Mailing List Archive

Mailing List: techdiver

Message Display

>jolieb@gr*.ci*.up*.ed* (Jolie Bookspan) writes:
>
>>About the Voice Change With Masks And Helium questions:
>>With helium, density of the breathing medium determines 
>>springiness of the vocal folds (cords) and so their vibrational 
>>frequency.
>

Barry Lanier replies

>I've seen this stated a number of times and it is quite incorrect.  The 
>medium is irrelevant to the vibrational frequency of a vibrating string 
>fixed at both ends (similar to vocal cords).  The perceived sound pitch from 
>someone talking is primarily a function of the resonant cavities in the 
>head, including the sinuses, throat, mouth, and even structures outside the 
>mouth (i.e. gas mask, etc.).  The resonant frequency of a cavity is 
>definitely a function of the sound media and that is what accounts for the 
>voice change in question.  The resonant frequency of a vibrating string is 
>strictly a function of the physical characteristics of the string itself, 
>such as mass/unit length, and tension.  A hollow cavity has a resonant 
>frequency determined by its physical dimensions and the speed of sound of 
>medium inside.  Thus when Helium, or other less dense gas is breathed, the 
>perceived pitch is higher.


This is quite correct, the voice change in helium is due to the increased 
conduction velocity of sound in helium compared to nitrogen (air).  This 
results in a frequency shift in the sound that can be corrected for by the 
voice unscramblers used at experimental deep diving chambers.

regards,

David Doolette
ddoolett@me*.ad*.ed*.au*

Navigate by Author: [Previous] [Next] [Author Search Index]
Navigate by Subject: [Previous] [Next] [Subject Search Index]

[Send Reply] [Send Message with New Topic]

[Search Selection] [Mailing List Home] [Home]