Pioneer HPM-150
(1975 - 1980)

Pre- Star-Wars-ish looks for a surpising loudspeaker topped with an HPM (High-Polymer-Mylar film) super-tweeter for a 270° dispersion of the frequencies above 8,5kHz.

The HPM-150 was designed by Bart Locanthi, formerly of JBL. A suprising move from a brand which made its reputation on loudspeakers but it proved a wise one. For from the HPM series evolved a new Pioneer division, still active and successful today : TAD (Technical Audio Devices), a specifically pro-oriented sub-brand chosen by most serious studios for monitoring needs.

Bass driver
40cm housed in aluminium diecast basket, wooden pulp & carbon fibers cone, long throw voice coil.
Mid driver
Rather small in size not to "upset the precisely calculated directionality characteristics", powered by a large magnet, edgewise voicecoil winding, "newly developed" light & rigid cone material, diecast aluminium frame and a "special design to assure substantially improved acoustic power handling, sufficient sound pressure and wide dynamic margin".
High driver
an acoustically compatible epoxy resin bonds the coil and cone to help increase rigidity ; aluminium diecast frame.
Super-high driver
Horn-loaded High-Polymer omnidirectional super-tweeter ; 3" cylindrical diaphragm loaded on a "five vertical-sectoral horns so that efficiency is improved by as much as 6dB in horizontal plane without loss of vertical directivity".
Enclosure
3cm chipboard baffle (top, front, bottom), 2cm chipboard sides and top for "optimum acoustical properties". Computer-assisted resonance analysis and "hard-headed practical experience" for the design of the bass-reflex port. The top of the HPM-150 is made of four wooden poles which support an unbreakable smoked glass and acoustically transparent cloth.

Despite its somewhat "dated" looks, the HPM-150 still is part of the crème de la crème in dynamic loudspeakers.