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Old 07-14-2002, 07:14 PM   #1
Lee

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What are "Thiele/Small parameters?"

Quote:
4.1 What are "Thiele/Small parameters?" [CD, RDP]
These are a group of parameters outlined by A. N. Thiele, and later R. H. Small, which can completely describe the electrical and mechanical characteristics of a mid and low frequency driver operating in its pistonic region. These parameters are crucial for designing a quality subwoofer enclosure, be it for reference quality reproduction or for booming.

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[/b]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[/b]s Q at resonance (Fs), due to mechanical losses; dimensionless
Qes - The driver[/b]s Q at resonance (Fs), due to electrical losses; dimensionless
Qts - The driver[/b]s Q at resonance (Fs), due to all losses; dimensionless
Qmc - The system[/b]s Q at resonance (Fc), due to mechanical losses; dimensionless
Qec - The system[/b]s Q at resonance (Fc), due to electrical losses; dimensionless
Qtc - The system[/b]s Q at resonance (Fc), due to all losses; dimensionless
Ql - The system[/b]s Q at Fb, due to leakage losses; dimensionless
Qa - The system[/b]s Q at Fb, due to absorption losses; dimensionless
Qp - The system[/b]s Q at Fb, due to port losses (turbulence, viscosity, etc.); dimensionless
n0 - The reference efficiency of the system (eta sub 0) dimensionless, usually expressed as a percentage
Cms - The driver[/b]s mechanical compliance (reciprocal of stiffness), in m/N
Mms - The driver[/b]s effective mechanical mass (including air load), in kg
Rms - The driver[/b]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 resistive 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 - Propagation velocity of sound at STP, approx. 342 m/s
p - Density of air at STP 1.18 kg/m^3 (rho)
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