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Dwiel 9th May 2005 12:45 AM

optimizing for efficiency
Hey guys, I was wondering if you could tell me, in general what the best combination of components would give me the best efficiency of source power. The plan is to be able to run off of batteries and I want the batteries to last as long as possible. This would be taking place outside and would probably be using it to play background music for a group say around a camp fire and maybe sometimes a little louder than background music. About the volume that you have to speak up to hear other people talking, but can still understand them. (I'm not sure how else to explain the volume I am looking for, if there is a better way, let me know)

Money is also somewhat limited as well as complexity. I would consider myself intermediate to advanced in the ways of electronics but I'd rather not make this a larger task than necessary. Most of my experience is in the field of digital electronics, not audio, so designing my own schematic is pretty much out of the question.

I have read that class D amplifiers are the most efficient, am I correct in that I should find a design using this class?

Also, am I right that horns tend to be high efficiency? If not, I think I will probably want to use speakers I already have, I don't know if I can afford buying speakers for this purpose only...

paulb 9th May 2005 06:14 PM

Yes, Class D designs would be the most efficient. And I think you're right about horns as well.

darkfenriz 9th May 2005 08:57 PM

efficiency of class D is very helpful above 100W or so.
If you need lower power there is hardly any point in building complicated switching amp.
About horns you are absolutely right.

Dwiel 9th May 2005 09:34 PM

Hmm, so I guess I shouldn't worry all that much about the amplifier type so much. I have been looking into horms and have found, as I expected, that they don't have a very low frequency response range. I would like to hear the bass and so I guess I will need to have a bass driver of some kind. From what I have seen, all high efficiency speakers that have the freq response I am looking for to cover what the horms can't (40 - 3,00) tend to be rather expensive. What is the best way for me to cover this range with the best efficiency and lowest cost? Sound Quality isn't terribly important, although I would like to stay away from the worst sounding ones. I was thinking that maybe some kind of car speaker would be good for me? Some have horn tweeters to cover the high range. They would also tend to be smaller, which is good because I am hoping to have a semi-portable setup in the end.

Thanks for the help!


ilimzn 9th May 2005 10:18 PM

Hm, if you were building speakers exclusively for this project, as well as an amp for them, then using 5th order ported boxes would be the way. Horns are much more efficient but need to be very large for good bass response.
Also, for efficient amps you may want to look at class G (rail commutation) amps. Sanyo actually makes some hybrid circuits that are fairly easy to use that implement this topology. Still, class D would be the ultimate efficiency-wise. There are several manufacturers (a few you can get to through this site) that offer finished modules - add power supply, input pot and enclosure + connectors, and you are set.

Nelson Pass 9th May 2005 10:20 PM

Try a Fostex FE206E. They are only a few bucks, and
have enough efficiency and will sound good for your application.
You'll scare the wildlife with a 2 watt amp, and a small bass reflex
enclosure will make it down to 50.

amplifierguru 10th May 2005 08:23 AM


Use speaker efficiency ( some are 100dB wide range) with bass reflex and Q=2 , thenpower it all from a car amp recharged from a solar panel. Party AND save the planet ( and scare the wildlife!)

AndrewT 10th May 2005 02:35 PM

I second the idea of using high efficiency speakers. At least 94db/watt. Be carefull to not confuse db/2.8v which can use lots of power if the impedance is low.
Fewer components in the xover helps efficiency and similarly fewer speakers helps in this regard.
A well designed classB with the driver stage optimised for low current consumption (opamp?) and low Iq should also be helpfull.

ilimzn 10th May 2005 02:44 PM


Originally posted by AndrewT
...fewer speakers helps [efficiency]
Not at all. Consider that two identical speakers in series produce the same SPL at half the power... which is the key to array efficiency.

AndrewT 10th May 2005 03:05 PM

Hi ilimzn,
same driving voltage with double the series impedance gives half absorbed power.
You say the two speakers in series will give 3db more SPL at the same driving voltage. Can you clarify that?
However, I was talking about a multi passband xover with dedicated speakers to each passband. I think that the extra complexity of the xover for multi passband will waste power in the xover due to extra resistors and inductors. Adding zobels to tailor the drive unit impedance will also reduce overall efficiency.
Avoid these and I believe that the speaker efficiency will improve.

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