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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Lounge => Topic started by: Dave Guilford on August 13, 2018, 12:41:55 PM
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Guys, i have a JBL MRX518 subwoofer and it doesn't work. so naturally i pulled the driver out to be sure it wasn't a problem with the input plate. it's the actual speaker driver itself.
I've had bad speakers where the magnet cracked. And i've had bad speakers where the voicecoil was knocked out of position the it had a grinding as you lightly push the cone.
But this one glides freely, and the magnet is fine. So is this probably a burned voice coil? How can I tell? Anything else i should check before i buy a replacement driver?
teach me, but don't lecture or belittle me. thanks,
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Try the ol' 9V battery test to the speaker terminals. Should be able to see movement on the cone and get an audible thump. Also check for impedance and continuity with a multimeter. If you get nothing, get ready for a recone or worse.
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My bet is it measures open circuit.
If it's not been on the receiving end of high-power use, you might find the join between the leads and the cone itself has failed. It can be repaired if you're good at that sort of thing.
When a driver burns out, the voice coil windings often find themselves loose of the voice coil former, so you'll get some kind of noise when you push on the cone, even if it's just half a mile of copper wire being smushed around at the back of the magnet.
I don't know how attached you are to these cabinets, but it might be time to consider an upgrade.
If you tell us the internal dimensions of the cabinet and bass ports, it might be possible to put in a newer high-power driver, too.
Chris
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My bet is it measures open circuit.
If it's not been on the receiving end of high-power use, you might find the join between the leads and the cone itself has failed. It can be repaired if you're good at that sort of thing.
When a driver burns out, the voice coil windings often find themselves loose of the voice coil former, so you'll get some kind of noise when you push on the cone, even if it's just half a mile of copper wire being smushed around at the back of the magnet.
I don't know how attached you are to these cabinets, but it might be time to consider an upgrade.
If you tell us the internal dimensions of the cabinet and bass ports, it might be possible to put in a newer high-power driver, too.
Chris
That's the critical test, taking a resistance measurement across the voice coil.
If it reads an open either the coil is bad or one of the tinsels has come loose
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My bet is it measures open circuit.
If it's not been on the receiving end of high-power use, you might find the join between the leads and the cone itself has failed. It can be repaired if you're good at that sort of thing.
When a driver burns out, the voice coil windings often find themselves loose of the voice coil former, so you'll get some kind of noise when you push on the cone, even if it's just half a mile of copper wire being smushed around at the back of the magnet.
I don't know how attached you are to these cabinets, but it might be time to consider an upgrade.
If you tell us the internal dimensions of the cabinet and bass ports, it might be possible to put in a newer high-power driver, too.
Chris
What if they have been on the receiving end of loads of power? I usually run a pair of them off one side of a macrotech 9000i. :-D
I’m also fairly attached to the cabinets. They’re lightweight and small. They match the rest of my rig. Generally they are used for gigs where I probably don’t need subs, but occasionally they’ll take a lot
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What if they have been on the receiving end of loads of power? I usually run a pair of them off one side of a macrotech 9000i. :-D
I’m also fairly attached to the cabinets. They’re lightweight and small. They match the rest of my rig. Generally they are used for gigs where I probably don’t need subs, but occasionally they’ll take a lot
Well, maybe not that much. Coil burnout is usually the result of thermal overload. Which comes from passing too much current for too long. At some point that was all she got captain.
You may be able to find out what the original drivers were, although they probably weren't something JBL sells on the open market. If you can find the T/S parameters, you may be able to find a modern neo substitute that is lighter and handles more power. But there's always the risk that the tuning won't come out quite right and the speakers will unload at some practical frequency and hit excursion limits. Be prepared to spend $400+ on a new driver for each box.
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Well, maybe not that much. Coil burnout is usually the result of thermal overload. Which comes from passing too much current for too long. At some point that was all she got captain.
You may be able to find out what the original drivers were, although they probably weren't something JBL sells on the open market. If you can find the T/S parameters, you may be able to find a modern neo substitute that is lighter and handles more power. But there's always the risk that the tuning won't come out quite right and the speakers will unload at some practical frequency and hit excursion limits. Be prepared to spend $400+ on a new driver for each box.
The driver in those is the 2044G IIRC, which is old enough that JBL did indeed publish TS params for it: JBL TSP PDF Link (http://www.jblproservice.com/pdf/Thiele%20Small%20Parameters/Theile%20Parameters.pdf).
The specsheet for the box shaws a response that's strongest around 70Hz, about 5dB down from peak just below 50Hz and 10dB down at 40Hz, so they were never going to sound super deep.
There's no impedance curve shown though, so until a measurement is made of that (or failing that, the net internal box volume and port dimensions as mentioned up-thread a few posts), we don't know the tuning frequency.
Cheers,
David.
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A recone kit is about $100...
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I usually run a pair of them off one side of a macrotech 9000i. :-D
Almost 2kw into a 500w driver.. I'd say the voice coil is burnt open like a fuse. That much power is fine for dynamic program like live sound but the box has to be derated for any kind of bass heavy recorded material.
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A recone kit is about $100...
You think it just needs a recone? I’ve never done it but terrible woth soldering. Any other obstacles to recone?
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You think it just needs a recone? I’ve never done it but terrible woth soldering. Any other obstacles to recone?
Buy 2 kits and figure you'll screw up the first one. After that you can probably do it right the first time.
It's not rocket surgery or brain science but it does require good prep work (like painting a house). Some cone kits are pretty much drop in replacements and others require finesse.
@ Geert, I take it that's an "after market" kit from Waldrom? Last I knew, JBL didn't sell recone kits to the public, only to accredited JBL service centers/technicians.
