Restoring Beyerdynamic M67 Mics
Let me start by saying I really like Beyerdynamic's M67 microphones. They're nice and flat through the kHz range, where many other mics have a big presence rise, and there's a switch that brings in a gentle filter to counteract proximity effect when the mic is used close-up. The fact that I think they look cool is also a bonus.
There's not a lot of information around online, except that these were once quite popular, and they only stopped manufacturing when the tools wore out and were too expensive to replace.
I picked one up the other day and found it didn't sound like the rest of the ones I have, so I decided to investigate. My previous attempts at this had included taking off the silver grille and removing any degraded foam, but on this one the capsule on this one was visibly out-of-place, and couldn't be properly accessed from the top. It needed to be fully dismantled.
Klaus Kirchhöfer at Beyerdynamic technical support has been incredibly helpful through this by suggesting I push the little pins that hold the microphone's head in place. They need a bit of force, but that is the correct way of dismantling these microphones.
With a little force, the pins can be pushed into the microphone's body to be found later. The head slides off smoothly to reveal the capsule:
This photo is of a healthy M67 that I dismantled for reference while I fixed the new one.
A couple of things to look at:
- The red-ish bit in the middle is the voice coil of the microphone.
- The black plastic bit facing us is holds everything in place when the head is fitted.
- There's an acoustic deflector over the top of the capsule.
- The white bit is a felt-like fabric that covers the rear entrance to the capsule.
We can, of course, strip the mic down further. This is the new microphone that needed careful reassembly and some glue to hold broken parts together:
Here we can see the diaphragm itself. Note there's some bits of rubbish on there, so I carefully removed those so that the diaphragm can move freely without any additional mass.
Originally, there was also a layer of fabric glued to the inside of the grille. It looked like this when I removed it:
Which isn't going to let much sound through at all. It went in the bin. There's still another layer of fabric inside the head of the mic, sitting around 1/8" below the grille.
Below is what you get when you lift the capsule out. It doesn't go very far before the wires are tight, so be careful!
There's some clear rubber just above the terminals which acts as a shock mount. Not great by today's standards, but better than nothing.
With the capsule cleaned and broken parts glued, it was time for reassembly. If you look into the grille here you can see where the top of the capsule ends up:
I believe that when the M67s were made, they had some foam in the gap above the capsule. Given the age of these mics, that foam tends to break down. I like to use these with an external foam filter, so I have omitted the internal foam in this case.
So, there we have it. There is also the M/S (Music/Speech) switch at the bottom of the mic, but the two screws there make it pretty easy to open up.
Thanks for reading. If you have any questions about these mics or would like me to work on your M67, please get in touch.