TV sound system
The Ferguson Hill FH009 System is a unique TV sound system both visually and sonically. It is an analogue system from input to output with class AB bass amplifiers and transconductance horn amplifiers. As such, it required a very special equalization filter to be developed. The filter had to be completely in the analogue domain whilst not disturbing the linearity of the phase response of the horns.
Audio3 Ltd. measured the system frequency response in an anachoic chamber and designed a unique active RC filter specifically for the system. The filter flattened the frequency response to within +/- 3dB while preserving the phase and transient response. The trade off was that the filter was hard to control due to overlapping poles. A special mute circuitry was developed to bypass this a-stability at switch on. The result is a wonderfully clear sound -- achieved through a creative and unusual engineering approach.
A point of interest is that due to their size, the horn drivers on the FH009 present an acoustic impedance similar to the human vocal aparatus. This system reproduces human voices more naturally than you may have heard before. It is an ideal TV system for this reason, and I urge you to have a listen to hear for yourself!