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Author Topic: Strange sound in Double 18  (Read 997 times)

Justin Myers

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Strange sound in Double 18
« on: September 13, 2017, 07:24:56 pm »

Hello

I have 4 double 18 subs and was checking over them and pushed on a driver. Scraping sound?

Thought the worst and removed it from the box. Pushed on it, no scraping sound. It would only happen when the two drivers were joined. The enclosures have a panel where you can seperate the drivers or paralell the drivers by changing a jumper. Also some NL8 stuff on there and other NL4 inputs and outputs.

Thing is, 2 enclosures have the sound when a single driver is pressed and 2 enclosures do not.

Whats going on ?

I'd be happy to accept it as some sort of back emf from moving one of two drivers joined if all 4 enclosures did it. But only 2 out of 4 do it.
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Paul G. OBrien

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Re: Strange sound in Double 18
« Reply #1 on: September 13, 2017, 07:33:13 pm »

Do any of the drivers make any strange noises when powered? If not then you don't have a problem. The VC gap is pretty small and on some drivers if you don't push on the cone in the exact center you will distort the suspension and rub the coil on the wall of the gap. And for some drivers the suspension is known to sag a little over time so it is recommended that they be occasionally rotated 180 deg on the baffle.
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Justin Myers

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Re: Strange sound in Double 18
« Reply #2 on: September 13, 2017, 07:48:46 pm »

Do any of the drivers make any strange noises when powered? If not then you don't have a problem. The VC gap is pretty small and on some drivers if you don't push on the cone in the exact center you will distort the suspension and rub the coil on the wall of the gap. And for some drivers the suspension is known to sag a little over time so it is recommended that they be occasionally rotated 180 deg on the baffle.

Its not a poling issue. When the drivers are not connected to each other they make no sound what so ever. Pushing them off centre doesnt even make them rub.
Haven't had a powered test yet. I only opened them up to check the driver screws were all tight as a check up. Thats when I decided to push on one driver because it was there.
Had no problem 2 days before at a gig.
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Bob Leonard

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Re: Strange sound in Double 18
« Reply #3 on: September 13, 2017, 11:17:04 pm »

Justin,
Very often the spider will distort if the bolts holding it to the baffle are over tightened. If you hear scrapping then you have a problem, although your pushing could also cause the scraping sound. Sometimes pulling the driver and rotating it will resolve the scraping when you tighten the bolts.

Here's what I suggest. Pull the driver and using both hands gently push on the cone to see if you still have the problem with scraping. If not put the driver back in and tighten the bolts in a cross pattern checking for scraping as you go. Also, if there is cork material or other cushion material you might try removing it so that the frame sits completely against the baffle when tightened. And please, don't over tighten or monkey fist the bolts.
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BOSTON STRONG........

I did a gig for Otis Elevator once. Like every job, it had it's ups and downs.

Justin Myers

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Re: Strange sound in Double 18
« Reply #4 on: September 13, 2017, 11:49:37 pm »

Justin,
Very often the spider will distort if the bolts holding it to the baffle are over tightened. If you hear scrapping then you have a problem, although your pushing could also cause the scraping sound. Sometimes pulling the driver and rotating it will resolve the scraping when you tighten the bolts.

Here's what I suggest. Pull the driver and using both hands gently push on the cone to see if you still have the problem with scraping. If not put the driver back in and tighten the bolts in a cross pattern checking for scraping as you go. Also, if there is cork material or other cushion material you might try removing it so that the frame sits completely against the baffle when tightened. And please, don't over tighten or monkey fist the bolts.

Gday Bob,

There is no problem when the drivers are not connected to each other. I can do this via the back input panel by changing a jumper so each driver is seperate. When like this, I can push on either driver and all is perfect. But when connected, ie 4 ohm operation parallel, strange sound can be heard when I push on either driver.



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David Allred

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Re: Strange sound in Double 18
« Reply #5 on: September 14, 2017, 07:14:28 am »

Gday Bob,

There is no problem when the drivers are not connected to each other. I can do this via the back input panel by changing a jumper so each driver is seperate. When like this, I can push on either driver and all is perfect. But when connected, ie 4 ohm operation parallel, strange sound can be heard when I push on either driver.

Are the drivers connected to via cable to an amp, or simply to each other in the cab?
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Justin Myers

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Re: Strange sound in Double 18
« Reply #6 on: September 14, 2017, 05:09:09 pm »

Are the drivers connected to via cable to an amp, or simply to each other in the cab?


to each other in the cab
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Craig Hauber

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Re: Strange sound in Double 18
« Reply #7 on: September 14, 2017, 06:09:58 pm »

to each other in the cab
Could be something in the wiring between the drivers causing the voltage induced by pushing on one cone from cleanly getting to the other and it crackles in response.
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Craig Hauber
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Mike Caldwell

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Re: Strange sound in Double 18
« Reply #8 on: September 14, 2017, 07:08:10 pm »

What kind of cabinet is it, name brand or home built.

Are there any crossover components in the cabinet.

When connected in parallel and you push on one speaker can you see any movement in the other speaker, it should move slightly in the same direction as your pushing the speaker.

Run some sine wave tone at various frequencies through the speakers and see if they sound clean.

Justin Myers

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Re: Strange sound in Double 18
« Reply #9 on: September 14, 2017, 11:02:01 pm »

Voice coils have no sign of rubbing but I think I have found the problem. The braid tails are starting to becaome intermittent. Right at the point they enter the cone.
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