Onkyo E-413Aoak (c. 1975–1976)
The E-413Aoak is a 3-way, 3-speaker airtight bookshelf system from Onkyo's mid-1970s lineup. It is an improved version of the earlier E-413A. It was priced at ¥49,800 per speaker, which put it in the upper tier of Japanese bookshelf speakers of the era. Sources date it to "around 1975," and one period Russian catalog lists 1976 as the year of release.
The drivers are where this model gets interesting. The low end is a 28 cm cone woofer (W-3022E) with a lightweight flat diaphragm made from selected foreign pulp, a high-compliance suspension, and a four-layer ribbon-wire voice coil. The coil design is meant to cut magnetic loss and raise efficiency and allowable input. The midrange is a 5 cm reverse dome unit (MD-504C) made from ultra-hard duralumin foil just 35 microns thick. It uses a double-support, inner-drive system for transient and directional behavior. A 2.5 cm inverted dome tweeter (TW-308D) with an aluminum voice coil handles the top end. Both mid and high drivers have 5-step level controls.
The enclosure is 20 mm hard particle board with internal bracing and sound-absorbing material. Rated frequency range is 28 Hz to 20 kHz, with crossover points at 700 Hz and 4 kHz. Sensitivity is 92 dB/W/m and impedance is 8 Ω. Maximum input is 60W. Each speaker measures 332 × 596 × 325 mm and weighs 17 kg.
Past the specification sheet, the record is thin. No period reviews, user impressions, or market history have surfaced. What survives is the technical design, mainly the unusual reverse dome midrange and the four-layer voice coil on the woofer.
- Type: 3-way, 3-speaker, airtight bookshelf
- Woofer: 28 cm cone (W-3022E) / Midrange: 5 cm reverse dome (MD-504C) / Tweeter: 2.5 cm reverse dome (TW-308D)
- Frequency range: 28 Hz – 20 kHz
- Crossover: 700 Hz, 4 kHz
- Max input: 60W · Impedance: 8 Ω · Sensitivity: 92 dB/W/m
- Dimensions: 332 × 596 × 325 mm · Weight: 17 kg
- Price: ¥49,800 (per unit, c. 1975)
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