering strands of flakes of wood in a specific orientation. It comes in both 4 X 8-foot sheets or as framing lumber--2 X 4 or 2 X 6 boards used for studs and joists.
P
Passive Monitors
A passive monitoring speaker has a passive crossover installed inside the enclosure and requires an external audio power amplifier. The speakers connect to the power amp with large gauge, two-conductor speaker wire and must have low resistance. Yamaha NS10Ms are an example of popular passive monitor speakers used in recording studios.
Phase
Phase refers to the position in time (an instant) of a waveform cycle relative to another waveform's cycle. In audio, it is measured in degrees and a single cycle of an audio wave travels 360-degrees before coming back to 0-degrees again. Phase cancellation is both frequency and time dependent.
Pink Noise
Pink noise is filtered white noise. It is reduced or rolled off by 3 dB per octave. Pink noise is produced by passing white noise through a -3dB per octave filter. Whereas white noise contains equal power at every frequency, pink noise contains equal power for every octave. Pink noise reflects the sensitivity of human hearing in different octaves and is typically used to test the frequency response of an audio loudspeaker system.
Pliable Materials
These are materials that bend and flex absorbing the incoming wave front energy. They work best at low frequencies.
Polarity (often stated incorrectly as phase)
Electrical Polarity refers to the positive and negative orientation of two or more AC (audio) signal waveforms. If two waves are of identical frequency but opposite polarity, one positive and the other negative, they will cancel out producing no output when mixed at equal levels. They are said to be "out of polarity." For example, two in-polarity loudspeakers will both produce a positive pressure when fed the same positive voltage. Out-of-polarity speakers, where one speaker is reversed-wired, results in little or no output when fed the same voltage and played at equal level. Loudspeaker polarity is maintained by matching + connections to each other and - connections to each other.
Porous Absorbers
Materials such as rigid fiberglass and foam that absorb more strongly at frequencies whose quarter wavelengths are less than the thickness of the material itself OR equals the distance the material is spaced off the wall. These absorbers work best at middle and high frequencies.
Power Handling
The amount of power, usually in watts, that a speaker can handle without being damaged. Power handling specifies either momentary (Peak Power Handling) or continuous (Continuous or RMS Power Handling) levels. Power handling is not an indication of output level of a speaker.
Pressure Absorbers
Pressure absorbers use absorptive or pliable materials and are placed right on the boundary.
Prime Number
A whole number greater than 1, whose only two whole-number factors are 1 and itself. The first few prime numbers are 2, 3, 5, 7, 11, 13, 17, 19, 23, and 29.
Pseudo-Random Numbers
A sequence of numbers, or any digital data satisfying one or more statistical tests for randomness but are produced by a definite mathematical procedure. Pseudorandom sequences are deterministic, reproducible and are used with Quadratic Residue Diffusers.
Q
Quadratic Residue Diffusers or QRD
QRD diffusers spread sound out in time, phase and space. Their design is based on prime number quadratic residue sequences to determine the different "well" depths or "skyscraper" heights on the surface of a diffuser.
R
Reflected Sound
Reflected Sound is sound that has bounced off at least one hard surface before it is heard.
Reflection Free Zone
The Reflection-Free Zone or RFZ is created at the listening position where the first reflections of sound coming from the monitor speakers (that has bounced off nearby walls, floors and ceilings) is minimized to increase intelligibility, clarity and improve stereo imaging.
Resilient Channel
A specially formed metal strip used to hang drywall; it provides an air space and isolation. It is used to provide attachment points for sheets of flat drywall on top of irregular or rough outer walls such as cinder block or stone.
Resonance
In physics, the amplitude of vibration of any resonant system is maximum at its natural or resonance frequency and much less so at frequencies above or below that frequency.
Resonance (as used in the study of acoustics)
The prolongation of sound by reflections or reverberation.
Resonance Absorbers
Pressure absorbers that use the resonant properties of a material or cavity to provide absorption.
Reverberation
Reverberation is the persistent of a signal in the form of reflected waves within an acoustic space that continues after the original sound has ceased.
RT60
The reverberation or decay time in seconds that reverberant sound takes to decrease 60dB or one millionth of its original intensity. It is directly related to the volume of the room and the total absorption coefficients of the walls, floors, and ceiling surfaces.
Rigid Fiberglas
Made from glass silicate, this is a porous velocity absorber material. Owens Corning 703 two-inch thick panels are the #1 material used to build acoustic panels. It's stiff enough to be easily cut into any shape and wrapped with cloth without requiring a frame.
Room-Within-A-Room
Floating the floor on rubber mounts or springs and also building double or triple walls and ceilings with air spaces between.
Room Modes Of Vibration
There are three types of room modes: Axial, Tangential and Oblique. Axial modes involve two parallel boundaries and are the most problematic. Tangential and oblique modes are more numerous but have less energy than axial modes.
Room Modes of Vibration or Room Modes are specific types of standing waves caused by frequencies below 300Hz reflecting back and forth between parallel walls, the floor, and ceiling boundaries. Modal activity occurs at frequencies that are directly related to the dimensions of the room. Room modes cause both (in-phase) amplitude peaks (called anti-nodes) and (out-of-phase) amplitude dips (called nodes) in frequency response when two or more waves meet and are the same frequency.
