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question about bridging?

Fun_Bucket

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Hey guys my question is about bridging a 4 channel amp..
If the amp puts out 100RMS per channel, i always assumed that if your bridged it to form 2 channels, then you would then get 200RMS x 2 channels? is this correct, because i have read on the specs for a few amps, that when given their rated bridged outputs, they are higher than the power of the 2 channels combined, with the impedance unchanged...
 

Fun_Bucket

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Hmm, got a little lost in reading that one lol
Ok well basically i'm looking at a 4x 100 RMS amp, which is only going to be used to run front splits.
I thought ok bridge the channels, to 2 channel, and run the splits.I thought this would give me 2 x 200 RMS, but the amp says it will give me 2 x 320, which i think would be way overkill for front splits.
 

sweefu

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hey mate, just what i've found but generally the power is increased when bridging, though 320 sounds like a big jump to me, i have a 50wrms x 4 and when i bridge that i get 120wrms x 2. Hope this helps.
Cheers
 

theSeekerr

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Advice: Too much power is never a bad thing - it's nearly always too little power, not too much, that will cause a speaker, particularly a tweeter to blow. Why? Because if you drive the output stage to clipping, you're suddenly dealing with DC power for a not-insignificant time period, and tweeters HATE that.

That said, obviously having the extra power can facilitate turning up the volume to the point where you'll exceed the speakers rated power output, either by mechanically destroying themselves by attempting to exceed x-mech, or thermally. But if you're listening that loud, you were going to try to do it anyway, and destroy your speakers when the amps clipped.

(nb - this advice comes from years of experience in the pro-sound industry, where we like to have at least 6dB, and preferably 10dB worth of headroom whenever possible - a 15 watt tweeter gets at least a 60 watt amplifier, a 200 watt sub will have an 800 watt amp, and so on - at the ridiculous end of the scale, it tends to scale back a bit - a so-called 2000 watt sub might be able to handle that thermally, but run out of mechanical excursion at 500.)

Actual answer you asked for: Most car amps are limited in the voltage they can swing, not the current they can supply. Bridging effectively doubles the voltage an amp can swing, and because Ohms law tells us that

Power = Voltage Squared / Impedance

you can see that what you should actually get is 4 times the power. However, having doubled the voltage swing, now you'll probably find the amp is current limited, so you'll see somewhere > 2 times the power, but not quite 4.

(At least, I think that's how it works. I'm only a first year Elec Eng student, so I do get things wrong sometimes.... :whistling: )
 

holdenboy

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Interesting read there mate ^^

You will never even get close to 3 times the power when bridging channels, twice the power is common.

100wrms turning into 320wrms when bridged? i do doubt that. Its basically turning a 400wrms amplifier into a 640wrms amplifier without changing the impedance. What are the power figures for 2 ohm not bridged?
 

Fun_Bucket

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So thats what i thought , twice the power, i dont understand where the extra power can come from. I have read through that entire post as listed above, but having a limited knowledge when it comes to audio, let alone electrical, i may have to do a bit more research/study...

here are a just one example, and a reason why i'm becoming confused. This is straight from Soundstream to BTW

Specifications
Power 4ohm:
80 x 4
Power 2 ohm:
155 x 4
Power 4ohm Bridged:
310x 2
X-Over Freq.
-
Dimension
390 x 52 x 205

See i thought, 80 x 4, would be 160 x 2, being it's still at the same impedance, but their claiming 310 at 4Ohm, which like HoldenBoy said earlier, is a big jump..
So if i'm reading right, bridging a channel/s, draws more voltage, which results in the extra power??? But i'm still confused because the figures were quoted at 13.8-14.4.V ect, how does the amp draw the extra voltage from the battery?

Thank you to everyone trying to help me to understand, there's only so much searching and reading i can do online....
 
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bezz

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Good advice by theSeekerr. Just to expand on what he said, bridgable amplifiers will have one of the two channels 180 degrees out of phase to the other. This effectively doubles the peak to peak voltage available, allowing for increased power output as proved above using the power eq and ohms law. Here's something I whipped up for ya to explain it (disregard the values on the axes, theyre leftover from something else):


The top plot is a sine wave, say from ch1 of the amp. If you were to draw a vertical line from the peak of the signal to 0 on the y axis, this would tell you the maximum voltage of the signal. The second is the same sine wave, 180 degrees out of phase as output by ch2 (same deal here with the peak voltage). Bridging these two channels gives you the third plot. If you look at the final plot, the first signal hits its maximum at the same time the second signal hits its minimum. Hence if you draw another vertical line, this time between the two peaks you can easily see why the voltage is effectively doubled.
 

2LOUD2OLD

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the extra power comes from the fact that the indivdual channels are running at a lower impendance ie 2ohms in order to run at 4ohms bridged
therefore you add the values at 2 ohms to give you what you will get at 4 ohms bridged.
if you were running the amp at 8ohms bridged then yes it would only be double as each channel would still be running at 4 ohms
 

StoneX

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theSeekerr is correct. A good amp WILL make 4x the power when bridged.

Interesting read there mate ^^

You will never even get close to 3 times the power when bridging channels, twice the power is common.

100wrms turning into 320wrms when bridged? i do doubt that. Its basically turning a 400wrms amplifier into a 640wrms amplifier without changing the impedance. What are the power figures for 2 ohm not bridged?
4 ohm bridged is actually 2 ohm stereo... Not 4 ohm stereo, so 4 ohm bridged HAS to be more than twice the 4 ohm stereo rating.

Examples:
Rockford Fosgate 800a4
Rockford Fosgate Power T4004
Precision Power PC21400.2
Precision Power PC4400.2
Soundstream Tarantula TR1600/2
US Amps USA-2000x
Xtant 403A
Xtant X604
Zapco Studio 500
Alpine MRV-1507
Coustic 321QE
Crossfire VR404
Diamond D3 400.4
Eclipse 3242
Hifonics Cupid VII

Anyway, there's a heap that can do it and a heap that can't... It's physically possible, but the amp has to be well built.
 
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