Anybody who has tried to record sound outside will have run into wind blast, the dreadful rumbling sound that can overpower the sound you want to record, as the wind catches the microphone diaphragm and distorts the signal.
Because this noise is much larger than the wanted sound, it is very intrusive, and it cannot usually be filtered out post recording. One option is, of course, to choose calm days for recording outdoors - a breeze of less than 5 m.p.h. can be dealt with by the foam 'windshields' provided with most microphones.
If you look at the microphones used by film and TV recordists, you'll observe that you don't normally see the microphone at all, it is enclosed in a large furry device. This is balled a basket suspension.windshield, and does two things. One is, of course, provide wind protection, the other is to provide some shock reduction to reduce handling noise.
How Microphone Wind Protection Works
The aim of the basket system is to create a zone of still air around the microphone. The larger this zone of still air is, the better, but there is a trade-off in making the rig manageable, so the zone of still air is typically 4-6 inches in diameter. The microphone is suspended in the middle of this zone of still air, inside a mesh basket which largely lets the sound in.
On its own the mesh basket would let the wind in as well, so it is covered with a closely woven fabric that is designed to reduce the wind velocity to almost zero, but have enough closely spaced holes to allow sound through. The shape of the basket should be rounded to minimise chuffing noses from turbulence on the structure. This results in the cylinder with hemispherical ends shape of the systems used with the medium shotgun microphones commonly used with booms for outside broadcast work.
Most of the work is done by the basket covered with material. For really high winds, the wind needs to be diffused before it gets to the basket, which is why they are sometimes covered in a synthetic fur, which softens the wind and reduces turbulence on the basket structure itself. You do sometimes see basket systems used without the fur cover.
Obviously the more material you but between the sound sound and the microphone the more risk you take that the sound will be modified, and the usual effect is a loss of high frequencies relative to low frequencies. Professional systems keep this low, less than 3dB @ 20kHz relative to low frequencies, but if you are trying to record in really high winds you will have to accept more loss of HF.
Improvising a Microphone Basket Windshield using Low Cost Readily Available Materials
There are two challenges to make a basket windshield,. One is to make the basket frame, and the other is to find a suitable material for the fabric skin of the windshield. Suitable candidates for both these materials can be found at a garden store. Plastic netting can be used for the cylindrical frame. Most microphones are end-firing, so for the hemispherical mesh you can use a small kitchen strainer, or shape the plastic netting ends to round the ends off. Plastic is better than metal for both the netting and strainer as it does not twang under the stresses of the wind. The microphone can be suspended in the netting cylinder using rubber bands or more durable elastic from a model shop.
Use Horticultural Fleece or Weed Control Matting for the Fabric Cover
For the fabric covering, gardeners have similar requirements to recordists - they need a fabric than keeps bugs out but lets the rain in. Horticultural fleece makes a good covering for moderate winds, if more wind protection is needed then weed control matting is a more substantial alternative. Fleece is usually white and weed control matting is usually black. You can test if the material will pass sound by exhaling through it - your breath will pass through. Fleece loses very little high frequency sound, the weed control matting does lose some top end, but is quite acceptable on voice.
The matting should be stretched tightly and soft twine used to hold it to the frame, it is important that there are no loose flaps of material that are not held by the twine. Some creativity is needed to take the microphone cable out through the material and to form a handle that can be attached to the frame with twine. One end may need to be detachable if the microphone is internally powered and needs to be switched on an off. A P48 phantom powered or plug-in-powered mic is definitely an advantage.
Commercial basket systems have engineered plastic clips to hold things tightly and yet allow easy opening, but this is harder to do on a DIY job. Only the back end needs to be openable, so if you have to tape it up this won't interfere too much with the sound.
DIY Wind Protection is a Big Improvement, But Less Convenient
If you're short of cash this will get you recording outdoors in most situations without the infernal wind blast ruining your takes. There is a balance between paying for the convenience of a pro basket system that can easily run to the same cost as the microphone, or the fiddly nature of the DIY approach. The materials are cheap, however, so if you can't afford a professional blimp there is still no reason why you can't record outdoors!
Richard Mudhar - Originally from London, now enjoying a less hectic pace of life in Suffolk, Richard Mudhar is a keen wildlife sound recordist and ...
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