Why my AM receiver cannot run 8 ohms speaker but runs 32 ohms ear phone?

Question

When I measure resistance, ear phone has more resistance than the spaeker, even ear phone is lot smaller than the speaker. I thought it should be easier for the circuit to move cone of the spaeker with lower resistance than the higher resistance.

Answer 1

A receiver can always run a earphone even if it can't run a speaker.  To run a speaker, you need an amplifier inside the receiver.  Does it have an amplifier?  No amplifier, no speaker.

It takes more audio power to run a speaker than it does for an earpiece.

Answer 2

The speaker takes more power.

The small current might flow without enough

movement for you to hear.

Answer 3

No, it's easier if it has high resistance.  Most simple amplifier circuits work at a relatively high impedance and low current, which is what a high impedance headphone works at.

4 ohms requires a lot of current to drive. For example, to get 1 watt (a reasonable level out of a cheap speaker) out of a 4 ohm speaker, you need:

P = E²/R

1 = E²/4

E = 0.5 volts, but

I = 0.5/4 = 125mA, a substantial current.

32 ohm headphones, with 100mW, you need

P = E²/R

0.1 = E²/32

E = 0.05 volts

I = 0.05/32 = 1.5mA, a low current.