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Discussion in 'Archived Threads 2001-2004' started by DanBrunet, Dec 12, 2001.
Is THD an important thing to consider when shopping for a receiver?
Not really, unless it appears unusually excessive. Most reputable manufacturers have thd low enough as to be inaudible during normal use.
I would like to disagree a bit with Tom that THD is ok to ignore.
It is TRUE that you cannot tell the difference between 0.01% and 0.05% THD.
But when you start trying to compare 2/3/4 different receivers, then you need to be able to read the fine-print. Then THD becomes one of the things to look for.
Receiver A announces it is 80 watts per channel.
Receiver B announces it is 100 watts per channel.
Since both are the same price, you would think Receiver B is the better buy.
Now you have to look at the fine print:
Receiver A: 80 wpc, all channels driven, 20-20,000 hz, 0.03 THD, 6 ohm resistive load.
Receiver B: 100 watts per channel stereo mode, 8 ohm load 0.09 THD.
First: notice that one receiver uses an 8 ohm load and the other a 6 ohm load.
A "perfect" amplifier could do this:
8 ohm load/speaker - 100 watts
6 ohm load/speaker - 150 watts
4 ohm load/speaker - 200 watts
So receiver B makes itself look more "powerful" by using an odd speaker load. The "true" power ratings for receiver B are something like:
8 ohm load/speaker - 75 watts
6 ohm load/speaker - 100 watts
4 ohm load/speaker - 125 watts
So receiver B is actually LESS powerfull than receiver A for the same speaker.
Second: notice the "all channels driven" vs "Stereo Mode". Receiver B is announcing that it can sustain 100 wpc x 2 channels = 200 watts continous power. But receiver A is announcing it can produce 80 wpc x 5 channels = 400 watts continous power.
So receiver A can produce twice the power of receiver B.
Third: Notice that receiver A announces "20-20,000 hz" and receiver B is silent. Here is the trick: It takes a lot more power to produce low-frequency sound. Think of those personal "shreeker" alarms - they produce a very loud sound from a battery. This is because the sound is very high frequency. Honest receiver companies will announce that their numbers are consistant across all the audible frequencies. Less repuitable companies will not tell you what frequency their power numbers were obtained at.
Fourth: (and it IS the lowest importance of all of these) notice the THD values. Receiver A has a lower value. It distorts the signal LESS than Receiver B. If your desire is for a highly-accurate music experience, a lower THD is important.
So THD IS one of the fine-print things to look for when comparing several amps/receivers.
Hope this helps.
If this were slashdot I would mod you up +1 Informative!
That was very enlightening for me.
Very informative, but I think you got your resistances backwards in your initial listing of specs, it caused a bit of temporarly confusion for me. Great post though.
Tom and Bob are really just demonstrating opposite sides of the same coin. What Tom said is succinct and reliable. Notice he mentioned "Reputable Manufacturers" which is the critical thing. Generally, all your good mass manufacturers use similar standards in their ratings. Denon and Harmon Kardon tend to be more stringent in their ratings, which is why their receivers are "rated" with less power than a similarly priced unit from someone else.
In fact, many tube amps, even though they sound very sweet, can have outrageously high THD. So THD is just one of many factors. Also, the practical difference between, for example, an amp rated at 80 watts and 100 watts under the same standards is insignificant.