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Author Topic: WTF are these mics?  (Read 2159 times)

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Offline DSatz

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Re: WTF are these mics?
« Reply #15 on: April 06, 2019, 04:46:50 AM »
> Perhaps they want to protect the executive from electric shock?

I've been told on good authority that all electric light switches in the President's quarters (and perhaps throughout the rest of the White House; that wasn't said) are on low-voltage circuits that drive relays. The relays then control the lights, so that the President never touches any part of a circuit that runs at 110 Volts.

In 2009 I discussed this with the engineer who set up the podium microphones for President Obama's inauguration, because I'd heard a rumor that inside the shells of the usual dynamic microphones, condenser microphones of a certain type had been used. He told me that one major consideration was that 48-Volt phantom powering was considered to be too high a voltage, given the regulations that protect the President's safety. Fortunately, the microphones in question allowed 12-Volt phantom powering as well.

Some day I would like to see the actual safety rule. The series resistance in any standard 48-Volt phantom power supply limits the total current to a maximum of 14 mA even in the event of a dead short; for each modulation lead the maximum is only 7 mA. It would be a little odd if the rule didn't consider current--since that, rather than voltage as such, is what could create a safety hazard if there were to be one. We are constantly surrounded by electrostatic charges of hundreds, thousands, even tens of thousands of Volts. As long as there's no (or minimal) current flow, those charges don't affect us; on a dry winter's day we walk across a carpet with our shoes on, and most of the time we get to the other side with our hearts still beating.

But even from a voltage standpoint, Ohm's Law says that the current drawn by the microphone will cause a voltage drop across the feed resistance (the standard says 6.8 kOhms for each modulation lead), so that a 48-Volt microphone that draws 4 mA is actually running at only 30-35 Volts or so.

P.S.: The Speiden ribbons were also widely known in this country as B & O (not the Baltimore and Ohio Railroad, but Bang and Olufsen, who distributed them under their own label).
« Last Edit: August 05, 2019, 07:18:18 PM by DSatz »
music > microphones > a recorder of some sort

Offline tim in jersey

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Re: WTF are these mics?
« Reply #16 on: April 06, 2019, 12:13:02 PM »
The recording engineer likely chose these mics and placement to reduce the amount of vocals captured in the recording...  :lol:

 

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