BillFitzmaurice.info

I have a T-39 that I built pretty close to the time that Bill first released the plans. I built it for use with a DR-250 to use with bass guitar. One DR-250 cab is usually sufficient for my use, so pretty much the only time I have used the T-39 is for playing outside...and that's not very frequently.

I recently have started to build a pair of J12Ls to use for bass or for light PA. Because of the latter they'll have 16 element piezo tweeter arrays. Did not really intend to build subs, thinking I wouldn't need them...

...but then I listened to Charles Jenkinson's youtube and got a little inspired: viewtopic.php?t=25374

He's using J12Ls with two T-30s...which made me wonder if I could get similar results with my two J12Ls and a pair of T-39s?

That got me wondering about the difference between old and new ones, and whether they are compatible. My T-39 is top loading, built with the passive crossover of the time. It's 20" wide on contains a single BP-102. Would this be compatible with a new T-39? I see that the T-39s are now front loaded...and perhaps have other differences?

That's the only difference, made necessary when neo's were too expensive and deeper ceramic drivers wouldn't fit through a top panel.

Mate,
Any music you play won't give a toss about how old the sub is, as long as it works.
There is essentially no difference between the top loaded and front loaded versions, IIRC, the front loaded version was to allow for putting in the lab12. So if you have the top loaded plans and want to build another, go nuts.

Also IIRC, Charles used 3012lf's.
Down to tin tacks on the differences.
The 3012lf will go about 6dB louder than the BP102 and can be used in a T39.
I've never measured it, but I believe each of my 28" wide 3012lf loaded T39's are at least as a loud as, or louder than, 2 x 20" BP loaded cabs.

T30's play lower than T39's.

While you have the passive crossover in your current T39, I'd be a little leary of doing that with a second cab and thinking that was as good as brick wall limiting, so it might be time to consider a driverack for protection.

In short, don't expect quite the same as what you heard on youtube (content and power), but you would still have a great experience doing that.
I think the BP102 is underated by many, those 4 x 20" wide cabs did me a lot of gigs before I built the wider pair with the 3012lf...

The passive should only be used under certain circumstances, like in a electric bass sub/top rig. Seldom if ever for PA.

If I build one it'll be with another 20" with a BP-102, and I'd probably build without the crossover. I love the one I have now. It's solid as a rock and louder than I have needed with my bass, even for outdoor parties. The most likely thing is that the two Jacks will be all the PA support I need...but man those guys sounded good on youtube... and my kids' bands are getting better...so in case one thing leads to another...

Bill Fitzmaurice wrote: ↑Mon Oct 31, 2022 4:55 pm The passive should only be used under certain circumstances, like in a electric bass sub/top rig. Seldom if ever for PA.

Ohh, snap: it's been 11 years since I built my T-39s, but I can't remember if I kept the passive crossovers that I built in them. Would there be any significant problem / drawback to running then with BOTH the passive crossover AND the signal split up by an active one? I've been using them seemingly without issue, that memory just popped into my head. They absolutely pound.

Rich4349 wrote: ↑Mon Oct 31, 2022 8:53 pm

Bill Fitzmaurice wrote: ↑Mon Oct 31, 2022 4:55 pm The passive should only be used under certain circumstances, like in a electric bass sub/top rig. Seldom if ever for PA.

Ohh, snap: it's been 11 years since I built my T-39s, but I can't remember if I kept the passive crossovers that I built in them. Would there be any significant problem / drawback to running then with BOTH the passive crossover AND the signal split up by an active one? I've been using them seemingly without issue, that memory just popped into my head. They absolutely pound.

Depends on how you wired them up.
If you used convention and wired +1 and -1 to subs and +2 and -2 for tops with NL4's then maybe not.
If you did anything else, perhaps that will be a problem.
Suss it out and let us know...

I wired mine to have a crossover in and a direct in. I can't remember if that was in the plans, but I am sure I did not invent it. Maybe you did yours that way? On mine, using it with a bass amp, I run a cable from the amp to the crossover in, and then connect the top to the crossover out. If you did it like I did you'd have three jacks on the back... Of course I used Speakon Combo jacks that only have two connections. If you used the 4 connector speakons all bets are off.

You can use the cab with the passive along with an active with no problem. The passive crosses at about 150hz if I remember correctly and you'd certainly be crossing below that in an active setup....so, the passive never comes into play.

I put a passive in my T24 for use as a drum monitor and now it's used as a small, standalone mono PA along with an SLA. Works great.