Can you underpower a Strong amp?

I'm familiar for the JL flash instructions as I've looked at that a couple of times. 

Another post that addresses this found at http://www.caraudio.com/vb/showthread.php?t=63933

according to it, the formula is Sqrt(Power*Resistance) = Voltage

If this is correct, I'd just dial in 24.49 volts with a dvm at 3/4 total headunit volume using the appropriate sine wave for the subs vs components.  I'm not sure how JL audio believes 3/4 volume is a good starting point but it should work I guess. 

After this is set, will turning up my subvolume on the HU to balance the system level affect this calculation?  It seems if I do it will the system flat, I wouldn't want to increase it at all (past 3/4 volume or using any boosts).  I wonder how you then balance the components and the subs?  Any help at this final stage?  Thanks so much, this has helped me tremendously

Dope!  I replied too soon, JL's site says you simply turn down the sensitivity on the AMP after everything is reached to the ideal voltage to balance the system. 

(to geepherder...)

No, I'm being serious (for once tonight).  There was a reason DYohn said that.

...and before I caught the update and was able to delete mine.  Now I have to go back and read everything...

Okay, I gotcha geepherder.  (To see if I got it right..)  It may not always be the case where you can just limit the turn of the gain.  There are times when you also have to limit the volume of the deck.  The test would be, I suppose, if you weren't ABLE to turn the gain down far enough to reach the target voltage (with the deck volume at full).  That's where you have to reset the deck volume to a new, lower high point and then again do the adustment from there.  You would have to strictly control the deck volume level!

You can't increase power output by using fades or balances.  Fading one way just takes away from the other side.   But when it comes to a balance of frequencies...if using the sub fade causes the signal to be larger in the sub frequencies....I can see how that would affect the signal that the sub amp receives.  So it the signal is larger than what you set the amp to, the voltage output should be greater than what you tested it at.  My initial take on this is to set that sub fade control to the highest point before setting the sub amp gain.  Or, if it has it, at the point of '0' or 'flat'.

Yeah, it's not a great way to do it, because the problem is then due to mismatched equipment.  That's just an example of what could happen if you're forced to use that equipment.  The best thing to do would be to change some equipment around.  Maybe a customer brought in their own ebay gear and refused to use anything else.  That's when this would come into play- kind of a "Mickey Mouse" way of "fixing" it. 

At this point you must also explain to the customer how critical it is that they do not turn the volume past what you have dictated, or they could easily smoke their speakers due to their poor choice of equipment.  Then when they do, you can tell them "I told you so" and set them up with new gear.

I see what you're saying, but here's my take- your ears won't know whether the speakers are recieving 75 watts a piece as opposed to 100 watts a piece.  It may still be possible to exceed a speaker's thermal limits without exceeding it's mechanical limits.  That means it may still sound good because you're not causing your speaker to "bottom out" yet (and the amp is not clipping), but you could be causing too much heat to build up in the voice coil.  When this happens, you can kiss your speaker good bye.  Just because a speaker has a certain rms rating does not mean that you need to feed it that much power.

So that the amp outputs more than the speaker is capable in RMS terms?  if you use RMS and continuous power handling numbers for the calculations (as in this case), there is room for peaks on both sides (amp and sub).  The amp still peaks at higher voltages and the woofer still handles those higher peaks.  Remember, we are using all-day RMS numbers on both sides. 

So, will the peaked voltages be "cleaner" if the amplifier is stronger than the woofer it feeds?  That, I think, is where a more equal match of equipment makes the most sense...the subwoofer has to produce the sound from that peaked voltage.  It doesn't matter how clean that peak is if the sub can't produce it faithfully.  With this rationale, matching RMS makes the most sense to me.