An FYI where the problem comes about. A stereo to mono TRS to TS adapter would connect both the TRS tip and ring connectors together to the TS tip while the TRS and TS sleeves would also connect together. If the TRS was wired to an XLR, the tip would get the "hot" XLR pin 2, the ring would be the "cold" XLR pin 3, and the sleeve the ground XLR pin 1. This means that the two sides of the signal would be shorted together at the mono TS plug, since both tip and ring are connected to the TS plug tip, and it's a miracle that anything gets through.

Bought a couple of TRS to Phono plug adapters a few weeks ago and found another oddball. The phonos are colour coded white and red. This usually means left and right channels respectively, at least in consumer stereo gear (such as the line inputs on most DV cameras). But these particular adapters are actually intended for mixer inserts and they follow the pro wiring colour code convention of red wire being the tip and white wire being the ring. On a stereo TRS like a headphone, the tip is left channel and the ring is right. This means that the TRS-phono adapter will reverse the channels if one connects them following the colour code one is used to with consumer stereo gear - right channel appearing on the WHITE connector instead of the RED connector as expected. Just one more "gotcha" to be on the alert for!

Interesting. I might just buy the "correct" parts, though I don't know when, if ever, I'll need the wireless boom setup again.

As for frequencies, the Sennheiser's set to the default, that is, whatever it was on when it came out of the box, and it's always worked everywhere I've used it when it was used as a lavalier. I did the wireless boom test in my house, and I've also used the lav in my house, and it was always fine. I hope I can find that receipt. Those cables were $25.

Those threaded TRS miniplugs that are correct for the Sennheiser transmitter are a little hard to come by. Something like the adapter cable from Trew that I mentioned before would be a lot less hassle and "rolling your own" wouldn't save more than a few dollars, hardly worth the trouble. If it takes you an hour to put it together, that translates to $50 or so labour cost to add to the parts cost.