The View Up Here

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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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Weatherproof Recording Box

Posted by Tom Benedict on 07/05/2017

In earlier posts I’ve mentioned that I do most of my field recording by dropping off my gear and recovering it later. This works great for a lot of reasons, not the least of which is that I make noise constantly. By using the drop-and-recover technique, I can get as far away from my mics as possible.

Another advantage of this technique is that I’ve found it takes between fifteen to forty five minutes for wildlife to return to their normal behavior after they’ve been disturbed. Since I can record for upwards of 24 hours using this technique, this means I get lots of time in each recording during which I know the animals I’m hearing aren’t stressed.

The big drawback to this technique, though, is that when something goes wrong I’m not there to deal with it. The first time I left my gear out overnight it rained. I’d planned for it by draping my recorder with a plastic bag, but it was a stop-gap measure at best. I wanted something more permanent.

Months ago the nearby Costco began selling ammo boxes. My wife picked one up for me, figuring it would be a good starting point for a weatherproof recording box. I hemmed and hawed about what I wanted the box to do and how I wanted it to do it, and finally came up with a plan.

Weatherproof Recording Box

I wanted the box to be able to hold my recorder and an external battery pack, and provide weatherproof XLR connectors I could plug mics into without risking the integrity of the weather seal. I came up with a couple of pencil sketch designs, but none of my plans beat a piece of equipment that already existed: the weatherproof outlet cover.

Four Channels

I had to modify the outlet cover so it had an opening large enough for the four XLR panel connectors. I did the work on the Bridgeport, but similar results could be had by using any number of other techniques such as saw and file, Dremel or Foredom, etc.

The panel connectors are standard Neutrik parts. I picked up the rainbow colored grommets (also Neutrik parts) to provide additional weather sealing and to let me color coordinate the connectors on the inside.

Weatherproof Routing

Cables route in through the slots at the base of the box (in this case I only opened up one, though I’ll probably have to open up the other once I start recording four channel sound.)

It Closes!

Once the cover is closed the only way water can get into the connector area is to come in through the slot at the bottom of the box. It won’t stop immersion or flooding, but it stops even the horizontal rain we get here in town. (I had my kids spray the box aggressively with the garden hose before I trusted it to hold my equipment. Everything stayed nice and dry!)

Color Coordination

I lined the inside of the box with foam that I covered with leftover head liner material I had from when I replaced the head liner in my Civic. The foam panels are removable in case I change my mind or need more space inside, but for now they provide some measure of cushioning and no small amount of insulation for when conditions turn cold at night.

The inside connectors are also standard parts from Neutrik with boots that match the colors of the panel grommets. Unfortunately connector lengths caught up with me.

The Tight Fit

When I started this design I hadn’t planned on lining the box with foam. That came later once I realized how much my gear would rattle around if I did any hiking with the gear inside.

But once the foam was installed, the full-sized Neutrik connectors poked out so far I could only plug things in on one side of my recorder. Since the fourth channel is located on the opposite side from the other three on the DR-70D, this means I can’t actually plug in all four channels yet. At some point down the road I’ll replace all four with low profile right angle connectors from Cable Techniques, but for now I get two (well… three) channel sound.

I’d intended to build this box in time for the 2017 International Dawn Chorus Day. Unfortunately I missed by hours. IDCD 2017 happened at dawn this morning, and I just finished the box an hour ago.

Ah well…

Meanwhile I’ve got a setup that will let me do drop-and-recover recording, rain or shine, and keep my gear safe, sound, and dry.

UPDATE: I finally had the chance to answer one question I had about this design: With the foam lining, would I run the risk of overheating the gear in the box?

The answer is a qualified no. I put my recorder and my 10000mAh battery pack in the box with a temperature probe and closed the whole thing up. Ambient temperature was 21C. The temperature in the box rose steadily for the first hour, then began to roll off. After seven hours the temperature reached 32.5C with clear signs it would asymptote at or below 34C. That’s a delta of around 13C.

