Hey all. For those of you using JL Audio amps, I have a question for you. Have you used the JL method for input sensitivity? For those who don't know, here's the procedure:

- Get reference-level (not attenuated) test tones. 1000Hz for mains, 50Hz for sub
- disconnect speakers!
- Set HU to 3/4 full volume
- Set Sub level (if separate) to 3/4 full volume

Then run the test tones and use an AC voltmeter to check the voltage. Set the voltage based on a chart from the JL manual.

I set the gains up initially using this method, figuring I'd do the final tuning from the HU. In my case, I have a JL 450/4 running the whole system. 75w/2 running the fronts (Alpine Type R components) and 150/2 -> 300w bridged running the sub (an AW100T in a WLAURENT V1 passenger side enclosure). Head unit is an alpine 9855.

So here's the deal - the sub was WAY too quiet. I couldn't even tell it's on when the top is down at highway speeds.

What I did to fix it:
- Backed the front channel gain down to make the sub relatively louder
- Increased the JL gain about 7 volts higher than the chart indicated for a 4 ohm load (I set it for that of a 6ohm load)

Now it thumps like it should, but I'm weary of exceeding JL's specs.

Anyway - anyone else sign off on this method? Is their manual a bit on the conservative side to cover their asses? I'm hoping that's the case! I dont notice any audible distortion (hard to tell w/ a sub), even at 32/35 volume.

 

i'd set the 9855 volume at 3/4 (around 24/25) and the sub output at full (+15), then reset the gains according to JL.

if it still is too low, comment back in this thread. pushing it up a bit probably won't break anything, but Alpine HU's have a confusing nomenclature for their sub out levels...
without going into too much detail here's the short version:

while the Alpine display shows 0 to +15, in reality +15 is an output that is equal to the level of your other RCA outs, and the 0 setting is being reduced below the normal level of your RCA outs.

it's confusing and i don't know why Alpine displays it that way... it should be a -15 to 0 indication.

 

Did exactly what you did Bimmer..

Voltage matching first.. then tweak it.

 

Good suggestion. I had the same thought initially and did tinker around with that. However, it actually ends up hurting (makes sense when you think about it). Basically, the higher you go on the HU, the more you have to turn the amp down to be in JL's target range. So setting the sub level to 15 actually still gets balanced out to the same voltage level at them amp, and hence the same volume. This also gives you nowhere to go if you ever needed to turn the sub up, since it's already maxed.

I agree regarding the display. I'd like to know where reference 0db is on the main volume too. Is 0db at 35/35 or is the HU actually boosting the signal (and potentially introducing clipping before it even gets to the amp)?

 

Do you happen to know how far over their specified voltage you ended up? Just curious.

 

true, but if you run it at +15 while at your 3/4 HU volume, you're sending a higher signal to the amp anyway... same as if you tweaked your gains higher...

however, it would provide some 'tweak' room for the sub at lower volumes. pretty much something you've got to decide, but just keep in mind what your max sub level is at higher volumes, otherwise you might (and i stress might) damage the sub.

generally there's usually a good bit of fudge factor in sub ratings, amp ratings, etc. that gives you a safety margin to play w/ some distortion...