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Author Topic: Interpret this spec  (Read 9935 times)

David Allred

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Interpret this spec
« on: December 20, 2014, 06:11:03 PM »

2 x 250w @ 4 ohms
2 x 140w @ 8 OHMS
4 Ohm min load

This on a Behringer PMP550M powered head with 2) 1/4" speaker outputs labeled as "parallel outputs".  There are 2) 8 ohm speakers on one output and 2) 8 ohm speakers on the other. 

What is the deal?  How can they be parallel AND allow 4 ohms on each output AND have a 4 ohm min load?
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John Roberts {JR}

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Re: Interpret this spec
« Reply #1 on: December 20, 2014, 06:27:25 PM »

2 x 250w @ 4 ohms
2 x 140w @ 8 OHMS
4 Ohm min load

This on a Behringer PMP550M powered head with 2) 1/4" speaker outputs labeled as "parallel outputs".  There are 2) 8 ohm speakers on one output and 2) 8 ohm speakers on the other. 

What is the deal?  How can they be parallel AND allow 4 ohms on each output AND have a 4 ohm min load?

Is this a trick question...

There are two channels of power amp. Each channel can make make 140W at 8 ohms or 250W at 4. Each output has two 1/4 jacks so when you plug in two 8 ohm speakers you get 4 ohms (2x8 Ohms in parallel is 4 ohms).

The 4 ohm minimum load is for each channel of amp. If you put all 4 speakers on one amp that would be less than 4 ohms but you don't have enough jack holes to use it wrong like that.

Whats the problem?

JR
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Paul G. OBrien

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Re: Interpret this spec
« Reply #2 on: December 20, 2014, 07:03:35 PM »

Each output has two 1/4 jacks Whats the problem?


This unit only has two 1/4 outputs total meaning 1 per amp channel.. if.. this unit actually has 2 amp channels and that isn't a typo. Also notice it only has a single LED bar graph meter on the front panel not a stereo pair so this is a mono amplifier meaning no matter what you connect to the inputs the output signal will be the same on both outputs. If this unit actually does have 2 discrete amps then that just means everything is combined to a mono signal before it gets to the power amplifiers.
I'd bet Behringer has muffed the description of this unit, It's probably just has a single mono amplifier and the advertising dept didn't quite understand the engineering dept when they got the description.
« Last Edit: December 20, 2014, 07:08:13 PM by Paul G. OBrien »
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David Allred

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Re: Interpret this spec
« Reply #3 on: December 20, 2014, 08:51:35 PM »

Paul, You read correctly and see the real issue.  The description I gave is straight from the rear of the head at the output.
"2 x 250w @ 4 ohms
2 x 140w @ 8 OHMS
4 Ohm min load"
&
"parallel outputs" on the only 2 1/4" jacks.
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John Roberts {JR}

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Re: Interpret this spec
« Reply #4 on: December 20, 2014, 09:29:02 PM »

Looking at the rear panel there are only two jacks, apparently one for each amp..

They are labelled parallel because it's a mono head so both amps have the same signal.  Apparently they don't have a 500 W mono amp but a 2x250W stereo amp, so they put the stereo amp into the mono head.

To use 4  8 ohm speakers you will have to figure out how to plug two into each amp channel. Some cheap speakers have mult jacks on the speakers to make them easier to parallel.

good luck.

JR

PS: I feel a little dirty doing customer service for behringer.  :o
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paul bell

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Re: Interpret this spec
« Reply #5 on: December 20, 2014, 10:28:43 PM »

The "paralleled speaker output" would normally mean the two output jacks are connected together in parallel.

Not so with this amp, they are NOT paralleled, they are two separate outputs from two separate amplifier channels. As per the specs, it's rated at 250 + 250 watts.

It should not be marked with "paralleled speaker output" as it's actually not connected that way.

Plug in a 4 Ohm load to each jack and you'll have 500 watts total.
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Keith Broughton

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Re: Interpret this spec
« Reply #6 on: December 21, 2014, 07:18:34 AM »

Also. should it not read 4 ohm MAXIMUM load?
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Scott Holtzman

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Re: Interpret this spec
« Reply #7 on: December 21, 2014, 07:30:19 AM »

No....4 ohms is less than 8....presenting a load with a lower resistance result in the amplifier exceeding it's abilities. 

Low  impedance loads require good engineering and a healthy margin of "over engineering" to work well.
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Scott AKA "Skyking" Holtzman

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David Allred

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Re: Interpret this spec
« Reply #8 on: December 21, 2014, 08:57:47 AM »

Thanks all.
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Keith Broughton

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Re: Interpret this spec
« Reply #9 on: December 21, 2014, 12:30:22 PM »

No....4 ohms is less than 8....presenting a load with a lower resistance result in the amplifier exceeding it's abilities. 

Low  impedance loads require good engineering and a healthy margin of "over engineering" to work well.
That is correct.
When you lower the resistance, you increase the load on the amplifier.
Therefore to say "4 ohm minimum load" is not accurate.
4 ohms presents the maximum load the amplifier is designed for.
It could read "do not use less than 4 ohm load"
I know...splitting hairs. ;)
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ProSoundWeb Community

Re: Interpret this spec
« Reply #9 on: December 21, 2014, 12:30:22 PM »


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