The DR-70D operating range is 0C – 40C, according to the Tascam web site. When I originally ran this test I thought this meant I was marginally safe. I’m pretty sure I was wrong. In the test I was measuring the air temperature inside the box, not the temperature of the electronics, which were considerably warmer than the air temp.

I came up with a fix for this and the connector issue, which I describe in the second part of this article: Weatherproof Recording Box – Part 2.


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Another Stab at Contact Mics

Posted by Tom Benedict on 07/05/2017

Several months ago I ran a bunch of tests on a contact mic to try to figure out the best (ok, best of several options) way to interface them to my recorder. It wasn’t the most exhaustive test, but it at least pointed me in a good direction.

Specifically I wanted to find which configuration had the best low frequency response. To that end the mic under test was a 35mm piezo element stuck to a subwoofer, and the tests consisted of running a frequency sweep through the subwoofer while I recorded the output of the contact mic.

I tried four configurations: 1 – direct TS plug-in, with all the high pass filtering that leads to. 2 – HOSA MIT-129 impedance-matching transformer. 3 – Alex Rice impedance matching preamp. 4 – Stompville impedance matching preamp.

It wasn’t the best subwoofer in the world so the data was lumpy, but a couple of things came through pretty clearly: Not surprisingly, the direct-plugin lost some of the low-end. The Alex Rice preamp is known to have noise issues, which also came out in the tests. As far as signal to noise went, the HOSA MIT-129 and the Stompville preamp were very close across the range of the test (10Hz-1kHz), but the Stompville had higher overall signal and required less gain out of the recorder.

My point in running these tests wasn’t to prove once and for all which setup was the best. It was just to get some direction for how to build my next round of contact mics. I decided to go with the preamp from Stompville and run with it.

Before going into just how I ran with it, here’s some background on the Stompville preamp: SmudgerD started the same place I did, with the Alex Rice preamp, but instead of just being frustrated with the noise floor, decided to redesign it, and then further refine it. The result is a very well thought out design. Even better, SmudgerD packed the whole thing onto a tiny PCB that fits on the back of a Neutrik XLR panel jack.

I bought two.

(But I wish I’d bought four.)

Then I stuck them in a box.

Contact Mic Preamp Box

The bottom of the box is tapped 1/4″-20 so I can attach it to the top of my DR-70D using the camera mount thumbscrew. Two of the Stompville preamps face out one side, and as soon as I buy another two they will face out the other side. The third face has a row of mini-XLR connectors for plugging in the contact mics themselves.

I was turned on to the mini-XLR connectors by Mo, who shared them in a comment on my EM-172 and XLR Plug article. I have to say these things are the cat’s pajamas. They’re small, they’re inexpensive, they have a positive lock, and they have the neat feature of having pin 1 make contact before the other pins. This ensures ground makes contact before the signal pins. I love ’em.

Unfortunately, right after I finished the box I was drawn into other things. So I only have two contact mics built so far. The first is the one that’s still attached to the subwoofer. The other is a prototype I built to test the preamp box in the field.

Prototype Contact Mic

It’s ugly, but it works remarkably well as long as you don’t apply any pressure on the center of the piezo. (This introduces a large DC offset.) The next rev, of which I’m building four, will be fully enclosed.

Just for grins I took the whole mess in to work to play.


– Tom

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Rest In Peace My Friend

Posted by Tom Benedict on 07/01/2017


5 May, 2010 – 6 January, 2017

Rest in peace, my friend

Can your tongue do THIS?!


Ember, Coned


Ember - Second Splint


Ember: Amputee


Edit Kitty


Ember - Done


Sunset Ember


Ember Sleeping - Close-Up


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(Yet More) Microphone Tests

Posted by Tom Benedict on 19/12/2016

Since writing my last post Homero Leal pointed out that I could mitigate some of the harshness of the Alice microphone (for field recording, mind you) by adding a capacitor across the 2.2k drain resistor. I didn’t have the size I needed (6.8nF), but I had everything to make a similar modification by adding an 8.2nF capacitor in series with a 750 ohm resistor, both across the 2.2k drain resistor. All of this is spelled out in Ricardo Lee’s ChinaMod+U87.doc file on the micbuilder forum.

