JBL 4641

Bobecca

Hi

I have two JBL 4641 subs. The setting that is described about EQ to get flat down to 25 Hz according to spec is what I am after.

http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3&docid=624

Is there any info about how this setting is implemented in 260?

Thanks

Dra

You aren't asking for much, are ya?

You could make some educated guesses. For example, you know that you are -3db @ 35hz and -10db @ 25hz, and that you want to achieve -3db @ 25hz. You also know the JBL recommends a very steep filter at 20hz so you don't destroy the speaker.
To bring the response up to the -3db point you need to boost (based on the printed response curve) approximately...
32hz (+1)
30hz (+2)
28hz (+4)
25hz (+6)
...and for reference only
23hz (+9)
20hz (+14)
To bring to -0- add another 3db each.

You might get by with using a single bell, centered at 25hz Q=1.4 Gain +6db (to start). Add a low shelf filter at 25hz with an S = at least 6 (maybe 12) db/octive. The goal here is to build a half bell. Adjacent inverted bells can also be used to accomplish similar results. Then add a very steep HPF, maybe even a slope of 48, no lower than 20hz. All this is really trial and error.

All this is logic and numbers. Real testing is more valuable and needed. Do you have the measurement mic? Have you ever done an auto EQ session? Do you have access to SMARRT? Take what I said with a grain of salt, but I did stay at a Holiday Inn Express a while back.

DRA

PS - Perhaps you should should call JBL and see if they have these "phantom EQ settings" of which they speak.

Gadget

The problem is with THAT much boost @ 25 hz you will be very likely to damage the woofers...Perhaps an inverse filter with a fairly large Q like 1-2 placed @ the peak (43 hz ) and lowered a hew dB to flatten the peak will have you not needing to boost the low lows so much...

If these are older speakers don't be surprised if asking 25hz response tear the cones or rips the spider or surround...If the 'spring' is still robust you might be ok..also hopefully you have LOTS of power because ultra low LF takes more power..

Placing the speakers together (since you said subs) will help with lower extension and smoother response...

Bobecca

Hello...

Dra, Gadget...I'm the twinbrother to Mctwins

Reason for not making to many questions was simply to start some brain storming.
I did some test with a LR12 at 25 Hz, Q=2 at 25 Hz and a boost +6dB in post PEQ. This is how I interpret the spec from JBL. After that I am measuring from the listening pos and correcting it in the pre PEQ to get an in room flat response. I have to come back to that setting. The computer is in another place.

And I do find this EQ very positive but want to make sure if the setting is OK or if there is something from dbx that can share some light to this. To contact JBL is not the easiest but maybe dbx can find out :idea:

I've been asking similar questions in the Lansing Heritage site and here is the Link
http://www.audioheritage.org/vbulletin/showthread.php?33759-JBL-4641-Subs

Dra...I'm not following you in your comment about "Adjacent inverted bells can also be used to accomplish similar results".

Gadget...Don't worry about power for the subs and they are together

BTW thanks for your inputs, as always.

Dra

Adjacent inverted bells...

PEQ 1) 40hz Q=2 +6db
PEQ 2) 40hz Q=2 -6db

If you apply the above, the net change to the audio signal is (in theory) nil.
But if you shift PEQ 2 down by 1/2 the Q (half the bell), then the bell to the right is unaffected, but the left side is (in theory) washed back to the pre-change state. The lower PEQ might have to change the Q, or increase the cut, to get the needed effect but the principle is valid.

DRA

Bobecca

Dra wrote:

Adjacent inverted bells...

PEQ 1) 40hz Q=2 +6db
PEQ 2) 40hz Q=2 -6db

If you apply the above, the net change to the audio signal is (in theory) nil.
But if you shift PEQ 2 down by 1/2 the Q (half the bell), then the bell to the right is unaffected, but the left side is (in theory) washed back to the pre-change state. The lower PEQ might have to change the Q, or increase the cut, to get the needed effect but the principle is valid.

DRA

Thanks for claryfying.

But what do you think of my interpretention of the spec and the setting I've been doing. Am I out of the loop here?

Bobecca

Hallo again....

Iv'e been in contact with JBL Pro and had my setting confirmed. My interpretation of the spec was correct, namely

Setting in dbx260 postPEQ is

LR 12 dB/oct at 25 Hz
Q=2 at 25 Hz
Gain with +6 dB at 25 Hz

For me, I have to say, that I prefer when this setting is applied. I had an long listening session with and without this EQ.

Thanks

Dra

Well, there you go. 8) Thanks for reporting.

DRA

Bobecca

Dra wrote:

Well, there you go. 8) Thanks for reporting.

DRA

Your welcome