Q about THD

[93 saturn sl2 10+ year member]

Ive been lookin at 4 channel amps, and their THD. For example is .005% better then 1%?

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[djman37 5,000+ posts]

yes.

That is the answer to the .005 THD better than 1%. If ALL things are equal, which is impossible to determine.

 

[JimJ 5,000+ posts]

This has been asked and answered before...

Generally, the amount of THD you can hear depends on the amp topology and more importantly, the frequency at which you're listening to it. Distortion is harder to hear at lower frequencies vs. higher ones...depending on the frequency, you may not be able to hear a difference between one percent and something much less.

 

[93 saturn sl2 10+ year member]

this sony amp has .005%

http://www.cardomain.com/item/SONXM4060GTX

and this Orion has

http://www.cardomain.com/item/ORI47440

 

[JimJ 5,000+ posts]

I highly doubt that Sony number was taken at anywhere near rated power //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[93 saturn sl2 10+ year member]

ok,well will anyone suggest an 4 channel amp for me that will do 50-60wrms that isnt too expensive. And isnt really big, it has to fit on the back of a seat that is about 17" wide.

 

[squeak9798 5,000+ posts]

And even then....at any frequency a THD below 1% is said to be inaudible.

You'd never hear a difference between .005% (assuming that's even accurate) and 1% (even though it doesn't say "1%", it says less than 1%).

 

[93 saturn sl2 10+ year member]

hows this amp?

http://www.cardomain.com/item/KENKAC8402

 

[squeak9798 5,000+ posts]

hows this amp?http://www.cardomain.com/item/KENKAC8402

Ugly.

 

[djman37 5,000+ posts]

Ugly.

but not as ugly as XPLOD

 

[Hundreth 10+ year member]

Ugly.

//content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif

 

[thch 10+ year member]

THD stands for total harmonic distortion. distortion is a signal that is not the signal being played, but related in some way to it. (noise would be a completely unrelated signal). In this case it is looking at harmonically related distortion. like if you played a 60hz test tone, you would get "harmonic" distortion at 120hz, 180hz, 240hz, ect... if you played a 100hz tone with a 60hz tone, you'd have THD at 120, 180, 200, 240, 300, ect...

THD is a simplification. research has shown that in some cases higher THD sounds better, and in others, lower THD sounds better. thus the spec has so nuances to it. lower THD is typically prefered though, and modern amplifiers can have very low THD specifications.

*fun fact -- IMD is intermodulation distortion and is not always measured. it is harmonic distortion from the sum and difference of two signals. for 100hz + 60hz, you'd have distortion at 40hz, 80hz, 120hz, 160hz, ect...

 

[///M5 10+ year member]

And to make it better there is no Standard to which it is measured. They could arbitrarily pick the 48-50th harmonic and call those the distortion (good ones to pick) or they could pick the 2nd. They can do whatever they want....specs are pretty much useless to look at for those sort of things.

If you want a recommendation, what are you willing to spend?

 

[squeak9798 5,000+ posts]

THD is defined as: 100* SQRT(F1^2 + F2^2....+ Fn^2)/Fo
THD = Total Harmonic Distortion

Fo = The amplitude at the Fundamental or test frequency (the standard is 1KHz)

Fn = The amplitude at frequencies in which harmonics are present.

Here is how it works:

The amplifier is given a source signal of some singular frequency, such as 1KHz as described above and with the amplifier at full output level. Test equipment is used to measure the output level of the fundamental as well as the output level at each harmonic of the input signal. These numbers are compared using the equation shown above to calculate the THD of the amplifier.

Kevin

Great explaination of how THD is supposed to be measured.

 

[thch 10+ year member]

actually, TOTAL means all of the harmonics, and it isn't too hard to measure if tested correctly. an FFT can be used to show this to an arbitrary number of harmonics. bandstop filters can be used to eliminate the fundamental and then all the power left is in noise/distortion.