The View Up Here

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

Archive for June, 2016

DIY Wind Protection for Custom Microphones

Posted by Tom Benedict on 19/06/2016

With the exception of some heavy-duty rain protection that I’ll need to build in order to get a set of sounds I’m after, I think I’m zeroing in on a field recording setup I’m happy to use for the foreseeable future.

DIY-SASS Wind Protection

The last(ish) step was to add real wind protection for the microphones. In the past I’ve used whatever I had on-hand to protect the microphones from wind: my t-shirt, my fleece, the headrest covers that came with the seat covers for my car, etc. They worked, but they weren’t pretty and they were a little frustrating to use. When tying a shirt onto a microphone it’s easy to leave gaps that wind can get through. After adding the anti-vibration mount I figured enough was enough. Time to make proper wind protection.

I made this out of the thinnest “wetsuit” material I could find. (Real wetsuit material uses closed-cell Neoprene foam. The core in this fabric is open-cell foam that bears a strong resemblance to foam microphone covers.) It costs some high frequency response, but the EM172 microphones are already pretty bright. I consider it heavy-duty in that it’s tough to breathe through this fabric, but most of the recording I’ve been doing has been in areas I’ve flown kites in the past. Heavy duty isn’t necessarily a bad idea. It’s removable, so if I record in an area that doesn’t need this level of protection, it’s easy enough to remove.

I’d do a whole write-up on how I did this, but it’s basically sewing. There’s not much point in posting the pattern, either, since it’s designed around this particular microphone array. This whole setup started life as a 3D CAD model. That provided me with a cut list for building the microphone array out of plywood, foam, and sheet metal. That same CAD model provided me with a pattern for making the wind protection. This material is pretty easy to work with, though hems tend to be a little fat. It doesn’t respond well to ironing, so all of the hems were done using pins. Lots and lots of pins. You do what you have to do to work with the material at hand. At some point I’ll make a fuzzy to go with this for when it’s really howling. But for now I think I’m done.

Last night I took the whole kit ‘n kiboodle down to Kua Bay to record the summer surf. Kua Bay is a white sand beach that’s exposed to open ocean. There is a reef, but it’s deep enough that waves break on the sand rather than out on the reef. When the waves come out of the right quarter they can break left-to-right, right-to-left, and across the entire beach one right after the other. The conditions last night were perfect. The gates close at 7pm, so by the time I got there at midnight the place was completely deserted. I set up my gear, grabbed my book, and walked off to enjoy the moonlit landscape while the recording gear did its work.

I’m pleased by how things turned out. And you can’t beat a deserted beach on a moonlit night. I had a blast.

Tom

Advertisements

Posted in Audio, Engineering | Leave a Comment »

An Inexpensive Shock Isolation Mount

Posted by Tom Benedict on 17/06/2016

One of the problems with building a funky microphone setup is that off-the-shelf gear won’t always work with it. It’s pretty straightforward to find wind protection for a shotgun mic or for a single omni. No one makes wind protection for do-it-yourself SASS arrays. (And no, that’s not what this post is about. That’s still a work in progress.)

Up until now I’ve run my DIY-SASS without shock isolation. It’s worked after a fashion, but any time I position my gear in foliage I wind up with tap-tap-tap noises of branches or long grass touching the tripod legs. More than one person has pointed out that even rudimentary shock isolation would get rid of most of that.

Unlike wind protection, it’s possible to adapt other shock isolation mounts to my DIY-SASS. Any of the lyre-style mounts for handheld recorders would work fine. But most of these are relatively tall. I wanted something more compact. And cheaper, if I could swing it. Here’s what I came up with:

Microphone Shock Mount Top

It’s adapted from an anti-vibration camera mount for a multi-rotor. As I received it, the mount consisted of two carbon fiber plates with four vibration damping balls (yes, that’s the real term). The balls are replaceable, and can be swapped out for harder or softer ones. The mount had 1/4″ clearance holes top and bottom. I wanted this to fit between a tripod and my DIY-SASS, or between my DR-70D and my DIY-SASS, so I needed a threaded hole on the bottom and a threaded thumbscrew on top.

Microphone Shock Mount Bottom

Adding a threaded hole to the bottom was relatively straightforward. This would’ve been prettier with a round piece of metal, but I had the plate stock in-hand, and it was almost the right size. I squared it up, transferred the hole pattern from the carbon fiber plate to the aluminum, and added a 1/4″-20 threaded hole in the middle.

Adding the thumbscrew to the top was a little more involved. I had some 2″ 6061 aluminum round on-hand, so I knurled it at that diameter, faced off the front to leave an 0.250″ diameter x 0.375″ long boss, and threaded it with a 1/4″-20 die.

Normally you’d want to single point thread a boss like that to avoid all the normal ills of die cut threads: drunken threads, off-axis starts, offset threads, etc. But since this only had to screw into a 1/4″ T-nut to hold my microphones in place, a die cut job was fine. I parted the thumbscrew off the bar, flipped it around, and faced off the other side.

The damping balls that came with the mount turned out to be a pretty good match for my DIY-SASS. I’d have to swap them out for softer ones if I used it with my DR-05 handheld recorder. But since this is probably going to be a permanent addition to my DIY-SASS, it’s fine as-is.

