Sony APM-4 (1982–1987)

A high-end 3-way bass reflex loudspeaker in Sony's ESPRIT series, produced from 1982 to 1987.

Overview

The Sony APM-4 is a floor-standing loudspeaker from Sony's premium ESPRIT component line. It was the penultimate product in the series, and it followed research on APM-8 post-prototypes around 1981-1982. The enclosure is thick, bent and carved wood. The front and back panels are solid, and they join to rounded, multi-braced top and bottom sections. The drivers match those of the APM-77, including interchangeable bass and tweeter units. The difference is the plates: the APM-4 has matte gray-ish aluminum driver plates, where the APM-77 has bright anodization. Production was limited, with an estimated 600 pairs made for the Japanese market and around 200 for all export markets combined.

Specifications

System	3-way bassreflex
Volume	70 L
Frequency response	31 Hz – 30 kHz (+4 / -8 dB) (thevintageknob.org); generally around 40 Hz to 20 kHz (hifi.fan for APM-4 E)
Active surfaces	530 cm² (bass), 27 cm² (mids), 7 cm² (highs)
Crossover frequencies	600 Hz, 4.5 kHz
SPL	90 dB / W / m
Measured SPL	94 dB / 1m at 500 Hz and 5.5 V input
Nominal impedance	6 Ohm (thevintageknob.org); 10W(NOM) (tapeheads.net for "Sony APM 4-907-715-02")
Max. peak power	200 W
Average sustainable power	100 W
Tweeter level adjustment	0 / -1.5 / -3 dB
Dimensions	54.5 x 89.5 x 34.5 cm (thevintageknob.org); 17'' w x 27'' h x 14'' d (Facebook post)
Weight	45 kg (thevintageknob.org); 47 lbs (Facebook post)
Original price	270,000 ¥ (1984)

Design

The enclosure is solid carved wood, not MDF, with a fully rounded and braced structure. The crossover is built like those in the APM-6 and APM-8. It uses polypropylene capacitors potted in SBMC, plus OFC wiring, and it sits at the bottom rear of the cabinet. The drivers use Sony's Accurate Pistonic Motion technology. The bass and low-mid drivers have four coil/magnet/diaphragm pistons instead of a single assembly, and they drive a honeycomb diaphragm. The drivers are shared with the APM-77, though the midrange unit has a different surround.

Context

The APM-4 came near the end of the ESPRIT series, with the TA-N902 as the final component. Sony's flat-driver speakers were less common than those from competitors like Pioneer and Technics. The APM-4 was a limited-production flagship that combined advanced materials with its crossover design.

Market

A 2016 listing showed an asking price of USD $5,500. Owners have reported the speakers as exceptionally linear and powerful, with very low distortion when restored. Some users are still looking for technical documentation such as the manual, crossover schematic, or cabinet drawings.