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.

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.


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.

Closed Back Headphones

Headphones with an enclosure around the rear of the speaker to that the headphone is only heard by the listener and not “out in the room.” Pros: privacy and isolation. Cons: exaggerated bass response and lack of stereo sound-stage. The Sony MDR7506 is a closed back headphone.

Compression (Data)

The process of reducing the storage size or number of bits required to represent information, allowing for more efficient transmission or storage. Data compression can be ‘lossy’ or ‘lossless’ (For example – MP3. files are a Compressed ‘lossy’ file).

Compression (Dynamics)

An audio process that reduces the volume of loud sounds or increases the volume of soft sounds to reduce the dynamic range of an audio signal. Compression is usually achieved with either compressors or limiters.


Decibels below full scale on a digital meter, where 0 is the maximum digital level. Example: -20 dBFS = 0VU. A dBFS meter can represent either peak or average levels and shows how close a signal is to digital clipping.


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).


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.

Equilateral 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.

Flat Sound

Describes an audio playback system where the output accurately reproduces the input signal over the full range of audio frequencies, with no significant variations in amplitude. Audio producers and engineers rely on playback systems that produce a flat sound.

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

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.


The amount by which a device’s maximum possible level exceeds the typical (nominal) operating level. Headroom typically indicates a system’s ability to handle short peaks without distortion or damage. Headroom is measured in dB. A digital recorder typically has 20dB of headroom above +4dBu.

House Curve

An EQ setting applied to a flat sound system to make it sound more pleasing. Usually slightly increased bass frequencies and slightly decreased high frequencies.


A measurement of electrical resistance in ohms (Ω) 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 8Ω and should be powered by an amplifier that matches the speaker’s impedance.

K System

An audio metering system that provides target loudness levels for different styles of music masters. K-20 is intended for classical music, K-14 is for pop music and K-12 is for Top40 broadcast music. The K meter provides both average and peak metering and can be applied to loudness meters, including the standard LUFS meter.


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. 

Lossless encoding

Data compression for audio that does not lose any audio quality. A file with lossless compression can be decompressed to a perfect copy of the original audio data and typically take up 50% to 75% of the original file size. Lossless file formats include FLAC and ALAC

Lossy encoding

Data compression for audio that irreversibly removes audio data to reduce the file size. The data is removed based on perceptual coding, or removing audio that is masked by other sounds. ‘Lossy’ formats include mp3 and AAC and typically take up only 10% to 25% of the file size of the original file.


An audio metering scale that accurately displays the perceived loudness of audio material. The measurements are relative to full scale, or 0 on a digital meter, so a typical master would measure something like -14 dB LUFS. (See also K System)


A maximizer is similar to a limiter that is optimized to achieve the final loudness for a mix or master without exceeding full scale, or any preset ceiling. A maximizer typically has automatic makeup gain, and adjustable ceiling, frequency dependent response times, and built-in dithering functions.


Data that describes other data, typically data included in a file to describe that particular file. Audio files typically use ID3 metadata, which includes information about a file’s copyright owner, images, lyrics and other information. Audio metadata is read and written by DAWs and music software such as iTunes.

Open Back Headphones

Headphones in which the speaker’s rear side is acoustically vented  “out to the room.” Pros: Natural sound. Cons: Lack of privacy and poor isolation from outside sounds. The AKG K240 is an open back headphone.

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.

PCM Audio

Pulse code modulation. A method of digitally representing analog signals, such as in digital audio. PCM audio is an uncompressed audio format defined by its bit depth and sample rate. WAV, AIFF and Audio CD formats use PCM audio.

Peak Level

Peak level denotes an instantaneous level. This is important, as any peak that reaches maximum level will cause distortion in a digital system. Peak level does not represent loudness, only the amount of momentary digital headroom.


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.

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.

Pink Noise

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.

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.

RMS Level

Root Mean Square. RMS Represents the average power level of an audio signal. RMS measurements represent the perceived loudness of an audio file. VU and LUFS meters are common RMS type meters.

Sealed Enclosure Speaker

Sealed enclosures have speakers mounted in opening, but provide no port or vent for sound pressure to escape the box. 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.


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 input, like 90dB/1milliwatt. Doubling the power (mW) will increase the loudness by 3 dB.

Soffit Mounted Monitors

Speaker cabinets are flush-mounted into heavily constructed, rigid cavities in front wall of a room. Soffit mounting speakers improves the efficiency of the loudspeaker (loading) and edge diffraction and rear boundary reflection problems.


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.

Symmetry (as applied to monitor loudspeaker setup)

Both left and right monitor speakers are to be placed the same distance from their respective surrounding walls and surfaces for proper stereo imaging and matching frequency response.


A mix is said to translate when the mix balance sounds, in a predictable way, about the same outside of the control room as it did inside of the control room. Translation is ensured by mixing and mastering in an accurate, properly treated room.


The characteristic or quality of a musical sound distinct from its pitch. Timbre is a perception of harmonic content and envelope. For example a piano sounds different than a clarinet when playing the same note due to their unique timbres. 

True Peak (Inter-sample Peak)

The instantaneous highest level of an audio signal, after it has been converted from digital to an analog signal. The true peak, or inter-sample peak, may be higher than any individual sample’s value, as the inter-sample peak is interpolated between sample values. True Peak meters can display the expected analog peak levels, which exceed 0 dBFS.

VU Meter

A Volume Unit meter that indicates the perceived loudness of an audio signal. 0 VU represents a voltage of 1.228 volts (RMS) or +4dBu. A VU meter displays an average voltage level and does not show the amount of headroom. In a digital system, 0VU is usually calibrated to -20 dBFS.


SPL meters can be weighted to measure either the typical response of human hearing at loud volume levels (C-weighting), or the response of human hearing at moderate volumes (A-weighting). dBA is used for environmental noise measurements while dBC is used to measure and calibrate sound systems. Z-weighting (dBZ) measures all frequencies equally.

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.

X Curve

The X Curve is a frequency response that represents the actual frequency response that a flat sound system creates in a large theater. In a large room, the level of the reflected sound becomes as significant as the level of the direct sound, so the listener hears a frequency response with rolled off high frequencies above 2kHz. To simulate the sound of a theater on near field monitors, you may apply an X curve EQ to your monitor chain.