The Legend of EL PIPE-O — Kent English / 2002

Most woofers just don’t quite do the lowest octave. You read the specs that say “usable response: 20 Hz – 20 KHz” and you know that the 20 Hz part of it is wildly optimistic. Achieving very low frequencies at reasonable power levels is not an easy job; the acoustic impedance experienced by a speaker cone declines as the inverse of the square of the frequency. As a practical matter, woofers and their enclosures need to be very large to properly reproduce the lowest octave. Even when you compensate with frequency equalization and more amplifier power, the performance suffers as… More...

Current Source Crossover Filters — Nelson Pass / 2004

In today’s marketplace, audio power amplifiers are conventionally viewed as voltage sources, delivering a given voltage at the output that is a multiple of an input voltage. To the extent that they are truly voltage sources, having a very low output impedance, they simply deliver whatever current happens to reflect the response of the loudspeaker to the defined output voltage. Recently I have been playing with current source power amplifiers that have high output impedances and deliver a specific current to the load in response to an input voltage. The voltage across the loudspeaker reflects its response to this defined… More...