setting gain to speaker rms?

I have a JL Audio 300/2 amp pushing a pair of Boston Acoustics Pro60's rated at 125rms @3ohms. I have searched and know how to set the amplifier gain properly but instead I plugged in the 125rms instead of 150 since that is what my speakers are rated for. My question is, I set my volume to 28 (goes to 35) and hooked up my voltmeter and set it to 19.4v. Just out of curiosity I turned the volume all the way up (speakers not hooked up the whole time) and the output went from 19.4v to 35v or so. Should I be concerned about my volume going beyond the 28? Should I set the gain this way with the HU all the way up to prevent the speakers from ever blowing?

Were you using a 0dBV sine wave? If you think you were, how do you know? If not, then you can NEVER know what you were putting into the speakers.

This is why I have so many issues with all of the "recommendations" for setting gains floating around the net. WITHOUT A KNOWN SIGNAL STRENGTH, you cannot ever know what the signal from the next CD is going to be, relative to the reference!!!

Example: If you use a -6dBV sine wave, and you set your gains to the 125WRMS, with your volume set to 28 (using your example) but the next CD you put in has signals that FREQUENTLY exceed +3dBV, (and not at all uncommon in today's "smiley-face-EQ'd, overprocessed, super-de-duper-clipped-recordings" world of pop/rap/rock "music") all of a sudden, you are now WELL into clipping range, if not, certainly within overpower range for the speakers. See what I'm saying? Your problem lies within the fact that you think you are safe turning the deck all the way up to 28, but in all actuality, you are running at 9dBV HOTTER than your reference signal! Danger, Will Robinson!

First Step: Put the meter away.
Second step: Find a loud recording, something you know pretty well.
Third Step: With the amp gain ALL THE WAY DOWN, set your deck's volume to ABOUT 75% of the total range.
Fourth Step: Set the gains till you hear complaining (either the amplifier or the speakers). Back gain off a scosche.
Fifth Step: Leave it alone. Never touch it again. Never turn the deck above 28.

Forget the meter method, it's inaccurate. Period.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

I pulled the sine wave off a web site that was recommended here somewhere, I dont remember the name off hand. I never really turn it up that loud, I really just wanted a reference point and after reading many of your posts on here I will take your recommendation.

To be direct in regards to your questions, the reason you have chosen "28" out of "35"  (80%) on the deck volume for the reference point is because you want to stay below the noisy, clipping range of the deck.  "28" DOES become the highest volume level you ever use after gains are set to it.  Setting gains to a higher volume reference point as a "precautionary safety factor" does this:  it allows you to feel as though you can turn the volume up past 26 or 28 where you start getting a crap signal.  Even if you temper your volume fingers, you'll know that the gains are set to 35 and the sub is really not as dynamic as it could be and maybe the gain could be touched up a bit and so on and so on.  But more importantly, gains will be incorrectly set and so best signal-to-noise ratio is not achieved.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.