I've been testing things with the MB SC01 speech recently and yesterday I stumbled across an Apple II game called Teleport while searching. This is supposed to have built in support for the Votrax Type N Talk, do ctrl-v to activate. I went looking to MAME to try it as I thought it had it emulated, but the TNT did not seem to be working well. I had a look and the interrupt was triggering immediately again before the previous phoneme had finished. When I add this in to update the callback immediately after it is cleared, then it seems to work ok. Not sure if this might affect other SC01 users.

in votrax.cpp:
m_ar_state = CLEAR_LINE;
m_ar_cb(m_ar_state); <--- added this

Is it possible to run two instances of MAME and connect them together via the emulated serial ports? I did try a few combo's but no luck. The other option was to hook MAME with the Votrax TNT emulation to a real Apple II, i didn't seem to have any luck with this either.