J&M 7 1/4 rokkrs and RF pbr 300 watt amp question - Harley Davidson Forums: Harley Davidson Motorcycle Forum
Harley-DavidsonForums.com is an independent enthusiast website owned and operated by VerticalScope Inc. Harley-DavidsonForums.com is not sponsored by or in any way affiliated with Harley-Davidson Inc.. The Harley Davidson names and logos are trademarks owned by Harley-Davidson Inc.

Go Back   Harley Davidson Forums: Harley Davidson Motorcycle Forum > Specific Model Areas > Touring General Discussions

» Insurance
» Our Partners
»ATV Reviews
»Motorcycle Games
Reply
 
LinkBack Thread Tools Display Modes
Old 11-05-2012, 12:26 AM   #1 (permalink)
Senior Member
 
pontiac69's Avatar
 
Join Date: Apr 2011
Location: PA
Posts: 129
J&M 7 1/4 rokkrs and RF pbr 300 watt amp question

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.
__________________
2012 FLHX Street Glide
pontiac69 is offline   Reply With Quote Quick reply to this message
Old 11-10-2012, 11:41 AM   #2 (permalink)
Senior Member
 
SonnyD's Avatar
 
Join Date: Jun 2009
Location: Overland Park, Ks
Posts: 525
Images: 23
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.....
__________________
2007 FLHX Street Glide
"The Herd" #35
SonnyD is offline   Reply With Quote Quick reply to this message
Old 11-10-2012, 12:04 PM   #3 (permalink)
Senior Member
 
Rhino40's Avatar
 
Join Date: Sep 2012
Location: Maryland
Posts: 130
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.
Rhino40 is offline   Reply With Quote Quick reply to this message
Old 11-10-2012, 02:13 PM   #4 (permalink)
Boooya!!!
 
streetnoyz's Avatar
 
Join Date: Nov 2008
Location: san diego
Posts: 2,764
Images: 2
Quote:
Originally Posted by Rhino40 View Post
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
__________________
MooooMember 00023

Father giving advice to son: Never do anything once around the house that you don't want to do for the rest of your life.
- Frank Briggs


A man isn't a man until he has to meet a payroll.
- Ivan Shaffer

You're not drunk if you can lie on the floor without holding on.
- Dean Martin

Last edited by streetnoyz; 11-10-2012 at 02:15 PM. Reason: add info
streetnoyz is offline   Reply With Quote Quick reply to this message
Old 11-10-2012, 02:57 PM   #5 (permalink)
Senior Member
 
Rhino40's Avatar
 
Join Date: Sep 2012
Location: Maryland
Posts: 130
Quote:
Originally Posted by streetnoyz View Post
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.
Rhino40 is offline   Reply With Quote Quick reply to this message
Old 11-10-2012, 11:38 PM   #6 (permalink)
Senior Member
 
pontiac69's Avatar
 
Join Date: Apr 2011
Location: PA
Posts: 129
I decided to buy the Rockford Fosgate 300x2 pbr amp. This one is 2 channel and 2 ohm stable.
__________________
2012 FLHX Street Glide
pontiac69 is offline   Reply With Quote Quick reply to this message
Old 11-11-2012, 07:42 AM   #7 (permalink)
Senior Member
 
SonnyD's Avatar
 
Join Date: Jun 2009
Location: Overland Park, Ks
Posts: 525
Images: 23
Quote:
Originally Posted by pontiac69 View Post
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.....
__________________
2007 FLHX Street Glide
"The Herd" #35
SonnyD is offline   Reply With Quote Quick reply to this message
Old 11-12-2012, 11:36 PM   #8 (permalink)
Senior Member
 
pontiac69's Avatar
 
Join Date: Apr 2011
Location: PA
Posts: 129
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
__________________
2012 FLHX Street Glide
pontiac69 is offline   Reply With Quote Quick reply to this message
Old 11-13-2012, 12:48 AM   #9 (permalink)
Senior Member
 
SonnyD's Avatar
 
Join Date: Jun 2009
Location: Overland Park, Ks
Posts: 525
Images: 23
Ah, 300x1 bridged, ok that's better... you can probably run the gains on about half or a little more......
__________________
2007 FLHX Street Glide
"The Herd" #35
SonnyD is offline   Reply With Quote Quick reply to this message
Old 11-15-2012, 11:30 PM   #10 (permalink)
Senior Member
 
pontiac69's Avatar
 
Join Date: Apr 2011
Location: PA
Posts: 129
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.
__________________
2012 FLHX Street Glide
pontiac69 is offline   Reply With Quote Quick reply to this message
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Harley Davidson Forums: Harley Davidson Motorcycle Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Display Modes

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Powered by vBadvanced CMPS v3.2.2

All times are GMT -5. The time now is 09:35 PM.



Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Search Engine Optimization by vBSEO 3.6.0
Garage Plus vBulletin Plugins by Drive Thru Online, Inc.
This site is in no way affiliated with Harley-Davidson
Motorcycle News, Videos and Reviews
Honda Grom Forum Harley Davidson Forum Honda 600RR Forum Kawasaki Forum Yamaha R6 Forum Yamaha FZ-09 Forum
1199 Panigale Forum Roadglide Forum Honda CBR1000 Forum Vulcan Forum Yamaha R1 Forum Yamaha R3 Forum
Ducati Monster Forum Harley Forums Honda CBR250R Forum ZX10R Forum Star Raider Forum Yamaha Viking Forum
Suzuki GSXR Forum V-Rod Forums Honda Shadow Forum Kawasaki Motorcycle Forum Star Warrior Forum KTM Duke 390 Forum
SV650 Forum BMW S1000RR Forum Honda Fury Forum Kawasaki Versys Forum Drag Racing Forum Ducati 899 Panigale Forum
Suzuki V-Strom BMW K1600 Triumph Forum Victory Forums Sportbikes BMW NineT Forum
Volusia Forum BMW F800 Forum Triumph 675 Forum MV Agusta Forum HD Street Forum Suzuki GW250 Forum
Yamaha Motorcycles Victory Gunner Forum Honda Vultus Forum HD LiveWire Forum Ninja H2 Forum Ducati Scrambler Forum Kawasaki Ninja 250SL Forum