It is a good thing for a voltage input, as if the input impedance is high compared to the source impedance then the voltage level will not drop too much due to the divider effect.
For example, say we have a \$10V\$ signal with \$1k\Omega\$ impedance.
We connect this to a \$1M\Omega\$ input, the input voltage will be \$ 10V\cdot\frac{1M\Omega}{1M\Omega+1k\Omega} = 9.99V \$.
If we reduce the input impedance to \$10k\Omega\$, we get \$10V \cdot \frac{10k\Omega}{10k\Omega + 1k\Omega} = 9.09V\$
Reduce it to 1k and we get \$ 10V \cdot \frac{1k\Omega}{1k\Omega + 1k\Omega} = 5V\$
Hopefully you get the picture - generally an input impedance of at least 10 times the source impedance is a good idea to prevent significant loading.
High input impedance is not always a good thing though, for example if you want to transfer as much power as possible then the source and load impedance should be equal. So in the above example the 1k input impedance would be the best choice.
For a current input a low input impedance (ideally zero) is desired, for example in a transimpedance (current to voltage) amplifier.
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.
Best Answer
High impedance generally means that as a source, the source impedance is high. And by high, it can also mean that the signal from the sensor needs to be amplified and the amplifier needs to have a high input impedance. If the load impedance on the sensor is low, it will pull the sensor voltage lower and create error in the sensor measurement.