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[Robert Chafe]

Alright here's an odd situation.  Recently installed a pair of JBL MRX 515’s in a small bar for live music as well as dj.  The pair is powered by a single XTi2000 in bridge mode - IE 2000W @ 4 ohm.  To start things off one the original cabs had an open horn right out of the box. I wrote it off as a 1 in a million fluke, swapped that box for another at the local dealer and installed the pair.  No issues during EQing that during the install, worked perfect the following night for the band & DJ.  On the second night both horns went out in both boxes in quick succession – at almost the exact same time. 

I’m scratching my head on this one.  Could it just be a bad run of horns?!?
Obviously I can swap these boxes out for another pair no problem, but I’m a little gun shy now. Is it a bad run of horns and if I swap this pair out will I have this same issue again?  Or do I just switch to a completely different box?  But at that price point only the EV TR1152 or Peavey SP2 are comparable. 

Thoughts please?!?

[Bob Leonard]

Heavy and sustained clipping will take out the drivers. I suggest you start by running those speakers in stereo mode and stop stepping on the gass when the amp starts to clip.

[duane massey]

+1 on Bob's post. The drivers in the MRX series are pretty wimpy, and I would use extreme caution in overpowering them.

[Robert Chafe]

The cabs are rated @ 800W program & 1600W peak.  XTi2000 @ 4 ohms is 2000W for a pair or 1000W peak per cab.  Which is why I matched a XTi2000 with the MRX515 cabs - roughly double the continuous power rating. And the internal limiter of the XTi2000 is set @ -6 db as well.  In general, input gain and channel levels are at unity and master output negative 10-15 db.  IE the amp wasn't close to clipping.

I've heard some complaints about the quality of those horns but common that is ridiculous!!

[Tim Perry]

Alright here's an odd situation.  Recently installed a pair of JBL MRX 515’s in a small bar for live music as well as dj.  The pair is powered by a single XTi2000 in bridge mode - IE 2000W @ 4 ohm.  To start things off one the original cabs had an open horn right out of the box. I wrote it off as a 1 in a million fluke, swapped that box for another at the local dealer and installed the pair.  No issues during EQing that during the install, worked perfect the following night for the band & DJ.  On the second night both horns went out in both boxes in quick succession – at almost the exact same time. 

I’m scratching my head on this one.  Could it just be a bad run of horns?!?
Obviously I can swap these boxes out for another pair no problem, but I’m a little gun shy now. Is it a bad run of horns and if I swap this pair out will I have this same issue again?  Or do I just switch to a completely different box?  But at that price point only the EV TR1152 or Peavey SP2 are comparable. 

Thoughts please?!?

Well... when you have "DJ" in the equation it greatly adds to the difficulty in keeping speakers functional. There simply is nothing to stop them from pushing the limits beyond what any sane person could tolerate.

You have two 400 watt rms  @ 8 ohm speakers. You have chosen to supply a max of  1,000 watts each to them.

Some of your choices might include:

1: switch to active speakers with separate appropriate sized amps with build in limiting.

2: modify the MRX for bi-amp operation and use a smal amp for the HF plus a limiter or driverack like speaker processor.

3: add series light bulbs to the HF section and ignore whatever small effect it has  in the crossover function.

4: add more speakers

5: stand over the DJ's with a SPL meter in on hand and a club in the other.


As an aside I did a hard rock show last night with MRX525 that was screaming loud. no problems, no clipping. the top amp was plx 1804 (900W @4 ohm /ch)

[Brad Weber]

The cabs are rated @ 800W program & 1600W peak.  XTi2000 @ 4 ohms is 2000W for a pair or 1000W peak per cab.  Which is why I matched a XTi2000 with the MRX515 cabs - roughly double the continuous power rating. And the internal limiter of the XTi2000 is set @ -6 db as well.  In general, input gain and channel levels are at unity and master output negative 10-15 db.  IE the amp wasn't close to clipping.

• The speakers are rated at 400W/800W/1600W for a 2 hour test, the 100 hour rating is 350W/700W/1400W.
• The speakers are nominal 8 Ohm rated, but the actual minimum impedance is going to vary with frequency and the minimum impedance is most likely lower.
• Clipping is not limited to the amp, clipping anywhere in the signal chain, say right at the start by the DJ, means the signal has been clipped.
• Sensitivity on the XTi2000 is about +5.14dBu.  For many mixers, -10 to -15 on the output meters represents a level greater than that.  Are you attenuating at the amp input?

[Robert Chafe]

Well, I'm assuming the DJ wasn't clipping the input but unfortunately that something I just can't control. 

Sounds like the safeest bet would be to redesign the system a bit.  I don't want to cut into the MRX cabs and rewire or change anything - especially since I'm not sure we're going to keep them.  How about switching the XTi2000 to stereo mode so it will be a peak of 475W @ 8 ohms per speaker?

Looking at comparitivly priced cabs from other manufactures...the only thing on paper that looks like it may be a more robust choice is the Peavey SP2.  Thoughts??

Thanks again for everyone's input!! 

[Chuck Simon]

My experience is that the MRX cabs are pretty robust, if properly managed, but nothing will stand up to abuse, and I think that is your problem.

[duane massey]

EAW VR51
http://www.eaw.com/products/vr51.html

[Chuck Simon]

EAW VR51
http://www.eaw.com/products/vr51.html

Yeah, you could let the DJ destroy a more expensive speaker!

[Chris Hindle]

....... or Peavey SP2 are comparable. 
Thoughts please?!?

as long as you're sure it's the DJ,
2 x SP-2 and a CS-800. 
Just try to kill that rig. Might not sound pretty, but it'll take a pounding, night after night.
( and Fuck em if thay can't take a joke. )

[Bob Leonard]

Well, I'm assuming the DJ wasn't clipping the input but unfortunately that something I just can't control. 

