Telefunken L70 speakers, one has a nasal sound with less bass

[Zonzi]

Hi everyone !


Once again I have an issue with old stuff I found for cheap, guess I have a taste for these.


I bought these two Telefunken L70 speakers for 20€ (https://www.radiomuseum.org/r/telefu...r_box_l_2.html), and they are in a superb state, component-wise. The box is scratched but I couldn't care less, I'm interested by whether it works or not.

They do work, and have a really nice sound, but one of the two has a problem with its 8" woofer. It's got practically no bass, and the mids are really pushed in the 400Hz-1kHz zone. I initially suspected bad caps, but after checking them all they all read kinda ok !

So I took the woofers out (here are their specs https://www.radiomuseum.org/r/isophon_psl_203_s.html) and tested them with a 9V battery, they're in great condition, no rotten foam, rubber is almost pristine, membrane as well. The excursion range looks OK on both, but even with the battery you can start to hear a difference in freq response of the bass.

Note that I consider that the bassless one is the faulty one, but that's a simple guess.

So I hooked them up (without the enclosure) to my usual amp and tried a variety of kick loops and other songs, which confirmed that the problem comes from the woofer. There's no audible distortion of the bass signal, but I didn't push them too much either. They don't rattle, and pressing them gently makes the membranes move smoothly.

The metal part that contains the magnet (or is it the magnet itself ?) is kinda rusty on both, more so on the faulty one, if that says anything. Both read 3.1Ω out of circuit, and the whole speaker read 4Ω before disassembly, as advertised.


What are my options then ? I have no experience opening these up and really I wouldn't want to ruin them, they look incredibly well-preserved for 50yo ones ! I can replace them but the thrill of using the original ones gives me a strong call


So, once again, my fate is in your hands as I call upon your expertise and advice ! You'll find a doc made by a fellow french guy with the circuit schematic, and a picture of both my woofers to prove that the membranes really do look OK. I'll also add a pic of the rusty parts just in case.


Thanks in advance !

[Zonzi]

Re: Telefunken L70 speakers, one has a nasal sound with less bass

If nobody has an idea then perhaps my question is stupid ! As a matter of fact I don't know a ton about this.

So perhaps another direction will encourage some answers :
What if I was to replace the woofer with one that has the same Thiele-Small parameters, or close to it ? Then, if my understanding is correct, the acoustics of the enclosure would react in the same way as with the original woofer, right ?