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Help me diagnose a problem!

Stinsok

Stinsok

Dec 16, 2002
7,464
3,487
62
Central Alabama
#1
I have been considering buying a speaker managment system like a driveRack or BBE, etc., because I may be having an issue with my dbx 234xl crossover.

Recently I pulled my PA out and tested each individual piece. Each amp, each speaker, etc. Everything checked out. I hooked everything up, cranked it and was satisfied with what I could get out of it.

I have been having a problem of late where recorded music (more noticeable with recorded stuff) is just about all lows and brittle highs. I run a 2-way mono system, crossed over around 90hz. The subs are 18''s and the highs are JBL SR4722's (12/horn.) I hear no mids coming through (on either top.) So, I am asking you-without seeing or hearing any part of my problem to help me! Crazy, I know.
 
#2
What is your source of the recorded music? If you are playing MP3s that may be at least part of the problem. Although generally those files are midrange-heavy which is exactly the opposite of what you're experiencing.

I just know in my old band we used to run our break music off an iPod and even though the P.A. was dialed in nicely for live music, when we put the break music on it sounded like garbage.
 
#6
I used and just sold the dbx 234xl and bought the DriveRack PA+ so I have some experience with both. I'll review the manual on the 234 and get back to you. It's easy to screw things up (I wear it like a badge of honor) as the in / out buttons are placed a little too closely to the XLR inputs & outputs. I accidentally depressed the "X 10" button which kicked the crossover freq. to 950 hz. Tim wanted to know why were getting vocal content through the subs.

If at all possible, hook up a CD player to your mixer for test / diagnosis projects.

Edit: what you're after is actually "Stereo 2-way"...anything else will essentially split your mixer signal into either bass / mid / high or bass / low-mid / high-mid / high. It's quite easy to inadvertantly configure a tri-amp or quad-amp output which may explain the loss of mids.

Riis
 
#9
My guess: the 12" is fried or damaged

Easy way to check if your mid is working OK

-Unplug the sub ,
-put your 4722 at "Bi-amp"
-put what's normally in "full range" to "LF bi-amp"
(there is no potential danger since it's after X-over and top end to a 12" won't do no harm)
-put some normal/full range music , not too loud !!!!!

Check both boxes to see if it is constant.
 
#10
Stinsok said:
I use the full range inputs only on the JBL's.
Click to expand...

Great...that simplifies matters. Before we jump on the "it's broken" bandwagon, let's make sure we eliminate the stupid stuff first:

*Check your 12" drivers with a speaker cable and 9 v battery. If they're jumpin', you at least know they're working!

*Bypass your crossover completely. Run a CD player to your mixer (flat EQ / no peripherals) straight to a power amp with a full-range signal feeding the JBL's. Are the mids now present? If so, the crossover is more than likely the culprit. If the mids continue to be absent, the problem resides with the aforementioned components.

Riis
 
#11
Zooberwerx said:
Great...that simplifies matters. Before we jump on the "it's broken" bandwagon, let's make sure we eliminate the stupid stuff first:

*Check your 12" drivers with a speaker cable and 9 v battery. If they're jumpin', you at least know they're working!

*Bypass your crossover completely. Run a CD player to your mixer (flat EQ / no peripherals) straight to a power amp with a full-range signal feeding the JBL's. Are the mids now present? If so, the crossover is more than likely the culprit. If the mids continue to be absent, the problem resides with the aforementioned components.

Riis
Click to expand...

bingo
 
#12
testing1two said:
bingo
Click to expand...

Thanks for the vote of confidence. I'm trying to read the JBL manual on-line but Susan is calling me for dinner, so let me add one more thing...

If there's a passive / bi-amp switch, make sure you've selected the passive setting for full-range operation even though, technically, you're aiming for a true bi-amped configuration (mains & subwoofers) as the end result. You want the JBL's to "see" 100% of the full signal provided by the mixer or 100% of the >90 hz signal when the crossover is placed in line.

Riis
 
#14
So it looks like the problem lies with the x-over setup or the mono summing in your mixer. Double check all the settings & connections on your x-over and if you haven't tried this already, reverse the polarity of either the lows or the highs and see if the response improves.
 
#15
Stinsok said:
When I tested all my gear, I hooked those tops up by themselves(full range.) They sounded great!
Click to expand...

Agreed...sounds like a dbx crossover setting problem.

The 234 is capable of bi-amping, tri-amping, and...yes...quad-amping although the quad can only be pulled off in mono as (IIRC) channel A "borrows" a freq. band from channel B. "...rob Peter to pay Paul." A few suggestions:

*Unless you're absolutely convinced you need a true stereo config. (for full-blown effects, etc.), I strongly suggest you use a single channel feed from your mixer to channel A of the dbx 234.

*Set your dbx 40 hz filters to "on".

*Set your phase inverts to "off"

*On the back, set the xover freq button to "X 1" (out).

*Set the LF Sum button to "normal" (out) unless you've decided to used both dbx channel A & B in which case you would depress the button for "summed".

*Under Mode, depress the button to "in" but leave the right button in the "out" position. This is stereo 2-way or bi-amped which means it's capable of handling two independent / L & R signals but is still appropriate for handling mono feeds / output. Confusing, isn't it?

*Unless you're feeding a signal to channel B (or Channel 2 as they call it), don't mess with it as it is not a part of the equation. If you insist on feeding a second signal (perhaps right or second ouput from the mixer), duplicate the settings as prescribed on channel A.

*If you haven't figured it yet, run your mixer to channel A input, High XLR output to your mains amplifer, and Low / LF Sum XLR output to your subwoofer amplifier.

*Let's swing back to the front of the console working left to right using the bottom-most labels for guidance:

Input - 0

Low / Mid - ~100 hz (this is your xover freq.)

Mid / High - inactive, ignore

Low Output - 0, controls subwoofer feed / level

Mid Output - inactive, ignore

High Output - 0, controls mains feed / level


Hope that helps! Get back to us with results. BTW, how far are you from the nearest fire station?

Riis
 
#16
What does it sound like with a band?

Tell us about the cable you're using to connect your mp3 player.
There are some that look correct and will pass some music, but aren't actually designed for the job.
If it has a 1/8" (or 1/4") stereo plug on one end, and a single XLR male on the other, that will NOT work correctly, and will in fact cancel-out many frequencies.
 
#18
This is old, but I recently bought two Crown 2000 XLS amps and never got around to testing them till today (it's 70 degrees and sunny!) Anyway, Zooberwerx's post really helped. I had the stereo two setting bypassed and it sucked. That is what the problem was all along.
 
#19
Stinsok said:
This is old, but I recently bought two Crown 2000 XLS amps and never got around to testing them till today (it's 70 degrees and sunny!) Anyway, Zooberwerx's post really helped. I had the stereo two setting bypassed and it sucked. That is what the problem was all along.
Click to expand...

Glad things worked out for the better. Hey...I get it right once in a while!

ROTSS: "Rule out the stupid / simple stuff".

Riis
 

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