PDA

View Full Version : Blown 2042H



Fred Sanford
07-14-2008, 05:52 PM
A band I've been working with has a JBL MR938 with a damaged 18" 2042H. I didn't see the incident, but was told that during a sudden wind storm the cabinet took a face-first tumble off stage onto grass from about 7' up- yikes!

The cone is damaged in a way I've never seen- it's separated from the center of the cone in a perfect circle around the dust cap. I'll try to grab a pic.

I'm looking for info regarding price & availability for the C8R2042 cone replacement, or for a replacement driver, or both. When looking for a quick fix, I found that the band's MR918 subs (which should also have 2042s) have 2241Gs- 4 ohms, among other differing specs. Any advice would be appreciated- they can handle their next small-club gig on Friday, but then have two outdoor shows where they'd like to have both mains running if possible.

Thanks in advance.

je

subwoof
07-14-2008, 06:49 PM
That damage is caused by either repeated over excursion - the soft, thin paper ( it really is a midrange cone ) folds when a distorted large signal is applied ( squarewave ) and over time it rips the folds/paper when mechanical maximum is reached..

OR the magnet / frame has shifted / broken.

Either way it is not a good thing - you probably need a whole replacement 18.

They cost more to recone than what they sell for used - the best alternative is to find some new 2268 Nd types but that is a lot of money and will require some network changes.

And they use this stuff for outdoor shows with just a pair of tiny screw-on HF drivers???

poof..:o)

sub

Fred Sanford
07-15-2008, 07:29 AM
That damage is caused by either repeated over excursion - the soft, thin paper ( it really is a midrange cone ) folds when a distorted large signal is applied ( squarewave ) and over time it rips the folds/paper when mechanical maximum is reached..

OR the magnet / frame has shifted / broken.

Either way it is not a good thing - you probably need a whole replacement 18.

They cost more to recone than what they sell for used - the best alternative is to find some new 2268 Nd types but that is a lot of money and will require some network changes.

And they use this stuff for outdoor shows with just a pair of tiny screw-on HF drivers???

poof..:o)

sub

Thanks for the reply- so, it's possible the magnet shifted in the fall, and then the cone gave out when fired up for the next soundcheck...or, it just died from use as a full-range cab due to flimsy cone material. They've invested in an electronic crossover and second amp, so hopefully these will have the lows rolled off a bit in the future for any gig that has bass & kick drum run through the PA.

Yeah, the high-freq drivers are a bit weak, but the band's been making incremental improvements and doing pretty well with it- when I met them a couple years ago they had a Peavey powered mixer and some SP1s from 1978. The drummer owns some Smith horns in cases, I'll have to check them out to see if they're viable and what driver might make sense to use with them. I'm still trying to convince them to invest in road cases, at this point the two Crown MacroTechs ride to gigs in the drummer's front seat.

I've been trying to push the band to have a good, long tech rehearsal- to inventory, test, & label all their gear and to weed out the crappy cables & connectors. There's always a scramble at setup time to guess where the cables are, and what's a guitar cable vs. speaker cable, etc. We'll see- they're booking enough gigs now that it might sink in that tech issues can wreck their reputation.

Thanks for the advice...

je

Fred Sanford
07-15-2008, 07:44 PM
Crappy cell-cam pic.

je

subwoof
07-16-2008, 06:30 AM
If the cone ripped after the fall the power could not of done it because the 1/2 with the coil could not move. That looks like a long-term slam-bam-thank-you-m'amm crease that finally ripped.

The PT-95H 1.5" horn will drop in the HF hole - but you still have a low power 8 and flakeboard box with mileage....

And yes - no lights, so what. Crap sound and NO REPEAT CUSTOMERS.....:)

sub

Fred Sanford
07-16-2008, 08:42 AM
If the cone ripped after the fall the power could not of done it because the 1/2 with the coil could not move. That looks like a long-term slam-bam-thank-you-m'amm crease that finally ripped.

The PT-95H 1.5" horn will drop in the HF hole - but you still have a low power 8 and flakeboard box with mileage....

And yes - no lights, so what. Crap sound and NO REPEAT CUSTOMERS.....:)

sub

Gotcha, the voice coil on this seemed to still be pretty free.

