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
Hi Redfuneral,

That’s a complicated one! It’s also to do with the music you play. :) For your 10 Watt tube amp, check the rated input. I’m sure it’s probably closer to 50 watts. I’m not a tube guy, so I could be way off.

I can tell you my ICEPower 250 units idle around 7 watts each, and I estimate around 85% efficiency. So at 100 Watts output, figure 22 watts (7 + 15) of heat will be generated. Even after playing for an hour or more the little cases get at most slightly warm. There are no heat sinks, the wrap around aluminum case is all they have or need.  I use a flea powered 20W/ch lepai digital amplifier at my desk. You should get the biggest one you can, they are severely over-rated, but they run cold compared to the ICEPower monoblocks I use in the living room.

I’ve never heard of anyone noticing the heating effect of speakers themselves except in a professional setting. The worst that would happen in terms of pure heat is often tweeter padding resistors.

Best,


Erik
Speakers typically churn out between 99% and 90% of energy as heat. Horns are the most efficient at 90% of power ending up as heat.
shadorne
Speakers typically churn out between 99% and 90% of energy as heat.
You might want to check your math - most speakers are much less efficient than that. A speaker with 92 dB sensitivity is only about 1 percent efficient.

As for the OP, the heat in his room is overwhelmingly from the amplifier - not the speaker. His hypothetical 95 dB sensitive speaker is about 2 percent efficient.
So I should assume all power(90+%) drawn from the wall will end up as heat. I should be looking to minimize the wattage at the speaker terminals. I should clarify that I’m looking at room temperature exclusively. An amplifier’s ability to cool itself has no impact on its thermal contribution(as I’ve learned from upgrading heatsinks in my conputer)

I’d say I don’t understand how to calculate power draw of amplifiers outside of class A. I was looking at an average power AB amplifier last night with power consumption rated 25-250W. I understand it idles at 25W and when in use is pulling 250W? Or does the power usage scale with the volume and demands of the speaker? How about Class D? Can a 50-100W AB or 250W D amp play music using less power than 5W of Class A? Do they all output the same wattage to the speaker all else being equal?
redfuneral
So I should assume all power(90+%) drawn from the wall will end up as heat. I should be looking to minimize the wattage at the speaker terminals
No, not at all.  You can achieve substantial increase in efficiency by choosing an efficient amplifier. As your friend suggested, you should be looking at your amplifier's class of operation.

Can you explain how that's the case? As I understand it now amplifier efficency only covers wall -> speaker terminal efficency. The wattage output to the speaker will mostly all be turned to heat. Where I stand Class A appears the answer only because there are 2-25W amplifiers all over the market where the alternatives all have higher output.
The heat gain in your room will be affected by the amplifier since nearly 100% of power consumed by the speaker is converted to heat.

If you have two amplifiers, one being a 100 wpc Class A and the other a 100 wpc Class AB, both will pass through the same power to the same speakers. However, the Class A amplifier will consume about 1,000 watts of power at idle and at rated power and that will be converted into heat as long as the power is on. The Class AB amplifier will consume about 175 watts at idle and 400 watts at rated power. The heat transferred to your room will vary from 175 watts to 400 watts. Therefore the room heat gain will be a lot lower with the AB amplifier since the heat gain from the speakers will be the same with both amps (listening SPL and duration being equal).
Air condition your room, or go to class D power amp!

Buy a horn speaker.
...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

To make this a bit simpler, Class A amps will typically generate the most heat because they draw full power all of the time. Class AB amps will generate less heat but the amount will vary depending on whether they are heavily biased into Class A (more heat) or less.  Class D amps generate the least amount of heat.  The situation where speaker efficiency will make a significant difference is if you go with very high efficiency speakers, because you can then use a very low power tube amp. 
















c
Ok, assuming I only require 2W of power at the speaker:
Class A will dissipate heat equal to its power consumption
Class AB/D will consume a tad over their idle power consumption with D being closer yo idle than AB.
Correct?

Maximizing my speaker efficency is my first priority. Also correct?
Red funeral,
As others have pointed out,  the amplifier is by far the greater contributor of heat in the room. Find a class D amplifier that in your opinion sounds good and go in that direction. 
Charles 
Your friend must pull his hair out at your inability to accept a simple, experienced answer. He is right, but you seem determined to prove your thought process, even though it has little operational  applicability.  A simple question resolves the problem, "Does this amplifier run hot?" Beyond that all the hypotheticals are meaningless. 

It reminds me of the story of two men who are in a hot air ballon and become lost. They see a small town, lower their altitude and ask someone on the ground, "Where are we?" The helpful citizen yells back, "You are in a hot air ballon!" Technically correct, and completely useless information. If I may be so bold, you are seeking technical information witch is fairly useless to success in building the audio system (i.e. cool running) you desire. :(

Class A and tube amps typically run warm to hot, but there are exceptions
Class A/B you can find hot ones, medium and cool running ones
Class D never runs hot; at least I have never encountered one which runs hot

Of course, all this has little to do with sound quality, which ranges up and down among all classes of amps. I suggest that seeking an amp which operates with the least percentage of heat loss is a grand way to build a mediocre sounding audio system. 

