The View Up Here

Random scribblings about kites, photography, machining, and anything else

Alice Microphone – Switchable Voicing

Posted by Tom Benedict on 10/05/2017

Back when I built my first Alice microphone I intended to use it for field recording. I took it out numerous times, but compared to other microphones I already had it always seemed noisy. Some testing indicated it wasn’t noise, just over-sensitivity to the higher frequencies generated by even the slightest wind in trees. Homero Leal pointed out that Ricardo Lee had documented an EQ modification to the Alice circuit on the Yahoo! micbuilders forum that could tame some of the high end sensitivity, so shortly after that I modified both of my Alice mics.

A couple of months afterward I started looking into voice acting. I have no aspirations of changing careers at this point, but I’ve been reading to my kids for close to eighteen years now, and one by one they’re starting to leave the nest. By the end of the summer the only way I’ll be able to read to my oldest is if I record each session and email the file.

To be fair the style of reading I do is closer to voice acting than straight reading. I like to give each character a unique voice. I like to read each book as if it was an old-school radio drama. So I knew my foray into voice acting would wind up being more than just figuring out how to record the sound of my voice. I wanted to become a better voice actor.

But yeah, I also wanted to learn how to record my sessions to the best of my ability. The more I poked into the technical requirements, the more I realized the Alice microphones make really nice voice mics. And the more I played with my TSB-2555B Alice, the more I realized I might want to disable the HF EQ mod for certain voices.

So I asked Ricardo if I could wire his HF EQ mod through a switch, making it an option rather than a default. He said the circuit isn’t particularly noise sensitive, and that he didn’t think there would be any problems. In the end I picked a switch that let me have three configurations: no HF EQ, Ricardo’s HF EQ to make the mic sound more like a U87, and one more that I haven’t committed to yet. (I’ll figure out how to wire that once I figure out which voices I need to EQ for.)

The fun part about adding the switch to the BM-800 Alice was figuring out how to mount it. I went back to the 3D CAD model I made of the mic, added the switch, and found I could fit some aluminum angle across the mounting holes on the opposite side from the PCB.

The only problem with that plan was that the aluminum angle had to fit inside the body tube of the mic. The top needed to be round, and for it to blend with the rest of the microphone I needed the sides to be tapered, just like the Alice PCB.

There are plenty of ways to make profiles like this, especially if you employ the aid of a CNC machine tool. But part of the joy of making things, for me, is spending time with the tools, hands on the handwheels, coming up with ways to get exactly what you want.

Switchable HF EQ

I wound up machining a lathe fixture to cut the profile. The fixture mimicked the internal frame of the BM-800 microphone, complete with screw holes and taper. Once I’d drilled the holes in the aluminium angle on the mill, I bolted it to the fixture and chucked it up in the lathe with the compound slide set over the necessary 2.3 degrees. It worked like a charm.

The switch isn’t the most convenient thing in the world since I have to take the body tube off the mic to change its position, and since the M-S Alice uses both sides of the frame it’s not something I can apply to that mic in its current form. But for now I’m not planning to use the M-S Alice for voice, and changing the mic’s characteristics isn’t something I’d want to switch on the fly, anyway. I think it’ll work out ok.

I’m still working through the nightmarish acoustics in my house, but with the help of a number of voice actors who have been kind enough to answer my barrage of questions, I think I’ll eventually get that sorted as well.

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