Math question - Speaker in parallel
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 7th January 2018, 03:56 AM #1 livingtool   diyAudio Member   Join Date: Jan 2018 Location: Argentina Math question - Speaker in parallel Hi all. I'm Pablo from Argentina. I'm putting together a medium PA system. 4 x 350watts full range, 8 ohms, passive speakers (2 for each channel, in paralell) Digital Power Amp with a 1200watts per channel at 4 ohms. As I understand it, each channel will have a load of 4 ohms and add to a maximum of 700 watts. That will leave a 500 watts headroom, taking into account the "rule" of "1.5 to 2 times the amp". Is my math ok? Thanks for the help. PS: sorry if my english isn't so good.
 7th January 2018, 07:20 AM #2 Keruskerfuerst   diyAudio Member     Join Date: May 2007 Location: Germany Yes, this is correct.
 7th January 2018, 07:37 AM #3 globalplayer   diyAudio Member     Join Date: Oct 2014 Location: =) Also the damping factor will halve. __________________ ◢◣◢◣◢◣◢◣◢◣
 7th January 2018, 10:33 AM #4 Keruskerfuerst   diyAudio Member     Join Date: May 2007 Location: Germany The damping factor is 1/output resistance of amp.
 7th January 2018, 10:38 AM #5 globalplayer   diyAudio Member     Join Date: Oct 2014 Location: =) Yes. It will be half on 4 ohms compared to the 8 ohms load. __________________ ◢◣◢◣◢◣◢◣◢◣
conanski
diyAudio Member

Join Date: Mar 2013
Quote:
 Originally Posted by livingtool 4 x 350watts full range, 8 ohms, passive speakers As I understand it, each channel will have a load of 4 ohms and add to a maximum of 700 watts.
Depends.. is that 350w speaker rating at rms, program, or peak?

Quote:
 Originally Posted by livingtool taking into account the "rule" of "1.5 to 2 times the amp".
Your math is good but unfortunately sizing amps is not that simple. That "rule" was developed when music had relatively high dynamic range with short duration peaks and the suggestion was to have an amp capable of up to 2 times the program rating of the speaker to be able to deliver music peaks without clipping the amp.
With the way the most popular genres of modern music are mastered for maximum loudness these days(almost zero dynamics), if you were to put that much power into a speaker it will only last a short period of time. So you need some way to limit amp output to something the speakers can survive on a case by case basis. Do your amps have adjustable limiters and are they simple peak limiters or are there rms limiters too?

Last edited by conanski; 7th January 2018 at 06:33 PM.

Ron E
diyAudio Member

Join Date: Jun 2002
Location: USA, MN
Quote:
 Originally Posted by Keruskerfuerst The damping factor is 1/output resistance of amp.
Damping factor = load impedance / output impedance

Quote:
 Originally Posted by globalplayer Also the damping factor will halve.
...and halving it is not a problem.
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globalplayer
diyAudio Member

Join Date: Oct 2014
Location: =)
Quote:
 Originally Posted by Ron E Damping factor = load impedance / output impedance ...and halving it is not a problem.
Not for you.
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 17th January 2018, 08:52 PM #9 nigelwright7557   diyAudio Member     Join Date: Apr 2008 Location: Carlisle, England Amp power 1.5 to 2 times speaker power will fry your speakers nicely if you don't take care ! __________________ PCBCAD51 pcb design software. 2018 version out now with lower prices >> http://www.murtonpikesystems.co.uk
Ron E
diyAudio Member

Join Date: Jun 2002
Location: USA, MN
Quote:
 Originally Posted by globalplayer Not for you.
Not for anyone who understands it.
Can someone explain damping factor
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Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. —Aldous Huxley

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