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Yes, aftermarket. Original will be about 200-250. Complete driver 350. I would give it a try.
Found recone video: https://www.youtube.com/watch?v=1nY_y0QmaCU
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Buy 2 kits and figure you'll screw up the first one. After that you can probably do it right the first time.
It's not rocket surgery or brain science but it does require good prep work (like painting a house). Some cone kits are pretty much drop in replacements and others require finesse.
@ Geert, I take it that's an "after market" kit from Waldrom? Last I knew, JBL didn't sell recone kits to the public, only to accredited JBL service centers/technicians.
Which begs the question: is there a difference between JBL cone and aftermarket cone?
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I have done a few recones, and they worked out well. All RCF drivers. Always with kits that had assembled voice coil/cones. The hardest part was cleaning off the old glue from the frame. Cleaning the gaps wasn't that difficult. Other than that the hardest part was making sure the voice coil is aligned, which for me wasn't as hard as I thought it would be. Also, be sure to use the right glues. There is not much soldering involved.
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I have done a few recones, and they worked out well. All RCF drivers. Always with kits that had assembled voice coil/cones. The hardest part was cleaning off the old glue from the frame. Cleaning the gaps wasn't that difficult. Other than that the hardest part was making sure the voice coil is aligned, which for me wasn't as hard as I thought it would be. Also, be sure to use the right glues. There is not much soldering involved.
I have a different opinion. I am pretty sure you will fuck it up. I know I would. I watch my speaker guy and there is an art to it.
I watched him shim in the 18" drivers out of our ancient Meyer 650's and carefully fill the ferrofluid. It was very tedious and I am glad I paid someone else to do it.
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So I’m still looking into this. The JBL replacement drivers are pretty expensive. I am basically looking at about 450 bucks including tax and shipping. For the same price I can get a pair of eminence Kilomax pro 18a drivers and make them both match.
Would that be a suitable replacement to the original 2044? Bonus points that they’re 8ohm which means no more 2-ohm loads on my amp. Because I run the subs off one side of a ma9000i amp.
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So I’m still looking into this. The JBL replacement drivers are pretty expensive. I am basically looking at about 450 bucks including tax and shipping. For the same price I can get a pair of eminence Kilomax pro 18a drivers and make them both match.
Would that be a suitable replacement to the original 2044?
Dave,
The Kilomax pro 18a has a Vas slightly less than the JBL 2044, and similar Fs, other T.S. parameters also similar, so should work OK in the JBL cabinet. As it handles more power, less likely to burn out, and recones with original parts are less expensive.
Art
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The Kilomax is not a good choice for these cabs.. or any cab IMO but that is another story. These boxes are only about 5.8cu ft internal tuned to 45hz so you need a modern driver designed for small boxes. The Eminence Definimax fits that description but are you limited to that brand, B&C has some really good drivers that would work well here too.
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Which one of you should I believe?
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Which one of you should I believe?
If you have the time & inclination, download WinISD or any other speaker modelling program and have a play your self.
Or, wait for someone to come along who's already got it.
Like me ;-)
Herewith the predicted output, at XMax, of the original driver, the two Eminences and the B&C 18RBX100, in my best guess as to the cabinet size and tuning.
(https://i.imgur.com/uoWwYsK.png)
Re the Kilomax specs, the biggest difference is that it has a higher Qes which results in the peakier response above tuning around 70Hz and earlier rolloff you see here.
The Definimax has the lowest nominal Xmax of the 4, hence it seeming to be the quietest.
HTH,
David.
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Which one of you should I believe?
You can believe me that the Kilomax would be an "OK" choice as a replacement for the original JBL 2044, but you can also believe Paul & David that there are better replacements ;).
The B&C RBX100, at just a bit over the cost of the Kilomax will definitely outperform it in your small cabinets.
Art
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Re the Kilomax specs, the biggest difference is that it has a higher Qes which results in the peakier response above tuning around 70Hz and earlier rolloff you see here.
Right, the Kilomax "wants" to be in a much larger box for nominally flat response, WinISD defaults to 23 cu/ft for it initially. If it is crammed into a much smaller box the response goes a bit wonky as David described. Is it usable? Yes certainly but it can only handle about 800w before exceeding xmax because of it's heavy cone and there are better options out there now like the B&C RBX or even the older TBX.
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I have used the Eminence Impero in my last few projects, and have been very pleased with them. I was never particularly pleased with the Kilomax, had better luck back then with the Omega Pro.
Understand that I am a "seat of the pants" builder, my satisfaction (and that of my clients) has always been subjective.
Anyone want to run the simulation on the Impero?
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I have used the Eminence Impero in my last few projects, and have been very pleased with them. I was never particularly pleased with the Kilomax, had better luck back then with the Omega Pro.
Understand that I am a "seat of the pants" builder, my satisfaction (and that of my clients) has always been subjective.
Anyone want to run the simulation on the Impero?
Qes is a little on the high side (albeit not quite as bad as the Kilomax) and Xmax is still low like the Definimax, so IMO no advantage to using it over either the RBX or even reconing the JBLs, unless it's substantially cheaper.
(https://i.imgur.com/RMfUA63.png)
FWIW,
David.
Edit: Absent Apostrophe Added
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The B&C RBX100, at just a bit over the cost of the Kilomax will definitely outperform it in your small cabinets.
Art
I suppose that's because Emi are based in America; here, the RBX is over 15% cheaper than the Kilo - making it a no-brainer.
That's part of why I suggested it - also to tie in with Paul's suggestion of looking at B&C in the first place, and the fact that it's probably not worth looking at drivers that are too expensive to refurbish older cab's of this type/size/quality anyway.