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# THD ratings

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### #1 of 3 OFFLINE Mike Mundt

Mike Mundt

Stunt Coordinator

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• Join Date: Dec 28 2002

Posted March 23 2003 - 03:43 AM

Ok, i understand common tests are done to reciever to figure out the harmonic distortion they produce.

i know they commonly use one test of 8 ohms 20Hz-20kHz to figure out the recievers THD. Then they also do another test at 1kHz 8 ohms to figure out another THD level.

my question is im looking at the Onkyo TX-NR900 and they give you the information like this
----------------------------------------------------------
THD (Rated Power) 0.08 % (all channels)
Damping Factor (1 kHz, 8 ohm) 60
----------------------------------------------------------
Is the 0.08% rating a 8 ohms 20Hz-20kHz test?
What does Damping Factor mean?
And what is 60 measured?

### #2 of 3 OFFLINE Mike Mundt

Mike Mundt

Stunt Coordinator

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• Join Date: Dec 28 2002

Posted March 23 2003 - 03:44 AM

*And how is 60 measured?

### #3 of 3 OFFLINE Jack Briggs

Jack Briggs

Executive Producer

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Posted March 23 2003 - 05:44 AM

• If the Onkyo's harmonic-distortion figures are given as stated in your post then it appears likely the measurement was taken at 1 kHz (which results in a lower figure). The preferred measurement stat would be the harmonic distortion measured across the entire audio bandwidth of 20 Hz to 20 kHz with all channels driven.

• Damping factor is the value of the output impedance at a particular frequency divided into eight. That measures the amplifier’s ability to deliver a flat frequency to the load. Also, according to orthodoxy, the higher the damping factor the swifter the amplifier's "recovery" from a transient peak.

This is debatable, however. McIntosh, for example, has long scoffed at the notion that really high damping factors improve transient response (the damping-factor numbers for its transistor amplifiers are more like those of tube amps). My psychological makeup results in my preferring higher damping-factor numbers, though I can't make a case for it. Perhaps somebody else here can.