Please suggest replacements for Eminence Beta 12CX - diyAudio
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Old 20th May 2004, 01:07 AM   #1
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Default Please suggest replacements for Eminence Beta 12CX

I just noticed a tear in the paper cone of one of my woofers I have no idea how long it's been there, or how it got there. I only noticed it because the blinds were open and it's light out, after dark it's possible it could have gone unnoticed with the living room lighting.

Anyway, that leaves me with two options - get another Beta 12CX, or get something better suited to my application. The driver was originally used up to a pretty high frequency in a 2-way, now it's performing woofer duties in a 3-way. So, the requirements:

* XO points are 100Hz and 500Hz, 4th order L-R at both ends. So the driver would need to do about 50Hz to 800-1000Hz, I guess.

* The enclosure has internal dimensions of 22.5" x 13.5" x 12.5". I just veneered these boxes, and don't want to build new ones.

So I need a 12" driver that can give me ~ 50 - 80Hz in that enclosure, with mid-to-high 90s efficiency (the system is bi-amped and I have quite a bit more power on the woofer than on the midrange/tweeter, so I have some room to play here). And something that wouldn't break the bank would be nice. I could go through the PE catalog and compare TS specs on all the 12" drivers, but I was hoping that someone here could give me a head start on specific models or product lines to look into. Any help would be most appreciated.

There's no way to fix a tear in a paper cone, is there? I'm not sure I can handle a re-coning attempt, but if a re-cone kit is pretty cheap, I could try that before spending the money on new woofers.

Thanks for looking,

Saurav
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Old 20th May 2004, 02:07 AM   #2
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I've heard that a mixture of toilet paper and wood glue on the front and back can fix that. Do you have the compression tweets and xovers for your 12CX's? If so, I'd be interested in buying them. Then you could get something better suited to 3way woofer duty.
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Old 20th May 2004, 02:20 AM   #3
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I'll email you.
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Old 20th May 2004, 03:17 AM   #4
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Default Repair

You will want something with considerably more strength than toilet paper.

For tears (no loss of cone material) I've used Japanese rice paper (long fiber, light, strong) from an art supply store. Given its archival nature, it is more likely to be acid free and less likely to do nasty things to the cone over time than some random paper you come across.

Others have recommended high end rolling papers (you'll have to ask around on that one).
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Old 20th May 2004, 05:59 AM   #5
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I think I'm going to try and repair these. Stuff happened at work today that may go south pretty quickly, so spending money on new woofers isn't the best idea right now. And I played these for a while today, and I can't really tell that anything's changed in the sound (that should earn me permanent entry into the golden eared audiophile club, right?).

Click the image to open in full size.

Click the image to open in full size.

Has anyone else tried repairing paper cones? I looked up "paper cone repair toilet paper" on Usenet and found some tips. I also saw people mention dryer sheets, coffee filters, and brown paper bags, along with several different types of glue and nailpolish remover. What should I stay away from on a paper cone that's been treated with shellac and then damar (I found it later, so I put a coat on for the heck of it)? I'll try the repair on the reverse surface of the cone, which isn't treated with anything.

I also figured out how this happened, I think. I was moving the cabinet yesterday and the open baffle that's sitting on top of it fell off. An edge must have hit the cone on its way down. I so totally deserve this for being stupid
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Old 20th May 2004, 07:31 AM   #6
sreten is online now sreten  United Kingdom
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Most tears in paper cones can be repaired by judicious application
of PVA wood glue, I've done it many times with great success.

The coffee filter paper etc is only needed if the edges of the tear
do not meet. A section is cut to fill the gap and lightly glued in
place around its edge. Once this has dried extra PVA is added
to stiffen up the whole added section.

For a normal tear just pva the torn edges of the tear and push
together with your fingers, then add a further small amount of
PVA along the tear, job done, just wait a few hours.

The coating will actually help, not hinder the repair, as only
the torn part of the cone will hold the PVA glue well, from
your photos it looks a very straightforward repair.

sreten.
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Old 20th May 2004, 02:16 PM   #7
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sreten,

Do I need to dilute the glue? And are you saying that I just line up the edges and then put the glue on the reverse side, with a foam brush or something like that?

tghoram,

I think I can find rice paper, my wife might even have some. Could you give me more detailed instructions on how I should use it?
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Old 20th May 2004, 02:59 PM   #8
sreten is online now sreten  United Kingdom
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There no point diluting the glue, it will just take longer to dry.

Make a cardboard cone and practise on that. The point is the
repair appears to be quick and straightforward, you should
see it that way before reparing the unit. Or trash a cheap
speaker in various ways and see how well you patch it up.

You wet the frayed edges of the tear and then push the tear into
alignment. There is no need to add any paper unless you have a
gap, you don't appear to. Flatten any distortion of the cone as
best you can before adding the PVA glue.

Use a toothpick or similar to apply the glue along the edges.

Do not be afraid to wipe of excess glue then apply along
the line, the exposed edges will soak up the glue.

From your photos it looks as though if you support the cone
from the back and wipe the front with a damp cloth to finish
off the repair will be very near invisible.
Wipe in the direction that flattens the tear.

sreten.
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Old 20th May 2004, 03:09 PM   #9
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Thanks, that sounds doable. Trying it on a trash speaker first is good advice.
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Old 20th May 2004, 03:27 PM   #10
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Default Rice Paper

I basically used it like you would a fiberglass mat.

I cut two pieces big enough to cover the tear. You'll have to use your judgement about how much overlap you would like. I had probably around 1/4 inch.

My driver had been "damared" so I used that as the adhesive taking a contact cement-like approach. Put damar around the tear front and back(the back hadn't been treated and soaked up a good bit of the varnish), pretty much saturate the two patches, let it get tacky, and applied a patch on the front and a patch on the back. It took another coat or so of varnish to make the rice paper appear "fiber glassed" to the cone. Damar probably isn't the best all round adhesive (thin, takes forever to dry) but it worked for me. The upside is that it remains flexible over time (which is why it is used over oil paintings) and isn't likely to craze or crack or crumble as a result of the cone being continually stressed. Be aware however that if I had to do it again, I would probably go the PVA route for expediency.

One thing that I would recommend, regardless of the approach you use, is to practice "fixing" some tears in construction paper. This will give you some practice working with the materials and will also prove their effectiveness. If you experiment with multiple adhesives, share your results.

I actually liked the suggestion about those non-woven fabric softener tissues. Those are surprisingly strong little beggers (having had to pick one out of the beater brushes of a carpet sweeper) and have a nice long fiber structure very much like rice paper. You would want to use one that was "exhausted".
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