S
Speaker-Boundary Interference Response
SBIR or Speaker-Boundary Interference Response is caused by low frequencies coming from your monitor speaker (bass is omni-directional) bounce off the wall behind the loudspeaker. Out in front of the speaker, cancellations called nodes will occur at 1/4th of the frequency's wavelength that equals the distance from the front of the speaker to the rear wall. That's because the round-trip distance to and from the rear wall adds up to a 1/2 wavelength.
When two sounds--the reflected sound wave from the rear wall and the direct sound coming out of the front of the speaker combine and are 180 degrees out-of-phase, they cancel out at that particular frequency.
At 1/2 wavelength from the rear wall, a boost called an anti-node will occur. Soffit-mounted monitors (see below) installed flush to the front wall preclude all SBIR problems
Schroeder Frequency
The Schroeder Frequency was named after acoustician Manfred Schroeder and is the frequency at which a room crosses over from acting like a resonator to acting like a reflector. Below the Schroeder frequency, a room acts like a resonator with low frequency room modes determined by the H, W, L dimensions. Above the Schroeder frequency, the room acts like a reflector with middle and high frequencies bouncing off hard surfaces.
Sealed Enclosure Speaker
Sealed enclosures have their speakers mounted in an opening, but provide no port or vent for sound pressure to escape. Therefore, the movement of a woofer is controlled by the volume of air inside the cabinet, which acts like a spring. Other types of sealed enclosures include Acoustic Suspension designs and Infinite Baffle designs.
Sensitivity
Useful for headphones or passive monitors. A measurement of a speaker's efficiency, or how much sound is produced for a given input level. Higher sensitivity numbers mean the monitor will play louder with a given input signal. Written as dB SPL output for a given power input, like 90dB/1milliwatt. Doubling the power (mW) will increase the loudness by 3 dB.
Sound Transmission Class
Sound Transmission Class or STC is the measurement of a partition's ability to block sound over a range of 16 frequencies spaced on 1/3-octave centers from 125 Hz to 4 kHz.
Soffit
A heavily constructed and very rigid cavity built into a wall where a speaker cabinet is mounted.
Soffit-Mounted Monitors
Speaker cabinets are flush-mounted into heavily constructed, rigid cavities in front wall of a room. Soffit mounting speakers improve the efficiency of the loudspeaker and edge diffraction and SBIR problems.
SPL
Sound pressure level measures the acoustic power, or pressure of sound against an eardrum. SPL is measured in decibels and some typical reference levels are: 0 dB SPL is the threshold of human hearing, 60 to 70 dB SPL is typical for television watching, 120 dB SPL is the threshold of pain. It takes an increase of about 10 dB SPL for a listener to perceive a sound as twice as loud. An SPL meter is used to determine SPL levels.
Standing or Stationary Waves
A phenomenon in which a wave remains in a constant and fixed position in physical space as the result of the interference between two sound waves of the same frequency and equal amplitude traveling in opposite directions.
Step-Down and Step-up Transformers
A "step-down" or 2:1 transformer is for changing 240VAC (Volts Alternating Current) into 120VAC. It is useful to power equipment in the U.S. that was built to operate only on the 240VAC mains voltages of other countries. Typically the world is 240 volts AC whereas the U.S. and its territories are 120 Volts AC. A "step-up" 1:2 transformer will step up 120 VAC to 240 VAC. Usually Step-Up/Down transformers are built to do both step-up and step-down functions. They are rated in VA or Volts/Amps or the total watts they can handle.
Stud
An upright metal or wood framing member on which drywall is attached to form a wall. They come in common sizes for construction such as 2 X 4 and 2 X 6-inches.
Sweet Spot
The Sweet Spot is the position between the stereo speakers with the best stereo image.
Symmetry
Symmetry (as applied to monitor loudspeaker setup) is when the speakers are placed exactly the same distance from each other, the same distance from the side walls, and the wall behind them.
T
The 20/20 Rule
At the listening position, sound reflections occurring within the first 20 milliseconds shall be 20 dB lower in level compared to the initial sound coming from the monitors.
The 38% Rule
The 38-Percent Rule optimizes the listening position lengthwise in the room.
Translates
This means your mix balance sounds, in a predictable way, about the same outside of the control room as it did inside of the control room given the playback system and the speakers it's played on in the outside world. Good translation is ensured by mixing and mastering in an accurate, properly treated room.
TRS
TRS or Tip-Ring-Sleeve is a 6.35mm or 1/4-inch stereo plug found on headphones and older patch bays. Generally, 24 TRS jacks in a patch bay row will fit in a standard 19-inch, 1U rack space.
TT
TT or Tiny Telegraph is the 4.4mm TRS plug/jack used in modern patch bays. Although less reliable and robust as the old 6.35mm (1/4-inch) TRS plugs, 48 TT jacks will fit in the same space as the 6.35mm TRS jacks.
U
UPS
A UPS or Uninterruptible Power Supply uses a small battery to power a DC-to-AC inverter that'll provide 120 VAC power to your computer for a limited amount of time. This system allows you to save your DAW session and shut down properly and wait until normal power is restored.
V
Velocity Absorber
Velocity Absorbers are typically porous absorbers that use dense fibrous materials to slow the velocity of sound. Air particles of sound waves vibrate within porous materials such as natural fibers (cotton), mineral wool fibers (Basalt), foam (polyurethane), carpet, acoustical tiles etc. The frictional loss is converted to heat. They work best at middle and high frequencies.
W
White Noise
White noise is random noise signal containing all frequencies at equal energy. White noise is useful for testing the frequency response of electronic circuits.
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