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Bug screen removal from K-55-V midrange?


wuzzzer

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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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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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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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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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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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Well, this will be the last derailment of the original thread on my behalf. Further messages will surely be included in some A55G thread, as I've place an order for the drivers from Bob! Very excited to listen to these and finally be rid of that noise. It makes me wonder just how much that driver has been altering the sound? I mean, it buzzes between 260hz - 300hz, so it must constantly be muddying the music. Who knows?

 

I decided to begin clearing out my closet of audio goodies and quickly came up with the money to purchase not only the A55G, but also a pair of SMAHL with DE120. What good is a closet full of interesting gear when it can be sold and reinvested in my primary system? Before long I'll get to work on the Claude's Qpies and then I'll officially be that guy who "changed everything" about the Lascala and will no longer be able to call it such ;)

 

Daniel

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4 minutes ago, Zim. said:

  Sorry to hear you had issues with those LaScalas, you should have got back in touch with me.  I would have been more then happy to buy them back(offer stands + cost of repair).  Odd though, I consider those pair of industrials among the two best sounding factory LaScalas (out of perhaps a dozen pair) I've owned; and no, I never monkeyed with the bug screens (or any components) of this pair.

no worries

i never noticed any issues until after a co worker returned them after borrowing them for 14 months!

I had fun tinkering with them and have re-purposed the k55Vs into a set of "Super Heresys" so they live on.

I have several standing offers if I ever choose to sell.

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