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DIY live sampling mic





For my live sampling tools Slice//Jockey and InstantDecomposer, I wanted lightweight microphones with the following qualities:

Turned out that such mics are nowhere offered for sale, so this became another DIY project. Crucial element is a unidirectional electret capsule, like shown on the picture below. Tuned vent ports in the back create phase effects which result in directional response: the front side is more sensitive than the rear side.








The pictured capsule is a Panasonic WM-55A103. This capsule is unfortunately discontinued, but Monacor's MCE-404U has identical specs, and is also sold as MP33619 by Farnell. Frequency response is plotted in the datasheet excerpt shown below. Zero degrees is front and 180 degrees is back.








Over a wide range of the spectrum, the rear side is ~12 dB less sensitive than the front side. Sure it does pick up sounds from the back, but with a factor 4 amplitude difference. To make this work properly, the microphone housing design should not obstruct the capsule's rear side.


materials and tools


Basically, my microphone housing is a tube with big holes drilled in the region where the capsule will be mounted. This tube is copper or aluminium in order to provide electromagnetic shielding.








Used bicycle tire inner tubes in different sizes are components in nearly all my DIY projects. Amongst other things, they replace rubber bands for better durability.








Wire from scrapped equipment is useful for simple purposes. In contrast, good quality shielded signal cable is rarely found just somewhere, and this is better purchased from renowned brand (like Tasker).









Stereo mini jack plugs are used for connection with onboard mic input or simple external sound cards like iMic.








Imitation fur is used for wind protection. It comes in many colors and 'hair cuts'.









Added a few small things like nut and bolt, a piece of foam and a stitching thread. These are all the materials that go into my mic:







The picture below sums all the tools I use for making my mics.






construction

So it starts with a simple piece of metal tube (copper or aluminium), with about 20 mm or 3/4 inch inner diameter to accommodate the capsule. Length can be anything, and I settled for 110 mm to make it small but still convenient to hold. Three big holes (10 mm) are drilled for the air to vibrate freely around the capsule's rear side. Three smaller holes (4 mm) will receive the capsule suspension.









A unidirectional electret capsule is soldered to asymmetric shielded signal cable (4 mm diameter). An extra length of isolated wire (the blue one here) is soldered to the cable shield, and will later be connected to the microphone housing for electromagnetic shielding.









The cable is embedded in a piece of foam, which will later be inserted into the metal tube.










The capsule suspension is cut out of thin bicycle tire. The center hole is done with a punch of slightly smaller diameter than the capsule itself.









The whole set is then inserted into the tube. The three ends of the suspension rubber go through their holes, and are held in place with a rubber band.










It is important to connect the cable shield and the capsule's ground terminal to the metal tube. Otherwise the tube can not function as electromagnetic shielding. An extra length of wire was already soldered to the cable shield for this purpose. The wire can not be soldered to an aluminium tube. With copper tube it will be hard to solder too, because the tube is to heavy for a fine soldering iron. Therefore I use a 3 mm nut and bolt in either case, to hold a (homebrew or official) solder terminal.








Alternatively you can use the metal part of a luster terminal as a combined strain relief + ground connector, like illustrated below:








At the other end of the signal cable comes the mini jack. These plugs are notorious for their flimsiness. Theoretically, an all-metal plug is best. But look in the picture below, how the rings in the metal plug are unaligned. Do never force a plug into a sound card input, if it does not fit well. Sometimes it helps to shape the insulation rings with a very sharp knife.















The mics are now almost complete, apart from their wind screen.









wind screen


A live sampling microphone should be useful for vocals too, so it needs protection from popping noises. The easiest remedy is an imitation fur wind screen like reporters use them for outdoor recordings. With the mic housing completely covered, it has the extra advantage that handling noise is reduced too.

Imitation fur comes in different qualities. I found that it is not so much the hair length but rather the density which counts. In the example pictures below, the blue fur has longer hair, but when it is held against the light you can look straight through it. The beige fur has shorter hairs but better density. This is the preferred material. Of course the fur must still let air through. The idea is that it must stop gross bursts of airflow, but allow vibrations. Compare with a capacitor, which stops DC and low frequencies, but lets higher frequencies through.



 




The fur is stitched by hand, inside out, and then reversed.








With an imitation fur wind screen, the mic can be used for ultra-close miking of vocals. You can 'eat the microphone' as they say. For this reason too, it is best to have short haired fur which doesn't tickle your nose so much.

The fur wind screen will definitely influence frequency response. Each type of fur has it's own characteristic. To an extent, the influence may be compensated with equalizing.