[Tech1] Sanitizing a mic.

[Alan Taylor]

I was working on a show where the director casually asked if I had a hydrophone to bring along the next day.  I didn’t have one, but I decided to try improvising using a stethoscope with an ECM 77 pushed into the acoustic tube instead of the Y piece feeding it to each ear.  The idea was that the microphone could remain above water while the diaphragm of the stethoscope was submerged. It worked impressively, I assume that the diaphragm within the head acted to better match the microphone to the  water.

After that show, I removed all the tubing and made a simple adaptor allowing me to push the ECM straight into the stethoscope head.  The head can be twisted  round, one side is the diaphragm, the other has an O ring seal and a short horn leading to the tube. Either side is useful under different circumstances, the O ring side usually sounds best.  It was small enough to live in my ECM box and could be used to pick up difficult FX.  Obviously a heart beat and tummy rumbles was easy. Another time I needed the sound of a futuristic machine.  The director suggested that it should sound like the finest Swiss engineering, but on a huge scale, but still,subtle.  Well obviously a Nagra is the finest Swiss engineering, but it’s nearly silent - until you put a stethoscope on it and play that recording back at reduced speed. It was one of the easiest sound design challenges I’ve ever done.  

Another show needed the sound of an ant running up a blade of grass, which had been shot mute using a macro lens in a laboratory.  I stuck a little piece of blu tack onto the stethoscope diaphragm, pushed a blade of grass into it and placed an ant on it by means of a small twig.  Ten minutes of messing around resulted in the ant running up and down the grass and producing a decent recording.  When we put it to the picture, it only needed minor tweaking to look perfectly in sync.  People asked what we used to get that effect, expecting it to be some sort of Foley and they assumed it was a wind up when I said that I recorded an ant running up and down a blade of grass.

Alan Taylor

> On 19 Dec 2020, at 09:50, Roger E Long <relong at btinternet.com> wrote:
> 
> Im amazed you got away with this Pat
> The MKH 125 was a full RF capacitor mic. The electronics were in a head amp separated from the  capsule with unbalanced cable
> It was a version of the MKH 405 , a cardioid TPower boom mic of v  high quality.
> Normally dynamic mics were put in a condom for underwater FX. (AKG D109, Sennhieser D211)
> That a RF omni condenser survived is testament to its construction.
> They were lovely mics , with a gentle rising presence, but expensive compared with dynamics and electrets.
> I have 6 of them still.
> Hydrophones are P48 powered, DPA do a cracker, but they are heavily shrouded and the cable armoured to withstand sea water and pressure.
> Roger
> 
>> On 18 Dec 2020, at 21:37, patheigham via Tech1 <tech1 at tech-ops.co.uk> wrote:
>> 
>> Alan’s mention of cling film reminds me of a need to waterproof a mic to obtain some underwater effects in a swimming pool. Using a Sennheiser MKH 125, their lavalier personal mic of the day, see attached photo, there is a raised rim around the diaphragm. Stretching cling film, tightly, over it and swathing  it in Blutac was eventually very successful. The first attempt flooded the mic, so it was dismantled and allowed to dry out in the sun.
>> It sounded good in the open-air, so I surmised that the outer covering of clingfilm acted as a primary diaphragm, and
>> the air trapped between that and the real diaphragm was working as a linking piston. In this case, the film was not close to the real diaphragm, so was not obscuring the holes, due to the design of the casing with the rim feature. 
>>  
>> With regard to sanitising the lip ribbon – maybe a replaceable mask filter can be applied above the nose shield, but probably too dense a material to place over the diaphragm entry, unless it’s sound transparent enough. More experimentation needed, methinks.
>>  
>> Pat
>>  
>> <4D56339BBBF14016B480CC0F20C23E9D.jpg>
>>  
>> Sent from Mail for Windows 10
>>  
>> From: Alan Taylor via Tech1
>> Sent: 18 December 2020 16:48
>> To: Tech-Ops-chit-chat
>> Subject: Re: [Tech1] Sanitizing a mic.
>>  
>> Cling film can achieve a similar result, with the advantage of staying in place and looking fairly inconspicuous, although it’s not particularly durable. Peeling it off can be fiddly, but I use slips of paper as identification labels and put them discreetly just under the last layer of wrap so that if you peel from there, it comes off easily. 
>>  
>> Alan Taylor
>>  
>>  
>>  
>> 
>> 
>> 	
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