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.
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.
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.
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.
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.
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.
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.
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.
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 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.
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.
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.
White noise is random noise signal containing all frequencies at equal energy. White noise is useful for testing the frequency response of electronic circuits.