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#198770 - 03/02/08 08:48 PM Re: Understanding Power Requirements [Re: jakewash]
mapatton Offline
local

Registered: 12/16/07
Posts: 243
Loc: Orlando, FL
 Originally Posted By: jakewash
When listening to the Planets, SPL meter in hand, the range peaks at 53 db. so 25 would not suffice, as we are talking total range.


Curious, how do you measure this with a SPL meter? I ask as mine is analog and the most range I can see at any range band is 16db.


Edited by mapatton (03/02/08 08:48 PM)
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Mark
Pio 94,SB3,BD30,A35,Pio 48AV.Pronto 7000 controlling all. Getting ready for 22s, 150 & QS8s.

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#198773 - 03/02/08 08:55 PM Re: Understanding Power Requirements [Re: mapatton]
SirQuack Offline
shareholder in the making

Registered: 01/29/04
Posts: 13344
Loc: Iowa
I've been told by a few audio manufaturers of amps that you can't totally trust the RS meter. You would need a more sophisticated meter like used in labs that cost lots more and respond much faster. Usually if a song has a 20dB spike, the RS meter will only respond as seeing 10dB.
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#198776 - 03/02/08 09:01 PM Re: Understanding Power Requirements [Re: SirQuack]
mapatton Offline
local

Registered: 12/16/07
Posts: 243
Loc: Orlando, FL
So get my friend who has a sudio with multiple SAs to pay me a visit \:\)

Was curious how Jake measured this
_________________________
Mark
Pio 94,SB3,BD30,A35,Pio 48AV.Pronto 7000 controlling all. Getting ready for 22s, 150 & QS8s.

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#198787 - 03/02/08 09:55 PM Re: Understanding Power Requirements [Re: mapatton]
jakewash Offline
shareholder in the making

Registered: 12/26/03
Posts: 10400
Loc: Calgary, Alberta
I just listened with my meter(not RS and digital) out in front of me and the medial low range was 53 for the quieter moments and I went back to the peak points with my meter in max hold range and found the loudest point was 103db, a 50db range on that cd.

I watched it for max spl while noting the low average and the average high was about 95db. I would guess using 40db insted of 50 would be a closer reality as the sudden and brief 103 db would be in that clipped area that might not be noticed.

Using the 40 db range gave me an amp power rating of only 50W\:\) while 2.5m @60SPL for 91 sensitivity.


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#198794 - 03/02/08 10:36 PM Re: Understanding Power Requirements [Re: jakewash]
mapatton Offline
local

Registered: 12/16/07
Posts: 243
Loc: Orlando, FL
 Originally Posted By: jakewash
I just listened with my meter(not RS and digital) out in front of me and the medial low range was 53 for the quieter moments and I went back to the peak points with my meter in max hold range and found the loudest point was 103db, a 50db range on that cd.

I watched it for max spl while noting the low average and the average high was about 95db. I would guess using 40db insted of 50 would be a closer reality as the sudden and brief 103 db would be in that clipped area that might not be noticed.

Using the 40 db range gave me an amp power rating of only 50W\:\) while 2.5m @60SPL for 91 sensitivity.



Thank you, I understand now you made a couple of measurement passes. Will offer my version a listen with the RS analog meter tomorrow as time allows.

Many thanks Again.
_________________________
Mark
Pio 94,SB3,BD30,A35,Pio 48AV.Pronto 7000 controlling all. Getting ready for 22s, 150 & QS8s.

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#198795 - 03/02/08 10:54 PM Re: Understanding Power Requirements [Re: fredk]
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10412
Fred, I quickly(too quickly)read the article and punched some of my typical numbers(3 meter listening distance, 89dB speaker sensitivity, 80dB average listening level, 20dB headroom above that to allow for an occasional peak on the most dynamic recordings)into the calculator. The result came up 113 watts, which was clearly far too high as I had in the past measured and calculated the power usage as about 32 watts in that 100dB peak situation. So, I read the article a little more closely to see what was wrong and saw that the factor they used in their distance formula was simply 20xlog(D2/Dref), and applying that indicated that what the calculator was doing with distance was reducing the sound level 6dB for every doubling of the distance. This is correct for an omnidirectional sound source operating either in an anechoic chamber or out of doors where room reflections don't reinforce the sound level, but a complete analysis in a typical listening room requires that this be taken into account, and makes a major difference.

Curiously, the article makes this rather basic point clear only near the end under "Other Considerations", where it's stated that the calculations apply only to anechoic or outdoor environments and suggests that a 6dB correction(i.e., reducing the power required to 1/4th of the previous result)be employed to account for the listening room. Following this suggestion, I used 14dB rather than 20dB of headroom in the calculator, and sure enough the result was 28 watts, much more closely in agreement with the 32 watt figure that I'd calculated.

So, without the room correction the calculator doesn't "work just fine for the rest of us", but gives power requirements about four times too high. Hopefully the fact that Crown deals in very high powered professional amplifiers wasn't a factor here.
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#198796 - 03/02/08 10:59 PM Re: Understanding Power Requirements [Re: mapatton]
jakeman Offline
aficionado

Registered: 10/03/05
Posts: 852
Loc: Toronto
I think your calculation is highly sensitive to your assumption that 40 db is sufficient. If you run the calculator at 40db you get 50W as sufficient.

However at just 43db you need 99W and if you tried to avoid clipping and used 50db, 496W. Once you hear it, clipping distortion is highly audible because its so annoying.

I actually like this AllegroSound calculator better because it factors in 5db room gain by adding it into the speaker sensitivity and uses peak SPL at the highest end of the range in the calculation.

http://allegro-sound.com/Power.html
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#198797 - 03/02/08 11:45 PM Re: Understanding Power Requirements [Re: jakeman]
jakewash Offline
shareholder in the making

Registered: 12/26/03
Posts: 10400
Loc: Calgary, Alberta
Funny thing is with the pop industry recording the music with very little dynamic range, it makes it easier to run lower wattage amps, since you have very little need for large amounts of head room. You would think the amp manufacturers would jump all over(support) the more dynamics in recording movements that are out there, which would hopefully lead to better recording again.
_________________________
Jason
-----------------
TTTHHHPPPPPTTTT!

My HT

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#198801 - 03/03/08 12:03 AM Re: Understanding Power Requirements [Re: JohnK]
fredk Offline
axiomite

Registered: 12/06/07
Posts: 7229
Loc: Canada
Thanks for pointing that out Johnk. I noticed it too, but I am not use to thinking in logarithmic terms.

Edit: I need to learn to read more carefully. First tiem 'round I assumed they did the subtraction in the formula.

OK, I built the calculator in Excell (minus rounding 'cause I know how you audiophiles like accuracy \:\) ) and it works.

So, where do I plug in the room adjustment? Where the formula adjusts for headroom? Hmm... need a sound engineer's help here. Now where would we find one of those??

Edit: ok, I see how the formula works now. Add 5 to sensitivity or take 5 off of listener spl or headroom, its all the same.

Maybe I should stick to simpler things at this time of night like cleaning my tub.



Edited by fredk (03/03/08 12:29 AM)
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#198808 - 03/03/08 07:37 AM Re: Understanding Power Requirements [Re: fredk]
jakeman Offline
aficionado

Registered: 10/03/05
Posts: 852
Loc: Toronto
Actually its better to add room gain correction to speaker sensitivity. Check out the calculator I posted above from Allegro Sound.
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