Vifa M21 Wg-09-08 Bass Drive Units (pair) Heybrook Hb1

This auction is for a pair of newly manufactured bass drivers of the type M21-WG-09-08.  These are an 8 ohm driver and are intended for use in sealed box (infinite baffle) speaker cabinets. They were commonly used in Hifi speakers throughout the 1980's and 1990's in designs such as the Heybrook HB1, JPW P1, AP2 and AP3 and the Snell Type K.

However, units produced during that period will, by now, have suffered from rotting foam surrounds and will need to be repaired or replaced.  Several companies offer re-foaming kits for generic 8 inch speaker drivers.  The foams supplied often do not exactly match the foam originally used. Fitting the kits also requires that the speaker assembly is accurately aligned centrally such that the voice coil is perfectly located in the magnet gap. Any deviation will result in increased distortion and possibly buzzing as the voice coil rubs against the edges of the magnet gap. 

In recent years the Vifa brand was acquired by the Tymphany Corporation and production of many of its new drivers was moved to the far east. What was the Vifa factory is now owned & still operated in Denmark by high end driver manufacture ScanSpeak. The factory still makes the original M21 drivers using the original tooling, jigs & staff and the drivers offered in this auction are new production items.

M21 refers to the magnesium cast 21cm chassis.  I am told by Scanspeak that the formulation of the foam surrounds used now will not deteriorate over time in the way that the old ones did.

Technical Data:

Frame diameter:    215mm

Sensitivity (2.83v/1m):   90dB

Nominal impedance:   8 ohm

Frequency range:   25Hz-3kHz

Free air resonance:   25Hz

DC resistance (Re):   5.6 ohm

Voice coil inductance (Le):   0.9mH

Effective piston area (Sd):   231.0cm²

Moving Mass (Md):   16.5g

Force factor (BL):   5.2Tm

Qms:   4.9

Qes:   0.82

Qts:   0.7

Vas:   81L

Voice coil diameter:   25mm

Nominal power handling:   80w

Physical Sizes:

Frame diameter:   215mm

Overall depth (front of frame to rear of magnet):   78mm

Flange thickness:   4.5mm

Fixing holes:   4 x 5mm diameter on 206.5mm PCD

Cutout diameter:   190mm

Vifa M21 Wg-09-08 Bass Drive Units (pair) Heybrook Hb1