I modified the procedure in the sticky for my setup (PBR300x2 amp and MM651 speakers) ..
Hoping someone can assure I did this right.. guess I don't need to post the whole process but will go ahead.. Main thing I want to assure is that my "V" of 28.46 is accurate..

Setting your amp gains with DMM

*IMPORTANT* Disconnect speaker output wires from amplifier to speakers during this procedure otherwise you will stress the speakers and could possibly damage them when sending this 1000hz tone through the amplifier. Also disconnect any speakers that are connected directly to the HU.

This is the down and dirty way to test and set your gain controls on your amplifier with a DMM to properly drive your speakers without the amplifier clipping. To test a subwoofer, the process is the same; you simply need a lower frequency test tone for subwoofer frequencies such as 50hz. I don’t suggest you use an iPod to do this mainly because you’ll have to worry about the equalizer settings on that device too. I recommend on 5.25”, 6.5”, or 7.25" coaxial or 3 way speakers, as most are using on their bikes, that you use a 1000Hz 0db test tone to conduct this procedure. This procedure is the same regardless if using RCA inputs to the amp or line-level inputs (speaker wire inputs)

Abbreviations
HU – Head Unit or Radio
DMM – Digital Multi Meter
AP – All Pass – allows all frequencies to pass to speaker
HP – High Pass – allows all signals over a certain frequency to pass to speaker
LP – Low Pass – allows all signals below a certain frequency to pass to speaker (used for sub woofers installations)

Information and items needed prior to test procedure:

1) V = √PxR (see below)
2) Test tone CD or thumb drive. This tone can be obtained here and simply burn to a CD (or whatever device you are using) that will play in your HU. Leave this test tone at 320kbps otherwise this will be a futile effort.
3) You will need a decent DMM set to AC volts with auto ranging enabled or if you don’t have an auto ranging meter, set it to measure at least 50vac.
4) Amplifier, HU, speakers already installed and fully tested for functionality.
5) Specifications for amplifier(s) and speakers.
6) For my example I will be referring to the Rockford Fosgate PBR300x2 amplifier and Polk Audio MM651 speakers.
a. Amp specs – RMS power 2-Ohm load per channel (2 channels) – 150Wx2 – 300W
b. Speaker Specs - 2.7 ohms
7) Set your HU to repeat play mode so it will continue to play the tone. The above tone is 2:00 in length so you have that much time before you will see the AC voltage drop on your DMM. If it does, no biggie, simply wait for it start playing again.

Procedure:

1) What you now need to figure out is the V in the above equation. We know the P and R from the specs above. So, P = RMS output of amp at required ohms and R = ohms the amplifier will see from speaker(s) on that specific channel. In this example P=300 (I’m running a 2.7 ohm load to each channel) and R=2.7. So P(300) x R(2.7) = 810. Now you need the square root of 810 which equals 28.46 so V=28.46. This is the AC voltage that you will achieve by adjusting your gain(s) on your amp.
2) Turn all equalizer settings, bass boost, etc. on HU to their minimum settings
3) Turn volume control all the way down on HU
4) Turn all gain controls, bass boost, etc. on amplifier to their minimum settings
5) Turn HP/LP filters to full range. On RF amps it’s called AP
6) Connect your DMM + (red) lead to the front right speaker output + on the amp. Connect your DMM – (black) lead to the front right speaker output - on the amp.
7) Put test tone CD you burned earlier (or thumbdrive) in HU.
8) Turn your radio up to ¾ volume.. On HD HUs there are 17 bars to max volume so set your volume at 13 bars.
9) Now look at your DMM. Whatever your AC voltage reading is coming out of the amp, adjust it up to 28.46 (or as close as you can get it)
10) On most 2 channel amps such as the RF PBR 300x2 has only 1 gain control.
11) After you have adjusted your rear gain control to match the front, turn your HU volume down to minimum and take out the test tone CD. Again, you do not want this test tone running through your speakers.
12) Turn everything off and reconnect your speaker wires.
13) Now you can adjust your equalizer or bass and treble back to your liking.

 

Your calculation looks correct to me. I have the same setup as you with the PBR300X2 driving a pair of Polk MM651s in the front fairing. Please let me know what gain setting you set using this procedure. I currently have my PBR300X2 set in HP with frequency set to ~85 Hz. I chose this because I was a little concerned that I would blow my speakers if the amp was set in AP and I didn't have the gain adjusted properly. So far, I think I'm alright in HP with my gain set at about 7; but I think I've clipped the bass too much and want to try something else - either lower the frequency to the minimum of 50 Hz or switch to AP. I'd like to be able to use AVC to adjust the sound volume for my speed. Currently I have AVC at 1 which seems to work pretty well.

I have an '08 CVO Ultra so my rear pod speakers are being powered by the HK boom amp under the tourpak (don't know what the gain settings are). It's taken some experimenting with the fader control to get the sound volume to balance front and rear with the fader favoring the front by a couple of bars. This surprised me as the PBR amp in the front is much more powerful than the HK amp in the rear; and although the speakers are different - Polks in the front (2.7 ohms) and J&M 5.25's in the rear (2 ohms) - the speaker resistance is nearly the same?

Any suggestions on optimizing my settings are appreciated.

 

Thx for input Gnarl78.. I will reply with results..

 

I have a pair of MM651s and a pair of the G1644R Pioneers running off of the PBR300X2 in the fairing. What voltage should I be getting?

Also, I'm running the Hogtunes speakers in the saddlebags off of a 2nd PBR300X2. I have no idea what the R would be on those speakers. What should that voltage be?

Thanks!

EDIT: not Hogtunes, but BOOM! Audio

 

R u running the Polks and the Pioneers in the fairing in parallel?

 

Looks like the pioneers are 4 ohm and the Polks are 2.7 ohms. Assuming they are in parallel the total resistance seen by the amp is 1.61 ohms. The voltage output seen at the PBR 300x2 using the dmm should be 22 volts. Maybe somebody can check my math.

 

They are in parallel.

 

I wasn't exactly sure how the resistance would work out. I knew that running them in parallel would be somewhat close to 2ohm, causing the amp to work at max efficiency. 1.61 actually exceeded my target. I will adjust the output of that amp to 22 volts and see how it works. I'm sure it's better than where I am now. I'm certified 1/2 deaf, so tuning by MY ear is a joke. Thank you sir.

On to the 2nd amp. Does anyone know what the resistance is "supposed" to be on the factory 6x8 speakers in the saddlebag lids?

EDIT: not 6x8, but 5x7 Boom! Audio speakers. The specs say 2 ohm, but doesn't give a wattage rating.

EDIT 2: nevermind....lol square root of 300X2=24.495 Correct?

 

Where are all the PhD Harley Riders when you need 'em.. Sorry guys.. I don't want to even gander a guess on if all is accurate.. My buddy runs a shop and one of the dudes is a bike mechanic and audio head.. Having them work on mine ... I will reply back w/ the settings them come up w/

 

How did you come up with 1.7 ohms seen by the amp?

4+4+2.7+2.7=13.4 divided by 4=3.35
thus, the square root of 300x3.35=31.701

OR

4+2.7 divided by 4=1.675
thus, the square root of 300x1.675=22.417