I have a 0.3W (RMS), .8ohm speaker coil + cone that I want to test using various music. However, the 8ohm impedance is lower than typical earbuds (24ohm), and also I can't find headphone jack power specs for my computer (Macbook Air 2010) or phone (Nexus S), so I'm worried I'll blow out my speaker sample.
I found this amplifier that's for 8ohm speakers, but it outputs up to 20W! I could turn it to its lowest setting but I'm worried that in tweaking the volume I'd accidentally exceed the speaker's rating just by the error of my hand's motor control abilities. Could I use that amp plus a current limiter, or will its digital electronics become under-currented?
Alternatively, if I can find a "powered / active speaker" product such as for desktop computers which happens to have a 0.3W, 8ohm coil internally, I could just swap out the coil. Know any?
Last resort would be to breadboard an amplifier circuit myself based on an 8ohm-load, 0.3W amplifier IC like the LM4864MM, but that's extra work just for a throwaway test circuit.
What is the laziest way to safely accomplish this test?
Best Answer
Don't be so shy.
0.3W is pretty loud! And don't forget that audio equipment potentiometers are logarithmical ones, so when you turn it halfway, it is roughly one tenth of the output power. So a 20W amp, driven with its rated RMS input signal would output 2W RMS when turned up halfway. A quarter setting would result in 0.2W RMS accordingly. And you said you'd want to test with music - rated music power is around 2x the rated RMS power for most of the speakers.
Don't fret, speakers are quite difficult to destroy in so low power situations. I did try with a PC speaker and a ~20W amp when I was young and feeble, to the point when it got quite warm on the outside - but no pops (it was horrible, by the way)... Ok, PC speakers are not too flimsy. I did build a tube amp from scrap parts, and on that I regularly used a way too -electrically- underrated speaker, and to make the situation even worse, I used it as a guitar amplifier - driven into the maximal power tube saturation I could achieve...
If however you'd want a professional approach, use an LM386 power op-amp to play with, a few external components and you are ready to go. I think that is far easier to obtain than an impedance matcher transformator - not to mention, it degrades and colours the sound a lot less.
LM386 datasheet