I have mentioned before the idea of stealth recording with my DIY omni mics (The Sockpuppets) stuffed into the mesh side-pockets of a backpack I have - and today, I tried just that.
In the clip below, I am walking down a busy pedestrian street (I was in a bit of a hurry) with a mic in each side-pocket, recording to my PCM M10. In reality, this is a sort of hybrid between a Jecklin disc and A-B stereo - with the backpack separating the mics physically to some degree.
Due to the way the capsules are mounted in the windscreens, and the way the windscreens are placed in the mesh pockets, the capsules are actually pointing upwards. This may have an effect on the sound, but perhaps more critically, there is rather a lot of fabric around the mics, which does seem to muffle the sound some. Or perhaps I don't know these mics and their sound well enough yet.
Still, this was an interesting thing to try, and it is not the last time I do it either. Has potential.
The main reason I built my stereo set of omni mics using Primo EM172 capsules, was that I wanted to be able to better do stealth recording. Better, as in better concealment (waving a handheld recorder around can hardly be described as stealth recording) - and better stereo spread that what is possible with the built-in omni's of the PCM M10 I use.
But anytime you bring mics out in the open, you need windscreens. I have been doing a lot of thinking on how to do this in a way that is inconspicuous in a public location, that offers sufficient wind protection in most cases, and which costs peanuts.
Since I have a backpack that has symmetrical side-pockets made of black nylon mesh, I figured - why not hide the mics in those? That's almost a foot of separation ( sort of like a bloated dummy head) and adequate space to hide small capsules. I could even scout for good recording locations just by walking around with my cans on, press record on the M10's remote, then just stand still and get a take. Veeerry neat - if it works.
Windscreens first: I had sort of surmised that nylon stockings could work as screen material. It is closely weaved, but by stretching it, you actually open up the mesh, allowing more wind in. It seems, that by varying the number of layers of material and/or the amount of stretch, I should be able to tailor wind protection to my needs. And, since I'm married, material cost in this case - is zero. Nylon stockings don't last forever, you know.
But what to stretch the stuff out over? I had a hard time finding the right approach - after all, it had to be durable, wind-transparent, resistant to moisture, light, easy to work with - and cheap (or free). I thought about building a frame from insulated solid-core electrical wire, or maybe chicken-wire - but those materials have the disadvantage of being easily deformed (and not easily re-formed).
I really wanted something along the lines of the plastic mesh used on Rycote products, so imagine my joy when I found almost exactly that: A roll of plastic mesh of the kind you put in your rain gutters to keep leaves and other debris from clogging up your sewers! 15 centimeters wide and 6 meters long, a roll costs the equivalent of 6 USD where I live.
Construction I just wanted to slap something together in a hurry as a sort of proof-of-concept. I cut two pieces of mesh just large enough to form cylinders around 7 cm tall and about 5 cm across. These will fit into the side-pockets of my backpack. Then, with 4 very standard household rubber bands, for each windscreen, I concocted a suspension for the mics inside the mesh cylinder. Fiddly to do, and it doesn't hold the mic completely securely in place, but it will do for testing purposes. Also probably works reasonably well as a shockmount. Lastly, I just pulled a stocking over each cylinder, taking care not to stretch the fabric.A different view of the rubberband suspension
Initial testing To figure out if I was getting any wind protection at all with this thing, I performed a simple test: Fit one of the mics with a windscreen and left the other without. Hook up the recorder, on with the cans - and then lightly blow in the direction of (not into!) each mic, at equal distances (about a foot). There was a very audible difference, as the unprotected mic crapped out completely, while the protected mic did not. Hurrah!Sockpuppets with new friend Sony. Rubberband around one windscreen denotes left channel mic. Gotta love that aesthetic.
Field testing Today was a frosty, low winds kind of day - a good starting point for a field test of a light wind protection scheme. The "sockpuppets" as I have named them, should at least be able to handle this. Out in a nearby valley I went, strapped the puppets to a branch about a foot apart, and pressed record.This area had some crows doing a bit of talking, plus a faint roar of a highway a couple of miles away.
As you see, the config was AB stereo with a distance of about 40cm. The Sensitivity on the M10 was set to Hi, and the gain was set to 7.
Clearly some audible hiss, but this setting is probably beyond what one should expect of cheap electrets into a cheap (but rather quiet) recorder. Still, I wonder what would happen if I actually supplied the 5V quoted in the EM172 datasheet as the ideal plug-in-power? I'll have to try it.
The windscreens did fine, by the way. The wasn't much wind of course, but even minuscule wind movement tends to set sensitive membranes off in cough-up-your-lungs kind of fit - and I heard none of that in this recording. A good enough result, that I will be working on improving the concept.
When I think of how long it took me to solder the capsules up (about 15 minutes) and how long it took me to make the windscreens (about 10 minutes) and how much it all cost me (maybe 50 bucks), then there isn't much excuse not to try these - especially if you have a recorder without XLR inputs.
However much I love the sound of the omni capsules on my Sony PCM M10, there is no getting around the fact, that they are a little too close together for a spaced omni pair. So I began looking for an external option and found this: http://www.micbooster.com/products/diystereomicroph.html (through the site of Zach Poff actually: ).
Apparently, the EM 172 electret capsules from Primo are used in some rather costly equipment and have very low self noise - datasheet says an S/N of 80db, 1kHz A-weighted. I ordered a kit.
Today, several months later (ahem), I soldered the things together - and let me just say; the whole thing turned out a LOT uglier than the work of mr Poff. Not really pic-worthy, but I'll probably put one up anyway.
They run on plug-in-power from the 3.5 mm jack on your portable recorder, but according to the datasheet, they need around 5V to be happy. That is more than My Sony will deliver (I think). Plugging them in, I did get sound, though - but seemed darker and definitely noisier than the internal omni's on the Sony. This is supposedly due to inadequate plug-in-power. Update: Upon playing with these a bit more, I realized there is simply more gain, when using the Primo's with the Sony, than with the internal mics. When taking the headphone level down a bit, the signal-to-noise ratio sounds subjectively the same.
I'll get a test-recording up here soon. Maybe I'll have to build a dedicated battery-box for these mics.