A discussion of maximizing one's speaker efficiency also has nearly zero relation to the question of how hot a room becomes with use of a certain class or model of amp. :(

You are way overthinking the issue, and it seems you struggle to accept simple, straightforward advice from experienced persons. I wish you success. 
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.   
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

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...
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.
@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!
shadorne
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!
But that's not what you wrote:

Speakers typically churn out between 99% and 90% of energy as heat.
I don't know of any speaker that's 90 percent efficient. That's why I wrote:
most speakers are much less efficient than that. A speaker with 92 dB sensitivity is only about 1 percent efficient.
 

Not a scientific response from me by any means but frankly I would not worry about how much thermal energy your speakers put out. Grab a sensitive measuring device and measure the air a few feet away from the speakers and right next to the speakers; I'd bet there is no meaningful variance in temperature (i.e. higher) right next to the speaker. You have to measure close in I would guess so you don't confuse the effect in that immediate area from your amp. If you are worried about speaker-produced heat, you should also be questioning how much heat your components and rack throw out as most isolation racks & platforms work on the principle of harnessing kinetic energy (vibration) and channeling it away as thermal...

The biggest concern is heat energy from tube and solid state gear, or hybrid (solid state with tube input and/or output stages, power supplies, etc...). In general class A and tubes of any kind are the worst with Class AB and ICE or Class D being the best in terms of producing little heat. The person who mentioned 'idling' characteristics is spot on...

Playing devil's advocate for a minute; if you have sound you like from gear and speakers that you like, instead of ditching the gear, taking a loss on the used market sale then buying-in again all from the beginning (speakers, amps, etc...), why not put a smaller some into a separate "split" heat-pump unit (so heat as well as A/C) for that room only. A split is a unit with a very quiet unit mounted in-wall with no duct work and the compressor/heat exchanger mounted outside on a concrete pad....just a suggestion.
Maybe I did not make my point clear.  Everything coming out of the wall ends up as heat.  Reduce current draw and you reduce heat.  Forget the speakers,  They are irrelevant.  They do not create energy, they only take the energy that is sent to them and convert it directly to heat or indirectly to heat by first creating sound waves, which then strike surfaces in rooms and is quickly converted to heat.  Energy enters the room as light, current, and body heat.  All of the energy in the room is conserved.  It does not disappear.  Reduce current draw and light entering the room and you have done what you can do.  As has been pointed out several times in this thread, a class D amp is about as good as you can do in reducing current draw.  Al, help me out here.  Am I missing something?  Isn't this just simple first and second law stuff?
I wish more manufacturers listed power draw, last night I found a few SET amp makers who listed this and I've been severely undervaluing it. 100W seems the minimum for any SE tube amp. Ok, I was assuming 10% efficency at worst hence my thought some class A was competitive. That helps put into perspective the other classes, I understand why some were frustrated with my arguments for low-power tubes.

I'd also like to clarify my dogmatic approach is about keeping the discussion as simple as possible, I won't be picking an amp based on its efficency but I will be counting out amplifiers which would prohibit summer listening moreso than my former SE Parallel EL84.

We have had a consultant look at the room before and were told it's not a candidate for AC. I do have an industrial ceiling fan down the hall but does neccitate listening breaks, it's loud. I ran smaller fans throughout the summer to blow equipment heat out the door and I couldn't tell you if it made a difference.

I believe I have the answers I set out to find, and am thankful for the posters above. Suppose next priority is finding amps which play best lower in their power band, and picking out new speakers without obsessing too much over db rating.
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
 
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
 

Why don't you take a look at cooling vest/jackets.  They can be active or passive and are designed to keep your body core cooler than the surrounding environment.
Al, thanks.  All of the caveats you listed I assumed would be understood so I did not explicitly state them.  Of course, the 2nd law demands that heat moves from an area of higher temperature to one of lower temperature.  If the listener is in a poorly insulated room, and the exterior is 40 degrees lower, and he opens the window, then the "disappearance" would be significant.   I also made an assumption that everyone participating in this discussion knows that less efficient speakers draw more energy into the room in order to afford a given dB level, and that energy ends up as heat. 
@cleeds

You are correct in your statements but you have twice misquoted me. You correct me but my statements more or less agree with yours just that I have stated things a little differently.

if I say a speaker churns out between 99% and 90% as heat then that equates to an efficiency of 1% to 10% in sound energy.

1% it typical for a high efficiency near full range speaker as you stated - it loses 99% of energy as heat (hot voice coils). 10% efficiency would represent the upper limit for a horn speaker - it loses 90% of energy as heat.


shadorne
... if I say a speaker churns out between 99% and 90% as heat then that equates to an efficiency of 1% to 10% in sound energy ...
Quite so. But I don't think you can cite a loudspeaker system with 130 dB sensitivity, which is what would be needed to have a 99 percent efficient speaker.
 
I suggest a affordable low heat producing amp for summer that is what I do in my office when it gets hot.