This group of parameters outlined by A.N. Thiele, and later by R.H.
Small, describe the electrical and mechanical characteristics of
mid and low frequency loudspeakers operating in their pistonic region. These
parameters are crucial for designing quality enclosures for sound quality
or loudness.
| B |
Magnetic flux density in gap, in Tesla-meters (TM) |
| BL |
The magnetic strength of the motor structure. |
| c |
Propagation velocity of sound at STP, approx. 342 m/s |
| Cas |
Acoustical equivalent of Cms |
| Cmes |
The electrical capacitive equivalent of Mms, in farads |
| Cms |
The driver's mechanical compliance (reciprocal of stiffness), in m/N |
| D |
Effective diameter of driver, in meters |
| F3 |
-3 dB cutoff frequency, in Hz |
| Fb |
Enclosure resonance (usually for bass reflex systems), in Hz |
| Fc |
System resonance (usually for sealed box systems), in Hz |
| Fs |
Driver free air resonance, in Hz. This is the point at which driver impedance is maximum. |
| L |
length of wire immersed in magnetic field, in meters |
| Lces |
The electrical inductive equivalent of Cms, in henries |
| L |
Length of wire immersed in magnetic field, in meters |
| Ms |
The total moving mass of the loudspeaker cone. |
| Mmd |
Diaphram mass, in grams |
| Mms |
The driver's effective mechanical mass (including air load), in kg |
| n0 |
The reference efficiency of the system (eta sub 0) dimensionless, usually expressed as % |
| p |
(rho) Density of air at STP 1.18 kg/m^3 |
| Pa |
Acoustical power |
| Pe |
Electrical power |
| Q |
The relative damping of a loudspeaker |
| Q - High |
Any rating over .55, usually better for high powered applications |
| Q - Low |
Any rating below .55, usually better without an enclosure in low powered applications |
| Qa |
The system's Q at Fb, due to absorption losses; dimensionless |
| Qec |
The system's Q at resonance (Fc), due to electrical losses; dimensionless |
| Qes |
The driver's Q at resonance (Fs), due to electrical losses; dimensionless |
| Ql |
The system's Q at Fb, due to leakage losses; dimensionless |
| Qmc |
The system's Q at resonance (Fc), due to mechanical losses; dimensionless |
| Qms |
The driver's Q at resonance (Fs), due to mechanical losses; dimensionless |
| Qp |
The system's Q at Fb, due to port losses (turbulence, viscousity, etc.); dimensionless |
| Qtc |
The system's Q at resonance (Fc), due to all losses; dimensionless |
| Qts |
The driver's Q at resonance (Fs), due to all losses; dimensionless |
| R |
Ripple, in dB |
| Ras |
Acoustical equivalent of Rms |
| Res |
The electrical resistive equivalent of Rms, in ohms |
| Revc |
DC voice coil resistance, in ohms |
| Rg |
Amplifier source resistance (includes leads, crossover, etc.), in ohms |
| Rms |
The driver's mechanical losses, in kg/s |
| Sd |
Effective piston radiating area of driver, in square meters |
| SPLo |
Sound Pressure Level, usually measured at 1 watt, at 1 meter in front of the loudspeaker |
| 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 |
| Vd |
Maximum linear volume of displacement of the driver (product of Sd times Xmax), in cubic meters. |
| Xmax |
Maximum peak linear excursion of driver, in meters |