Alice with ChinaMod U87

I walked out into the park behind my work, recorded for about five minutes, and headed back inside to modify the microphone. After adding the HF EQ mod I walked back out into the park and recorded again.

Prior to the mod my recording had a background hiss that sounded like microphone self-noise. I knew from testing the mic inside my car that it’s not, and is actually a sound from the environment. While testing the mic with a 22″ parabolic dish a couple of weeks ago I panned around to try to identify the source. I’m almost certain the hiss comes from the sounds of tree leaves rattling against each other in the wind. It only takes a breath of wind to make the leaves rattle, so the sound is almost always there. After the mod, that background hiss was reduced quite a bit. Enough so that I wanted to try it more rigorously out in the field.

Last night conditions were almost perfect. We had a storm system rolling in, the air was still, and the sky was overcast. Perfect conditions for people to stay home, get off the road, and let people like me lurk in the shadows with headphones on. I packed both my Alice microphones along with my SASS and Olson Wing, and headed out to an old cane haul road to record coqui frogs and insects. I was rained out in the end, but even that worked to my favor.

The tests!

Alice with HF EQ vs. Stock Alice

This is an A-B test between the Alice with Ricardo Lee’s HF EQ mod (thanks for the pointer, Homero!) and an unmodified Alice. The mics alternate every ten seconds, with a two-second cross-fade. That’s probably excessive on the cross-fade, but c’est la vie. Keep in mind there was very little wind during the test, so the difference is subtle. But it’s there.

SASS vs Olson Wing

While I was there I also tested the SASS against the Olson Wing. In this case both were populated with Primo EM-172 capsules. After I got home I realized I had wind protection on the SASS, but none on the Olson Wing. So this isn’t a fair test of frequency response, but it should be a fair test of the depth of stereo imaging, and to some degree, sound localization. (The frogs really don’t move around that much.)

I was content to let this setup run for a while, but it started to rain. Without any rain protection on either array, I knew the rain would eventually soak the mics. So I packed it all in and pulled out my rain gear.

Rain Gear

I’m still trying to get a good, clean recording of rain. A while back I took a tip from Gordon Hempton and built a microphone rain shelter. It’s a hard aluminum plate covered with two inches of non-woven air filter material. The aluminum plate keeps the mics dry, and the filter material diffuses the rain drops to a soft “fuff” sound. I also added a layer of carpet foam underneath to cut down on the residual “fuff” sound. It’s set up to take my DIY shock isolator, a small ball head, and my ORTF bar. (Sorry, no pictures of the whole setup just yet.) With the whole mess set up on a tripod or c-stand, it protects the mics from rain while minimizing the sound of the drops hitting the rig.

Finally finally I had a chance to use it in the field. And it worked! It worked great!

Only problem is that I managed to damage one of my EM-184 cardioids while testing the Alice mics. It barely responded at all, and produced a deep wumping noise in the recording instead. So the stereo recording is rubbish, unfortunately. I thought the wump sound was the mic picking up rain drops hitting the tripod legs, so I switched to a c-stand, re-arranged, tied up cables, did all sorts of things. None of it helped. After about half an hour I finally admitted to myself that the mic wasn’t working, and packed it all in.

But the rain gear worked! It worked great!

And once I dried the EM-184 mics out they worked great again, too. (Lesson learned:Don’t let it rain on your mics. DOH!)

All in all it was a good night of testing. I have one other test I’d like to do with the two Alice mics (ocean waves!), and I’d like to do one more side-by-side of the SASS and the Olson Wing to see if I can shorten the length of the Olson Wing and still get a good boundary effect out of it. But I’m pleased as punch with the rain gear.


P.S. I also learned that I need to finish this project before watching another season of Stranger Things. There’s something about driving way the hell out on some abandoned road to some spot in the woods in the middle of nowhere with fog and rain and nothing but the buzz of the insects and the calls of the frogs to… WHAT THE HELL WAS THAT?!

