Can anyone help me with 1960's vintage Leak 2 Way Sandwich Speaker System Cure??? - diyAudio
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Old 7th August 2004, 09:34 AM   #1
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Smile Can anyone help me with 1960's vintage Leak 2 Way Sandwich Speaker System Cure???

Hi Guys!

I don't suppose anyone on this board has this vintage original (from Leak in the UK) 2 way speaker system ???

Well I do. Got them about 5 or 6 years back and I've never used them, basically because I know they have a problem...

Designed in 1960, and came onto the market in 1961 with a unique woofer that is a polystyrene plastic fused with an aluminum foil surface for light-weight and high-stiffness. Anyway in the UK, it was proclaimed something like "the best speaker in the world" in the early 1960's reviews...

But with a unique design... came [problems] over time. Seems the magnet is some huge ten Kg. alnico or something and the frame is massive, and attached to the wood cabinet; but the weight of the cone isn't supported well enough and all of the woofers tend to start to rub the voice coil twenty to twenty-five years later. Now it is over 40 years later and so I dare not use this until its been "fixed".

So if anyone has ever heard of the proper process to use... please let me know, don't want to destroy it in the process of tryin' to "cure" what ails it.

Luckily I've got several other sets of speakers I use. One is a four way system which used the older "Large Advent" box with a new front baffle board that I an a good friend designed about 20 years ago... The design uses a French Audax 9.5" Woofer with rubber surround and a nearly perfect Qts of 0.7; designed using the Thiel equations on an HP-41c... They seem to go down flat to around 30 Hz. but lacking an acoustic chamber, that's just a guess.

Beyond around 700 Hz. there is a 3" dome midrange (was it a Seas, I think so). The tweeters have changed several times over the years, the best being the current 3/4" inverted Focal dome, in for about the last decade; and a rather inexpensive ribbon tweeter that comes in somewhere around 10Khz. and is mounted outside the box. The massive crossover that I designed by ear about 20 years back, and never needed to revise, also sits outside the box, the rear of the cabinet having six Banana Jacks to connect to it. While this allows for Tri-Amping, I've really never had the time or space to put that into action.

While its great sounding by itself; it is actually used as one-third of a unique Column System. Each side also connects up to a pair of 2 way B&O (Danish) designed speakers which are known in the USA as the Dynaco A-25's. That is a highly resistive speaker, with a simple crossover network and excellent traansient response, but it can't go as low or as high as my speaker does. The A-25's do have fairly good efficiency, so these are placed in series, which makes them around 16 ohms, reduces the efficiency a bit, matching them to my speaker. That 16 Ohms is then wired in parallel with my speaker, total impedance probably comes in at around 5 Ohms on average.

Not sure what the efficiency is but I can say, the sum is more of a total than the individual parts. I can get very listenable moderately loud sound using a 3.5 Watt per channel SETA, and it thunders using a 60 wpc amp. As far as I can tell, its still the best cone type "speaker" I've ever heard, shy of the Soundlab-1 full-range electrostats that I could never afford, driven by a 100W+ output transformerless tube amp ( a setup my friend does have for many years now ).

I've also got some Dynaco A-35's and some KLH 6's, the latter used to listen to TV mainly, but I'd love to try these Leaks, if I can get the woofers back in shape... Thanks for any suggestions!

Now to try and post a pix of MY speaker...
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Old 7th August 2004, 10:25 AM   #2
dnsey is offline dnsey  United Kingdom
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I've had a few Sandwiches over the years, but have never had this problem with them.
It's certainly common, however, with Lowthers, and the cure there is to turn the drivers 180* every so often.
Obviously, this is not so easy with Leaks, because of the way they're mounted, but it might be worth turning the whole cabs upside down for a few weeks and see what happens.
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Old 7th August 2004, 10:27 AM   #3
dnsey is offline dnsey  United Kingdom
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BTW, IMO the Sandwich is a great bass driver - tuneful and controlled, without being too 'lean'.
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Old 7th August 2004, 08:51 PM   #4
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The Leak sandwich was a great idea. Why is the technique not used today? I am aware of only Focal who use the concept. I suspect it is labour intensive and hence costly. Basically 2 strong sheets of material sandwiched by a lightweight space filler. The wooden dehavilland mosquito aircraft used sheets of plywood sandwiched with balsa wood for its wings.
Here is the original publicity blurb
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Old 7th August 2004, 08:58 PM   #5
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Here is the other half of the publicity sheet. Apologies for the quality
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Old 25th June 2005, 07:18 AM   #6
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slbender
Did you ever resolve the rubbing problem with your Leaks ?

I recently bought a pair of 1968 or so Leaks in the UK and had my brother drag them over as luggage. Bought on ebay unheard and unseen, they were OK except that one of the bass drivers rubbed as you described. A replacement was expensive and hard to find and I could not find anyone who would commit to repairing it. I found a website that suggested that by loosening the magnet screws and recentering it any pole/coil rubbing could be eliminated. I tried it and to my immense gratification it worked !. Now I can play my heavy dub without an annoying buzz.

If you need more info let me know.
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Old 25th June 2005, 10:11 AM   #7
sbrads is offline sbrads  United Kingdom
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I'm NOT recommending this method, but I fixed a pair of Castle woofers that went into overheat/distort mode when they both got masses of DC up them (don't ask). I cut the dust caps with 2 straight cuts at 90deg, so I could peel the four pieces back for access to the polepiece and coil former gap. I then forced feeler gauges down into the gap, more towards the side that was rubbing the worst, removing the feeler gauges until there was free movement with no rubbing. I then folded back the dustcap and lightly glued them back into shape (Bostik if I remember correctly). They've been OK for 5 yrs since this operation.
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Old 25th June 2005, 10:36 AM   #8
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Looked at this thread and was surprised to see my old posts
Ok I was wrong about the sandwich technique not being used today see this link for Infinity CMMD cones:
http://www.infinitysystems.com/homea...apers/cmmd.pdf
Although the filling of the sandwich is thin and heavy as opposed to being thick and light, it is a sandwich.
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Old 7th February 2006, 01:32 AM   #9
bob_v5 is offline bob_v5  England
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i have some leak sandwich's. I had the same problem once. You can turn the cones upside down quite easily. Its just the mounting nut on the back thats a pain, but its doable with a little patience.
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