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Bug screen removal from K-55-V midrange?

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13 minutes ago, Ray_pierrewit said:

I ran some test tones and it seems to be buzzing from the left channel between approx 260hz - 300hz. Sounds pretty awful.

 

So does this sound like I need a replacement diaphragm?

At that frequency, it sounds, like a cabinet rattle or a damaged woofer and not the K-55 (mid-range). One step closer ...

 

Skip the DC voltage check and let's look elsewhere.

 

Why not disconnect the mid-range at the crossover output. Runs the test tones and see if the "rattle" remains

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Well I think I've ruled out a damaged woofer or cabinet rattle as I've switched the drivers from one side to the other and the buzz follows the driver.

 

 

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So is it strange that the squawkers are producing sound at those frequencies? If I understand properly the crossover to the woofer should be at 400hz, yes?

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29 minutes ago, Ray_pierrewit said:

So is it strange that the squawkers are producing sound at those frequencies? If I understand properly the crossover to the woofer should be at 400hz, yes?

 There will be some output since you are still within an octave. The filter is not very steep.

 

Since the rattle followed the driver to the other cabinet, you need to be precise in what you are hearing. Is it a "rattle" or a "harshness" when you run a tone through it? Is there a chance that the gasket between the driver and horn has dried and rotted? Are the bolts snug? Was the bug screen ever removed? Was the diaphragm ever serviced (perhaps it was not centered correctly)

 

Since I am not there, my ignorant guess is that the diaphragm is failing or something got into the gap on the voice coil and is rattling or has shorted something. I would contact BEC about this since probabilistically you are probably looking at a new set of diaphragms. 

 

Good luck,

-Tom

 

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1 hour ago, Ray_pierrewit said:

Well I think I've ruled out a damaged woofer or cabinet rattle as I've switched the drivers from one side to the other and the buzz follows the driver.

 

 

Put your hand on the back of the driver when the noise happens.  Apply pressure and see if you can make it stop.

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On 12/1/2019 at 8:07 PM, Ray_pierrewit said:

 

I've since taken both K55V drivers off and measured them.They are testing 11.9 (L) and 12.0(R) with my multimeter, so no need to change the diaphragm according to Bob Crites' site.

Both drivers testing well on the ohm meter "usually" means they are fine. I had a pair of 55v that tested great but i could not get them to sound right. When I emailed Bob about it, he said that the 40 year old diaphragms had led a full life. He put new diaphragms in and they now sing beautifully.

(the drivers actually came from @Zim.so they may have even been the ones he removed and replaced the bug screens on -  small world) 

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2 hours ago, CECAA850 said:

Put your hand on the back of the driver when the noise happens.  Apply pressure and see if you can make it stop.

 

Was thinking along those same lines...

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The ohm reading showing that it is not "open" is a fairly crude diagnostic of the diaphragm. The diaphragm can still be damaged or not centered properly and give you "normal" ohm readings. Perhaps you should e-mail BEC directly and tell him the symptoms and diagnostics already performed. As noted above, the diaphragms are old and they can fail in different ways.

 

A note to the other guys: Are these diaphrams easily replaced by the user (self aligning etc)? I recently replaced some JBL diaphragms that were a bit picky and required some adjustment and measurement (rinse and repeat ....). 

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Reseat the diaphragm. 

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If you are going to re-seat the diaphragm, then Google for info on how to use a post-it note to clean where the diaphragm sits (there may be some debris or corrosion) Also inspect the voice coil winding for any burn marks and do not touch the the diaphragm's inside. 

I guess Dean is saying the K-55 diaphragm is self-aligning. I did not know this. 

 

Good luck,

-Tom

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Thanks everyone for the replies.

 

By reseating the diaphragm I suppose that would imply desoldering then resoldering, right? 

 

I read through the diaphragm replacement guide on Crites' website and saw the post-it note trick.

 

I will update as it develops.

 

Daniel

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I wrote to Bob last night and he says he hasn't run across that particular problem before. He advised me not to try reseating the current diaphragm because they tend to be stuck and will likely break when I open the driver up. He suggests changing the diaphragm on both drivers as they are old and likely failing. He did stipulate that he doesn't know if it'll fix the issue.

 

I'll go ahead and try my hand at changing it, and if it doesn't work I'll be obliged to consider ordering new drivers, surely the A55-G. It's tolerable when I'm listening to background FM music, but my evening sessions are compromised to the point of being unpleasant. 

 

I've sort of highjacked this thread, haven't I?

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