February 16, 2017 2 min read
This classic drive unit was conceived by Vifa in the mid to late 80s specifically for inclusion within high performance sealed baffle designs of moderate size (20-40 litres), with a final rolloff of 12dB / octave thus offering good bass extension and immediacy (fashionably now called PRAT - Pace, Rhythm, Attack, Timing) - without the 4th order / 24 dB octave rolloff and corresponding poorer transient response of ported enclosures.
Selected by legendary speaker designer Peter Comeau for his very fine and multi award winning Heybrook HB1; other designs that made good use of this driver include the JPW P1, JPW AP2, JPW AP3 and the Snell type K - all fine speakers to this day and well worth repair.
The M21WG-09-08 has a critically designed motor system comprising a very high compliance suspension (Vas 81 litres) with a surprisingly modest magnet coupled to a cast magnesium chassis and a treated pulp fibre cone. The highish Qms value gives this drive unit a lovely open midrange which easily integrates with 25mm dome tweeters hence it's popularity in various successful historic designs.
Like so many drive units from this era, the original M21WG-09-08 suffered from ageing / UV degradation of the foam surround hence many HB1's etc. turn up on auction sites with missing bass units or crumbling surrounds.
This new version is manufactured with an improved formula foam surround.
One of the few excellent 8" drivers suitable for 2 or 3 way infinite baffle enclosures.
Direct replacement for the following models:
Heybrook HB1, JPW P1, JPW AP2, JPW AP3, Snell type K.
These units are now manufactured at the Scanspeak facility in Denmark and may be badged as Vifa or Scanspeak.
Click on the image for more details: