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Heat/Efficency of Speakers

What % of power sent to the speakers is turned to waste heat? That's the short version of my question.

I'm looking to minimize waste heat accross my stereo as my listening room is unforgiving come summer; no cooling and a computer system which cannot be relocated. I understand amplifier efficency & the classes as well as speaker efficency measured as W/db however the interplay eludes me.

Taking two hypothetical amplifiers: a Class A amplifier outputting 10W w/ 100W from the wall & a Class D outputting 200 w/ 220W draw I understand the D will be the cooler operator however this is where the discussion tends to end, D only wasting 20W vs the A amplifier's 90W. Considering appropriate speaker matches to each amp(as well as a standard HE speaker at say 95db/w), how do I determine the wattage converted sound and the watts spent as heat?

I'm asking because 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.
redfuneral
brownsfan
1,508 posts
 
Uh, maybe I am missing something here.  According to the law of conservation of mass and energy, any energy taken from the outlet will be conserved.  That energy must either remain as energy or be converted to mass, which is extremely unlikely.  What form does the energy take?  It could be retained as potential energy (also unlikely, unless you are charging a battery) or remain as some form of kinetic energy.  When a source of audible energy stops, the sound quickly stops.  Where does it go? It does not cease to exist, but it continues in a form of energy which is not audible, i.e., heat. The OP can simplify his problem by simply selecting active components that draw the least amount of current, since all of the current that is drawn is quickly converted to heat.   Have I got something wrong here?  Its been about 44 years since my last physics class.   
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almarg
9,670 posts
 
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

mr_hosehead
207 posts
 
redfuneral - Current reply excepted, you've heard from some very involved and competent folks so far and they really do know their stuff.  I also know this might not be what you'd requested, but this situation sure sounds like it could be better (and maybe  more inexpensively) addressed by acquiring an appropriate fan or even a quiet air conditioner...
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bcgator
355 posts
 
redfuneral, I don't know where you are, but I understand your dilemma...somewhat.  I'm in Phoenix, and for some reason the room I chose in the house for my office doesn't seem to get as much AC airflow as some of the other rooms.  From June through September, my office can be uncomfortably warm.  I bought a Peachtree integrated, based on Class D amplification, specifically for summer use so that I could enjoy music without adding to my heat problem.  I'm very happy with it and now use it year-round (I also have an Audio Research tube integrated but don't use it).   I'm no engineer so I can't give you the technicals, all I can do is echo what others have said - it runs cool, sounds great, and takes up very little space.   Your friend steered you in the right direction with the Class D recommendation.
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shadorne
7,467 posts
 
@cleeds  

You might want to check your reading comprehension while I am checking my math!

 If 99% of energy is lost as heat as I stated then this makes a speaker very inefficient - a mere 1% being converted to acoustic energy - exactly what you concluded!
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