Axiom Home Page Forums General Discussion Advice from Axiom Owners Help! I think I need more power.

How many threads must a man walk down.....

See, that's why being a troll is easier. Only one thread required!

Yeah, but that whole under-the-bridge thing never appealed to me.

Dean,

My speakers are about as far away from my seating area as your proposed room locations. When I was running the 3808 alone, and then later added the NHT (5X200) external amp, the differences were there, but not dramatic. I never bothered to set up the meter and see just how loud the room would get with the 3808, because it would play music much too loud for me to be in the room at max volume. I would have had to use double hearing protection, which would have made it impossible to detect clipping. So having said that, I have no idea what the max SPL level is before / after adding the amp. Where I did notice a difference (to the better) with the amp added, is scenes where there are large dynamic peaks. Master and Commander’s battle scenes are good examples to demonstrate this. No, this wasn’t a controlled double blind and sober test, just what my gut tells me. I’m pretty good about not getting swept away with the whirlwind of bullshit telling me how “things” can make my system sound better, for what it’s worth. Considering the 3808 has more power than your Denon, I think it’s safe to assume that you would in fact be able to detect an honest improvement if you add an amp or buy a more robust AVR.

Tom, your avatar has some competition.

Well, ya do get what ya pay for when it come to amps Tom. Rotel is among many brands that give a good bang for the buck, try one ya might just like what ya hear .

Oh, Rotel doesn't do ecommerce.

The calculators like that provided by crown are based on the physics of sound dispersion in free space from a point source. I expect that that would apply much more to the great outdoors where you don't have a lot of surfaces reflecting sound back at you.

Dean, when you used the Crown calculator did you remove 6db from your headroom to account for reflected sound in an enclosed space. Using the 95DB in room sensitivity of the M80 would be similar but only adjusting by 4 db. Either way, you will find that your power requirements drop a lot with this adjustment. 5-6db is what is suggested or implemented in calculators out there.

I suspect that in a small enclosed room, your gain could be a lot more, and in a very open large room smaller.

Have you considered a pro amp? They give the most bank for the buck on power.

From all the soundscape chart [thingies] I have seen, scenes like this pump out a lot of sound in the 40-200Hz range. I expect that the power demands would be quite high because this would drive the woofers in your mains quite hard, even with a crossover engaged.

I just wanted to point out that there's no real conflict between the 6dB loss per doubling of distance which Alan mentioned in his article and the 3dB loss per doubling which Dr. Toole describes(pp. 59-60). There's no question that a 6dB loss of sound intensity results when the distance is doubled with an omnidirectional sound source operating in an anechoic chamber or wide open area(e.g., top of the Axiom test tower)offering no sound reinforcement. This results because an omnidirectional source spreads out as a sphere, and the formula for the area of a sphere is 4pi x radius[squared], so when the radius of the sphere of sound is doubled, the surface area of the sphere is quadrupled since the doubled radius is squared. The intensity of the sound per unit of area is therefore only 1/4th what it was before the doubling of distance. Since 3dB gain is a doubling and 6dB is a quadrupling of sound intensity, conversely a 1/4th intensity represents a 6dB loss.

However, this number isn't applicable to home audio where the room boundaries add support to the sound and reduce the loss. This is the major reason why the Crown calculator doesn't give realistic results for home use, since its formula simply uses the 6dB per doubling figure. Only near the end in "other considerations" does it point out this key difference and suggest a 6dB adjustment(which would reduce the power number from the calculator to 1/4th of its previous value). Strangely, instead of suggesting that a much less powerful amplifier be bought, Crown suggests that the 6dB correction be applied to yet more headroom.

Dr. Toole, using previous research by Schulz, combined with his own work on the subject with speakers, finds that 3dB is the best number to use. Because of this research and earlier work I'd read about, I simply deduct 4dB from the 1 meter sensitivity number for a typical 9-10' listening distance and calculate the requirements at various dB levels from there, rather than using the Crown or other similar online calculators.

@ Chris - Thanks! I was pretty much set on just upgrading to a newer more powerful Denon but I started thinking it doesn’t make much sense to keep paying for a new power supply every time I feel the need to upgrade to some new feature in the processor.

@ Alan - Thanks for the clarification on the dB weakening with distance. Using either number puts me in the same general power range as my preferred average SPL of 80dB is well below the M80/QS8 91-95dB range.

@ michael - I was eyeing a 3808 for the move and am still considering one of the newer Denons near that range.

@ Fred - Yes I ran the number for both the 91dB and 95dB ratings coming up with a pretty wide range of power needed, however using the more realistic numbers supplied by John (-3dB/distance doubling and 18dB headroom) even the 91dB sensitivity leaves me needing at the most only 100-110 watts of power for the M80s and even less for the QS8s.

I would prefer to err on the side of a little more power than an insufficient amount and I wouldn’t mind the option of bumping up the stereo M80s higher when occasionally showing off or demoing the speakers.

What exactly is a “pro amp?” If that means going the separates route it’s looking more promising. Any suggestions on good pre/pro combinations?

An AVR is still a viable option I’m just not sure how to figure out if one will supply all the channels with the power they will need to reach the 80dB average with peaks of 18dB. Plus like I said above I’m not seeing the long term cost savings in replacing the power section every time I want to upgrade the processor side.

@ John - Thanks for the explanation. Either set of number seems to put me in the 100 to 110dB range for the max power I’ll need per channel. Is there any way to know from manufactures stated power ratings how much total power an AVR can deliver between all it’s channels or is an independent test needed?

Also, what are your thoughts on the long term economic advantage of using separates vs and AVR?