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Whales, Waves, and Unexpected Urination

Posted by Tom Benedict on 12/12/2016

“See any whales?”

I’d been recording at Kiholo Bay for several hours before the man spoke to me, but the first hour had been plagued by technical issues. For some reason my DR-70D kept reporting a write timeout error – something usually attributed to using a slow memory card – but I knew the card was good. Helicopters and airplanes had ruined the rest of the first hour.

At that point I was almost done with my first completely clean hour of waves on my SASS and Mid-Side setup. My other recorder, a DR-05, was positioned at a small beach to the south of me, recording waves receding off of loose pebbles.

I turned around to see who’d spoken to me. He was an older man who’d been hiking along the coast and had stopped to talk. I knew his words would show up on the recording, so I figured if I’m editing I’m editing. I might as well be civil about it.

“No, not from here.”

He nodded and walked on. I turned back to my gear, but out of the corner of my eye I saw him turn and head down to the little pebble beach.

People here are, on the whole, really nice about other people’s stuff. At one point years ago I left some kites at Hapuna Beach, one of the busiest beaches on the Big Island. It wasn’t until I was unloading my car at home that I realized my kite bag was missing. I jumped back into my car, headed back to the beach, and found that someone had brought my kites up off of the sand and left them for me at the showers. People here really are great.

But still… Strange guy hiking down to a beach where I’d left gear… I didn’t want him knocking my gear over inadvertently or anything. So I kept an eye on him as he made his way down to the beach and… proceeded to relieve himself not four feet from where I’d left my gear. Recording sound. All sound. Beach sound. And now his sound. His very personal sound. He kept glancing up at me like I was being rude. I did turn away while he was occupied with his… task. But eventually I knew he’d finish and realize I’d been recording him. Which he eventually did.

One of my more awkward sessions.

(But I got a lot of really good winter wave on rock sounds!)

Anyway, I think I’ve finally answered some open-ended questions about microphones. The Alice microphones I’ve been building are beautiful, crisp, and punchy, but not all that great for recording outdoor sounds. They’re very bright, which works great for a number of subjects. Waves, streams, and wind in the trees just don’t happen to be any of those subjects. Unfortunately those are the subjects I’m interested in.

I also don’t think I’m a huge fan of mid-side recording for creating big spacious soundscapes. No matter how much I play with the balance of mid to side, I just can’t get as much of a sense of space as I do with the SASS. I find myself firmly in the camp of the partially baffled microphone array. So for now I’ll save the mid-side and LDC Alice mics for indoor recording and go back to my Primo-based mics for nature. (Though I still intend to convert my Behringer C-2 mics to surface-mount Alice electronics. They’ll make good instrument mics, if nothing else.)

There’s one last test I want to repeat, though. Early on I built an Olson Wing – a baffled double-boundary array invented by Curt Olson. This pre-dated my SASS. I remember I liked the sound, but that I liked the sound of my SASS better. Now that I’ve had a chance to try a number of other stereo recording techniques (X-Y, A-B, ORTF, M-S, and SASS), I’d like to resurrect my Olson Wing and try it and the SASS side-by-side. I’ve still got all the bits, so it’s just a matter of rigging everything back up and getting out with the gear.

It’s something of a pressing question because of something else that happened. Earlier today my wife bought me an early present: a pair of ammo boxes.

I joked with the kids that they’re for the Zombie Apocalypse. They just rolled their eyes. They know me too well. She got me the ammo boxes for a recording project.

One of the problems with unattended recording is that conditions change, weather turns, and gear gets rained on. My first unattended overnight session wound up that way. I set up to record the dawn chorus in the Upper Waiakea Forest Reserve on International Dawn Chorus Day, but during the night the clouds came in and rained on my gear. The evening chorus was spectacular, but with the rain on the leaf mast making a staccato drumming sound, the dawn chorus part of the recording was practically useless.

My gear survived, but the weather proofing was tentative at best. I’ve been looking for a good way to build a completely watertight, rain proof recording setup. Enter the ammo box.

