Glossary
Acoustic center
The effective point from which a driver’s sound appears to originate. Its position can vary with frequency.
Acoustic suspension
A sealed-box system in which the enclosed air contributes a substantial part of the total restoring stiffness.
Baffle
A structure that controls interaction between radiation from the front and rear of a diaphragm.
\(B\ell\)
The motor force factor: magnetic flux density multiplied by the effective conductor length in the gap.
Breakup
Operation in which different parts of a diaphragm move with different amplitudes or phases.
Compliance
The inverse of stiffness. A more compliant suspension moves farther for a given static force.
Crossover
A filter system that divides the audio spectrum between drivers.
Directivity
The variation of sound radiation with angle.
Efficiency
The ratio of acoustic output power to electrical input power.
\(f_B\)
The tuning frequency of a bass-reflex enclosure.
\(f_S\)
The free-air mechanical resonance frequency of a driver.
Impedance
The frequency-dependent opposition to alternating electrical current. It includes resistance and reactance.
Nominal impedance
A simplified impedance classification such as 4 Ω or 8 Ω.
Phase
The relative timing position of a periodic signal or frequency component.
Power compression
The reduction in sensitivity that occurs as heating and other high-level effects increase.
\(Q_{ES}\)
The electrical Q of a driver at resonance.
\(Q_{MS}\)
The mechanical Q of a driver at resonance.
\(Q_{TS}\)
The combined electrical and mechanical Q of a driver.
\(Q_{TC}\)
The total Q of a driver in a sealed enclosure.
Sensitivity
Sound-pressure level produced under a specified input, distance, and measurement condition.
\(S_D\)
The effective radiating area of the diaphragm.
Thiele-Small parameters
A set of small-signal parameters used to model a driver’s low-frequency behavior.
Voice coil
A coil of wire that produces force by carrying current in a magnetic field.
\(V_{AS}\)
The volume of air with the same acoustic compliance as the driver suspension.
Woofer
A driver intended to reproduce low frequencies.
\(x_{max}\)
The specified one-way linear excursion of a driver. Definitions vary among manufacturers.