Pioneer S-955III

Big bass-reflex loudspeaker with Beryllium drivers - yes, not only Yamaha used that.

The S-955III is an updated 1979 S-955.
The differences are limited and mostly non-visible : a PT-R7III ribbon tweeter instead of the PT-R7A, plus input power handling and filter wiring & componentry.
Also changed was the front bass-reflex port which was reduced to a quarter of the one carved in the S-955 !


The tweeter of the S-955III is a PT-R7III beryllium ribbon, as described elsewhere on TVK : 9mg weight and 120Khz frequency response - twenty years older but already ready for SACD !

The previous PT-R7A also went up to 120Khz, but couldn't handle as much power and was a slightly less sensitive. It seems however it was better at horizontal dispersion, but less so that the original 1974 PT-R7 - there's always a give and take somewhere.

The bass is a 36cm cone held by a diecast aluminium frame which probably had some design equivalences in the TAD lineup, even if distantly.

The mid driver is the most... original :
it is a Beryllium dome where the diaphragm is suspended by five wires which allow for an even more linear piston motion and avoid having too much sound radiate from the edges of the diaphragm, where dispersion isn't linear and distortion higher.

The wires are made of an elastomer and allow the driver to rotate around when sound is to be produced : the diaphragm's movement is therefore something like a (very slightly) circular piston.

The inside of the mid driver is damped with felt pieces and its dedicated enclosure is further damped with glass wool. The front center cap is copper-plated and topped by a 5-arm phase plug ; resonance frequency lies at 300Hz - 650Hz lower than the crossover frequency used.

Although the mid driver itself is the same between the three versions (CS-955, S-955 and S--955III), the protection grille is much tighter, finer, on the S-955III.

The 47kg enclosure is a thick and heavily braced box made of plywood - the best wood for audio uses.
The filter allows tri-amping or normal all-together-now powering.


The chronolgy of the Pioneer loudspeakers using the suspended trick is as follows :
CS-3000 (december '72)
CS-3000A (september '73)
CS-955 (june '77)
S-955 ('79)
S-933 ('79)
S-955III ('82)
S-9500 & 9500DV ('85)

Whatever the name, CS-955, S-955 or S-955III (btw, what happened to the S-955II ?) I really wish I could import one from Japan - I have a hunch I'd really love music from this biggie.