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#382488 - 09/05/12 02:13 PM Re: Looking for pre/pro all channels driven [Re: Ken.C]
pmbuko Offline
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Registered: 04/02/03
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Keep in mind that the Pin portion of an amplifier's efficiency calculation -- a ratio of Pout/Pin -- is measured after the electricity from the wall has passed through the amp's power supply, where some loss inevitably occurs.
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#382489 - 09/05/12 02:47 PM Re: Looking for pre/pro all channels driven [Re: pmbuko]
J. B. Offline
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Registered: 01/19/11
Posts: 1237
Loc: Quebec, Canada
if my memory is intact, the PC12-Plus (Bash) shows around 22 Watts on stanby and i know the PC13-Ultra (Sledge) is at 6-8 Watts.
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#382490 - 09/05/12 02:59 PM Re: Looking for pre/pro all channels driven [Re: Ken.C]
J. B. Offline
connoisseur

Registered: 01/19/11
Posts: 1237
Loc: Quebec, Canada
i wrote this to illustrate that, even with the efficiency of the Axiom speakers, the power needs for good reproduction of (mainly) movies is higher than we often suppose. 10 Watts or 100 Watts per channel is, in most situations, simply not enough power to give a crystal clear rendition.
this may well be the reason why some people who have 100 Watts/ch. find that suddenly their speakers "open up" and gain lots of transparency when they change their amplifier for a much stronger one.

the SPL meter readings are peak readings, at 0.125 second, but not instantaneous. as regards the Watt meter, i don't know the sampling time they use.


Edited by J. B. (09/05/12 03:07 PM)
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#382491 - 09/05/12 03:05 PM Re: Looking for pre/pro all channels driven [Re: pmbuko]
J. B. Offline
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Registered: 01/19/11
Posts: 1237
Loc: Quebec, Canada
Originally Posted By: pmbuko
Keep in mind that the Pin portion of an amplifier's efficiency calculation -- a ratio of Pout/Pin -- is measured after the electricity from the wall has passed through the amp's power supply, where some loss inevitably occurs.


i know only that on the Internet, i've read a few times that my amp's efficiency is around 70%.
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#382500 - 09/05/12 07:34 PM Re: Looking for pre/pro all channels driven [Re: J. B.]
fredk Offline
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Registered: 12/06/07
Posts: 6960
Loc: Canada
Originally Posted By: J. B.
i wrote this to illustrate that, even with the efficiency of the Axiom speakers, the power needs for good reproduction of (mainly) movies is higher than we often suppose. 10 Watts or 100 Watts per channel is, in most situations, simply not enough power to give a crystal clear rendition. ...

I don't have the time or energy to track down the difference between what you found and what is offered up in the standard formula for calculating power requirements.

Based on my experience to date, I'm still siding with the traditional calculator. My original receiver was rated at 90 wpc two channels driven and delivered crystal clear sound up to unreasonably loud levels (pushed it to 90db briefly one afternoon).

It can't hurt to have 300 wpc, but really, unless you have a very large space, its not needed.
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#382501 - 09/05/12 07:46 PM Re: Looking for pre/pro all channels driven [Re: fredk]
J. B. Offline
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Registered: 01/19/11
Posts: 1237
Loc: Quebec, Canada
what we're talking about here is that the main speakers should be able to do 105 DB and the sub 115 dB, at Reference Level, for those who like to have it like in the cinema or better as regards quality.

you're talking about max levels of 90 dB; that's a whole world of difference.
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#382503 - 09/05/12 09:28 PM Re: Looking for pre/pro all channels driven [Re: J. B.]
fredk Offline
axiomite

Registered: 12/06/07
Posts: 6960
Loc: Canada
Originally Posted By: J. B.
you're talking about max levels of 90 dB; that's a whole world of difference.

I am? Where did I write that? wink

It may well be the case that the average and maximum were close to the same as it was no more than 30 seconds before I turned the system down. No need to annoy the neighbours and all.

I've also measured some classical pieces where I had peaks over 105db. This was on my 2808 which is rated at 110 wpc I believe. Again, all was very clean.

OK, you sucked me in. According to the Crown calculator at a distance of 3 meters, a listening level of 85 db, sensitivity of 91 db, head room of 20 db (a lot more than needed for most applications) and room gain of 5 db, I still need only 71 watts of peak power. Push that up to 25 db of headroom and you get close to 300 watts.

Some reading on power requirements from the Crown site. Note that their calculator is intended for outdoor use so you need to factor in room gain. Crown recommends 6db. I use 5.

Since Crown makes these commercial amps, and amps are usually driven harder in commercial applications, I'm inclined to take their recommendations seriously.

Now, I don't often listen at 85db. Its usually closer to 70, so to give me that 20 db of headroom I crave, I need a whopping 2 watts. grin

By the way, have you checked out the Peavy IPR series? The folks at Danley Labs did some testing and these things are the real deal.
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#382504 - 09/05/12 09:52 PM Re: Looking for pre/pro all channels driven [Re: J. B.]
JohnK Offline
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Registered: 05/11/02
Posts: 10307
Jacques, rather than getting into the complexities and possible inaccuracies of using those watt meter numbers and that amplifier efficiency figure, I'll analyse the needed power in the way I always do. First, as you point out, to play at the movie "reference level"(which I'd never do, being too loud for home use)requires a maximum output of 105dB per speaker channel and 115dB for the .1 LFE channel. For an M80 to hit a 105dB peak at a 7' listening distance requires the following power: the 91dB at 1 meter for 1 watt input sensitivity(anechoic)is reduced 3dB at 2 meters(using the reduction of level per doubling of distance in home rooms found in the work of Dr. Toole and others), 1 watt being needed for an 88dB level. 100 watts would produce a 20dB increase, i.e., 108dB, and the peak maximum of 105dB per channel would therefore require 50 watts.

Both my studies of audio technology and my personal experience indicate that this is the reality of the situation. Receivers rated anywhere in the 100 watt area have ample capacity for safe listening levels with speakers of average or better sensitivity, such as the Axioms.
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#382507 - 09/06/12 07:39 AM Re: Looking for pre/pro all channels driven [Re: gearcruncher]
J. B. Offline
connoisseur

Registered: 01/19/11
Posts: 1237
Loc: Quebec, Canada
i thought my method and tools were good enough for a reasonably close approximation of the power needed at Reference Level, but i seem to be wrong.

i'll have to give it a closer look so i don't fool myself with wrong logic or calculations as i seem to have done.

thanks. :-)
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#382508 - 09/06/12 07:49 AM Re: Looking for pre/pro all channels driven [Re: gearcruncher]
J. B. Offline
connoisseur

Registered: 01/19/11
Posts: 1237
Loc: Quebec, Canada
Fredk,

when i was looking for new amps, the Peavy amps were right up in my list along with the QSC.
i had one model of each make in my final choice and i bought the QSC because the Peavy had a too high HPF

it's after i had bought the QSC that a Peavy engineer told me he could alter the HPF to the frequency of my choice, but it was too late.
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