Speaker relative efficiency/sensitivity when using a high pass filter


Is there a formula/algorithm/rule of thumb for calculating how a speaker's power requirements might change when the lower frequencies are handled by a subwoofer?  Specifically for a ported speaker with a supposed frequency response down to 35Hz and an a 89dB sensitivity with a second order crossover at 80Hz. I know it goes down but by how much? I recognize that power requirements increase as frequency decreases but is the difference enough to allow for a less powerful amp? I would think so.

 

tcutter

Showing 4 responses by erik_squires

100 Watts is not enough, but it is enough.. ... but you can't tell by wattage... Funny.

I love how @phusis refutes my claim, and then in a couple of paragraphs refutes himself.  Hahahaha, have at it guys, I've said my peace.

So it appears there is a decrement in the current/voltage required to drive a speaker to only 80Hz instead of 35 or so.

For music, this is correct. :) I would imagine if you started thinking 100W was OK you could do a 35 W amp after high passing it. Truthfully, 100W is overkill for most speakers and your average or modest listening room. I however am not on the Class A camp. I’m not especially drawn to those amplifiers, and the reduced wasted electricity and higher output of AB amps is a much better situation for me.

OTOH, if we are talking a sweet tube set up, say a 60 W Conrad Johnson or something, that's something worth thinking about for me. :)

The sensitivity does not change. That is, the volume of output at 1 kHz relative to 2.83 V input remains the same.

However, since most of the voltage swing required in music is in the bass, cutting it out reduces the amplifier output for the same volume maybe by a factor of 2 in voltage, and 4 in power.