Part 1 of restoration:
Chapter 1 – Introduction of restoration
Chapter 2 – Disassembly and getting ready for cabinet restoration
– high gloss finish of walnut veneer
– re-sprayed black front and top
– re-sprayed brown rear
– set of extra castor wheels
– clean Super Tweeter
– new crossovers with all new parts attached in cabinet
– new internal wiring
– new high quality banana binding posts
– extra damping material
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.
40cm housed in aluminium diecast basket, wooden pulp & carbon fibers cone, long throw voice coil.
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”.
an acoustically compatible epoxy resin bonds the coil and cone to help increase rigidity ; aluminium diecast frame.
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”.
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 is one of the milestones in dynamic loudspeakers, the kind one always comes back to – like a Technics SB-7000.
The HPM-150 (and the HPM series at large) is however part of those which made far more mousse outside Japan -like an RT-707 or SX-1250- and remaining available in the US or Germany beyond 1980.