The mid driver on these is the MI-10-1...dunno about the cab construction, the brochure calls it "Oriented Strand Board" hardwood enclosure material, which does sound like flakeboard to me.

Thanks,

je

Rudy Kleimann
08-16-2008, 11:57 PM
Subwoof accurately explained it to a "Tee". Too small of drivers pushed way past their limits. It can be difficult, if not impossible, to make musicians understand the ins and outs of proper equipment selection, setup, and operation of a PA system. It is painful to watch -much less be a part of- a bad setup run improperly, and even harder to watch/listen to. I feel for you, and hope you can get these guys on the right track, or at least save them from self-destruction of their PA system.

Good luck with your efforts. Hopefully you'll be able to identify the weak links and they'll be able to either afford the upgrades or accept the limitations of the current setup. And don't put too much money and effort into those cabinets without exploring other ready-to-use options. While the MR 3-ways are good in their intended application, you apparently need a lot more. At least some subs with another amp, and a crossover. Those 2042's were only rated for 250RMS, 4-500 Music program, and (supposedly) 1000 peak watts, with no amplifier clipping.

Years ago I came to work with a Tejano Band/Sound Company that had a lot of gear- some good, some... not up to the task. They had 25,000 watts of QSC MX-series amps and Mackie 1400's for the horns in a triamp configuration running their Front-of-house system which originally consisted of 8 Cerwin-Vega L36PE 18" folded horn subs and 8 Cerwin-Vega double 15" three-way tops. Shortly after I joined them, the owner bought 8 JBL4733A (dual 2226 with 2447's on 2381 horns) to replace the Vega tops and added 4 JBL 4719A's (dual 2241H 18's per cabinet) to the Vega subs. A lot of power, and a lot of speakers. But poorly set-up and connected...

Like yourself, I was the guy who knew what was crippling them but was in a long uphill climb to get through to them what their problems were, much less get them out of it. They didn't have a clue why they had so much trouble. First thing I did, once I got brave enough, was snipped the suspect end off every cable I found that was faulty. They were pissed- at first. But after a few gigs, when things worked right the first time -and stayed working through the gig- they started to see the light. When the setup time was cut in half, and went without a hitch, they started listening to me. When I cut the 50' speaker snake to 1/4 its original length and parallelled the 16 gauge wires in the snake to effectively make the equivalent of 13 gauge, it blew their minds! It sounded like twice the power, and cleaned it up like night and day!

They still had problems with blowing up speakers on occasion. "The speakers are rated for the power we're pushing them with- why are they blowing out?" I told them, "You can't drive the amps into hard clipping without these consequences." When I hooked up one MX-2000 in bridged mode to each 4719A sub cabinet, they coudn't belive their ears. And when I convinced them to buy compressors to use as limiters and the speakers stopped burning out, they really started to realize the err of their ways.

Fred Sanford
08-17-2008, 04:50 AM
Thanks for the post- I've been working with this band for about a year & a half now, and still haven't gotten them to have a "tech" rehearsal. Any time they ask me why something doesn't work, or breaks, or takes a while to set up, I say, "Tech rehearsal. You want to book gigs at this level, run a bi-amped system with 6 monitors & 16 mics, you need a controlled situation in which to test & label everything. I'm not figuring it all out during soundcheck at an outdoor water park in a lightning storm."

We'll see...one band member (the guitarist) is a very good friend, and has been doing a good job at learning how & why things work. The drummer owns about half the gear, and also has good reason to learn. Some day we'll start from scratch & find where we're at. Then maybe they'll stop handing me shielded input cables to hook up the monitors with.

je

Rudy Kleimann
08-17-2008, 08:01 AM
Reminds me of the old days:

"Why do the monitors sound so puny? Turn 'em up- I can't hear 'em!

You smell something funny?

Oh, S--T! the wire is melting!

Been there too. Got to sort those cables and keep the containers as far apart as possible to avoid screwups like that.

Fred Sanford
08-17-2008, 10:33 AM
Reminds me of the old days:

"Why do the monitors sound so puny? Turn 'em up- I can't hear 'em!

You smell something funny?

Oh, S--T! the wire is melting!

Been there too. Got to sort those cables and keep the containers as far apart as possible to avoid screwups like that.

