Axiom Home Page Forums General Discussion Technical Questions A different 8 Ohm vs 6 Ohm question

This will be my first Home Theatre setup and my first High Quality sound setup, aside from my Headphones. The Home Theatre system is going or be for a small space, about 100 sqft so I'm only looking at a small Receiver.

The Denon 1909 receiver is rated as follows:
- 90W (8 Ohms, 20Hz - 20 kHz, THD 0.08%)
- 120W (6 Ohms, 1 kHz, THD 0.7%)

I'm looking at:
2x M60
1x VS150
2x QS8
1x EP350

I know, the M60s may be overkill in this space but I'm really looking for full range sound from my mains. Now on to the questions!

1) I've never had really good Audio gear before. Is 0.7% THD noticeable? If not, question 2 below doesn't matter.

2) Is THD a function of the Wattage you're pushing? In other words if I'm putting less than 90W into the VS150 will the receiver be running at 0.08% (or less) THD, and the THD will increase as the Wattage runs up to 120W?

or… is the THD a function of the resistance. In other words if I plug a 6 Ohm speaker will the distortion be running at 0.7% regardless of the Wattage / volume I'm listening at?

Thanks

Byron, welcome. No, in a typical situation listening to music a 0.7% THD shouldn't be noticeable. In some tests using pure test tones heard through headphones a THD as low as 0.3% was detectable, but with real music a threshold of 1.0% or even slightly higher was found.

Yes, THD is a function of power output and remains very low up to the rated output number and then generally increases quite rapidly. Incidentally, despite the term being quite commonly used for some reason, you're not "pushing" power into a speaker; it takes only what it needs for a given output level at a particular moment. For speakers of typical sensitivity playing at a comfortably loud average level that's about 1 watt. Brief split-second peaks use much more, of course.

You're paying unnecessary attention to both THD and speaker impedance. As was indicated above, distortion in the well- designed receivers available these days is a non-factor at least up to(and usually beyond)the rated power output. Speakers vary in their impedance at different frequencies and a "6 ohm" speaker may average that over a certain range, but attempts to finely evaluate distortion possibilities aren't very realistic.

Thanks John. That's pretty much what I expected in regards to power and THD.

In relation to 'paying unnecessary attention to specs,' that's why I first asked if 0.7% is really noticeable. Since I'm new to the Audiophile world, I'm still figuring out what is significant and what isn't when it comes to gear.

Thanks again.