Ammo boxes are made out of steel. They’re tough. And they have a rubber weather seal that’ll keep out a hurricane. Perfect for cramming recording gear into! My plan is to use the larger of the two boxes to house my gear, and either build an Olson Wing or an SASS around the box, depending on which one I like better. The microphones would be the only thing poking out. Everything else goes inside the box, which can then be latched shut. The whole unit can then be left overnight without any chance of rain getting inside and killing my gear.

Or pee, for that matter.

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Building the MS Alice Microphone – Part 2

Posted by Tom Benedict on 23/11/2016

This is the second half of a two-part article describing my build of the mid-side Alice microphone, following the Instructable written by Jules Ryckenbusch: Build the MS Alice Stereo Microphone. In Part 1 of this article I ran through how I was planning to build it (mostly following the same steps I used in another two-part series I wrote about another of Jules’s Instructables, Modify a Cheap LDC Condenser Microphone, namely: BM-800 Microphone Conversion Part 1 and Part 2.) I also covered my design for the saddle and post that holds the three capsules in the particular orientations required for Jules’s MS microphone build. (Jules used a different method, using PVC pipe, which you’ll see in his Instructable if you decide to build one of your own.)

Since writing Part 1 all the bits and pieces came in. I was eager to see how the 3D printed saddle and post turned out, and how well the TSB-165A capsules fit.

M-S Alice Capsule Saddle and Post - Unpopulated

I designed the cavities for the capsules at-size, meaning I didn’t leave any slop for fit. The plastic Shapeways uses to make their least expensive printed parts is described as “strong and flexible”. I took them up on that, figuring the part would flex enough to allow the capsules to snap into place. It worked like a charm.

M-S Alice Capsule Saddle and Post - Populated

The fit is snug, but not snug enough to hold the capsules in use. As with my first Alice, I glued the capsules into the saddle with E-6000 adhesive.

I’m a little disappointed with the handling noise on my first Alice mic. I chalk some of that up to the metal saddle and post, but some of it I chalk up to the relatively stiff wire I used to connect the capsule to the PCB. It was stiff enough that manipulating the wire wound up breaking off one of the ground tabs from the TSB-2555B capsule I used on that mic. Rather than repeat that experience, and in an effort to reduce conduction paths for handling noise, I gutted some of the Mogami cable I use for all my microphone projects and used the wires to connect the capsules. (NOTE: It didn’t actually affect handling noise that much. After thumping various bits of the mic, I’ve come to the conclusion the dominant frequency of the handling noise is driven by the resonant frequency of the mesh in the headbasket.)

I already had two Pimped Alice PCBs built, tuned, and ready to go for this project. The remaining steps were to screw one board onto each side of the mic frame, solder the capsule wires to the boards, solder the four 0.022uF capacitors between the ground pin (pin 1) and the remaining pins of the XLR connector (2, 3, 4, and 5), and to solder wires between the XLR and the PCBs.

M-S Alice Internals

Since I oriented the two capsules of the figure-eight mic side-by-side, they won’t fit inside the headbasket with the foam liner in place. So I stripped the foam out before closing up the mic.

The very last step was to build the 5-pin XLR to dual 3-pin XLR splitter cable. There are a number of ways I could’ve done this, but I followed (mostly) Jules’s build on the cable as well, using separate Mogami lavalier cables for each channel. This is a wonderfully floppy wire, and does an excellent job of reducing handling noise transmitted through the cable.

The one change I made to Jules’s design was to jacket the central eight feet of cable in a woven sleeve to keep it from tangling.

M-S Alice Patch Cord

I left the last foot and a half at each end loose, though, to take advantage of the wire’s floppiness. (Hey, that’s actually a word spellcheck recognizes!)

And at long long last I’m able to play with mid-side recording and compare it against my EM-172 based SASS.