Sounds like the safeest bet would be to redesign the system a bit.  I don't want to cut into the MRX cabs and rewire or change anything - especially since I'm not sure we're going to keep them.  How about switching the XTi2000 to stereo mode so it will be a peak of 475W @ 8 ohms per speaker?

Looking at comparitivly priced cabs from other manufactures...the only thing on paper that looks like it may be a more robust choice is the Peavey SP2.  Thoughts??

Thanks again for everyone's input!!

Here's one. Set the gain structure so that you don't have more than 1.5  or 2x the long term handling power of the cabinet available to the speaker. This can be done with a DSP. As a matter of fact I wouldn't waste money on speakers when a Driverack 260 will match the speakers to the amps, and do everything you need to protect them from the "ahem", DJ.
 
Buying more speakers is not the answer to an improperly set system, wrong components, or poor practice and improper use. Education is the answer here and I suggest you start by learning how to limit the output either through a good xover or DSP.

[Glenn A Williams]

Alright here's an odd situation.  Recently installed a pair of JBL MRX 515’s in a small bar for live music as well as dj.  The pair is powered by a single XTi2000 in bridge mode - IE 2000W @ 4 ohm.  To start things off one the original cabs had an open horn right out of the box. I wrote it off as a 1 in a million fluke, swapped that box for another at the local dealer and installed the pair.  No issues during EQing that during the install, worked perfect the following night for the band & DJ.  On the second night both horns went out in both boxes in quick succession – at almost the exact same time. 

I’m scratching my head on this one.  Could it just be a bad run of horns?!?
Obviously I can swap these boxes out for another pair no problem, but I’m a little gun shy now. Is it a bad run of horns and if I swap this pair out will I have this same issue again?  Or do I just switch to a completely different box?  But at that price point only the EV TR1152 or Peavey SP2 are comparable. 

Thoughts please?!?

My thoughts are that a speaker rated at 400/800/1600 or 350/700/1400 is optimiumly driven by 400-600 rms given that they are not subject to music with a very heavy duty cycle. Driven by 475rms @ 8 ohms in stereo is just about perfect, which is what your amp puts out.

There is a JBL White Paper that suggests derating a speaker to the rms level is prudent with a heavy duty cycle program material.

But for some reason you feel that by bridging into a pair of these with 2000 watts rms @ 4 ohms and thus providing 1000 watts rms to each 8 ohm speaker is a better idea.

Have you considered that 1000 watts rms is 2.5 times the rms rating and thus produces 2000 watts PEAK into each 8 ohm speaker may be excessive, considering that either of the listed ratings quote a PEAK maximum capability of either 1400 watts or 1600 watts?

IMHO, you will continue to have problems if you are feeding each of these speakers with that much power.

475 watts rms will get you to a gain of just under 27 db continuous or just under 30 db. peak.

1000 watts rms will not get you anymore than another 1 db or so, (once mechanical and compression losses are taken into account), despite the JBL Differential Drive configuration's ability to diffuse heat, since 2000 watts peak will exceed both the thermal and mechanical abilities of the speaker.

The term for exceeding the maximum rating of a loudspeaker is abuse, especially by 400 to 600 watts peak.

[Mark Chrysostom]

I give mine 500W each and they've been thumping along happily for 6 months. If you really need that extra ~3dB you get from 1000W, you need a bigger rig.

[Robert Chafe]

Final decision is that we're going to do all of the above.

Switch the XTi2000 to stereo supplying 475W @ 8 ohm per side with the internal limiter @ -6db.

And switch to Peavey SP2 speakers.  May not sound as "pretty" but hopefully will stand up to more abuse.  The bottom line is that they have to take the abuse from the ignorant Dj's and random "sound guys" that mix on the system.  IE make it is bulletproof as possible with the very limited budget.

Most definitely though the horns JBL uses in both the JRX and MRX series definitely leave quite a bit to be desired. 

[Chuck Simon]

Most definitely though the horns JBL uses in both the JRX and MRX series definitely leave quite a bit to be desired.

 

I don't think so.  Your MRX uses the 2408 High freq driver, the same used in some of the JBL Vertec speakers.  You are assigning the blame to the wrong culprit.

Good luck with your Peavey.

[Bob Leonard]

Most definitely though the horns JBL uses in both the JRX and MRX series definitely leave quite a bit to be desired.

Wrong again Robert. An abused system is an abused system regardless of components.

[duane massey]

The drivers in the MRX/JRX are not very robust drivers. The smaller Vertecs do use them, but paired in series. The larger Vertecs use a significantly beefier driver (2431H). 

Not suggesting that some realistic protection and proper settings are not needed, just that there are more solid speakers out there, including the more up-scale JBL boxes.

[Chuck Simon]

Right, so if you don't use the right tool for the job, don't blame the tool.

[Glenn A Williams]

Most definitely though the horns JBL uses in both the JRX and MRX series definitely leave quite a bit to be desired.

Wrong again Robert. An abused system is an abused system regardless of components.

I agree totally, you can't blame a speaker,when the problem is operator abuse even if it induced by the users.

I have four of the MRX-512ms and depending on the amp and configuration they get from 400-550 rms each and at those levels they are very robust considering that they are well within the wattages that really stresses the surrounds and spider assemblies.

It is also well within the Differential Drive VC's ability to diffuse heat and thus do not lose alot due to thermal compression losses.

They will live a long and happy life.

[ProSoundWeb Community]