New Jack 12s: Low bass output

[Kirk Baptista]

So I recently finished a pair of Jack 12s, with 3012HO drivers and 16 piezo melded arrays. I am very pleased with how they came out, but I have concerns as to the sound quality. I have hooked them up both with a Gallien Krueger MB Fusion head unit, (500W@4ohm, Jacks stacked) and as a PA with an American Audio VLP300 (100W stereo @ 8ohms). With either it seems that they are lacking in low bass output. Based on the numerous reviews, which made me decide on the Jack 12 in the first place, I am assuming there is something wrong, and it's not just that my expectations were too high. I've checked for leaks and I'm reasonably sure there aren't any. I don't yet have an equalizer, other than the 10 band one in iTunes and the 4 band one on the GK. I have fiddled with those, and I can get it to sound pretty nice at low volumes, but I am unable to get any low punch or any sort of bass you can feel. When I turn up the volume I get distortion pretty quickly. Even at low volumes, they sound like tops that are missing their sub.

I know that the 100W PA amp may be underpowered, and I know a proper EQ would help as well, but it’s what I have at the moment.
Tonight when I go home I will pull the backs and check to make sure the crossovers are wired correctly. Is there any way to test them for proper setup using a multimeter, other than continuity and checking the resistance of the individual components? What I am after is a way to verify that I assembled them correctly. Is it possible to install any of the componenets backwards?

I will also retest the back, connector plates and handles for air leaks. The rest of the cab is all glued well and covered with Tolex, or a few coats of gloss paint, so I’m pretty sure they aren’t leaking anywhere else.

If anyone has any idea, please let me know what to check. I want to be blown away with these like everyone else seems to be.

Thanks!
Kirk

[Dantreige]

If you are running two cabs and you are getting low bass output, I would think that is a polarity issue. Recheck your wiring. I can knock stuff off the wall with my two Jack 112's.

[Steve Regier]

+1 on polarity. I can't count the number of times I have been bitten by that one. I now keep a 9v battery in my toolbox to make sure the cone in each of my creations moves the correct direction.
Jack should give you good low frequency bass , nice and full with some rumble but if you are looking for pound -me-in-the-chest bass Jack may not quite deliver. I think Otops, Jacks, and even the WH10s are great sounding cabinets but if one looks at the graphs they dip by 8Db or so below 150Hz. You will need some EQ to get them right. I recommend Radian's reversed EQ curve technique where you plot an EQ in the inverse of the response graph.

[Kirk Baptista]

Steve,

Thanks for the 9V tip. To clarify, if a 9V is applied with correct polarity, the cone should move out, correct? Towards the front of the cabinet?

[CaseFAceMcGee]

Steve,

Thanks for the 9V tip. To clarify, if a 9V is applied with correct polarity, the cone should move out, correct? Towards the front of the cabinet?

Seconding this question. I'm installing my Omni15's speakers tomorrow, and this sounds like a painfully easy method to check polarity.

[ewetho]

Yes when Steve and I check polarity the cone move outward when hooked up Positive to Positive & Negative to Negative.

[Steve Regier]

Yes, forward is correct but most importantly connect the battery the same way each time and make sure the driver moves the same way each time.
As far as the output goes after polarity is checked and correct, check input volage before the passband/woofer crossover and then at the driver. Voltage should be about the same since most of the energy is at the low frequencies. If it not look for defects in the crossover.

[Kirk Baptista]

Verified the polarity with the 9V, (Nice trick) all OK.

Found that the two coils in both my crossovers were reversed. They came unmarked, so I sort of guessed which was which. Fixed that. Resealed, checked for air leaks.

VIOLA! Much better. There is bass now! I think with proper EQ and a more powerful amp, it will be even better.

Thanks for the help!
Kirk

[LelandCrooks]

Found that the two coils in both my crossovers were reversed. They came unmarked, so I sort of guessed which was which. Fixed that. Kirk

Coils don't have polarity. Please clarify so others can look for the same thing. I troubleshoot by email all the time, and always am looking for solutions.

[Rune Bivrin]

Found that the two coils in both my crossovers were reversed. They came unmarked, so I sort of guessed which was which. Fixed that. Kirk

Coils don't have polarity. Please clarify so others can look for the same thing. I troubleshoot by email all the time, and always am looking for solutions.

I suppose he swapped the coils. 2 coils with missing or unclear markings => 50% risk of getting it wrong.

Big coil goes to woofer, little coil across tweeters.

[Kirk Baptista]

Yes, exactly. I had the big coil in the high pass and the little one in the low pass. Kind of obviously backwards, now that I think about it.

Anyways, they are only marked in the plans by thier value, and I had no way to tell which was which.

[Steve Regier]

Many inductors are marked but in an odd way; a superfluous 0 prefix and a comma in place of the decimal.

[Harley]

Many inductors are marked but in an odd way; a superfluous 0 prefix and a comma in place of the decimal.

In Europe, the decimal is often a comma.