SASS vs. M-S Comparison

Big big thanks to the following for making this all possible:

  • Jules Ryckenbusch – for writing the two Instructables that got me going on these microphones
  • Homero Leal – for coming up with the PCB layout for the Alice boards used in Jules’s Instructables
  • Scott Helmke – for designing the Alice circuit in the first place
  • Ricardo Lee and all of the above – for their endless patience with all of my questions and what-ifs
  • Dr. Ing – for designing the Schoeps CMC-5 in the first place, without which none of this would exist

For my own contribution, here’s the link to the MS Alice capsule saddle and post on Shapeways. I’ve listed these at-cost, with no mark up (meaning I don’t see a dime of the 5.35 USD price tag at the time of this writing – labor of love).

Have fun recording!


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Building the MS Alice Microphone – Part 1

Posted by Tom Benedict on 11/11/2016

This is a short pair of articles that glosses over most of the details of how I’m building a self-contained mid-side (MS) Alice microphone into a Neewer NW-800 microphone body. Part 1 covers most of the design and preparation, and Part 2 will cover the build.

The reason why this pair of articles is so brief is that most of the nitty-gritty was already covered in another pair of articles: BM-800 Microphone Conversion Part 1 and Part 2. The major differences between that microphone and this one are a change in capsules (Transsound TSB-165A instead of a Transsound TSB-2555B), the number of capsules (three instead of one), the number of Pimped Alice boards (two instead of one), and a change tof XLR connector (5-pin rather than 3-pin).

With the exception of how I’m planning to mount the capsules, all of this follows the Instructable written by Jules Ryckenbusch: Build the MS Alice Stereo Microphone. That’s the real reference for this build, so if you decide to build one of these yourself be sure to follow Jules’s notes.

The easy stuff first:

When I built my first Alice microphone I built three PCBs rather than just the one I needed, so I already have two Pimped Alice boards ready and waiting in the wings. I was on the fence whether to build a second mic around a TSB-2555B capsule or go straight to the MS Alice. After some recent field tests, I decided to commit the two boards to an MS Alice.

Jules pulled a neat trick for getting two signals out of a single XLR connector: use a different XLR connector! In his build he replaced the 3-pin XLR that came with his BM-800 microphone with a 5-pin. The two outputs share a common ground, but have independent signal pins. I’m following this part of his plan to the letter. (As a side note, this also gives me a spare 3-pin XLR connector to use when I finally build out my parabolic mic. New project in the works!)

The only things left to do were to order three TSB-165A capsules (done) and to figure out how to mount them.

Jules has a nice tutorial on how to build a 3-capsule saddle out of PVC pipe, but I had so much fun machining a custom saddle for my TSB-2555B capsule, I couldn’t pass up the opportunity to massively over-complicate life by designing a custom saddle for the MS Alice as well. Here’s what I came up with:

MS Alice TSB-165A Capsule Saddle

Which looks neat and all, but would be stupidly difficult to machine. It’s possible, provided you got rid of, or at least filleted the inside corner between the two side capsules, but it wouldn’t be fun. And since this is all about fun, I cheated. I sent it off to be 3D printed out of nylon. (If this pans out and there’s any interest, I’m happy to make the 3D model available for other people to print.)

So now I’m back to playing the waiting game. I’ve got parts coming in from Redco Audio (5-pin XLR to dual 3-pin XLR splitter cable), Mouser (smaller capacitors for the Alice boards to address the space constraint issue I ran into), Amazon (Switchcraft 5-pin XLR connector, NW-800 body, and associated doodads), JLI Electronics (three TSB-165A capsules), and finally Shapeways (the 3D printed mic saddle).

I’ll write the second half of this series once all the goodies show up.


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A Lack of Noise Measurements

Posted by Tom Benedict on 10/11/2016

When I built the Alice / TSB-2555B microphone, my intention was to get out with my normal recording gear, bring the Alice along, and get some side-by-side nature recordings to demonstrate how good or how bad the self-noise on the Alice is.

