Speaker Impedance: Effects on Sound Quality & Power

[muh_j18]

what is the effect of speaker's impedance on the qualiy and the power of the sound?
for example: tow speakers one has 10 ohms impedance and the other has 50K impedance, which one is better? which one gives a louder voice?

 

[f95toli]

There is no generic answer to that, the two speakers will present very different loads so which one is "best" will depend on the design of the power amplifier.
Although there are no speakers with 50K impedance; the highest nominal impedance you will find in real speakers is about 20 ohms or so (one famous example of a high-impedance speaker are the BBC monitors, they have a nominal impedance of 15 ohms).

 

[Pumblechook]

Piezo devices can be hi-Z. You need to (roughly) match the speaker impedance to the output of the amplifier otherwise it may increase distortion, reduce the volume or even damage the amp. The impedance will vary with applied frequency and maybe the audio level. It is a 'dynamic' impedance...depends on the coil moving in the magnetic field and the cone coupling with air. The DC resistance of the coil will be less than the stated impedance.

 

[f95toli]

You need to (roughly) match the speaker impedance to the output of the amplifier otherwise it may increase distortion, reduce the volume or even damage the amp.

I am not sure what you mean by "matching impedance". Almost all audio amps are voltage amps (there are a handfull of exotic exceptions) meaning they are designed to have very low output impedance, typically less than 0.1 ohms and in good amps lower than that (my power amp has a nominal output impedance of 0.01ohm ).
The impedance of most speakers shouldn't drop below 1-2 ohm, and is usually above 0.5 ohms even for very difficult speakers (such a speaker would trigger the short circuit protection in many amps).

 

[Averagesupernova]

I suspect what he means by impedance matching is you wouldn't want to hook an amp designed to run a 1 ohm load to a speaker with an 8 ohm voice coil because to get the same sound level from an 8 ohm you will need more voltage. Ohms law and all. Also, for obvious reasons you would not want to try to run a 1 ohm speaker with an amp designed for 8 ohm loads since it is not likely able to source the current required without damage.