Axiom Home Page Forums General Discussion Home Theater XPA 2 Now! A Keeper?

OK tonight everything sounds much better again at the 8 ohm setting, thanks for that tutorial, will have to experiment with the HT passage in question again at the 8 ohm setting through the right outlet, from every indication sound will be greatly improved, i.e., certainly not noxious/distorted as it was before at the 6 ohm setting with the 663 even if not as high impact in terms of SPLs as the XPA2 was trying to be, which became moot because nullified by protect.

Very interesting how what you state may relate to dynamic peaks and the need for/benefit of headroom, and how the logarithmic nature of sound perception may give rise to the idea, "You can never have too much power," or does that idea arise mostly because most of us cannot compute how much power we would actually need to propel a given space to a given clean spl?

It seems that the dynamic peaks of HT in general require more headroom than music due to the dynamic range involved, I suppose that is more or less obvious but I still do not entirely grasp the implication in terms of how much head room I actually need/want in my setting due in part to the logarithmic distortion in perception whereby you need 10 times as much power to perceive sound that seems twice as loud (is this not approximately correct?).

BTW what's up with the power ratings with the Yamahas, the 661 is rated at 90 watts into 7 but S&V finds only 53 watts into 6? The 663 is rated at 95 watts into 7, that suggests the amp is not as powerful as I was led to believe, even in terms of backup or surround duty.

If you go to some of the amp power calculators you can get a rough estimate as to how much power you need.

Try some classical music if you want to experiment with dynamic range. Most popular music has very limited dynamic range around 5-10 and I would peg a good action movie between 10-20 while classical can go to 50db in some instances.

Welcome to the world of misleading numbers. I know somewhere around here Alan has posted the usual amp testing procedures and it is within these procedures that the specs are taken. I believe the procedure is 1 channel driven fully and the others driven at 1/8? to achieve the ratings. S&V run all channels driven to determine the actual output which usually never takes place in regular use.

Sure, it's commonly said that to be perceived as "twice as loud"(whatever that means)requires an increase of 10dB in sound level, which requires 10 times the power.

The power measurements are fine and exceed the rating numbers. As with most receivers, the Yamaha rating is in accord with the FTC power regulations which require two channels to be driven simultaneously at the full rated power for at least five minutes continuously. All channels driven is neither a legal nor a real-world home usage requirement for the power rating, since all the channels aren't called upon to output full power simultaneously on real program material. Note the comments of the tester on this point at the end of the second page in the linked 661 test results.

It might not be a requirement but if you are running a system in 5/6/7 channel stereo would you not be asking the receiver to run all the amps at nearly the same output?

Of course, to the extent that both stereo channels would be equal in level.

I never realized just how compressed popular music was until I plugged in the M80s, that's a good suggestion to check out some classical music at least for reference (my wife loves the pop stuff, what can you do? Maybe the M80s will expand her range of musical taste ), although I suspect the few classical recordings I have will have to be upgraded to provide decent sound quality.

Jason/Myrison provided a link to one of those amp power calculators but I was a little fuzzy on how to perform the calculations, I'll have to go back to that link and dig into it.

I think what you say about misleading numbers is also an issue with the power amp calculator equations, since the numbers are somewhat biased it takes a bit of experience to know how the numbers are actually going to translate into a real world situation, especially with regard to ordering equipment over the internet. Thank God for Axiom!

Thanks for pointing out page 2, I did miss that one.

Yeah Sat, there's a whole world of great music waiting for you out there. I stand ready to make classical suggestions in almost unlimited numbers(I have about a thousand classical CDs). There's quite a few in the "Stunning Recordings" thread in "Stereo".

This is what I have been wondering about the most in terms of headroom, because the promo (AL video on You Tube?) I saw for the A1400-8 seemed the same as the latest Emotiva rap; both eschewed the monoblock model (e.g,. MPS-2 in Emotiva's case) in favor of a high power amp with a massive power supply that could provide maximum power to the one or two channels that need it most to facilitate HT or front speaker content and support dynamic peaks. I am now leaning toward Outlaw (rather than XPA1s, anticipating I will give up on the XPA2) due to budget yet am trying to decide just how many watts and whether the statements regarding a unitary high wattage A/B amp with minimal cross talk versus a couple of powerful monoblocks will be more satisfactory, given that HT is the priority and I have a pretty big room to fill.

Yes I saw that thread, that's why I didn't bother to ask, I already see some suggestions I can get started with.