Need help from Sound Engineer. Drive Rack setting?!?!?!?

[Whiterob]

(I copied a post I put on DJF as I think you guys will be more knowledgeable)

OK, so the bar I play at has this gear that I want to properly set up, but have a lot of learning to do.

JBL SR4719X (dual 18" Subwoofer) http://www.jblproservice.com/pdf/SR-...es/SR4719X.pdf

Crown MicroTech 2400 - http://www.crownaudio.com/pdf/legacy/136733.pdf

DBX Driverack 260 - http://www.dbxpro.com/260/

QSC K12's - http://www.qscaudio.com/products/spe...series_k12.php


So anyways, this is my first time messing with a driverack, and have yet to see if I can use my serial to USB converter to hook it up to my MBP. I bring my own mixer etc (DJM-800, CDJ-400's and more) as theirs sucks. I am usually really good about figuring this stuff out, but I have never set a limiter before. The way I have been told to do it is by "dummy loading" the amp, set it to max, send pink noise through, and check the voltage. Then adjust the limiter to the correct max voltage. Well on the spec sheet it says 1800 watt continuous for the subs, but how do I convert that to Volts when you don't know the amperage? I assume since it is a 4ohm load I may be able to figure it out somehow. V=IR P=VI So since I don't know V or I how do I do it backwards to find out V from having just R and P?


*edit*


Ahha, So just found this I = Square Root of (P / R) which gives me 21.2132 Amps, so if I take 1800/21.2132 that leads me to believe I can send 84.85 volts continuous to it... Am I right?

[Whiterob]

After I get my T30's done I will more than likely have them sell their subs, and have me build some T60's for them, but until then this is what I have to work with.

[Bruce Weldy]

These are direct radiators....don't worry about the limiters - if they haven't blown 'em up yet, you won't. You'll hear 'em farting out - turn it down.

I would be more concerned with the EQ of the system. If it's been properly set up, it should be fine, if not - then you need to ring it out. Changing out mixers won't effect the system's sound.

[Bruce Weldy]

Also, the Crown only puts out 800 watts at 4 ohms and the JBLs are 4 ohms speakers rated at 1200 watts. I don't think you really need to worry about it.

[Whiterob]

Also, the Crown only puts out 800 watts at 4 ohms and the JBLs are 4 ohms speakers rated at 1200 watts. I don't think you really need to worry about it.

Unfortunately I have already blown 4 subs with this setup. So there is something not right. I have tried to watch and listen for farting, but with the setup there, I can't always directly hear them. So would like to set a limiter so that it doesn't happen again. (bar owner doesn't like paying for re-cones)

[Bruce Weldy]

Also, the Crown only puts out 800 watts at 4 ohms and the JBLs are 4 ohms speakers rated at 1200 watts. I don't think you really need to worry about it.

Unfortunately I have already blown 4 subs with this setup. So there is something not right. I have tried to watch and listen for farting, but with the setup there, I can't always directly hear them. So would like to set a limiter so that it doesn't happen again. (bar owner doesn't like paying for re-cones)

Ok....gonna need a little more info here.

Did you replace the blown drivers with the same JBLs? Or, something else? It sounds like you've been re-coning, but are the drivers in there the original JBLs?

Are you sending sub-30hz material to 'em?


Sounds like you need to make sure they are hi-passed, and while you can certainly limit them - the question would be where? The higher you set the hi-pass, the more they can handle.

[Whiterob]

Yes they were the orginal.. Well, recones from like 2006 that had been sitting in their old warehouse for a few years after they closed down their previous bar. I am pretty sure I had them highpassed at 35hz, but it is possible I didn't. The other subs I blew only lasted a few hours if that as I was just seeing how much they could take, and really blew them on purpose. (some old Gemini's I had laying around haha.. That smelled really bad) the one thing I think is weird I forgot to mention is that all but one of the subs completely froze up, which most of the times in my life of blownig subs they just end up farting super bad. These went from light farting to me walking away for a minute to absolutely no sound whatsoever. Another thing is I will have to check, I think they told me they had them bridged, which probably isn't a good idea.

Wow this post makes me sound like a total Newb. haha

[Bruce Weldy]

I think they told me they had them bridged, which probably isn't a good idea.

The reason it wouldn't be a good idea in this case is the the JBLs are 4 ohm boxes. Two of those would be 2 ohms and the Crown only bridges to 4 ohms. I'm surprised that the amp didn't shut down - I'm not surprised that it might have fried the speakers...no telling how much juice got put to 'em.....at 2 ohms, it could have been from 2500 to 3000 watts or more.

It's important to know your speaker impedance when choosing how to operate the amp....obviously they didn't if they bridged that amp.

[Grant Bunter]

Try a sine wave at 60Hz rather than pink noise to set your subs voltage, with no cabs hooked up, if you're going to limit.

Check your subs output and HP and LP settings on the dbx
What's the crossover on the dbx set at?
You should be able to set a HP for your tops on the dbx also. I had a quick look at the K12 manual and it says: "When using one of the top boxes with a subwoofer, the switch should be moved to the “EXT SUB” position to engage the 100 Hz high-pass filter". So if you can't work out how to set it on the dbx then you can still get 100Hz HP on the K12's. The switch to check is to the left and above of input A.

Hope this helps...

[Gregory East]

JBL says they are -10dB @ 25Hz, pluck a number out of thin air....45Hz highpass might be ok? Crazy business.

[Whiterob]

I will check them tonight, but I actually have the woofers wired parallel so it is an 8 ohm load. We do have the k12's crossed at 100, and that is the Low pass setting for the subs. Upon doing more research, the actual drivers are rated for 600 watts each, so how does jbl rate the enclosure for 1800? So maybe I did just over power them?

So far I think I have been doing everything correctly based upon the great advice you all have given. Once we get these reconed, (hopefully this week) I will try setting a limiter just to be safe. (after a couple shots and beers, I tend to get careless haha)

[Bruce Weldy]

but I actually have the woofers wired parallel so it is an 8 ohm load.

Two speakers wired parallel to an 8 ohm load would be 16 ohm speakers.....that ain't what you have.

Those JBL boxes are 4 ohm boxes....two in parallel would be 2 ohms, not 8.

Unless the actual guts of the boxes have been altered, you need to be looking at running one box off one side of an amp.

[Whiterob]

but I actually have the woofers wired parallel so it is an 8 ohm load.

Two speakers wired parallel to an 8 ohm load would be 16 ohm speakers.....that ain't what you have.

Those JBL boxes are 4 ohm boxes....two in parallel would be 2 ohms, not 8.

Unless the actual guts of the boxes have been altered, you need to be looking at running one box off one side of an amp.

Yes the guts have been altered. but I had a brain fart, yes it is still 4 ohms for the box..