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From: Kevin McMurtrie
Subject: Re: OT ? Amplifier Accuracy
User-Agent: MT-NewsWatcher/3.2 (PPC Mac OS X)
Date: Sat, 07 Dec 2002 03:56:30 GMT
NNTP-Posting-Date: Fri, 06 Dec 2002 19:56:30 PST
In article <firstname.lastname@example.org>,
>Apologies if this is OT:-
>For the electronically uninitiated (which definitely includes me!), what
>parameters (THD, S/N Ratio etc.) are important in determining whether an
>audio amplifier is accurate?
>What values of these important parameters have to be achieved before
>accuracy is achieved?
>Are 'linearity' and accuracy the same thing?
THD - Total Harmonic Distortion. This is when the amplifier creates
additional frequencies that don't exist in the input. For example,
crossover distortion is when there's a high frequency glitch in the
output every time the current flow to the speakers reverses. It sounds
like sand rattling on the speaker cone. There are many types of
distortion that will increase the THD rating.
S/N Ratio - Signal to Noise ratio. It's the maximum signal level
compared to the background noise. Noise could be AC hum, analog hiss,
or digital static. Higher ratios are better.
Peak power - Not defined well. It's often calculated from the peak
voltage. Car stereo ratings sometimes take this to absurdity by
calculating the difference between the minimum and maximum peak voltages.
RMS power - The continuous power output for a sine wave.
Music power - Not defined well. The continuous power output for a
sample of music.
Frequency response - Human hearing is officially said to be 20Hz to
20KHz. Actual hearing varies by age and other factors. Frequencies
down to about 1Hz can be felt and contribute to hearing.
Out of context, "Linearity" doesn't mean anything more than its
dictionary definition. It's often used to describe subwoofer distortion
at large excursions.
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