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 developed as part of Sony’s premium ESPRIT component line. It was the penultimate product in the ESPRIT series, preceded by research on APM-8 post-prototypes around 1981–1982. The speaker features an advanced enclosure design made entirely of thick, bent, and carved wood, with solid front and back panels joined by multi-braced, rounded top and bottom sections. It shares driver designs with the APM-77, including interchangeable bass and tweeter units, though the APM-4 uses matte grey-ish aluminium driver plates compared to the bright anodization on the APM-77. 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 APM-4 features a uniquely constructed enclosure made of solid carved wood, not MDF, with a fully rounded and braced structure. The crossover is built similarly to those in the APM-6 and APM-8, using polypropylene capacitors potted in SBMC and OFC wiring, and is mounted at the bottom rear of the cabinet. The drivers utilize Sony’s Accurate Pistonic Motion technology, with bass and low-mid drivers employing four coil/magnet/diaphragm pistons instead of a single assembly, driving a honeycomb diaphragm. The drivers are shared with the APM-77, though the midrange unit has a different surround.
Context
The APM-4 was positioned near the end of Sony’s ESPRIT series, with the TA-N902 being the final component. While Sony’s flat-driver speakers were less common than those from competitors like Pioneer and Technics, the APM-4 represented a high point in the company’s speaker engineering, combining advanced materials and crossover design in a limited-production flagship model.
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 seek technical documentation such as the manual, crossover schematic, or cabinet drawings, indicating a niche but dedicated collector interest.
eBay Listings
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