Bass Guitar Crossover

[DaveK]

I've always wanted to try my J110 and T39 as a bass combo and I finally got a crossover built. I built it in an external box for flexibility. With a little trimming, the inductor fit just right in an FS electrical box. Pic below.

Anyway, the J110/T39 combo has a lot more bottom end than 2 J110s and sounds great in my garage. However, while testing I noticed something strange. I tried connecting the J110 and T39 full-range with no crossover and I can't hear any difference from the same pair with the passive crossover. Shouldn't there be an audible difference? Otherwise, why do I need a crossover?

[AntonZ]

The crossover might not be functioning correctly. Have you listened to the cabs individually with some music fed into them? Low end should be missing from the top and vice versa.

Other than that, I'm not sure if you are supposed to be hearing a difference. It will show when you turn up. Without crossover I would expect the top to bottom out on low E/low B notes. With proper crossover applied the rig ought to be able to play a lot louder before bottoming out.

[Bill Fitzmaurice]

I've always wanted to try my J110 and T39 as a bass combo and I finally got a crossover built. I built it in an external box for flexibility. With a little trimming, the inductor fit just right in an FS electrical box. Pic below.

Anyway, the J110/T39 combo has a lot more bottom end than 2 J110s and sounds great in my garage. However, while testing I noticed something strange. I tried connecting the J110 and T39 full-range with no crossover and I can't hear any difference from the same pair with the passive crossover. Shouldn't there be an audible difference? Otherwise, why do I need a crossover?

You can't hear any difference because the low frequencies are omni-directional, so you can't tell where they're coming from, while midrange frequencies going into the T39 are filtered out by the horn bends and can't be heard coming out of it. If you had the volume high enough to cause the J110 to exceed excursion without the filter you'd hear that. But the secondary function of the crossover is to maintain an 8 ohm load; without it the speakers would be parallel wired and would be a 4 ohm load, causing the amp to deliver twice the current for no good reason.

[DaveK]

So it's not about sound, it's about power conservation? Since we often have limited A/C outlets to work with I can definately see the benefit of that. Nobody wants to blow the breaker just as things get rocking.

Perhaps the chart below shows it visually. If I'm pumping equal low-end power into both the red and blue lines, the red line is adding very little to the overall low-end volume and is mostly a waste of watts.

[Ron K]

Part of that lies in the fact that at those lower frequencies the T39 is just way more efficient and there fore dominant.If the raw Jack efficiency was equal to the T39 then I would think you will get an increase due to mutual coupling. In this case since the Jack efficiency is roughly 5db lower I doubt there's any gain in the lower region under 100 hz.

If you dont get at least 3db increase your just not gonna hear it.Of course there's the mixing cabs thing to worry about as well. The Jacks I believe are no longer horn loaded in those lower ranges so basically that becomes a direct radiator with reflex ports running with a Horn sub. That I believe is a no-no!.

Crossed would be the proper arrangement I would think.

i think I would look for a crosover point up around 190-200 to get the flattest response from that rig.

[Bill Fitzmaurice]

i think I would look for a crosover point up around 190-200 to get the flattest response from that rig.

With a high order crossover true, but with the 1st order passive at 150 Hz per the T39 plans he's fine.

[DaveK]

Another interesting chart is this one. It's an equal voltage comparison of the low end for a J210 (4 ohm) and a single T39 (8-10 ohm). The graph says they are about the same volume and that's what I found with an informal listening test in my garage. Of course, as we learned earlier the T39 is getting there with half the power.



I don't want to push them to war volume in my garage, but I'd like to figure out which rig has the highest maximum output (assuming unlimited amp power). The J110s are loaded with 2510s and the T39 is loaded with a BP102. The BP102 has more xmax, but the J210 has two speakers. Do those cancel each other and leave it a wash?

[Bill Fitzmaurice]

The BP102 has more xmax, but the J210 has two speakers. Do those cancel each other and leave it a wash?

Pretty much, though as you noted the T39 gets there with half the power. That's always the trade off, size versus power. A smaller box can equal the larger one with adequate driver displacement and enough power. But load that T39 with a 3012LF and enough power to drive it to full output and it leaves the J210 well behind.

[DaveK]

Thanks for all the discussion; it's been very informative.

3012LF is definately the way to go for a stand-alone setup like this. I may try retrofitting my T39-20 someday when I cough up the money for a 3012LF.

I also thought of another advantage for the J110/T39 rig. If there is a wall nearby the T39 can be oriented correctly for boundary loading while still leaving the J110 top pointing at the audience.

I did some more listen tests, although still at moderate volume and in a garage. I confirmed again that the J110/T39 and the J210 sound about the same volume-wise to me, but I decided the J110/T39 has a fuller, "rounder" tone to my ears. I also tried some more tests with and without the crossover and decided the lower mids sound a little smoother to my ears when using the crossover.

I should mention for anyone still reading along that a pair of jacks bass rig is plenty for most stages and will carry a typical loud bar just fine. For anything larger I would really want to run my bass through the PA instead. However, the jack/titan rig is a good option to have in the arsenal for special situations. I'll probably road test it at my next gig, but at 2-3x the pack space I doubt it will become my mainstay.

[Israel]

you may do a test out of your garage

which bass head do u use and how much power it has

[DaveK]

GK 700RBII. 480W @ 4 ohms, 320W @ 8 ohms.

[Israel]

awesome head I tried my genz benz with a t39 and an omnitop12 the sub was overly loud inside my room but it was more leveled outside I neither notice too much diffrence with or without a xover