Here's a classic quote from the bass player- "It can't be my cables, I just bought them in town this week. Great deal, too- only $5 a piece!"

je

speakerex
08-26-2008, 11:23 AM
it is not unusual for the cone to break around the dustcap as you indicate it did during a face front fall. this can happen from the air compressing against the cone during the fall. as long as the voice coil still moves freely, then the magnet has not shifted. if the voice coil is "frozen" then the magnet might have shifted. either way, the driver can be reconed back to exact new condition either with or without a magnet recenter. if the magnet has broken into pieces rather than shifted, then it cannot be repaired. cathy@speakerex.com

Woofer
09-07-2008, 09:46 AM
......
The cone is damaged in a way I've never seen- it's separated from the center of the cone in a perfect circle around the dust cap. I'll try to grab a pic.

I'm looking for info regarding price & availability for the C8R2042 cone replacement, or for a replacement driver, or both.
je

In the mean time, and you have nothing to lose, why don't you just try re-gluing the torn cone back to where it's broken off?
Your typical 'White Glue" ( we call it Aquadhere here in Oz) should do the job easily.
Of course you'd need a bit of logic and patience, but if you stare at it long enough, it'll come to you. (".... use the Force Luke.") ;)
Just gently rub some glue with the tip of your finger around the break and just leave it for 2-3 minutes.
Then slowly run a 20 -30Hz signal through it to see if it's poling (rubbing) at all, and if not, then allow to dry overnight. (Signal Generating s/w for your PC - if you got one - is easy enough to source)
It's important that you do this before the glue sets, otherwise if the speaker is poling, then you can simply re-align if necessary. Easier to do when wet.
Test again, then if all's OK, flip it over, and do the back of the cone.
Then once that's dry, get some more glue, dilute it to about 1 part glue, to 3 parts water, and then thinly paint the whole cone with the solution, being careful to not saturate the cone.
Allow to dry again overnight, and what you have is a working speaker with a much more stronger cone, with a coating not much different to an Aquaplas speaker.
The added mass is negligible compared to the amount of work it does when being driven hard.
Try it. Like I said, you have nothing to lose, and lots to gain, until you can afford either a proper re-cone, or buy a second hand something to replace it.

Good luck, and all the best.
Woofer.

PS: Yes, I've done lots. This is very common with the JBL 2220 or K130.
Or any other large JBL that doesn't have the ribbed cone.
:bouncy:

Fred Sanford
09-07-2008, 10:38 AM
Sorry- I thought I'd posted it here, but we've already sourced a new-in-box replacement, and we're looking into OEM or aftermarket re-cones for a spare.

Haven't been able to reach the drummer lately- the band's on a vacation hiatus and I know the drummer's actually caring for a very sick relative, so I'm sure the PA is low on his priority list right now.

je

darkmatter
06-07-2017, 05:29 PM
Does anyone know if the mounting holes for the 2042H bass unit are in the same position as the 2240 or 2245 i.e. a bolt circle diameter of 441mm?

I could not find an datasheet for the 2042H online!!

Thanks

Lee in Montreal
06-07-2017, 09:27 PM
JBL MA15 Mounting Clamps are what is used to mount these drivers usually.

http://img05.shop-pro.jp/PA01015/403/product/1704404_o1.jpg

http://i31.photobucket.com/albums/c378/BMWCCA1/4345-14-2s.jpg

darkmatter
06-08-2017, 12:15 AM
Thanks Lee,

But my mounting regime uses the bolt holes of the drive unit

Regards,

Simon




JBL MA15 Mounting Clamps are what is used to mount these drivers usually.

http://img05.shop-pro.jp/PA01015/403/product/1704404_o1.jpg

http://i31.photobucket.com/albums/c378/BMWCCA1/4345-14-2s.jpg

1audiohack
06-08-2017, 06:00 AM
Does anyone know if the mounting holes for the 2042H bass unit are in the same position as the 2240 or 2245 i.e. a bolt circle diameter of 441mm?

I could not find an datasheet for the 2042H online!!

Thanks


They are the same, the cut out diameter for the 2042 is 16.5", the bolt circle is 17.375"

Whats this MM crap? You're in the UK right? You guys created the Imperial measurment units! :)

Barry.