Heat/Efficency of Speakers

Redfuneral 12-12-2016
... my former SE Parallel EL84.

OK, then my previous supposition that the amp was biased in class AB was not correct, as a SE parallel amp will operate in class A.  So the 60 to 75 watt estimate I stated for the power consumption of the amp under typical listening conditions was probably somewhat low.

Regards,
-- Al
 

Hi Bill (Brownsfan),

I mostly agree with your points, as far as they go.  But regarding the relevancy of the speakers, I would add a couple of things.

First, for a given listening volume a given class AB or class D amp will draw less current from the wall if higher efficiency speakers are used than if lower efficiency speakers are used, resulting in less heat being introduced into the room.  Second, as Swampwalker noted greater speaker efficiency would allow the use of a less powerful amp, which within a given bias class will tend to correlate (at least loosely) with reduced power consumption.

Also, regarding "All of the energy in the room is conserved.  It does not disappear," some of it will in a sense disappear.  Although it is pretty much just an academic point some of it will disappear **from the room,** assuming the temperature of the room is higher than the temperature of the adjacent spaces (both indoor and outdoor), given that the thermal insulation between the room and those spaces will not be perfect.

Best regards,
-- Al
 

I was previously running a 10W tube amplifier in this room(4xel84 tubes) with 96db speakers. This was bearable in two hour doses this last summer. My friend assures me any Class D amplifier and many AB amps would have no such heating problems and says it’s class not wattage that is my issue. Before I move to a different amplifier technology(and swap speakers, these voiced for SE tube partnering) I want to understand this issue fully. I’m unconcerned with power usage and only care about the heat.

To add some perspective to this, I would suspect that your 4 x EL84 amp was biased in class AB, and under typical usage conditions was probably consuming something roughly in the area of 60 to 75 watts. If so, the amount of heat put into the room would be essentially no different than the amount of heat that would be put into the room by a 60 or 75 watt incandescent light bulb. (Although if the light bulb is located on the ceiling a greater fraction of its heat output would go toward warming the ceiling rather than warming the air in the room). That doesn’t seem to me to be a large amount, and even if you were to reduce it to say 10 watts by choosing some class D amp, and a compatible speaker, I’m not sure it would make a great deal of difference in your comfort level.

Regards,
-- Al

...does the power usage scale with the volume and demands of the speaker?

Yes, absolutely, in the case of class AB, and even more so in the case of class D. For class A, though, the AC power drawn from the wall outlet will be determined by the amplifier and will be essentially the same all the time, with the power that may be supplied to the speakers at any instant subtracting from the power that is dissipated (converted to heat) in the amp. (But as stated above almost all of the power supplied to the speakers will then be converted to heat in the speakers).

Also, keep in mind that most of the time under most circumstances just a small fraction of the amp’s power capability will be utilized. Brief dynamic peaks in the music will typically result in much more power being delivered to the speakers than the time-averaged amount of power that is delivered. Although different recordings can differ greatly in that regard. Recordings that are dynamically compressed to a severe degree (which is particularly common among pop and rock recordings) may have less than a 10:1 peak to average ratio of the amount of power delivered to the speakers, while there are some classical symphonic recordings having minimal or no compression for which that ratio may be more than 1,000:1. In the latter case very little power will be supplied to the speakers, on average, and hence a class AB or class D amp will not generate much more heat than when idling.

Regards,
-- Al