Hi,
I have am IC that can drive a 30ohm speaker, I want to use a PCB mounted speaker and find they are 8ohm's will connecting the speaker damaged the IC?
Also is there a rule here, like driving a lower load than specified is OK but not a higher one or vice versa?
Reduce the supply voltage to the IC so that the peak current in the 8 ohm speaker is the same as the peak current in a 30 ohm speaker at its normal operating voltage. But the losses in the IC might cause the power output to be low.
A 22 ohm resistor in series with an 8 ohm speaker reduces the max power to the speaker to only 30%.
The resistor in series with the speaker ruins the damping from the amplifier of the resonances of the speaker. BOOM, SHRIEK, BOOM, SHRIEK.
if the ic is designed to drive a headphone i doubt it will have the power to drive a loudspeaker properly - and then add the impedance issue you first raised, I doubt you will hear very much at all.
what's the power output of the ic, and the rating of the speaker?
The datasheet doesn't say how little is its output power. The output amplifiers require a DC blocking capacitor to feed the 30 ohm headphones so they are single-ended and are not bridged.
The absolute max supply voltage is 3.6V so if it uses a 3V supply and the output amplifiers have a 2.6V swing (probably less), then the power at clipping is only 28mW per channel. Flea power.
Every semiconductor manufacturer makes stereo amp ICs.
Your 3V power supply is too low for an amplifier. Some bridged amplifier ICs have an output of 1W into an 8 ohm speaker with low distortion when the supply voltage is 6V.
Be careful of the details of the IC. Nothing says that the manufacturer cannot build into a 3.6v IC a switcher that will boost the output amp voltage higher for more power.
Is the pcb big enough for you to put your ear on the earphone speaker?
Without a properly designed enclosure the speaker will just be a low power tweeter. SSSST, SSST, SST.