J&M 7 1/4 rokkrs and RF pbr 300 watt amp question

[pontiac69]

I have the rokkrs installed and I bought a 300 watt 4 channel Rockford Fosgate amp to run the 2 speakers. The speakers are 2ohm and the amp says 75 watts per 4 channels at 4ohms. Is this a problem? I only have 2 fairing speakers.

[SonnyD]

Well if the amp is capable of 2 ohm operation..most good amps are, it will double the output to 150.. You only have to use 2 channels...just leave the other alone....or sometimes the amp is capable of being bridged from 4 channel to two, usually doubles the power again...I know nothing of the amp you have other then the Name.....

[Rhino40]

Amps rated at 4ohms per channel are stable and will operate with 2ohm speakers with no problem. As a rule of thumb cutting the ohms in half will double the power output, so make sure the speakers in question are designed to handle that much power.

There is an option with most amps to bridge two of the channels with one speaker (connect the positive wire from the speaker to the possitive terminal of one channel, and the negative wire from the same speaker to the negative terminal of the second channel, hence the "bridge"). This however will drop the rated impedence of the speaker by half as well. Thus if you have a 2ohm speaker and you bridge 2 channels, the amp will be seeing 1ohm of connected impedence. There are very few (and quite expensive amps) that are rated to function under those conditions.

So the long story short is, the amp you have will work fine, but only connect each speaker to their own channel and leave the other two channels of the amp alone. Your other option is to get new speakers rated at 4ohms and bridge one across channels 1&2 and bridge the other across channels 3&4.

[streetnoyz]

Originally Posted by Rhino40

Amps rated at 4ohms per channel are stable and will operate with 2ohm speakers with no problem. As a rule of thumb cutting the ohms in half will double the power output, so make sure the speakers in question are designed to handle that much power.

There is an option with most amps to bridge two of the channels with one speaker (connect the positive wire from the speaker to the possitive terminal of one channel, and the negative wire from the same speaker to the negative terminal of the second channel, hence the "bridge"). This however will drop the rated impedence of the speaker by half as well. Thus if you have a 2ohm speaker and you bridge 2 channels, the amp will be seeing 1ohm of connected impedence. There are very few (and quite expensive amps) that are rated to function under those conditions.

So the long story short is, the amp you have will work fine, but only connect each speaker to their own channel and leave the other two channels of the amp alone. Your other option is to get new speakers rated at 4ohms and bridge one across channels 1&2 and bridge the other across channels 3&4.

According to the manual for the rockford PBR amplifier page 7 4 OHM STEREO LOADS ONLY. if you have the boosted rail technology amp it will overheat and shut down at two ohm.
also this amp is not bridgeable.

great amp but limited cofigurations
Rockford Fosgate® - RFTECH Support

[Rhino40]

Originally Posted by streetnoyz

According to the manual for the rockford PBR amplifier page 7 4 OHM STEREO LOADS ONLY. if you have the boosted rail technology amp it will overheat and shut down at two ohm.
also this amp is not bridgeable.

great amp but limited cofigurations
Rockford Fosgate® - RFTECH Support

My appologies, I have an Arc Audio 125x2 in my bike, and a couple of JL audio amps in my mustang, all of which are bridgeable and stable at 2 ohms. I assumed the fosgate (given the high quality of the name) would have used similar technology, I learn something new every day. Good luck to the op ..... If you are set on the 2 ohm speakers, check out the Arc Audio KS1252 bx2 amp, it pounds thru my focal speakers and is designed to run at 2ohms.

[pontiac69]

I decided to buy the Rockford Fosgate 300x2 pbr amp. This one is 2 channel and 2 ohm stable.

[SonnyD]

Originally Posted by pontiac69

I decided to buy the Rockford Fosgate 300x2 pbr amp. This one is 2 channel and 2 ohm stable.

There ya go....but remember you will probably have to set the gains fairly low... that will be a lot of power to those speakers... Is that 2x300 at 4 ohm or 2.... if that is at 4 you will definitely have to "tread lightly" with the gain.... Hope all works well for you.....

[pontiac69]

Number of Channels: 2
Rated Power
(RMS Continuous Power): 100 Watts x 2 @ 4-Ohm
150 Watts x 2 @ 2-Ohm
300 Watts x 1 @ 4-Ohm Bridged
Total Power
(Sum of Rated Power): 300 Watts

[SonnyD]

Ah, 300x1 bridged, ok that's better... you can probably run the gains on about half or a little more......

[pontiac69]

No not 300x1. I am running a 300x2. That's 150 per channel. Right now I have a pair of J&M Rokker 7 1/4" speakers. They are rated at 170 watts.