[LINK] Hearing tests for free by phone (o/t)

stephen at melbpc.org.au stephen at melbpc.org.au
Fri Feb 29 16:32:10 EST 2008


BRD writes:
 
> Ivan Trundle wrote:
> 
> >  And why just a fixed phone? The acoustic ability of my 'fixed' phone
> >  is no better than that of my mobile - or perhaps someone who knows
> >  can tell us what frequency ranges are possible across both options
> 
> The frequency response of POTS is about 400 Hz to 3400 Hz.

I'm not sure that the NAL specifically request that people wanting to do
an initial screening-test of their hearing use a fixed-line phone, rather
than a mobile phone, because of any differing audio frequency responses ..

(Quote) A mobile phone's audio quality depends on its audio amplifiers' 
power output and its speakers' impedance. Typically, a standard 3.6-volt 
battery powers two class D amplifiers to drive a pair of 8-ohm speakers.

In the CAP-XX tests, this set-up delivered peak power of 1.2 watts (W) to 
2.25W. This lack of power can result in thin-sounding music with a weak 
bass beat.

Another problem arises when the battery becomes taxed from simultaneous 
peak power demands to transmit wireless data and respond to a network poll 
[networks periodically poll phones to locate them and determine needed 
transmit power] while the user is also listening to music. The battery 
voltage droops, and the audio amplifier supply voltage may droop enough to 
cause distortion which the user hears as a "click." This problem is worse 
in GSM/GPRS/EDGE phones which require particularly high power for radio-
frequency (RF) transmission.

In addition, a 1-Amp or greater peak-power demand on the battery will 
cause a ripple in the audio amplifier supply voltage which the user hears 
as audio noise, or as a 217Hz buzz during a phone call. <http://www.cap-
xx.com/news/BriteSoundPowerArchitecture.htm>
--

Cheers, people
Stephen Loosley
Victoria,
Australia

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