Onkyo U-2500 (1971–1973)

The Onkyo U-2500 is a compact 2-way bookshelf speaker from the early 1970s, produced from roughly 1971 to 1973 and priced at ¥14,300 per unit. It's a bass reflex design. The port is the one distinctive part: a special bass reflex duct shared with the larger U-3500 in Onkyo's lineup. Beyond that, the historical record is thin. No period reviews, no deeper engineering commentary and no documented market positioning have surfaced. What we know comes from the spec sheet and from the speaker's appearance in Onkyo's 1971 Japanese speaker brochure.

Electrically, the U-2500 is straightforward. It pairs a 20 cm free-edge cone woofer with an 8 cm free-edge cone tweeter, rated at 8 Ω with 15W allowable input and 30W maximum. Frequency response is listed at 45 Hz to 20,000 Hz, with output sound pressure of 99 dB/W (measured at 50 cm). The cabinet measures 290 × 486 × 322 mm (W×H×D) and weighs 8 kg.

One surviving Yahoo! Japan auction from 2026 gives a small look at the collector market. A pair sold for ¥2,100, starting at ¥2,000, described as having scratches and dirt, shipped from Saitama Prefecture, with no returns. The seller noted that a Hard-Off used-goods store had confirmed the pair operates normally, but that detailed sound quality couldn't be verified. It's one data point, and a modest one.