Why Frequency Response of 10Hz - 79kHz

I’ve been corrected. The word is infrasonic not subsonic but you get the idea. My old Classe’ Audio amplifier employed this strategy. I thought part of it was to prevent turntable rumble from being transmitted to the speakers.

If the speakers are the weak link in the distortion chain, does it make sense to NOT ask them to respond to signals outside their capability? Otherwise, seems like the result would only be more distortion.

A pipe organ and classical piano can reach down to 16.4Hz, with custom organ pipes designed to reach 8Hz! Only turntables are designed to mitigate infrasonic rumbles, and many TT preamps include a rumble filter for that purpose.

The amp is supposed to be a straight-wire-with-gain, ranging from DC to infinity, so limiting its frequency range does not fulfill that purpose. Let the loudspeakers be the limiting factor, as they always are, both on the low and high ends of the frequency spectrum.

mikewxyz wrote:
I’ve been corrected. The word is infrasonic not subsonic but you get the idea. My old Classe’ Audio amplifier employed this strategy. I thought part of it was to prevent turntable rumble from being transmitted to the speakers.

If the speakers are the weak link in the distortion chain, does it make sense to NOT ask them to respond to signals outside their capability? Otherwise, seems like the result would only be more distortion.

Hi @mikewxyz

Further to @SmartOne_2000 comments, another reason for the extended response is to ensure that the amplifier behaves in a linear fashion in the frequency band of interest (obstensively 20Hz to 20kHz).

As you approach the frequency range limits, or if you deliberately filter the signal to limit the response range, you can encounter undesirable effects such as phase shift. So it's good practice to have an extended frequency response.

Turntable rumble is a different case. It is essentially a noise signal at such low frequency and high amplitude that it can make woofers hit their end stops (woofer excursion increases with lowering frequency). So it is best filtered out, however in doing so you can also rob the music of its lowest frequency content. Of course this is a non issue with modern digital playback.

My March Audio stereo P452 is a few years old, has been and still is performing wonderfully, but has developed a slight click in one channel only when the preamp is muted (which shorts the inputs), as if there was DC in the circuit. By reversing the input XLRs & the click staying on the same side I've established that the click is caused by the power amp, not the pre. Its very low level, similar to the sound of a switching relay. Wondering if anyone else has a similar problem & if it should be attended to given that there's no problem with actual performance?