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Author Topic: Ohm and speaker question  (Read 5023 times)

chad kaleb

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Ohm and speaker question
« on: July 16, 2011, 11:54:08 pm »

So I have a Behringer EP4000 power amp that I am running two mains on one side and two subs on the other.  At 4 ohms the power is 1400w and at 8 it is at 750w, so if I am running two 4 ohm speakers on one side would that be 8 ohm power output.  And if that is 8 ohm power output is it putting 750w to each speaker or is it split in half.
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Chris Davis

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Re: Ohm and speaker question
« Reply #1 on: July 17, 2011, 12:19:49 am »

So I have a Behringer EP4000 power amp that I am running two mains on one side and two subs on the other.  At 4 ohms the power is 1400w and at 8 it is at 750w, so if I am running two 4 ohm speakers on one side would that be 8 ohm power output.  And if that is 8 ohm power output is it putting 750w to each speaker or is it split in half.
First off, two 4 Ohm speakers on the same amp channel would be 2 Ohms.  Furthermore, let's say a single 4 Ohm subwoofer draws up to 1400 Watts.  If you put two of them on the same amp channel, then you would be potentially drawing 2800 Watts at 2 Ohms.
So you better have an amp that can dish that out.  When you are thinking about wattage, think from the speaker and work your way backwards to the amp, and make sure it can supply the amount  the speakers need, not the other way around.


P.S. Just remember...wattage "happens" at the speakers, not at the amp.
« Last Edit: July 17, 2011, 12:36:32 am by Chris Davis »
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Brad Weber

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Re: Ohm and speaker question
« Reply #2 on: July 17, 2011, 01:04:09 am »

So I have a Behringer EP4000 power amp that I am running two mains on one side and two subs on the other.  At 4 ohms the power is 1400w and at 8 it is at 750w, so if I am running two 4 ohm speakers on one side would that be 8 ohm power output.  And if that is 8 ohm power output is it putting 750w to each speaker or is it split in half.
First off, two 4 Ohm speakers on the same amp channel would be 2 Ohms.
Two nominal 4 Ohm speakers in parallel would be a nominal 2 Ohm load, but two nominal 4 Ohm speakers in series would an an 8 Ohm load.  The resulting total impedance is a factor of not just how many speaker but also how they are wired.
 
Furthermore, let's say a single 4 Ohm subwoofer draws up to 1400 Watts.  If you put two of them on the same amp channel, then you would be potentially drawing 2800 Watts at 2 Ohms.
So you better have an amp that can dish that out.  When you are thinking about wattage, think from the speaker and work your way backwards to the amp, and make sure it can supply the amount  the speakers need, not the other way around.


P.S. Just remember...wattage "happens" at the speakers, not at the amp.
Power is delivered into the speaker by the amplifier, however speakers do not 'draw' power, the amp delivers voltage and current into the attached load (the speaker).  Also, the power rating on a speaker it does not reflect how much power is needed, it indicates how much power the speaker can handle based on a standardized test.  How much power is needed is a factor of the desired speaker output and the speaker sensitivity.
 
 
Chad, the power would be split between the two speakers on that channel, however it may be important to identify how the two speakers are wired as together they could be a 2 Ohm or an 8 Ohm load.  I'd also skip the 'Peak Power' ratings of the EP4000 and use the lower 20-20kHz at 1% THD ratings.
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chad kaleb

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Re: Ohm and speaker question
« Reply #3 on: July 17, 2011, 01:26:28 am »

First off, two 4 Ohm speakers on the same amp channel would be 2 Ohms.
Two nominal 4 Ohm speakers in parallel would be a nominal 2 Ohm load, but two nominal 4 Ohm speakers in series would an an 8 Ohm load.  The resulting total impedance is a factor of not just how many speaker but also how they are wired.
 Power is delivered into the speaker by the amplifier, however speakers do not 'draw' power, the amp delivers voltage and current into the attached load (the speaker).  Also, the power rating on a speaker it does not reflect how much power is needed, it indicates how much power the speaker can handle based on a standardized test.  How much power is needed is a factor of the desired speaker output and the speaker sensitivity.
 
 
Chad, the power would be split between the two speakers on that channel, however it may be important to identify how the two speakers are wired as together they could be a 2 Ohm or an 8 Ohm load.  I'd also skip the 'Peak Power' ratings of the EP4000 and use the lower 20-20kHz at 1% THD ratings.

Okay, I have the two speakers wired in series so that would mean it is an 8 ohm load and the 750 watts would be split between the two speakers, so each would be getting roughly 375 right?
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Chris Davis

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Re: Ohm and speaker question
« Reply #4 on: July 17, 2011, 01:33:10 am »

First off, two 4 Ohm speakers on the same amp channel would be 2 Ohms.
Two nominal 4 Ohm speakers in parallel would be a nominal 2 Ohm load, but two nominal 4 Ohm speakers in series would an an 8 Ohm load.  The resulting total impedance is a factor of not just how many speaker but also how they are wired.
 Power is delivered into the speaker by the amplifier, however speakers do not 'draw' power, the amp delivers voltage and current into the attached load (the speaker).  Also, the power rating on a speaker it does not reflect how much power is needed, it indicates how much power the speaker can handle based on a standardized test.  How much power is needed is a factor of the desired speaker output and the speaker sensitivity.
 
 
Chad, the power would be split between the two speakers on that channel, however it may be important to identify how the two speakers are wired as together they could be a 2 Ohm or an 8 Ohm load.  I'd also skip the 'Peak Power' ratings of the EP4000 and use the lower 20-20kHz at 1% THD ratings.

Good academic points.  In trying to provide the "short version", one inevitably will miss out on other tangible ideas and possibilities. 
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Chris Davis

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Re: Ohm and speaker question
« Reply #5 on: July 17, 2011, 01:37:31 am »

Okay, I have the two speakers wired in series so that would mean it is an 8 ohm load and the 750 watts would be split between the two speakers, so each would be getting roughly 375 right?

Right - if they are wired in series.  But are they mounted in the same box or something?
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Chris Carpenter

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Re: Ohm and speaker question
« Reply #6 on: July 17, 2011, 06:13:17 am »

Chad, the reason Chris D asks, is because if the speakers you are asking about are not in the same cabinet, and you have not specially fabricated cables to wire them in series, they are probably wired in parallel.

Also, pay attention to what Brad said about peak vs RMS power. Those behringer amps are already very optimistically rated (1%THD vs 0.1%THD), and going by the peak rating doesn't really give you any usable information. At RMS, your amp is rated at 550w for 8 ohm, and 1250w for 2 ohm per side.

To answer your original question, yes. If you have two speakers wired on the same amplifier channel, regardless of how it is wired, the output power is split between the two speakers. How much power the amplifier delivers to each channel depends on the total impedance, which depends on the wiring.

If you ran a cable from one side of the amplifier to speaker cabinet A, then from speaker cabinet A to speaker cabinet B, you have wired them in parallel, and are sending 625watts to each speaker. If you connected the positive terminal of speaker A to the negative terminal of speaker B, then wired the negative terminal of speaker A and the positive terminal of speaker B to one side of the amplifier, you have wired the speakers in series and are sending 275watts to each speaker.
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ProSoundWeb Community

Re: Ohm and speaker question
« Reply #6 on: July 17, 2011, 06:13:17 am »


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