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question about THD


memphismanx88

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i could be way off base here, and im sure somebody more knowledgable will chime in, but imo THD only makes a HUGE difference if you are heavily into sound quality. the lower the THD at a given ohm level, the cleaner the sound is gonna be...but i always look at when comparing amps...

i likes me some audio stuff...

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- Total Harmonic Distortion -

The measurment of distortion in the reproduction of the sine wave.

Super laymen terms: The measurment of an amplifiers ability to reproduce a signal without unwanted noise or *coloration* of the input signal.

The measurment is usually considered a final percentage of the output signal. Ie. 10% THD = 10% of the signal comming out of the amplifier is unwanted crap. Out of 100% of course.

It comes in *many* forms and can be caused for many reasons (bad PS design, poor stage designs, clipping, etc)

Without getting too far into it, I can just give you the stuff you need to consider.

1) The average human ear cannot detect below 3% THD on sub harmonics (lows)

2) The average human ear cannot detect below 1% THD on top end harmonics (mid or >)

3) Your speakers are likely to cause more audible distortion then your amplifier.

4) If it is still a major concern always shop using THD @ rated output.

THD @ rated output is the THD rating at the amplifiers RMS output levels. Some companies like to do the ratings at MUCH lower levels creating a biased measurment for the sake of publishing beter specs. Do you listen to your stereo at MUCH lower levels? I don't think so..

At any rate most if not all current amplifier technology exceeds realistic needs in this area (yes, even pyramid amps). So it's not as important to observe as it once was. And as long as your ears are the only MIC's that are ever going to measure your system, I wouldn't be cashing in a savings bond on that McLintosh amp you've had your eyes on anytime soon.

Hope this helps. May the force be with you..

- Matt

SMDsigbannr4.jpg FTW?
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- Total Harmonic Distortion -

The measurment of distortion in the reproduction of the sine wave.

Super laymen terms: The measurment of an amplifiers ability to reproduce a signal without unwanted noise or *coloration* of the input signal.

The measurment is usually considered a final percentage of the output signal. Ie. 10% THD = 10% of the signal comming out of the amplifier is unwanted crap. Out of 100% of course.

It comes in *many* forms and can be caused for many reasons (bad PS design, poor stage designs, clipping, etc)

Without getting too far into it, I can just give you the stuff you need to consider.

1) The average human ear cannot detect below 3% THD on sub harmonics (lows)

2) The average human ear cannot detect below 1% THD on top end harmonics (mid or >)

3) Your speakers are likely to cause more audible distortion then your amplifier.

4) If it is still a major concern always shop using THD @ rated output.

THD @ rated output is the THD rating at the amplifiers RMS output levels. Some companies like to do the ratings at MUCH lower levels creating a biased measurment for the sake of publishing beter specs. Do you listen to your stereo at MUCH lower levels? I don't think so..

At any rate most if not all current amplifier technology exceeds realistic needs in this area (yes, even pyramid amps). So it's not as important to observe as it once was. And as long as your ears are the only MIC's that are ever going to measure your system, I wouldn't be cashing in a savings bond on that McLintosh amp you've had your eyes on anytime soon.

Hope this helps. May the force be with you..

- Matt

^^^ X2 

I only pay close attention to THD when getting equipment for the upper end of the frequency spectrum (mids and highs). But if you need an amp for subs then a slightly higher THD will be more forgiving since it is difficult to detect distortion in lower frequencies

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  • 1 year later...
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  • 7 months later...

Thanks for the write-up

But remember... This THD number is only useful WITHIN the same brand.. Different brands rate this in different ways (different watts) to make it seem better...

The "Better" brands are more accurate in their reading, while MOST are not accurate under real world applications... Just use this number for the same brand..exp. Two Arc Audio amps, etc

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  • 2 years later...

All that matters with THD when setting gains on subs is that you can get to your RMS power without exceeding 1% THD. The DD-1 will help you find 1% THD why a DMM will help you measure output.

Basically, set gains with DD-1 until you can go as high as you can without 1% distortion. Then use the DDM and fine tune to RMS wattage you need.

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