Thanks everyone and audioholic especially for those lengthy summary replies. Just a couple things to point out...1. They did not claim that I placed the amplifier in any danger or damaged the amplifier in any way. They were only talking about the sub. They think that I blew the voice coils on the sub because I played the volume too loud before the sub had time to break in properly. They never mentioned anything about amplifier damage.
2. They originally tried hooking it up with an LOC but the system was not putting out much at all so they got rid of the LOC and hooked the high-level signal inputs straight into the amp. The LOC is no longer part of the setup.
I talked with JL on the phone today and they said that I should be OK with the bass knob as long as I tune the gain while the knob is all the way up and the head unit is at 3/4 volume. If I tune the gain in this manner, then I do not need to turn the gain artificially low, right? There is also a "Q" setting that goes along with the bass boost that looks like it tells what frequencies to boost over. If the "Q" is turned down low, then the boost applies to most or all of the frequencies rather than a narrow range of frequencies. JL recommended tuning the gain with their 9 step method using a DMM to get a reading of 54.7 volts (since the sub is 3 ohms). So I would put the head unit at 3/4 volume, have the bass boost all the way up, turn the "Q" setting down, and then look for a reading of 54.7 volts for the gain. He said as long as I do that and turn on the infrasonic filter (since I have the high output ported box), I should not have to worry about blowing out the amp or the voice coils. I am going to set the rest of the settings on the amp according to page 8 of this link:
http://mobile.jlaudio.com/pdfs/557.pdf ....and btw, the steps they recommend to set the gain are on page 14 of that .pdf
The JL rep said the same thing that you all are saying though...that break in is a myth and that as long as I kept the volume below 3/4 of the head unit, the sub should not have had an issue if the gain and amp settings were correct. He said he would bet that the shop set the settings on the amp wrong. Ironically, I looked in my amp box today and saw that the instruction manual was still sealed. Who knows if the shop tried to adjust the gain by ear or what they did...but they are definitely at fault. I am considering asking for a refund on some of the labor since I am without a sub for a few weeks and since they are blaming me for this problem. They are the ones that have caused me an inconvenience. I definitely won't be going back there again.
Glad to help. We'll get you straightened out, just be patient.
When setting your gains, even using JL's method, yes you will have to set the gains artificially low. But, if the Q adjustment (a common adjustment in parametric EQ's) really allows you to boost all freqs within the passband the crossover is passing, then using the knob will be fine. The bass knob is a bass booster. All it does, basically, is increase the signal voltage of the freqs within the band of frequencies defined by the Q factor. Turning the volume knob up on your deck does the same thing, increases signal voltage, but to all freqs. So turning up the bass knob means you are simply turning up the 'volume' artificially early on the bass freqs (again, as defined by the Q factor). In order for this artificially high signal voltage in the bass freqs, the gains must be adjusted artificially low so as to not send the amp into clipping in those bass freqs when trying to turn the deck's volume up high enough to max the output on the rest of your stereo.
In essence, what the +6db boost to your bass freqs will do is create a 6db difference in output between the bass, and the rest of the freqs your stereo plays. Yes, you can use the bass knob if you set the gains as described by JL (deck at 3/4 volume, bass knob all the way up). But all you are really doing when you set your gains is limiting the output of the rest of your system, to allow this 6db difference to occur. So, you aren't really "boosting" the bass, you are cutting all the rest of the freqs to make it appear as though the bass is being boosted. There is simply no way to get around this flaw inherent in a bass boosting style bass controller knob. I recommend using gain attenuator knobs, when the amp in question has one available. But when the bass controller is one like yours, a true bass booster, I recommend leaving it out of the system. JL's method for setting the gains makes using the knob safe, but it still doesn't make it a good idea imo.
My mistake about the amp damage. I read somewhere in this thread that amp damage was being discussed, and thought that was the claim the shop was making. The artificially stiff suspension in a pre-broken-in sub *can* lead to coil damage due to having less cone/coil motion (so less cooling effect), but this is unlikely if the gains were set properly by the shop.
After thinking about this further, and reading this latest reply, there is no doubt the shop set the gains incorrectly, almost definitely leading to the failure. Two things you've said tell me this is true. 1) You said the shop set the gains before the system was running. IIRC you said the installer said he hoped it was set right because he couldn't adjust them once the enclosure was mounted. 2) They tried the system with, and without, the LOC. Taking out the LOC should have changed the signal voltage going to the amp, which would require an adjustment of the gains, which they obviously didnt do.
When you first said they set the gains prior to listening to the system, I was suspicious. But I figured they must have had experience with that amp's gain settings while inputting from an LOC. But now its clear they were setting the gains by the seat of their pants, and they f
ucked up.
