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Cadenza rebuild possible or not?

 
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freddyuk
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Joined: 29 May 2010
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Location: kent

PostPosted: Mon May 31, 2010 1:25 pm    Post subject: Cadenza rebuild possible or not? Reply with quote

I have just acquired my Dad's Cadenza's from 1971 vintage. I remember them being delivered!
He has no use for them any more so i thought great! They are mint condition. I had read about the possible problem with the Bass foam surrounds and sure enough these are toast.
I did read that i could obtain B139's and remove the magnets to substitute for the damaged units.
I am not a purist as such and would like to bring these units back to life even if they are not 100% of what they once were.
I hope that is not "heresy" and someone can give me some advice. I am not an expert in electronics but would happily pay to have these repaired if it makes sense.
Many thanks
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ColinR
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PostPosted: Mon May 31, 2010 2:07 pm    Post subject: Reply with quote

I gave you my reponse yesterday.

http://audiokarma.org/forums/showthread.php?t=301975

Replacing the foam surrounds probably is not an option as the round bits may be sourced but finding a bass unit with a sufficiently large diameter so you can piece together the "straight" bits is unlikely.

Commercial concerns like Wembley Loudspeakers www.wembleyloudspeaker.com/ or DC Boultons Tel: 01493 750075. Fax: 01493 751155 may be able to assist.
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freddyuk
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PostPosted: Mon May 31, 2010 2:41 pm    Post subject: Reply with quote

Many thanks.
Not sure i fully understand the technical implications. There are some B139'S on Ebay but how do i know if they are suitable for your "fix". I am happy to have a go but £80 to find out i have the wrong bits is going to get expensive.
The item number is # 280505506399 would you be able to advise further ?
I really appreciate some help

Thanks
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ColinR
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PostPosted: Mon May 31, 2010 3:02 pm    Post subject: Reply with quote

Nick Beasley's offering is rather expensive i.m.h.o. I'd contact a rebuilder first to see if anything can be done with the originals.

Next, depending upon your location a visit to http://thamesvalleyaudiofayre.co.uk/ might enable you to get the same for less.


Technical implications - your current ABRs have a metal collar on their rear's right?

You'd have to graft this bit with a bit of Araldite onto the voice coil of any A6171 drive unit with the magnet removed.

As you have to make the magnetless replacement's cone weigh the same as the original, so it has the same mechanical properties i.e. it resonates at the same frequency.


Look at my "List of Spares" in the List, exchange and buy section only if you're going to be in Bracknell and can use silicone caulk.


Off the wall idea I've one example in my collection of an A6171 with a cambric surround, so following the model glider route, could you piece together a couple of layers of muslin in the shape of your surrounds (2" wide), dope (the central 1") with cellulose and fix to the cone and frame wth PVA woodglue?
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freddyuk
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PostPosted: Mon May 31, 2010 3:45 pm    Post subject: Reply with quote

OK now we are talking.
I understand a bit more now and yes existing units do have a metal frame.
I have not really touched them yet just saw the mouse nest of foam and put it back in the box.
I will check the company link you suggested and as it happens i go down the M4 quite often so Bracknell would not be a problem.
Have made model planes in my youth so know what you are talking about there.
I was not looking for another project but seems i have fallen into this one.
Can i safely remove the existing damaged units without causing more damage? I mean are they reasonably robust.
Thanks again for all your help.
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ColinR
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PostPosted: Mon May 31, 2010 4:04 pm    Post subject: Reply with quote

Quote:
Can i safely remove the existing damaged units without causing more damage? I mean are they reasonably robust


Smile "Like a tank" springs to mind, the rear cambric suspension will be holding things together.

Let me know how you get on and I'll be at Bracknell behind a stall, being the "anonymous helper" Cool , driving some of the visiting tyre kicking sleezeBayers nuts as usual Very Happy .
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freddyuk
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PostPosted: Mon May 31, 2010 7:58 pm    Post subject: Reply with quote

Right i have had a proper look now and understand the issue.
The foam "ring" supported the edge of the cone to the metal frame.
Why can't we cut a piece of similar foam and re glue that in the same way?
I can see the foam would need to be of a certain consistency and it is hard stuff to cut neatly. Obviously there is a good reason why we can't do this - i just have no clue what it is.
If we try the muslin method i need to glue the edges first and then dope so it tautens it. If it is too tight (or to loose) it will not work - correct?
I will try the professional repairers first thing tomorrow.

A bit more....

Now i have had an even closer look and can see there was thin fabric under, i assume, the foam which is glued across what looks like polystyrene.
As the cones are hanging off the rear coil will this have caused any damage potentially? They have not been dropped or anything violent.
Is it just polystyrene?
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ColinR
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PostPosted: Mon May 31, 2010 9:23 pm    Post subject: Reply with quote

Quote:
Why can't we cut a piece of similar foam and re glue that in the same way?


You can get the foam for the round ends but not the straight parts Sad .

Quote:
Is it just polystyrene?


Yes covered in Aluminium foil, hence the reference to PVA glue as most solvent based glues will damage it.
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freddyuk
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PostPosted: Mon May 31, 2010 9:42 pm    Post subject: Reply with quote

Yep i am getting it now. Looks like a challenge.
Sorry to be a pain but is the foam critical to a model or is speaker foam generic. ie. what specific foam am i looking for; does it have a reference.

I see the foam suppliers on google - all nice round circles!
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ColinR
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PostPosted: Mon May 31, 2010 11:26 pm    Post subject: Reply with quote

Quote:
but is the foam critical to a model or is speaker foam generic. ie. what specific foam am i looking for; does it have a reference.

I see the foam suppliers on google - all nice round circles


Yes, no you have different profiles, no idea, no idea.

So contact the pro rebuilders first then look at alternative materials and strategies.
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speakerguru
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PostPosted: Wed Jun 02, 2010 5:42 pm    Post subject: Reply with quote

I know it's kind of heresy, but you could replace the passive radiator with a port. You just have to adjust the diameter and length to get the same box resonance as the original. Also flare BOTH ends to prevent turbulence at high levels.

If you build the port on an adapter plate you can always go back to PRs if you ever get them rebuilt.
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TL 200
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Joined: 27 Jul 2009
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Location: Emmer-Compascuum The Netherlands

PostPosted: Fri Jun 04, 2010 11:20 am    Post subject: Reply with quote

speakerguru wrote:
I know it's kind of heresy, but you could replace the passive radiator with a port. You just have to adjust the diameter and length to get the same box resonance as the original. Also flare BOTH ends to prevent turbulence at high levels.

If you build the port on an adapter plate you can always go back to PRs if you ever get them rebuilt.


If you consider to deviate from the original design perhaps you might just as well try to find another passive radiator who has the same parameters as th B139's.
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freddyuk
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PostPosted: Sun Nov 28, 2010 1:04 am    Post subject: Reply with quote

Just want to say thanks to the forum and especially ColinR for the helpful advice.
I finally got time to fit a pair of replacement ABR'S - SP1042 and siliconed the very small gaps s suggested. Reset the fixing bolts and everything appears to be great.

Cheers guys.
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speakerguru
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PostPosted: Mon Nov 29, 2010 9:42 am    Post subject: Reply with quote

Always nice to hear a happy ending.
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