Tannoy HPD-385A

The following data has been obtained by dismantling and inspecting the HPD-385A low frequency cone:

Tannoy HPD 385
Voice Coil Measured Parameters
August 2000
Depth 13 mm
Layers 4
Turns 128 approx
Inside Dia 53 mm
Outside Dia 54 mm
Wire Gauge 0.313 mm
12.30 thousandths of an inch
based on counting turns per mm
includes insulating enamel thickness
29 gauge
11.26 thousandths of an inch
rounded to nearest standard wire gauge
with allowance for enamel thickness
Wire length 21.51 m
70.58 feet
Resistance/foot 81.3 Ohms/1000 feet for #29 gauge wire
Resistance 5.5 Ohms
measured
Resistance 5.74 Ohms
calculated from wire resistance per 1000/feet
Magnet Plate Depth 9 mm
Turns in Magnetic field 69.23 percent
Wire length in field 14.89 m
B*L driving factor 19 Tesla-meters = Netwons per Amp
Published by Tannoy
Magnetic Gap Flux 1.28 Tesla
(average) calculated using estimated wire length in field