Coupling Audio signal to speaker
You apparently want to "hear" a voltage signal someplace, and want to be able to adjust the volume for some reason.  Your implementation has some problems:

Putting a capacitor in series with the speaker is a good idea.  However, you used a polarized capacitor.  That by itself isn't wrong, but it does mean you have to be careful with the polarity when you connect this circuit to the signal you want to listen to.  Since your capacitor is only 1 &micro;F, there is no need for it to be electrolytic, and therefore polarized.  1 &micro;F ceramic caps are readily available.

1 &micro;F in series with a 8 &Omega; speaker is way too little.  1 &micro;F and 8 &Omega; have a rolloff frequency of 20 kHz.  Everything below that will get attenuated inversely proportional to frequency.  You're a factor of 100 down at 200 Hz, for example.  You'll mostly hear high frequency components of the signal.

A few 100 &micro;F would be a better match for the 8 &Omega; speaker.  However, then you're back to using a electrolytic capacitor, so watch the polarity.

A 22 k&Omega; potentiometer as a volume adjustment for a 8 &Omega; speaker is a gross mismatch.  It will essentially act like a volume switch, not a fader.  Consider the case of the pot only being set 1% down from full volume.  The top part of the resistor would be 220 &Omega;.  That will attenuate by a factor of about 30 just by being in series with the speaker.



So what to do?  Go buy a "powered speaker".  A cheap set of "PC speakers" will do fine.  These come with a amplifier and volume control built in, and usually have a isolated wall wart supply so that you can float the speakers to whatever signal reference exists in the circuit you want to listen to the signal in.