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Author Topic: raw speaker moves nicely, but no audio.  (Read 1016 times)

Dave Guilford

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raw speaker moves nicely, but no audio.
« on: August 13, 2018, 12:41:55 pm »

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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Taylor Hall

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Re: raw speaker moves nicely, but no audio.
« Reply #1 on: August 13, 2018, 12:44:47 pm »

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.
« Last Edit: August 13, 2018, 12:47:12 pm by Taylor Hall »
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Chris Grimshaw

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Re: raw speaker moves nicely, but no audio.
« Reply #2 on: August 13, 2018, 03:06:05 pm »

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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Scott Holtzman

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Re: raw speaker moves nicely, but no audio.
« Reply #3 on: August 13, 2018, 04:53:42 pm »

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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Dave Guilford

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Re: raw speaker moves nicely, but no audio.
« Reply #4 on: August 13, 2018, 09:50:05 pm »

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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Stephen Kirby

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Re: raw speaker moves nicely, but no audio.
« Reply #5 on: August 13, 2018, 10:37:17 pm »

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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David Morison

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Re: raw speaker moves nicely, but no audio.
« Reply #6 on: August 14, 2018, 07:56:29 am »

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.

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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Geert Friedhof

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Re: raw speaker moves nicely, but no audio.
« Reply #7 on: August 14, 2018, 02:24:46 pm »

A recone kit is about $100...
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Paul G. OBrien

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Re: raw speaker moves nicely, but no audio.
« Reply #8 on: August 14, 2018, 06:10:40 pm »

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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Dave Guilford

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Re: raw speaker moves nicely, but no audio.
« Reply #9 on: August 14, 2018, 07:36:41 pm »

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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