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.
The LM386 amplifier's inputs are an internally biased differential pair, with common mode input range extending to the indicated ground, Vee, or actually 0.4 Volts below ground.
In order to not disturb this internal biasing, the input signal must be capacitively coupled (or perfectly ground-referenced) - a capacitor in series on the input line is needed.
Next, for a voltage gain of 200, the input signal peak to peak needs to be under 1/200 of the output voltage range of the amp. While I could not find this specified in a quick scan of the datasheet, if we assume 7 volts output voltage range with a 9 Volt supply, the input signal needs to be under 35 mV peak to peak, to avoid clipping the signal. Clipping would result in mild to severe distortion of the output - though this does not explain the complete lack of signal you find on output.
If the incoming signal is higher than this 35 mV P-P, a potentiometer as an attenuator on the input is suggested.
Once these fixes are done, please revert with results, so the answer can be added to if needed.
Best Answer
The LM386 is worth a little try: -
The above is a mono channel so you'll need to duplicate it for stereo. Note that the 0.05uF capacitor can be a 0.047uF (or 47nF) cap. The 10k pot will control volume and it needs to be a logarithmic type to get a realistic adjustment range. You can use a linear pot but you'll find that all the adjustment of volume is in the last quarter of the pot rotation.
I'm not sure what power supply you plan to use but running this amp from 9V (Vs) is typical and you'll get about 0.5 watts per channel into an 8 ohm speaker.
If you want something a bit more challenging there is this: -
And if you want more power there is this: -
Note that the TDA2030 can be used on its own to get 5watts to 10watts - look up the data sheet and give it a read.