Help with JBL 4645C subwoofer

[brandtlj]

Looking for some advice here from some HT enthusiasts:

I just purchased a 4645c sub to pair with a couple 4670d's used as L/R mains in a HT set-up.

The 4670's are incredible, the dynamics and midbass impact are really something to behold. With room gain, I get usable output to about 30hz.

The 4645c sub was intended to fill out the frequencies below 30hz whilst keeping up with the mains in output. I am running it off one of the 200w channels from a Anthem MCA50 power amp (same as the 4670's), but currently without eq. I am also using an Integra 80.6 pre/pro to handle the crossover, which I've set to the lowest point at 40hz.

Unfortunately, without EQ, the 4645c doesn't seem to be adding much that the 4670's aren't already handling. The bass output below 30hz using seems to be creating some port noise and interference with the bass from the 4670's. I actually prefer it turned off. I know this has a lot to do with room positioning and standing waves, but unfortunately due to its size, my options for placement are very limited.

My question is, before I go down the rabbit hole of buying more equipment to supplement the 4645c, should I be looking at a smaller subwoofer to handle the sub-30hz domain in my room where there is more flexibility for placement - or should I try to pursue using an eq to augment the FR of this behemoth? If so, what EQ would be a good fit for my current set-up? Not trying to spend a lot more $$$.

TIA

[grumpy]

Several things going on. Below 20Hz (below port resonance), you can expect weird speaker noises and complaints from the driver, as the motion will be fairly uncontrolled. A sealed system might be more to your liking if real subsonic action is what you're after vs impact... and as you noted, you may be able to place it (or them) more easily/effectively.

You can (should?) peak some EQ at 25Hz, but then roll it off below (peaking HP filter). The specs have that in there (4645C_20Spec_20Sheet.pdf).

That will also make your 200w run out steam much sooner (800w would not be excessive) in the 20-ish Hz range...(a 6dB boost with the prescribed filter).
Having the sub closer to your seating location might help (can turn it down some), but could be sub (haha) optimal for other reasons.

Are you letting the 2470s roll off naturally, or crossing them over with a complementary crossover to the 4645?

Hard to guess what's going on in your room, and I'm not an AV consultant
The avnirvana folks might have some ideas for you (no association) re placement, measuring, optimization, etc... or someone here might

[brandtlj]

Several things going on. Below 20Hz (below port resonance), you can expect weird speaker noises and complaints from the driver, as the motion will be fairly uncontrolled. A sealed system might be more to your liking if real subsonic action is what you're after vs impact... and as you noted, you may be able to place it (or them) more easily/effectively.

You can (should?) peak some EQ at 25Hz, but then roll it off below (peaking HP filter). The specs have that in there (4645C_20Spec_20Sheet.pdf).

That will also make your 200w run out steam much sooner (800w would not be excessive) in the 20-ish Hz range...(a 6dB boost with the prescribed filter).
Having the sub closer to your seating location might help (can turn it down some), but could be sub (haha) optimal for other reasons.

Are you letting the 2470s roll off naturally, or crossing them over with a complementary crossover to the 4645?

Hard to guess what's going on in your room, and I'm not an AV consultant
The avnirvana folks might have some ideas for you (no association) re placement, measuring, optimization, etc... or someone here might

Thanks for the advice...is there a equalizer you can think of that would be appropriate in this situation (to put between the pre/pro and the amp)...but something that won't break the bank either?

[jblnut]

We had the exact same issue with the 4670 system in a buddy's man cave. I looked into those JBL subs and concluded that they weren't going to add anything that the 4670 wasn't already doing. We added a Velodyne self-powered sub to get the lowest octave and MAN does it deliver :-). I think it's a DD10 iirc and has something like 2000 watts of power.

jblnut

[nedseg]

Try a Crown 1502 amp, they have built in xovers for the 4645C (+ other DSP functions) and are relatively inexpensive.
(They make smaller and larger ones, too.)
I got my 4645C before upgrading to 2216ND1 woofers, so don't really need it now, BUT it does add a good bit of extra SLAM! to movie night!
I'm using it for just 20-40hz, and can turn it on/off with a remote key press.
Quite a bit of fun for not much money.

[brandtlj]

Thanks guys for the input. I believe I am going to have to find an alternative to the 4645c...it is just one too many large JBL boxes that my wife will tolerate in the family room anyway. I may have to look into the Velodyne DD10, Sunfire true sub or other small sub box with high RMS wattage that I can place more optimally and unobtrusively. There is a Hsu VTF3 MK2 and a sunfire 10" truesub on my local FB marketplace...i hope one of these can fill the order for movie night.

[dezmond]

You need to run a b6 eq alignment to get the 4645c flat to 20-22hz. Basically you use a low cut filter at 20hz and a 6db boost at 25hz. Also 200 watt is not going to cut it for the real low stuff.