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Old 18th October 2004, 02:26 AM   #1
percy is offline percy  United States
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Default Understanding headroom and required power

Just want to make sure I am understanding this correctly -

While playing music it is not uncommon to have 10-12db peaks.(right?)

If an amplifier can deliver 100W rms into a load before clipping the signal, then to accomodate a 12db peak without clipping it, the amp should be playing normally at no more than 6.25W rms. Anything more than 6.25W rms would make the amp deliver more than 100W on the 12db peak and hence it would clip.

Am I within the navigational beacons or way off course ?!
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Old 18th October 2004, 02:50 AM   #2
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That's about it. Remember, though, that many amps will have anywhere between 2 to 5db of head room allowing them to deliver greater short term power.
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Old 18th October 2004, 02:52 AM   #3
Eva is offline Eva  Spain
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You are right. Average power of music signals is very low in comparison with peak power. Ratios from 4:1 to 20:1 are common

Class G and H take advantage of this fact to reduce dissipation by changing rail voltages depending on signal requirements
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Old 18th October 2004, 04:26 PM   #4
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The Crown Macro Reference amp was touted as the only true amp capable of 120dB of headroom!

It has a monsterous power rating of 760W @ 8ohms per side+++

This is an amazing amp from a specs point of view. the white paper on it was fascinating!

The output Impendence is so low, they were able to acheive a damping factor of 20,000!!!!! thats right 20K!!! most amps are what??? 100-200???

The white paper stated that the only way to effectively couple the amp to a speaker, without affecting the output impedance would be to use 00 welding cable or 2" copper pipe filled with solid silver!!!!

Now thats a monster!

Even the Big Boy Krells tuned there nose up at it!

it supposedly comes very close in sound quality to the big Krells, just a slightly recessed midrange from what i have read when compared to a KSA-250!!!

This is 2nd on my list of Dream Amps!!


Zero
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Old 18th October 2004, 07:23 PM   #5
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Quote:
Originally posted by Zero Cool
The Crown Macro Reference amp was touted as the only true amp capable of 120dB of headroom!

I don't think so. How about 12db?
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Old 18th October 2004, 08:12 PM   #6
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Nope, 120 dB! as in one hundred twenty!!!

I am using headroom wrong in this description however. the amp was stated as having 120dB of dynamic range. i guess thats a better description.


I will dig up the Audio magazine article and see if i still have the white paper on it.
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Old 18th October 2004, 09:00 PM   #7
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120dB dynamic range makes more sense. Yes.

In fact 120dB dynamic range is really impressive, if true.
To be honest, my own designs usually are limited much lower...
...already limited by the S/N ratio, where I typically range between
100dB ... 110dB.... (including hum)
Well, there is always somebody who can do better


@Percy:
I agree to you & eva & bill.
Average power load during normal music is far below the
peaks.
And that's the reason, why I do not really understand the discussion about some ultraoversized PSU. A discussion about a low impedance PSU would make much more sense in my perception.

Cheers Markus
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Old 18th October 2004, 10:07 PM   #8
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This is why we are fond of high efficiency loudspeakers. If you really want lifelike dynamics, nothing else will do, especially if you want those dynamics while using a 20W JLH amplifier!

http://www.highefficiencyloudspeakers.com/default.asp
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Old 18th October 2004, 10:58 PM   #9
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Originally posted by ChocoHolic
120dB dynamic range makes more sense. Yes.

Well, there is always somebody who can do better


Cheers Markus
If you over design enough, just about any result can be achieved. When compared to cost?? Well, this is another subject.
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