DIY Audio & Video

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for Speaker Boxes, Crossovers, Filters,
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Definitions of Audio Terms

Here are some definitions of variables commonly found in audio related equations.

AAttenuation, loss of db
BMagnetic flux density in gap
BlElectro-magnetic force factor
BLDriver motor strength
cPropagation velocity of sound at STP, approx. 342 m/s
CabAcoustic compliance of air in the enclosure
CasAcoustical equivalent of Cms
CmesThe electrical capacitive equivalent of Mms
CmsThe driver's mechanical compliance (reciprocal of stiffness)
DEffective diameter of driver
F3-3 dB cutoff frequency
FbEnclosure resonance (usually for reflex systems)
FcSystem resonance (usually for sealed box systems)
FsDriver free air resonance. This is the point at which driver impedance is maximum
lLength of wire immersed in magnetic field
LcesThe electrical inductive equivalent of Cms
LeDriver inductance (voice coil, mainly)
LevcDriver voice coil inductance
MasAcoustical equivalent of Mms
MmsThe driver's effective mechanical mass (including air load)
n0The reference efficiency of the system
pDensity of air at STP 1.18 kg/m^3 (rho)
PaAcoustical power
PeElectrical power
QRatio of reactance to resistance (series circuit), or resistance to reactance (parallel circuit)
QaThe system's Q at Fb, due to absorption losses
QecThe system's Q at resonance (Fc), due to electrical losses
QesThe driver's Q at resonance (Fs), due to electrical losses
QlThe system's Q at Fb, due to leakage losses
QmcThe system's Q at resonance (Fc), due to mechanical losses
QmsThe driver's Q at resonance (Fs), due to mechanical losses
QpThe system's Q at Fb, due to port losses (turbulence, viscosity, etc.)
QtcThe system's Q at resonance (Fc), due to all losses
QtsThe driver's Q at resonance (Fs), due to all losses
RasAcoustical equivalent of Rms
ReDriver DC resistance (voice coil, mainly)
RevcDC resistance of the voice coil only
ResThe electrical resistive equivalent of Rms
RgAmplifier source resistance (includes leads, crossover, etc.)
RmsThe driver's mechanical losses
SAFSpouse Acceptance Factor
SdEffective piston radiating (surface) area of driver
VabThe volume of air having the same acoustic compliance as the enclosures
VasThe volume of air having the same acoustic compliance as the driver suspension: Cms
VbNet internal volume of enclosure
VdMaximum linear volume of displacement of the driver (product of Sd times Xmax)
XmaxMaximum peak linear excursion of driver
ZTotal driver impedance