This was my last ribbon speaker system. It replaced the four piece system which is shown elsewhere. The four piece system had very low SAF (Spouse Approval Factor), These new ribbons seemed to fit the bill. It uses Tony Moore's Ambience Ribbon Speakers actively crossed over @ 280Hz to a Scan-Speak 21W/8555-01 woofer section. These 8" woofers have very low distortion and are the most powerful 8" woofers I know of which was required after living with the previous system. The woofers are in a 30 litre box tuned to 26Hz, this gave me very powerful and clean bass, a good match for the transparency of the ribbons. The woofers boxes are braced 18mm MDF and used constrained layer damping to make them dead. The 63mm heavily radiused port fires to the back.

The preamp in my system is one I designed, and is fully discrete. It provides balanced outputs with a drive impedance of 47 Ohms. This drives a balanced line under the house to the amplifier rack which is directly under the piano stool in the photo. The active crossover in the amp rack, which I also built, has a 600 Ohm balanced input. This feeds two amplifiers which provide around 1 KW/channel to the ribbons and 250W/channel to the woofers.(All power figures are continuous RMS) The only reason I used the big amp for the ribbons is that I think it sounds better. It takes a heap to clip the amplifiers, so I don't see any sense in swapping them. The amp rack also houses the power supply for the pre-amp (+/- 35 V) , slow start for the power amps and speaker muting for 10 seconds after power up. I designed the big amp, and the small J one is from a kit available here in Australia.

System Frequency Response

Here is the in room frequency response for the right hand side of the system. The left is essentially the same. The bumps in the lower end of the curve are room interactions. Also between 6 and 7KHz the cavity resonance can be seen. This peak is smaller than the cavity resonances visible on some ribbon drivers because of the improved magnet geometry.

Specs for the 21W/8555-01

Sensitivity 1W/1m 87.5 dB Lin. & Max. excursion ±6.5 & ±12mm
Free Air Resonance 19 Hz Air gap flux density 1.16 T
DC resistance 5.5 Ohms BL 9.3
V.C. inductance 0.6 mH Moving mass incl. air 37.5 g
Power handling 100 W Net weight 2.2 Kg
Effective cone area 232 cm^2 Vas 145 ltr
V.C. diameter 42 mm Qms 4.97
V.C. height 19 mm Qes 0.28
Air gap height 6 mm Qts 0.27

This 8" features a very stiff paper cone, heavily impregnated to reduce resonances normally associated with stiff cones. The magnet system is the new SD-1 system which eliminates modulation and dynamic distortion, as well as clipping distortion created as it exceeds its maximum linear excursion. The low loss rubber surround is designed for better dynamic capability, detailing and less compression. The 21W/8555-01 will perform well either sealed or vented.

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