I have yet to pull this off. But in the process I became utterly paranoid about my gear, and feared I’d somehow broken it. In the process I made a number of completely useless recordings in the Upper Waiakea Forest Reserve and out on the Cane Haul Road north of Honokaa. I got some really interesting bird calls and some halfway decent coqui frogs, but most of all what I recorded was what sounded for all the world like… noise… (I’m pretty sure it was wind, but I’m giving away the punch line.)

This finally led me to do a series of recordings in the back seat of my car, parked in the relative un-quiet of my yard, under what is finally a wind-free clear night. In the process I think I demonstrated the excellent noise characteristics of the Alice microphone, and I’m pretty sure I recorded my own heartbeat from the seat next to my gear. (Yes, I had the gain cranked up that high.)

I found that the Alice edges out the Primo EM-172 capsules for noise, potentially by more than -3dB. I also found that even at ten o’clock at night there are very few windows of time when cars aren’t going by on the nearby highway. (I also found there’s a limit to how long I can sit still, not tic, and breathe shallow.)

With my faith in my gear restored and an expectation of the performance of the Alice microphone, I’m planning to head out Friday to record inside a lava tube. It’s not the rain recording I’ve been trying to nail for the past several months, but if I manage to get water dripping from the roof into underground pools, I’ll count that as something pretty cool.

This also gave me the confidence to order all the parts to build Jules Ryckenbusch’s MS Alice microphone. I still have mixed feelings about how mid-side is likely to fit into how I record in the field, but I know I’ll have a good mic to try it with.


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Alice and Behringer Sitting In A Tree – Part 1

Posted by Tom Benedict on 03/11/2016

The field tests on my BM-800 Alice conversion will have to wait. Late last week I handed it over to a friend for tests I’m not equipped to make, including several mic comparisons. I’m eager to see (and hear!) his results.

Meanwhile my Behringer C-2 mics showed up. These are the ones I placed a bid on over at Ebay before I realized they were coming from Haifa, Israel. Despite the distance the shipping was actually less than FedEx charges to ship a letter-shaped package from the mainland US to Hawaii. (Go figure.) It still ramped the price of the mics up almost to market value, which on Amazon with its super saver free shipping basically means I could’ve ordered them new and had them weeks ago.

But they’re here. And they’re mine. And… to be honest they’re in pretty ratty shape. One of them had something loose in the capsule. If you pointed the mic up and shook it, it made a hellish noise and clipped constantly. Turn it upside down and shake, and you hear something rattling around. The other mic has something massively wrong with its circuit board. It sounds for all the world like a Huey is hovering overhead. Bup bup bup bup bup bup bup… It never ends.

So long story short, I don’t mind gutting these things and building something new. In the short term I put the good capsule on the good mic body so I have one working mic to play with. The other one I started taking apart.

Behringer C-2 Capsule Removed

These have interchangeable capsules, though I don’t know if Behringer (or anyone else) makes any other capsules for it. The one that came with my mics is a hypercardioid. (At least that’s what the icon on the side of the capsule looks like.) Given the size of the vents at the back, I can believe it.

Underneath the capsule is a white plastic plug with a pogo pin centered in it. Not much to look at. And no real clue how to open things up past there.

To gain access to the innards of the mic, peel back the the “Behringer Condenser Microphone” name tape at the base. This reveals a small set screw that should be familiar to anyone with Switchcraft XLR connectors. Screw the set screw all the way in. This releases the XLR connector from the body. Next, center the pad/high-pass filter switch and pull the switch button out with needle nose pliers. Finally, push on the white plastic plug to expose the circuit board.

Behringer C-2 Stereo Pair - Partially Disassembled

Here’s what’s inside:

Behringer C-2 PCB Top

Since one of my mics has a damaged board, rather than figure out how to tweak what’s already here, I went ahead and tried to figure out how to pack a Pimped Alice into the same board space. I started by taking measurements.

The board is 15.5mm wide x 52.35 mm long, and is 1mm thick. The thickness is important because the board slots into the white plastic insert. One nice thing about this method of mounting the board is that there are no screw holes, and except for the humongous XLR pins and the 2mm area that slots into the plastic insert the rest of the real estate on the board is free. The board is mounted just below the centerline of the mic, so there’s vertical room as well. Up to a point, anyway. Those capacitors are 6.5mm diameter x 8mm tall. Nothing bigger than that will fit, even centered on the board.

