Coral Beta 8 (x2)

The Coral Beta 8 is a 20 cm (8-inch) double cone full-range speaker unit from the Beta series, manufactured in Japan from approximately 1970 to 1985. It features a diaphragm made of pulp mixed with chemical fibers to minimize uneven thickness and density, resulting in a white-colored cone to avoid sonic coloration. A specially treated high-density pulp subcone enhances high-frequency performance. The voice coil uses copper-coated aluminum wire for improved efficiency, and the speaker incorporates Coral’s unique skybar edge and star-shaped diffuser to expand directivity.

Two versions exist: the 1970s model rated at 16W with a smaller magnet, and the 1980s model rated at 35W with a slightly larger magnet (4 mm diameter increase). Sensitivity is approximately 94 dB/W/m, despite some datasheet ambiguities. The speaker is noted for its bright, detailed sound, particularly in high frequencies, which may require equalization in bass reflex enclosures (e.g., using a network with R1 = 10 Ω, C1 = 1.0 µF, L1 = 0.22 mH). It is well-suited for back-loaded horn applications and pairs effectively with single-ended or push-pull tube amplifiers.

Technical specifications include:

• Impedance: 8 Ω
• Resonance frequency (Fs): ~51.4–53.5 Hz
• Qts: ~0.40–0.43
• Vas: ~75.2–79.9 liters
• Moving mass (Mms): ~7.17–8.29 g
• Sensitivity: ~94 dB/W/m
• Original price: ~17,500 Yen (~250 DM)

The Beta 8 is praised for its open, refined midrange and lively treble, though some find its high-frequency response peaky or overly bright, and its midrange may not suit all preferences compared to modern drivers. Its lightweight cone and short cone motion contribute to its full-range capabilities. Due to its rarity, finding new old stock (NOS) pairs is challenging and often expensive.