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12.16 What are all of these abbreviations people use for speakers?




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This article is from the rec.audio.* FAQ, by with numerous contributions by Bob Neidorff others.

12.16 What are all of these abbreviations people use for speakers?

Most of these parameters are well documented in the Loudspeaker
Design Cookbook. (see 12.9) In summary:

Fs Driver free air resonance, in Hz. This is the point at
which driver impedance is maximum.
Fc System resonance (usually for sealed box systems), in Hz
Fb Enclosure resonance (usually for reflex systems), in Hz
F3 -3 dB cutoff frequency, in Hz

Vas "Equivalent volume of compliance", this is a volume of
air whose compliance is the same as a driver's
acoustical compliance Cms (q.v.), in cubic meters

D Effective diameter of driver, in meters
Sd Effective piston radiating area of driver in square meters
Xmax Maximum peak linear excursion of driver, in meters
Vd Maximum linear volume of displacement of the driver
(product of Sd times Xmax), in cubic meters.

Re Driver DC resistance (voice coil, mainly), in ohms
Rg Amplifier source resistance (includes leads, crossover,
etc.), in ohms

Qms The driver's Q at resonance (Fs), due to mechanical
losses; dimensionless
Qes The driver's Q at resonance (Fs), due to electrical
losses; dimensionless
Qts The driver's Q at resonance (Fs), due to all losses;
dimensionless
Qmc The system's Q at resonance (Fc), due to mechanical
losses; dimensionless
Qec The system's Q at resonance (Fc), due to electrical
losses; dimensionless
Qtc The system's Q at resonance (Fc), due to all losses;
dimensionless

n0 The reference efficiency of the system (eta sub 0)
dimensionless, usually expressed as %

Cms The driver's mechanical compliance (reciprocal of
stiffness), in m/N
Mms The driver's effective mechanical mass (including air
load), in kg
Rms The driver's mechanical losses, in kg/s

Cas Acoustical equivalent of Cms
Mas Acoustical equivalent of Mms
Ras Acoustical equivalent of Rms

Cmes The electrical capacitive equivalent of Mms, in farads
Lces The electrical inductive equivalent of Cms, in henries
Res The electrical resistave equivalent of Rms, in ohms

B Magnetic flux density in gap, in Tesla
l length of wire immersed in magnetic field, in meters
Bl Electro-magnetic force factor, can be expressed in
Tesla-meters or, preferably, in meters/Newton

Pa Acoustical power
Pe Electrical power

c propogation velocity of sound at STP, approx. 342 m/s
p (rho) density of air at STP 1.18 kg/m^3

 

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