Features a 400mm long-throw carbon fiber woofer, 100mm edge-wound voice coil midrange, 45mm lightweight diaphragm tweeter (all three mounted in die-cast aluminum frames to prevent basket resonance) and an omni-directional polymer horn super tweeter with 270 degrees of horizontal dispersion.

The HPM-150 can drive amplifiers up to 300 watts per channel. Pioneer US when it published its July 1977 dedicated catalog nor the various European pioneers were made aware of this as they both refer to HPM as High Polymer Mylar or High Polymer Foil... Convenient blur in the description was replaced in 1980 as High Polymer Molecular in US advertisements, but not in European catalogs or advertisements...

However -

The HPM-150 was designed by Bart Locanthi, formerly of JBL.

A surprising move by a brand that has made a name for itself in speakers, but it has proven to be sensible. As a new Pioneer division has evolved from the HPM series, still active and successful: TAD (Technical Audio Devices), a specifically professional-oriented sub-brand of choice for the most serious monitoring studios.

Midrange driver

Rather small size so as not to "interfere with the precisely calculated directivity characteristic", powered by a large magnet, voice coil winding along the edges, "newly developed" lightweight and rigid diaphragm material, die-cast aluminum frame and "special construction for much better acoustics power handling, sufficient pressure acoustic and a wide margin of dynamics".

High transducer

Acoustic compatible epoxy bonds voice coil and cone for added rigidity; aluminum die-cast frame.

Super-high transducer

High polymer horn loaded omnidirectional super tweeter; 3" cylindrical diaphragm loaded on "five vertical-sector horns, thanks to which performance improves by as much as 6 dB in the horizontal plane without losing vertical directivity".

Housing Divider made of chipboard

3 cm (top, front, bottom), chipboard 2 cm sides and top for "optimal acoustic performance".

computer-aided resonance analysis and "hard hands-on experience" in bass-reflex port design.

The top of the HPM-150 consists of four wooden poles that support unbreakable smoked glass and acoustically transparent fabric.

Despite its slightly "dated" appearance, the HPM-150 is one of the milestones in dynamic loudspeakers that you always come back to.

The speakers have undergone a complete overhaul. Woofers, midrange speakers and supertweeters have been regenerated by a professional company AR SOUND REGENERACJA SPEAKERS.

Specification:

Type: 4-way speaker system with 4 drivers

Frequency response: 25Hz to 25kHz

Power handling: 250W

Crossover frequency: 750, 2600, 8500 Hz

Impedance: 6.3Ω

Sensitivity: 92.5dB

Bass: 1 x 400mm cone

Midrange: 1 x 100mm cone

Tweeter: 1 x 45mm cone

Super Tweeter: 1 x High Performance HPM Polymer

Housing: bass-reflex

Dimensions: 450 x 984.5 x 450 mm

Weight: 37.3 kg

Year: 1978

Vintage Pioneer HPM 150