Yamaha NS-451 (circa 1977–1978)
The Yamaha NS-451 is a 2-way, bass reflex bookshelf speaker from the late 1970s, when Yamaha was putting considerable engineering effort into even its mid-range models. The record on this model is thin, and production years are disputed (sources suggest 1973, 1977, or "around 1978"). The technical documentation that survives is unusually detailed for a speaker of this class. It was sold as a single unit for ¥26,500 in Japan.
The woofer is a 20 cm cone type. The diaphragm is made from foreign coniferous wood pulp, processed with traditional Japanese papermaking techniques. Yamaha claimed this sheet manufacturing method produced fewer density and thickness inconsistencies than molded cones. The voice coil is copper ribbon, edgewise-wound on a Nomex #410 bobbin (Du Pont's heat-resistant material, rated for continuous use at 220°C). The magnetic circuit uses an internal Alnico magnet. The high-frequency unit is the more unusual design: a 5 cm compound tweeter combining a cone base with a 2.3 cm dome. The idea is that each reinforces the other. The cone handles the middle and upper range, and the dome improves high-frequency dispersion. Its diaphragm weighs just 0.13 grams.
Rated input is 25W (JIS continuous) with a maximum of 50W, though Yamaha claimed the design could handle instantaneous peaks of 200-250W. Frequency response is specified at 50 Hz to 20 kHz, sensitivity at 92 dB/W/m, impedance at 8 Ω, and the crossover sits at 2 kHz with a 12 dB/octave slope. A continuously variable high-frequency level control is fitted. The enclosure is bass reflex, built from high-density particleboard with a Century Walnut finish. Each speaker measures 320 × 540 × 284 mm and weighs 10.3 kg.
Surviving owner commentary is sparse but positive. One Canadian owner recalls paying $149 each when new, and a later forum post describes them as "vintage beast[s]" that "still sound so clear that would satisfy audiophile hears." A Gearspace thread asks how they compare to the studio-standard NS-10s, which is a fair question given the shared era and Yamaha's house sound, but no substantive answer is recorded there. One Kijiji listing mentions a "pretty rare" Canadian-made variant called the NS-451 RM "Rock Monitor" with replacement CTS tweeters. A YouTube video links the NS-451's woofer to the JA2059 driver unit. A Reddit thread title ("Yamaha NS451 speaker sounding muffled") exists, but no details survive.
One crossover restoration parts supplier calls the NS-451's network "an exceptional component," and a used pair appeared on Yahoo Auctions with a ¥3,300 bid. That is about the extent of the documented aftermarket.
Known Specifications
- Type: 2-way, 2-speaker, bass reflex, bookshelf
- Woofer: 20 cm cone (wood-pulp sheet diaphragm, Alnico magnet)
- Tweeter: 5 cm compound type (cone + 2.3 cm dome)
- Frequency response: 50 Hz – 20 kHz
- Output sound pressure level: 92 dB/W/m
- Impedance: 8 Ω
- Rated input: 25W (JIS); max 50W
- Crossover: 2 kHz, 12 dB/oct.
- Dimensions: 320 × 540 × 284 mm
- Weight: 10.3 kg
- Original price: ¥26,500 (per unit, circa 1978)
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