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Old 08-07-2008, 02:09 PM   #1
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Default 8 ohm bridged vs. 2 ohm stereo

When an amplifier manufacturer gives an RMS rating for bridged mode, do you assume that it is at 4ohms if unspecified?

The reason I ask is because my 2 channel amplifier (Power Acoustik BAMF 1250) has a rating of 560 Watts Bridged, but does not specify at what impedance. However, it says it recommends 4-8 ohms only in bridged mode.

After hooking my 4ohm DVC Rockford Fosgate subwoofer (wired at 8 ohms), it seems a little weak (also sounds distant) even though it's RMS is 400 watts. I'm assuming at 8 ohms it's only getting 280 watts bridged.

I know I will get more power by running this subwoofer at 2 ohms stereo rather than 8 ohms bridged/mono, but are there any pros and/or cons of wiring it this way?

I've searched and can't find much info on 8 ohm bridged vs 2 ohm stereo, only 8ohm brigded vs 4ohm stereo which is not applicable to this subwoofer.


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Old 08-07-2008, 02:38 PM   #2
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Default Re: 8 ohm bridged vs. 2 ohm stereo (MilanoLude)

This is power acoustik specs page for this amp . pdf. @ the bottom of page 5

http://www.poweracoustik.com/p...8.pdf

Bridged 2 ohms is 560 rms. It is 2 ohms to answer your question.
2 ohms is 280x2
4 ohms is 220x2
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Old 08-07-2008, 02:49 PM   #3
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Default Re: 8 ohm bridged vs. 2 ohm stereo (schmiddr2)

I have that same spec chart here in the owner's manual. I guess I didn't think to do the addition myself. It claims it's only 2 ohm stable in stereo, so why would they say 560 watts at 2 ohms bridged when they recommend 4-8 ohms bridged?

I'd imagine it wouldn't be a good idea to bridge 2 ohms with this amp. Even though they give the power rating for doing so. Pretty misleading.

So really at 8ohms bridged I am only getting 187 watts, correct?

Modified by MilanoLude at 3:55 PM 8/7/2008


Modified by MilanoLude at 3:55 PM 8/7/2008
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Old 08-07-2008, 03:53 PM   #4
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Default Re: 8 ohm bridged vs. 2 ohm stereo (MilanoLude)

Being a 2 channel amp they assume you will be using it for component speakers. And in that case 4-8 is great for sound quality. It allows the speakers to produce a more clean sound for vocals and mid/high sounds.

When a subwoofer is connected to an amp at 2 ohms it is less of a sound issue and more of a power issue vs. wired at 4 ohms. I don't see a problem with using this amp at 2 ohms bridged. It all depends on your subwoofers though.

Probably around 187, yes.

What subs do you have and what kind of box?
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Old 08-07-2008, 05:15 PM   #5
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Default Re: 8 ohm bridged vs. 2 ohm stereo (schmiddr2)

I have one (RFP-1212) 12" Rockford Fosgate Punch DVC 2x4 ohm subwoofer in a sealed box filled with polyfill that is a little smaller than the recommended enclosure size. It's one of their older models, but all the specs are archived in this pdf: http://www.rockfordfosgate.com...n.pdf

400 watts RMS
800 watts Peak

I actually had that particular subwoofer connected to a RF Punch 75.2 amplifier , it was bridged at 2 ohms and worked for many years, but it took a crap recently so I replaced all the wiring and amplifier with something new. It ran pretty hot at 2 ohms, it would overheat sometimes during moderate length trips on hot days.

For that amp the specs are
37.5 x 2 @ 4 ohms
75 x 2 @ 2 ohms
150 bridged @ 4 ohms

I figured this new amplifier would be better matched with the subwoofer (closer to 400 watts RMS @ 8 ohms) , but I didn't check that the 560 watts of the power acoustik was at 2 ohms. I just assumed 4 ohms. . . and you know what assuming does.


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Old 08-08-2008, 09:13 AM   #6
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Default Re: 8 ohm bridged vs. 2 ohm stereo (MilanoLude)

You have 2 options.

1 - 8 ohm (series) bridged 374watts rms of power. Cannot max out the sub but will have better sound quality. Not as stressful for the equipment. Since the box is a little small I would recommend this route.
2 - 2 ohm (parallel) bridged 560watts rms power. Will max out sub, but amp will need to be turned down to match the subs needs. Stand a chance of burning something up especially if played at high volume for a long time.
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