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Math question - Speaker in parallel
Math question - Speaker in parallel
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Old 7th January 2018, 03:56 AM   #1
livingtool is offline livingtool  Argentina
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Question 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.
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Old 7th January 2018, 07:20 AM   #2
Keruskerfuerst is offline Keruskerfuerst  Germany
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Yes, this is correct.
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Old 7th January 2018, 07:37 AM   #3
globalplayer is offline globalplayer  Germany
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Also the damping factor will halve.
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Old 7th January 2018, 10:33 AM   #4
Keruskerfuerst is offline Keruskerfuerst  Germany
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The damping factor is 1/output resistance of amp.
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Old 7th January 2018, 10:38 AM   #5
globalplayer is offline globalplayer  Germany
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Yes.
It will be half on 4 ohms compared to the 8 ohms load.
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Old 7th January 2018, 06:31 PM   #6
conanski is offline conanski  Canada
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Quote:
Originally Posted by livingtool View Post
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 View Post
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.
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Old 14th January 2018, 10:12 PM   #7
Ron E is offline Ron E  United States
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Quote:
Originally Posted by Keruskerfuerst View Post
The damping factor is 1/output resistance of amp.
Damping factor = load impedance / output impedance

Quote:
Originally Posted by globalplayer View Post
Also the damping factor will halve.
...and halving it is not a problem.
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Old 17th January 2018, 08:48 PM   #8
globalplayer is offline globalplayer  Germany
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Quote:
Originally Posted by Ron E View Post
Damping factor = load impedance / output impedance


...and halving it is not a problem.
Not for you.
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Old 17th January 2018, 08:52 PM   #9
nigelwright7557 is offline nigelwright7557  United Kingdom
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Amp power 1.5 to 2 times speaker power will fry your speakers nicely if you don't take care !
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Old 8th February 2018, 10:29 AM   #10
Ron E is offline Ron E  United States
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Quote:
Originally Posted by globalplayer View Post
Not for you.
Not for anyone who understands it.
Can someone explain damping factor
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