I finally had the opportunity to test this in a systematic way. I put two contact mics on my tripod legs and tapped the center column while adjusting the gains on those channels until they both read the same. Then I moved one of them to the top of my SASS and tapped the center column to see how much attenuation the isolator provided. I recorded both configurations so I could compare in Audacity. The isolator very consistently provided 21dB of attenuation. I don’t know how that compares to a commercial isolator like one of the lyre mounts I mentioned earlier, but it’s a darned sight better than the zero dB attenuation I’ve had up to this point.

I always feel a little weird posting a DIY that requires the use of a machine tool. In this case it involved both a lathe and a mill. But the core idea of this is to adapt a multirotor camera mount to microphones for field recording. There are other ways to get that threaded hole and thumbscrew. Imagination and ingenuity are powerful tools of their own.

Have fun!

Tom

Posted in Audio, Engineering | Tagged: , , , , | 2 Comments »

A Self-Contained Stereo Field Recording Setup

Posted by Tom Benedict on 16/06/2016

A project I’ve been working on more or less led me by the nose toward a type of field recording I really enjoy doing. The project requires relatively long recordings of an ambient soundscape – an hour or longer. The recordings must be in stereo, and ideally serve to put the listener in the soundscape as completely as possible.

Because I can never really stop making noise, especially now that I’ve developed some rather energetic motor and vocal tics, the only way I’ve been able to pull this off is to set up my gear, leave it for an extended period, and recover it later. This drop and recover technique works great for these extended soundscape recordings. But because I often have to hike in for an hour or more to reach the locations I record in I’ve tried to shrink the setup as much as possible, resulting in a relatively compact arrangement. Here’s what I’m using at the moment:

Self Contained Stereo Recording - Front

It’s a self-built pseudo-SASS microphone array sitting on top of a vibration isolator that was made for attaching cameras to multirotors, which is then attached to my Tascam DR-70D recorder.

The vibration isolator took some modification to make it work for this application. I added a plate to the bottom that has a 1/4″-20 threaded hole in it. This lets it mount to practically any tripod or light stand, or to the top of my DR-70D using the camera attachment that came with it. The top of the mount had a 1/4″ through hole in it, but I had to make a big aluminum thumbscrew so I could thread it onto my DIY-SASS. It’s barely visible between the rubber balls on the shock mount in the photo above.

Self Contained Stereo Recording - Rear Quarter
In order for the shock isolator to work well I needed to use very flexible XLR cables to connect the mics to the recorder. And to keep things compact I needed them to be short. These are two things that make for some really hard to find cables. So like most of my gear I rolled my own.

The connectors are all from Neutrik and the cable is some leftover Mogami cable I had from building other sound bits. I really like the right angle female Neutrik connectors. They’re just as easy to use as the straight variety, and you can set the angle at which the cable comes out of the plug when you build the cable. I set mine to come out 45 degrees to the right to make the cable run a little cleaner and to clear the controls on my recorder.

Self Contained Stereo Recording - Back

The whole thing acts like a big wooden bobble-head doll. There’s not a lot of damping in the isolator, just a lot of spring, so once you thwack it it bounces around for a while. I’ll have to see how that works out in the field. Just testing indoors, though, the isolator does a good job of minimizing coupling between the tripod legs and the microphones. This should help minimize noise from grass, twigs, and branches that tap against the tripod legs during a recording. (This naturally occurring handling noise has ruined several recordings I’ve made in the past.)

The one obvious problem with this setup is that there’s no real way to monitor while recording. But since I’m leaving my gear in the field and walking away from it, it’s not really an issue for me.

I’m still working on wind protection. For light wind I have a lycra slip cover that goes over the pseudo-SASS. But for stronger wind I’ll need something more involved. (Hey, more problems to solve! My favorite!)

Tom

Posted in Audio | Tagged: , , , , , | 8 Comments »

SPIE 2016 – Poster Done Too

Posted by Tom Benedict on 09/06/2016

And now the poster’s in the bag, too.

SPIE 2016 Astronomical Instruments and Telescopes - Poster

It’s not my most visually appealing poster, but the subject matter doesn’t really call for a lot of elaboration. It’s mostly a data dump of all the spectra I took over the past several months. Just for grins, the bar at the bottom is a gallery of all of the samples photographed with my NIR-converted A2200 point ‘n shoot. (Yes, this actually factors into the paper.)

The two columns on the left contain spectra from all of the samples, scaled from 0-50% reflectivity. The two columns on the right are where the good stuff is: With the exception of the bottom two graphs, it’s only the materials that reflected less than 10% of the light across the whole spectrum. That’s where the useful materials are.

So why include the others? Those are the ones to avoid! The paper wouldn’t be complete if I didn’t include them. Unfortunately, some of the materials we’ve been using for years for stray light control fell into the “avoid at all cost” columns. Bummer. But now we know better.

The poster is printed, and I shoved it in the mailing tube with all of the other posters from our group this morning. All that’s left now is to get my butt on a plane to Edinburgh and present the thing.

Hip hip hooray! Scotland, here I come!

Tom

Posted in Astronomy | Tagged: , , , , , , , | Leave a Comment »