Pioneer HPM-100 - Features

Features

HPM stands for “High Polymer Molecular”, in reference to its then newly-developed high polymer molecular film supertweeter, a design that is used to convert electrical energy into sound to a degree that had previously only been theory. It is damped by elastic materials to prevent the deterioration of its best characteristics, and eliminates excessive harmonic distortion. It is housed in a plastic case, with the film (and grille) shaped semi-cylindrically in order to project the sound all 180 degrees around the front of the speaker. The HPM super-tweeter design has no dome, magnet, voice coils, or any moving parts at all. The frequency response of this driver ranges up to 25 kHz.

At the time, most speaker drivers were manufactured using paper cones and foam surrounds. Another revolutionary feature that the HPM-100 speakers had was carbon-fiber blended tweeters, mid-ranges, and woofers; all with greased cloth surrounds. Carbon fiber, a technology which has an unparalleled strength to weight ratio exceeding titanium and is used in the construction of military aircraft, is lighter, more rigid, and does not rot away over time like paper and foam do. The weight of the carbon fiber, combined with cloth surrounds, allows the drivers to move and vibrate more easily, replicating sound much clearer. Compared to the usual cheap, stamped steel baskets most speakers incorporated at the time, the three drivers also have solid aluminum die cast frames, intended to eliminate resonance and unwanted rattling and noise. These features have contributed to the endurance, reliability, and longevity of the drivers.

The size of the mid-range driver is 4 inches in diameter as to match the directional characteristics of the entire speaker. Though it is small in diameter, it features a larger magnet with a lightweight cone and edgewise voice coil.

The voice coil, voice coil assembly, and cone in the tweeter are bonded with an acoustically compatible epoxy resin to help increase the rigidity of the entire vibrating configuration, meant to improve transient characteristics and aid in clean, low-distortion performance. The tweeter has a diameter of 1-3/4 inches.

The carbon fiber cone of the woofer is coated with a special resonance-damping compound to widen the frequency range and smooth out response. The woofer has a 12 inch diameter and a 6-1/8 inch magnet with a pure copper ring, to minimize third harmonics in the mid-range. These features are intended to eliminate noticeable distortion.

The crossover was designed so that frequencies at the driver crossover level overlap in order to prevent the separation of musical tones. It has crossover slopes of 6dB/oct. to avoid complicated crossover network design which could deteriorate phase characteristics. The crossovers have two potentiometers at the top front-right of the speakers, allowing the user to control the volume of both the tweeter and the mid-range drivers.

The enclosure is made of extremely dense particle board, using ported 1-1/4 inch baffle board and 1-3/16 inch chipboard sides, back, and top/bottom. The enclosure also has fiberglass insulation stapled to the interior, allowing minimal sound pressure to be absorbed by the cabinet itself. The outside of the cabinet is finished with a thick, fine grain, furniture-grade walnut veneer and has a removable black fabric grille. The HPM-100 weighs 58 pounds, 14 ounces. This was intentional, as the weight of the cabinet contributes to a richer sound. Although it is considered to be a bookshelf speaker, it is clear that it must be a floor-standing speaker because of its immense size and weight.