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Why are low impedance speakers harder to drive than high impedance speakers

I don't understand the electrical reason for this. I look at it from a mechanical point of view. If I have a spring that is of less resistance, and push it with my hand, it takes little effort, and I am not working hard to push it. When I have a stiffer spring (higher resistance)  I have to work harder to push it. This is inversely proportional when we are looking at amplifier/speaker values.

So, when I look at a speaker with an 8 ohm rating, it is easier to drive than a speaker with a 4 ohm load. This does not make sense to me, although I know it to be true. I have yet been able to have it explained to me that makes it clear.  Can someone explain this to me in a manner that does not require an EE degree?

Thanks

128x128crazyeddy
bdp24's avatar
bdp24
9,821 posts
 
In a related matter, Roger Modjeski of Music Reference recommends hooking up your speakers to a tube amp on the lowest impedance tap that provides the power you need. So if an amp puts out 45 watts at 8 ohms and 30 at 4, and 30 watts is enough for your needs (with the combination of speaker sensitivity, room size, listening level, etc.) with an 8 ohm speaker, use the 4 ohm tap for lowest power amp distortion and best sound. 
crazyeddy's avatar
crazyeddy OP
381 posts
 

Lots of food for thought here. Thanks guys for all your responses to help me see this a little clearer. As charles1dad pointed out, in response to Ralphs explanation, it does seem to be (at least to me) in the best interest of design, to provide a speaker with a higher impedance value. So why would a designer go the other direction?

Oh, boy, where will this be leading the thread

unsound
7,329 posts
 
Charles1dad, sometimes a speaker designer will add components to a cross-over to lower the impedance  in order to make the impedance flatter/smoother. Sometimes lowering the impedance allows for more current delivery in order to facilitate stronger bass response.
mapman's avatar
mapman
22,308 posts
 
I think the trend towards speakers with lower impedance corresponds to the trend for speakers to be smaller yet more full range to fit into people’s lifestyle. Also as we know from experience the best sounding gear is not always the ones that measure lowest in distortion. Lower impedance tougher load speakers just means amps must work harder. Some are able do that much mbetter than others. Newer more efficient amp technologies like Class D perhaps do it best. Class D offers a much larger higher pressure "garden hose" for your speakers.   For example I have 500 w/ch class d amps that can deliver almost 40 amps of current  that are about the size of a shoebox.    My harder load speakers shine and easily surpass my smaller easier load ones with these.     


charles1dad's avatar
charles1dad
10,250 posts
 
Unsound,
That makes sense and with the advent of transistor power amplifiers I can see where the 4 ohm load speakers becomes more plausible to manufacture . One could make a case for either type of load characteristic. Higher impedance =easier load and less work for a given amplifier. Intuitively this seems to be ultimately more desirable.

There was a time when 8 to 16 ohm speakers were the norm and one could use modestly powered amps that were of high "quality ". 16 ohm speakers are quite rare these days. This would present an enormously easy load for virtually any power amplifier.
Charles
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