I have an old telephone handset that I am playing with. It has a small (well actually quite large for what it is) speaker in it that I am trying to get working. Problem is it had about 120 ohm resistance so it doesn't work at all from a headphone jack. If I plug it into an amp I can hear it but it is pretty quiet even with the amp cranked up high. Is this just an ohms law thing and I am stuck with these limitations or might there be some clever workaround? A massive amp for a tiny speaker seems overkill (and might it actually kill one of the components?)
You could play around with transformers but without that or other fancy electronics it's not going to work with domestic hifi
("Ye canny change the laws of Physics Jim" etc)
A transformer would do it. They often exist to convert between standard 8 ohm 'hi fi' speakers and the 100V systems you get in buildings. You get different ones depending on the output power you need so you might need to do some numbers :(.
Edit: these sorts of things
https://m.thomann.de/gb/transformers.html
If it’s a telephone handset, it’s likely to be tuned to 4KHz bandwidth compared to the full audio range of 20KHz+ so even if you get the resistance sorted, it’ll probably sound crap
depending on age, it may also be limited in output to 118dBSPL. This is still loud, but a standard speaker won’t have it and so may give you better dynamic range at higher volumes
If you just want the handset to "work", I'd ditch the original speaker and look for a replacement full range speaker, ideally a headphone speaker.