Theile Small Parameters for PM4 with 8 ohm Aluminium Voice Coil
DC Resistance of Voice Coil Re 7.4 ohms
Free Air Resonance Fo 70.111 Hz
Emission Piston Area Sd 0.021M²
Equivalent Volume Suspension Vas 36.880 Ltrs
Suspension Compliance Cms 588.938 u M/N
Mass of Cone Mmd 7.0 g
Mass of Moving Parts Mms 8.75 g
Force Factor Bl 10.5 T-M
Mechanical Q Factor Qms 1.851
Electrical Q Factor Qes 0.259
Total Q Factor Qts 0.227
Voice Coil Inductance @ 1 kHz Le 42.401 uH
Reference Efficiency No 4.751%
Sound Pressure Level SPL 98.786 Db
EXPLODED VIEW OF PM4A DRIVE UNIT
The above drawing illustrates the construction of a Lowther drive unit. The unit shown above is a PM4A, and is typical in it's complexity.
1 & 2 Full Stabilizer (2) with Fixing (1). For use with forward radiating horns.
3 Forward Suspension of polyester foam specially treated for tropical climatic conditions of high humidity.
4 Coil Former with balanced Voice Coil.
5 Treated Whizzer Cone.
6 Treated Base Cone.
7 Rear Suspension of polyester foam specially treated for tropical climatic conditions of high humidity.
8 Cast aluminium support Chassis, with tapered flange at rear to create perfectly air tight seal to baffle.
9 Magnet Top Plate of high permeability magnamax.
10 Top Plate Insert of super alloy capable of maximum permeability of 2.4 tesla.
11 Cast Magnet of Alcomax 5 alloy.
12 Pole Piece of super alloy to match Top Plate Insert.
13 Magnamax Centre Pole.
14 Magnet Fixing Rods.
15 Base Plate of lead free low carbon rolled steel.
16 Cast aluminium Support Housing.