View Full Version : 4645C recommended EQ??

05-15-2008, 07:09 AM
I searched this forum but couldn't find any information about what is the recommended EQ curve for the JBL 4645C.

I had a 4645C test yesterday with a VERY powerful amp driving one 4645C FLAT. NO EQ and NO subsonic. With jurrasic park the 2242 was nearly jumping out of the cabinet. No way to leave it this way.

05-15-2008, 07:51 AM
4645C.pdf from jblpro has plot showing an example HPF & LPF (details in text below plot... 2nd page).

I've seen that. But Q2 at cabinet tuning frequency (25Hz)? This will result in an xmax of several inches :(
Something must be wrong.

05-15-2008, 10:08 AM
But adding a bump at the box tuning is at the smallest driver excursion. Kind of like a B380. Unless I am missing something isn't that what they are doing?? Q of 2 is +6 at 25hz


05-15-2008, 11:08 AM
Thank you! I've got it now :o:

I was misled by BB6 that gave me weird curves for cone displacement. Something is wrong in that simulation. I'll find out.

Don Mascali
05-16-2008, 03:09 AM
A Q of 2 and +6 at 25 HZ is right and I use a 20 HZ high pass like the BB6.
For the levels I normally run at I usually leave the infrasonic off.
All of this is discussed in that 1983 Audio Magazine construction article by Greg Timbers. It is arcived here somewhere.


05-16-2008, 08:31 AM
... yep, I'd think it would be even more important to include a HPF for a 2245-based
sub in a high-volume HT situation. 2242 spec shows as 9mm Xmax, but 25mm (one way)
before damage. Shown below is -modeled- cone excursion (mm) for 2242H in 8ft3
box tuned to 25Hz, without (yellow) and with (green) 25Hz,Q=2 bump filter running at
800W. Same color scheme for voltage drive plot. Also keep in mind that using +6dB
will "ask" your amp to produce 4x the power at and around 25Hz (even if your tuned
2242H system can absorb it, the amp might balk ... and your walls might crack, and
your hearing... :))

Don Mascali
05-16-2008, 09:40 AM
I totally agree with your plots, but in a home HT application the levels never get there if you use a little caution and many of todays DVDs have output to 10 HZ or so.

The air movement tickles my beard and gives out some visceral punch with a 700 wpc Yamaha P7000S Pro Amp driving 2-2242s and the same setup on the 2-2245s. The level on the 2-2245s is set lower due to the fact that they are only 4 feet behind me in the rear corners. They are obviously more sensitive to that kind of excursion.

05-16-2008, 10:25 AM
if you use a little caution yep. :)