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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

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Showing 8 responses by charles1dad

charles1dad's avatar
charles1dad
10,227 posts
 
Sorry, I thought Ohm's  Law is self evident in its equation.  As R decreases I must increase for a given V  I.e. voltage. There's an inverse relationship,  more current is needed to maintain the voltage as the resistance diminishes. It all seems straightforward to me.
Charles 
charles1dad's avatar
charles1dad
10,227 posts
 
Hi,
If you keep the Ohm’s law equation in mind it’s easy to explain. I = (current), V=voltage and R = resistance (speaker load impedance expressed as ohms).
I=V÷R. So the smaller R becomes, the larger I becomes.
If for example V=10 and R=10 then I will =1. If R is reduced to 1 then I now =10. Reducing the R (speaker impedance expressed in ohms) will increase the value of I (current demand). So a 2 ohms load (lower R) will demand more current  (I) than a 8 ohm load  (larger R). 
Charles
charles1dad's avatar
charles1dad
10,227 posts
 

Light loading like many audio techniques has to tried on an individual basis, results will vary depending on circumstances. My amplifier has 8 and 16 ohm taps and my speakers are 14 ohm nominal. The 16 ohm tap sounds better than using the 8 ohm tap.

Charles

charles1dad's avatar
charles1dad
10,227 posts
 

Mapman,

I don't get the sense of "pundits" taking sides. The OP raised an interesting question regarding the popularity of 4 ohm speakers. This generated a very good discussion. We agree that one fine aspect of High End audio is the many choices/paths that lead to a good sounding home audio system. Your system and mine are at opposite ends of a component/system spectrum, yet we're both very happy respectively. This is a good outcome. I appreciate the multitude of perspectives provided here.

Charles

charles1dad's avatar
charles1dad
10,227 posts
 

Well, if high efficiency speakers are more difficult to build by a factor of 10! that pretty much confirms my suspicion as to why their numbers are much less compared to the  many 4 ohm speakers available. Why would a speaker designer "bother" with the increased difficulty particularly knowing the popularity/high usage of solid state amplifiers. This makes sense as most SS amplifier owners with gravitate to 4 ohm speakers for the most part.

Charles

charles1dad's avatar
charles1dad
10,227 posts
 
Hi Bdp24,
For sake of this discussion I’m referring to speaker load impedance characteristics that remain "relatively flat. So my hypothetical comparison would be a 4 ohm vs a 16 ohm. A speaker such as the Quad that you cite with its extreme fluctuations renders nominal rating meaningless lf both the 4 and 16 ohm speakers are stable, the higher ohm speaker demands less current and work from the driving amplifier as predicted by Oohm’s law.

In reality there are speakers with both reasonably flat impedance characteristics and gentle phase angles. There are also those with widely fluctuating impedance and steep phase angles. It seems that the former would be preferable as it is far less demanding on a power amplifier assuming that either provides comparable sound quality. 
Charles
charles1dad's avatar
charles1dad
10,227 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
charles1dad's avatar
charles1dad
10,227 posts
 
gs5556,
That is a very good analogy!
I’ve often wondered why given the reality of Ohm’s Law, why do many speaker designers revert to 4 ohms rather than 8 ohms (or higher) speaker impedance. As Al noted in his reply, Ralph (Atmasphere) has pointed out that the higher the impedance load ,the lower the amplifier  distortion produced (which is a desirable result you'd think).

It would seem that a concerted effort to design easier to drive high impedance speakers would yield obvious benefits. The most logical explanation for the plethora of lower impedance speakers is that the higher impedance speaker is probably more difficult to implement to get things right and presents more design challenges.
Charles
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