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|5th September 2009, 22:29||#1|
Senior - BHPian
CEA 2006 Ratings
Found an amazing article by Andy Wehmeyer on the CEA 2006 ratings.
Tried pasting the text here, but it's formatted for a PDF.
Attaching the PDF link here.
It's a very interesting read by one of the respected men in the industry, and whose knowledge scales great heights.
Peruse the article and discuss it here. It will change a lot of perceptions about power ratings and amplifiers.
This article has been written by Andy, and no one else. SO any part of the text, if copied from this article, directly or indirectly, should give due credit to the original author of the article.
|7th September 2009, 15:37||#2|
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A bit OT :
You do know that Andy is a member here right ?
|8th September 2009, 10:58||#7|
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Say speaker impedance is 4 ohms.
Amplifer outout resitance is 0.1 ohms.
damping factor should be 4/0.1 = 40 right? worng!
you see a speaker impedance is 4 ohms not it's reactance (which is the working part of the impednace). The speaker is 3.2 ohms DC resistance and 0.8 ohms reactance.
so the 3.2 ohms is in series with the amp's output and has to be added to the amp's output. so the amp's effective output resistance is really 3.21 ohms.
now 4/3.21 = 1.24! ouch. now the good part. Speakers need damping most when they are least controlled (at resonance) which is when their impedance goes to 20. Now 20/3.21 = 6.23 much better but not 40 or 100 or 500 as oftne stated in amp specs. Hence Andy's conclusion.
Hope this helps. It is as simple as I can make it. Sam is better at simplifying things but these days he seems to have abandoned us. :-(
What Andy should have stated to freak more people out is "Most amplifer's nominal damping factor (meaning damping factor at nominal impedance) does not exceed 1.5" now that would ne theoretically true too. But Andy is a practical man. So he stated what is a practical damping factor in real world conditions over a wide range of speakers from PA to Pro to Car audio.
You see Andy is an old man. Like me his introduction intp audio amplifers was at a time when Valves (Tubes) ruled the roost. In those days we all knew that 'good iron' made all the difference. the reason being was that 'good iron' had high primary impedance and a very linear seconadry impedance. In those days single digit damping factors were common and hey the speakers did not sound all that bad.
Age still retains some of it's priviliges I guess! :-)
Last edited by navin : 8th September 2009 at 11:21.
|8th September 2009, 12:25||#8|
Thanks Navinji, that definitely helps. I believe that article was supposed to be an over-simplified one. I understood what he implied by most portion (at least I thought so!), except damping which was not clear.
BTW, does that mean general belief that a 4-ohm sub or mid would be better "controlled" by any given amp, as compared to 2-ohm or lesser, is a myth? or does it still hold true?
(I guess better answer lies in your experience from tubes to the modern day amps, rather than calculations)
|8th September 2009, 13:05||#9|
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See the problem is that high current low DCR voice coils also tend to be heavy which is why there has been a move towards aluminum EFW (Edge wound flat voice coils) ever since the mid 80s. Most manufacturers can use these coils only that AL-EFW coils cost significanlty more to make than the regular copper coils.
I see a lot of advantages with AL-EFW coils.
1. Anodised AL is an excellent conductor of heat with very high thermal breakdown voltage and yet is also an excellent electrical insulator
2. Edge wound coils have more contact area than coils made of round wire. Dynaudio, Morel and some others use hexagonal wire to get better contact area and hence dissapate heat faster
3. Copper coils need an enamel insulation which is a poor conductor of heat compared to anodised aluminum
4. Anodised AL is 1/2 the weight of a copper coil having the smae current carrying capability (Density of Copper is 8.9, Al is 2.3 but copper can carry twice the current for the same area (1.5x the dia) hence 8.9/4.6 = 2).
It used to be that terminating AL wire used to be more diffcult but today with ultrasonic welding this is not nesscarily true. EFW technology is now 3 decades old still many companies use it ony for the high end and Pro audio applications.
Last edited by navin : 8th September 2009 at 13:20.
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