Electronic – Hi fi speaker impedance

You use different speakers in different systems and even different serial and parallel configurations; that's one of the reasons there are different impedance values. 8 Ohm speakers are the standard for home, while 4 ohm are usually found in car audio systems.

If a lower impedance loudspeaker generally has better dynamic range and can achieve louder volumes, why do we still see 6, 8 or even 16 ohm speakers? Shouldn't we be "progressing" toward more efficient speakers with lower impedance?

While yes, the benefit of 4 ohm speakers is that the increased current means they have a wider dynamic range, they will be harder on the amplifier (if the amp is made for 8 ohm) and at higher volumes they will have larger THD (total harmonic distortion.) Essentially the output voltage will be unstable during high power application as the Amp will struggle to supply enough current to drive the load.

Using a 4 ohm speaker on a generic home amplifier that is made for an 8 ohm speaker will draw twice as much power and can cause the amplifier to go into protect mode or even overheat and break.

why do we still see 6, 8 or even 16 ohm speakers?

Different serial and parallel configurations are used to change the load on an amplifier. For example, you can have two 4 ohm speakers in series so that the load will be 8 ohms. Or (common in custom car systems,) you may have two 4 ohm speakers connected in parallel so the load on the amplifier is only 2 ohms, thus doubling the current.

Or in this case, four 8 ohm speakers are connected in series parallel so that the total impedance is only 8 ohms.

Are higher impedance speakers merely a product of backward-compatibility?

No they have their place, from allowing different speaker configurations, or less wear and tear on amplifiers to improved sound quality.

Using speaker with higher than minimum impedance may improve quality as the Amp will generate more stable voltage and current. Hence the THD will remain lower at higher impedance while the maximum power output by the Amp will be reduced due to higher load impedance.

Loudspeakers have impedances of 8 ohms, 6 ohms or 4 ohms (those are "nominal" or approximate values, because the impedance of a speaker changes all the time with the different frequencies of music

They are also referred to as at rest values, and if you connect a ohm meter to the speaker it should read 4 or 8 etc. ohms. Then if you gently move the speaker that reading will change. If you measure a speaker and it shows a different value than what it is supposed to then it may be defective of blown or at least slightly damaged.

"Obviously these speakers have a much higher impedance than the amplifier is rated for, so could this be why the original amp failed immediately?"

NO it cannot. If it would be a problem then such an amplifier would also fail when you would operate it with no speakers installed. That would be plain silly. Audio amplifiers have a voltage output (low impedance) so only a very low impedance could cause it to fail. But almost all modern amplifiers can handle loads of 4 ohms or higher. Also, most modern amplifiers have some form of overload protection so it would just shut off.

OK, it appears there are four 16 ohm speakers in parallel. This would give a total impdedance of 4 ohms. That would be OK if the speakers are indeed 16 ohms. But if they are bit lower in impedance then the combined impedance will be below 4 ohms and for some amps this can be a problem.

A solution might be to instead of switching the 4 speakers in parallel, to make 2 pairs of 2 in parallel and put those 2 pairs in series. Then the total impedance will be around 8 ohms, that should not give any problems.