DIY Miniature Omnis

in Blog

18 May 2012

For a while now I have been looking to buy a pair of miniature omnis so I can make nice recordings with my handheld sound recorder without having to carry lots of equipment. I’m glad I didn’t buy any because I just discovered that you can make your own low noise omnis for not a lot of money at all.

New product by making-sound.co.uk:

MINI-PIP – stereo phantom power adapter for electret capsules
This allows you to plug any electret microphones or capsules into professional 48V phantom powered microphone inputs.

There are various articles online about how to build your own binaural microphones for field recording. If you have a portable recorder with plug-in power, they are easy to make. All you need to do is solder a couple of electret capsules to a stereo minijack socket. If you want to plug them into professional 48V phantom powered XLR inputs, then you need an adapter like this one.

Most articles recommend the Panasonic WM-61A miniature omnidirectional electret capsule. But I found that the Primo EM-172 capsule has a reputation for particularly low self noise which is important for the kinds of recordings I’m likely to make (I record quiet sounds more often than loud sounds). They are slightly larger than the Panasonic capsules (10mm diameter vs 6mm), but I can live with that.

I bought the Stereo Microphone Kit of Parts with Primo EM-172- Z1 capsules from FEL Communications Ltd in Middlesex, UK. A day later they arrived. I didn’t think they’d be much good, but at £25 for the kit, worth a try. It turns out they are very good indeed. Here’s how I made them.

The kit comes with two Primo EM172 electret microphone capsules, cable, stereo minijack plug and a simple instruction sheet. All the parts in the kit are good quality (I prefer right angle minijack connectors, so I swapped the perfectly adequate straight minijack with a right angle minijack I already had). The cable is particularly nice, being thin and flexible. To house the capsules and wiring, I bought two 6.35mm jack sockets from Maplins and discarded everything but the barrels. Helpfully, they come with red or black stripes to distinguish left from right.

The cable stripped easily and I bent the bare ends 90 degrees so that they would be easier to solder onto the capsules.

I used heatshrink to protect the cable and to insulate any exposed copper from the metal barrels.

Once the capsules were inserted into the metal barrels, I filled them with hot glue. I did try mixing some epoxy resin for this, but it was too thick and would not pour into the barrel.

A couple of spare foam windshields provide effective protection from the wind.

After a few quick test recordings around the house, I am very happy to say these microphones are brilliant. They sound nice and and their noise floor is low. Whilst I wouldn’t record classical recitals with them, they certainly are good enough general purpose use (recording random things when out and about).

These EM172 miniature omni mic capsules are a bargain. Having used various ‘professional’ miniature omnis from other manufacturers, my opinion is that one would have to spend much more money to get a better out-and-about-recording mic.

Add a phantom power adapter and these become a very versatile and compact recording solution.

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