[BC] Headphone polarity and bone conduction...

[Burt I. Weiner]

Actually, what you had here was a classic case of cancellation or 
partial cancellation due to phase shift.  The voice was arriving from 
two separate sources and acoustically mixing in the ear.  One path 
was from the earphone transducer itself and the other path was via 
bone (and other stuffs in the head) conduction.  By reversing the 
polarity of the audio arriving in the headphones you brought them 
back into phase or at least, less out-of-phase.

A test you can do is to put on the headphones, open the mic channel 
(in audition) and say "Oooooooooooooooooooooooooooooooooh".  As you 
do, turn the headphone volume up and down.  If they are out of phase 
with the bone conduction you will hear the volume go through a 
null.  Not a deep null, but a an obvious null that is typically in 
the lower mid range.  This can cause the talent to claim they don't 
have enough earphone volume and try to turn things up to the point of 
distortion.

On my remote gear I have a switch for headphone polarity that I can 
flip to correct the problem when it arises.

Burt

At 03:40 PM 8/13/2006, you wrote:
>From: "Ron Cole" <rondcole at gmail.com>
>Subject: Re: [BC] Absolute Polarity (was XLR pinout debate)
>To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
>Message-ID:
>         <2f88e090608131036w19c0cb2ek6e1259dccb98b426 at mail.gmail.com>
>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>In the pre digital days, I had an jock that was constantly complaining about
>the off air sound of the headphones.  I could never find anything wrong with
>the off air audio feed then one day I swapped the balanced audio polarity
>and She quit complaining.  I guess she was sensitive to "absolute polarity"
>of the whole transmission path.
>That was not an issue after the Digital STL was installed, too much delay to
>listen live any more.
>
>Ron

Burt I. Weiner Associates
Broadcast Technical Services
Glendale, California  U.S.A.
biwa at earthlink.net
K6OQK