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#382393 - 09/02/12 08:34 PM Re: Looking for pre/pro all channels driven [Re: gearcruncher]
gearcruncher Offline
enthusiast

Registered: 04/16/12
Posts: 37
Loc: Red Lake Ontario
My daughter just moved out of the basement giving me an extra 900 square feet of listening space . Basement theatre is planned to be 3000 square feet with the exception of a bathroom . I tell ya , these older homes with the oil furnace built in the centre of the home only makes my efforts a tad more difficult . Do I move the furnace or build around it lol . With some proper dampers , I am sure i could stuff a new small efficient gas furnace in one of the corners which would give me more room to play .
Your suggestions so far are excellent . Keep em coming
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#382401 - 09/03/12 06:34 AM Re: Looking for pre/pro all channels driven [Re: gearcruncher]
J. B. Offline
connoisseur

Registered: 01/19/11
Posts: 1269
Loc: Quebec, Canada
gearcruncher, in your calculations, don't forget that cubic feet is the important thing in audio;
sound "fills" a room, from floor to ceiling.
after that, it's distance from the sound source; square feet doesn't come in the equation.


Edited by J. B. (09/03/12 06:35 AM)
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#382413 - 09/03/12 02:33 PM Re: Looking for pre/pro all channels driven [Re: gearcruncher]
J. B. Offline
connoisseur

Registered: 01/19/11
Posts: 1269
Loc: Quebec, Canada
gearcruncher,

have a look at this post, you might find it interesting:
http://forum.blu-ray.com/showpost.php?p=6407443&postcount=13400
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#382464 - 09/05/12 12:12 AM Re: Looking for pre/pro all channels driven [Re: J. B.]
fredk Offline
axiomite

Registered: 12/06/07
Posts: 7042
Loc: Canada
Quote:
if you have a look at my room, you will see that it's quite small - around 1500 cu. ft. plus an open doorway to the kitchen = 3000 cu.ft. - and i sit about 6-7 ft from the front speakers.
when i play some demanding movie at Reference Level, the front speakers need around 300 Watts/ch.

How did you get to this number?

Originally Posted By: J. B.
gearcruncher, in your calculations, don't forget that cubic feet is the important thing in audio;
sound "fills" a room, from floor to ceiling.
after that, it's distance from the sound source; square feet doesn't come in the equation.

Physics dictates that it is distance from the sound source that determines the power required.
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#382472 - 09/05/12 07:59 AM Re: Looking for pre/pro all channels driven [Re: fredk]
J. B. Offline
connoisseur

Registered: 01/19/11
Posts: 1269
Loc: Quebec, Canada
"How did you get to this number?"

Just some measuring and maths.
numbers are approximate but close.
some movies take more than 300 W/ch for the FR/FL speakers.
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#382473 - 09/05/12 08:14 AM Re: Looking for pre/pro all channels driven [Re: gearcruncher]
Ken.C Offline
shareholder in the making

Registered: 05/03/03
Posts: 17766
Loc: NoVA
JB, that's FAR higher than any number I've seen before. Love to see your math.
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#382474 - 09/05/12 09:16 AM Re: Looking for pre/pro all channels driven [Re: Ken.C]
J. B. Offline
connoisseur

Registered: 01/19/11
Posts: 1269
Loc: Quebec, Canada
I put a Watt meter in between the wall socket and the amp.

once a movie or music CD is ended, i check the maximum wattage indicated on the watt meter, multiply it by 0.7 and this gives me the approximate # of Watts that were sent to both front channels; i then divide this number by 2 to get Watts/channel. (The QSC amps are about 70% efficient).
this is not precise in any way, but it does give me an idea about what's going on, power wise.
the best instrument for this would be a peak hold function on an oscilloscope.


when i want to know the movie's max SPL at my MLP, i put an SPL meter on the nearby armrest with the meter set to "peak hold" and "Fast".
this is quite precise, as the meter has an accuracy of +-1 dB and is user calibrated; Freq. Resp. is 20-12 500 Hz, and readings are taken with the Flat "curve".
The flat curve takes into consideration bass frequencies without attenuating them, like C weighting does. it shows the real bass level, in a linear manner.

one must never forget that instantaneous power peaks can be 10-20 dB higher that the average or RMS value. this is very important because caring only for average levels will mean peaks will be clipped.

most of the time, very high power demands last only small fractions of a second and as long as there is no distortion (clipping) in these instantaneous signals, one is not aware of them.
the more those peaks are cut off, the more distortion that can be heard.

of course, this does not apply to highly compressed music.


Edited by J. B. (09/05/12 09:33 AM)
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#382482 - 09/05/12 12:25 PM Re: Looking for pre/pro all channels driven [Re: gearcruncher]
J. B. Offline
connoisseur

Registered: 01/19/11
Posts: 1269
Loc: Quebec, Canada
as i now have the time, let me give an example.

a few days ago i played the movie Super 8 at Reference Level; once it was over, i checked the Watt meter to which the FR and FL speakers are connected to the house current, through one QSC amp.
it said Max Watts = 1278 Watts. that's a total for 2 speakers.
for one speaker, we divide the number by 2 = 640 Watts/ch.

the amp efficiency is around 70%, so i multiply 640 Watts by 0.7 which gives around 448 effective Watts for one speaker.

now, the sensitivity for the M80 is 95 dBSPL/Watt/meter, in room.
as i sit at a distance of about 2 meters, then i get around 91 dBSPL/Watt/2 meters. The loss for doubling the distance is 6 db, but that's for open spaces; in my room, it's more like a 4 dB loss.

going from one Watt to 448 Watts is an increase of around 26 dB;
so, 91 + 26 = a SPL of 117 dB for one speaker.
the total output for the 2 front speakers is doubled, to 120 dBSPL, at 2 meters (MLP).

then, my SPL meter said that the loudest peak registered was 122.3 dB/flat scale.
I think the difference between 120 Db and 122.3 dB comes from the fact that the subs have to be taken into account as well as also the 4 surround speakers.

this is all approximate, but should be quite near the real numbers.
true peak power indicators are too costly for my needs.

if my method is wrong or does not make sense, please tell me how, i would be grateful for that.


Edited by J. B. (09/05/12 12:32 PM)
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#382485 - 09/05/12 01:50 PM Re: Looking for pre/pro all channels driven [Re: J. B.]
pmbuko Offline
shareholder in the making

Registered: 04/02/03
Posts: 16273
Loc: Leesburg, Virginia
J.B., what does the watt meter show when the amplifier is powered on, but no source is currently playing?
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#382486 - 09/05/12 02:00 PM Re: Looking for pre/pro all channels driven [Re: gearcruncher]
Ken.C Offline
shareholder in the making

Registered: 05/03/03
Posts: 17766
Loc: NoVA
I think what you've got there is the instantaneous power, rather than the RMS or average power, which could be distorting (ha!) the discussion somewhat.
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