There’s really not enough room to use through-hole components everywhere, so I converted most of the Pimped Alice circuit to 0805 SMT components. The exceptions are the filter capacitors, the 1Gohm resistor, and the FET.

There seems to be some resistance to using surface mount technology for DIY mics, but SMT has been used for over a decade for DIY robotics and electronics. I’ve built AVR processor boards using SMT components, and figured this wouldn’t be much different. With the exception of the big filter caps and the FET, that’s how Behringer built the original board for the C-2, so I figured it was a safe way to go. As soon as I have a new PCB layout, I’ll send it out for fab.

Meanwhile I started taking apart the capsule. Just looking through the grille, it seems like the C-2 uses a Transsound capsule similar to the TSB-165A Scott Helmke used in the original Alice.

Behringer C-2 Capsule Front

I started by removing the back plate. This is just pressed into place, but it’s a bear to get out. I eventually removed it by gripping it by an inside edge with needle nose pliers (pushing outward), and spinning it out. It took a couple of attempts, but it came apart.

The rear side of the capsule has an open cell foam washer in it, presumably to provide wind protection and to act as a delay plate to shape the hypercardioid pickup pattern. With the washer removed, the back side of the capsule is visible, held in place by a brass retaining ring

Behringer C-2 Capsule Back - Baffle Removed

The holes in the ring are really tiny. My existing pin wrench didn’t work, so I used an old divider with dull points as a pin wrench. There’s a bit of red enamel to prevent the ring from backing out, which took a little force to crack. Once that was done, though, the ring backed out easily. (I’ll need to be sure to apply a fresh bit of enamel when I get the new capsule installed.)

Behringer C-2 Capsule Disassembled Back

Behringer C-2 Capsule Disassembled Front

I was hoping the capsule was a Transsound TSB-165A, the same one Scott Helmke used in his original Alice microphone. Unfortunately it’s not. The capsule in the C-2 is 16mm in diameter x 6mm thick. The TSB-165A is 16.5mm x 8mm. But after some poking around on the JLI Electronics web site I think I found a match: the TSB-160A. The specs are almost identical to the TSB-165A, so it should play nicely with the Alice circuit (yay!), but the form factor matches what’s in the C-2. I’ll order a pair of these when I place the order for the 165A capsules for my MS Alice.

Behringer C-2 Capsule Mesh Outside

Another concern with the C-2 capsule holder is how the capsule is recessed, and how close the edges of the holder come to the input ports on the capsule. From my experiences with my first rev of mic bodies, I know that can color the sound enough to hear it. I’d like to open this up, if possible. It’s a simple enough job on a lathe as long as I can get the grill out.

Behringer C-2 Capsule Mesh Inside

The grill looks like it’s a two-layer mesh that’s either glued or soldered into the capsule holder. That should be easy enough to remove with heat, one way or the other. I might even be able to re-use it if I’m not too rough getting it out.

The grill serves two purposes. First and foremost, it’s an RF shield to keep stray electromagnetic radiation from getting into the signal path. Second, it helps to keep the capsule free of debris. Third, some manufacturers will stick enough mesh in front of the capsule to act as a rudimentary pop filter, and at least reduce the effect of wind. The problem with that third purpose is that you need a lot of tight mesh to pull that off. Enough so that it colors the sound of the mic. Not surprisingly, one of the more obvious mic mods is to remove a layer of mesh from the capsule housing.

But given how open the outer mesh is, I’m afraid it will make the mic prone to RF interference. For now I’ll leave it alone.

The next steps are to finalize the design of the new board, send it out for fab, and source all the components and capsules. But before I can finalize the board design I want to see if I can add in one of the features of the C-2: The switch on the side of the mic lets you select a high pass filter or a -10dB pad. If I can find the real estate on the board to accommodate the switch and the components necessary to add these into the Alice circuit, I will.


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