Of course, our customers use their microphones even during the Covid-19 pandemic. But microphones--especially those used for close-range speech or vocal recording--require special care to avoid carrying the virus from one user to the next. Here are some tips on how to minimize this risk, based on our knowledge as of July, 2020. Please follow the current recommendations of your local health authorities.

use of plastic bags

This is no time to be delicate; the main risk comes from the spit that everyone has in their breath to some extent. Droplets of spit can be so small as to be nearly invisible, but they carry viruses among other things. Thus the immediate goal for health purposes is to prevent those droplets from landing on the surface of a microphone, where they could be passed along to the next user of that microphone, or to the engineer who handles it. A thin plastic bag pulled over the microphone, neither too tightly nor too loosely, will effectively protect the microphone.

See www.bonedo.de/artikel/einzelansicht/lassen-sich-mikros-mit-plastiktueten-vor-viren-schuetzen.html for the photos, even if you don’t understand the German text.

(The article is mainly concerned with reporters’ use of hand-held microphones for interviews, but the same principles apply elsewhere as well. The bag should be as thin as possible for minimum effect on sound quality, but it must be free of holes. And while the article doesn’t mention this, the bag must obviously be changed after each person uses the microphone, or else it itself will become a vehicle for contagion.)

The plastic bag changes the transfer function of the microphone, so this method should only be used if absolutely necessary. The thicker the plastic bag, the greater the risk of disturbing resonances and a loss of higher frequencies. When using a plastic bag, the directivity at lower frequencies decreases significantly, especially if it is very tightly stretched. This is illustrated by the following measurement:

use of wind & pop screens

If a pop screen doesn’t cover the entire microphone, it will not protect the microphone sufficiently from the attachment of viruses. Thus it is no substitute for a plastic bag. If a person sings or speaks into a pop/windscreen at close miking distance, the screen must be cleaned sufficiently after use; see below. Alternatively, the virus will die in a few days if the windscreen is set aside in storage. The easiest way is to use only one windscreen per person. Most foam windscreens are not expensive and can be delivered quickly.

Cleaning a windscreen

Windscreens made from plastic and other solid materials can be cleaned with cleaning agents or disinfectants (e.g. 70% Isopropyl) with no problem. Foam can be carefully washed with warm water and mild detergent and dried at up to 70°.

Information from Rycote for windjammers: "We recommend only hand washing with either lukewarm or cold water in a mild detergent. Then allow the fur to air dry (NEVER tumble dry your Windjammer), and then brush out to avoid the fur becoming matted".

Many plastics are generally not explicitly UV-C resistant. It is assumed that the plastic can at least change colour and become brittle.

Cleaning the microphone

The microphone housing can be cleaned with a cloth moistened with 70% Isopropyl. Other alcohol-based cleaning agents can destroy the paint. Do not soak the cloth in cleaner or disinfectant, however. To prevent damage, great care must be taken to ensure that no liquid gets inside the microphone or (especially) reaches the diaphragm inside the microphone capsule.

The most reliable way to make sure that a microphone is virus-free is to store it for a long enough time, i.e. for several days after use.

The virus dies off much more quickly at higher temperatures. Our microphones are heated to 60° C (140° F) during manufacture (“artificial aging”), so we know that a temperature of 50°- 60° C will not harm the functioning of the microphone.

Disinfection with UV-C

Many plastics are generally not UV-C resistant. It is assumed that the plastic can at least change colour and become brittle. Paint manufacturers warn that UV-C can destroy the paint. It can be assumed that the coating can at least fade and become brittle if exposed to UV-C for a long time.

UV-C tests at Schoeps
there was a UV-C lamp both above and below the product. The distance between the lamps and the product was about 4 cm. Two lamps with a wavelength of 254nm and 24W each were used, with 7.3W radiation acting on the products. The irradiation time was 30 min and 60 min.

Many thanks to Gilles Tête de Mort, who made this test possible.

During our tests with UV-C radiation we could not detect any significant effects on plastics and varnishes. Only the development of odours over a long exposure time (60 min) indicates that the foam and the Nextel coating are beginning to decompose.