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103/4 - B160 SP1278 Swap w/ B160 SP1314

 
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sydbar81
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Joined: 12 Apr 2018
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PostPosted: Thu Apr 19, 2018 5:42 pm    Post subject: 103/4 - B160 SP1278 Swap w/ B160 SP1314 Reply with quote

Hi - I recently refreshed the ferrofluid in my 103/4 tweeters.

At reassembly I made the bonehead mistake of over tightening one of the nuts that secures the Mid range drivers in place to the enclosure and it broke through the boss on the cage.

My 103/4 set have the B160 sp1278 mid range drivers, KEF still has the B160 SP1314 in stock for purchase of the pair.

My question is can this driver be adapted to mount in my version of the 103/4? This drive unit appear to be used in the magnetically shielded variant. The mounting points are different.

My current damaged unit is still somewhat usable, I was able to just put a washer to cover the gap left from the fastener breaking through, but this is not ideal. The magnet appears to have shifted a bit and the voicecoil is not centered as it should be(there is a slight rub if you push down on the cone in one particular spot)
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speakerguru
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Joined: 18 Nov 2005
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Location: Green Hut, Tovil

PostPosted: Sat Apr 21, 2018 10:40 am    Post subject: Reply with quote

I'm a visual person so I'm sorry but I need pictures to work out what the problem is. I also can't remember the differences in mounting between the 1278 and 1314. Photos please and I might be able to come up with a solution.
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sydbar81
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PostPosted: Sat Apr 21, 2018 7:21 pm    Post subject: Reply with quote

These are not my photos, but here are examples

The SP1278

https://imgur.com/a/CPd2AA4


The SP1314

https://imgur.com/a/uQ82kwO

I'm thinking that I should be able to use the sp1314s if I swap the hardware that fixes the magnet to the basket.

Is it safe to assume that this can be accomplished by swapping one bolt at a time? I'm just worried about the magnet shifting. Also, I'm not certain of what the proper torque specification should be for securing.

On my unit there was some sort of thread locking adhesive used, I did not realize that the the entire threaded rod was turning when I was turning the nut to tighten, which led to over-torquing and breaking through the boss on the cage.
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speakerguru
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Location: Green Hut, Tovil

PostPosted: Tue Apr 24, 2018 4:37 pm    Post subject: Reply with quote

sydbar81 wrote:
The SP1278 https://imgur.com/a/CPd2AA4


I don't recall ever seeing this arrangement with studding (long threaded rods) and spacers in production - maybe you've got some early prototypes?

Uni-Q units normally had a three-footed plastic moulding which screwed up through the centre of the woofer magnet to the hex stalk on the back of the tweeter. The three feet screwed to the centre of the inside back of the shielding can.

Yes, to only transferring one screw at a time.
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sydbar81
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PostPosted: Mon Apr 30, 2018 5:05 am    Post subject: Reply with quote

Thanks, I went ahead with ordering a new pair of drivers.

A couple more questions from a novice:

Should all of these drivers have gaskets?

During disassembly I noticed that only the uppermost bass driver had a gasket installed. The lower driver was in direct contact with the cabinet. There is no gasket sealing the mid bass/uni-q drivers as well.

Also, all of the mounting hardware on all of the drivers was barely finger tight. Is that just something that happened from age, or are they supposed to be secured with very little torque?
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speakerguru
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PostPosted: Mon Apr 30, 2018 10:25 am    Post subject: Reply with quote

The bass drivers are mounted in opposition, to partially cancel non-linearities, so, the gaskets will be on opposite faces of the chassis rims. i.e one woofer is mounted with the magnet inside the inner box the other is mounted with the magnet out, therefore the gaskets will be on different sides of the rims.

Not sure what you mean by mounting hardware, but I suspect you mean the just the fixings to the cabinet. They should allow the whole 2 woofer + coupling rod assembly to float. The drivers are mounted so that reaction force vibrations are cancelled out. The woofers are mechanically in opposition and electrically in opposite phase which results in them adding acoustically in phase (I hope that helps and does not confuse). N.B. The woofers should still seal to their inner boxes despite being able to "float" together. The coupling rod to magnet fixings should be rigid/tight.
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sydbar81
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PostPosted: Thu May 10, 2018 8:34 pm    Post subject: Reply with quote

speakerguru wrote:
The bass drivers are mounted in opposition, to partially cancel non-linearities, so, the gaskets will be on opposite faces of the chassis rims. i.e one woofer is mounted with the magnet inside the inner box the other is mounted with the magnet out, therefore the gaskets will be on different sides of the rims.

Not sure what you mean by mounting hardware, but I suspect you mean the just the fixings to the cabinet. They should allow the whole 2 woofer + coupling rod assembly to float. The drivers are mounted so that reaction force vibrations are cancelled out. The woofers are mechanically in opposition and electrically in opposite phase which results in them adding acoustically in phase (I hope that helps and does not confuse). N.B. The woofers should still seal to their inner boxes despite being able to "float" together. The coupling rod to magnet fixings should be rigid/tight.


I got the drivers swapped and everything sounds great now, installing gaskets had a tremendous impact on bass response (There was gasket material applied, i just did not notice it since it had become paper thin and deteriorated.)

There were some slight differences between the two versions of the B160 drivers:

The sp1278s had a hand written 'P' on the backs of the cones

The sp1314s had a coating on the backs of the cones which the 1278s did not.

Also, the 1314s had threaded M6 inserts on the cages to secure the magnets which the 1278s did not. Since the metal enclosure for these drives was already drilled for m4 studs I still needed to run a m4x.7 bolt through, I applied some heat shrink tubing around the bolt so it was snug where it went through the cage. I applied blue thread locker to the coupler threads as well.

Thank you for your help on this.

I found these on local craigslist and someone was going to just throw them away (who does that?) I was happy to make the 5 hour round trip drive for them.

I replaced all of the deteriorated surrounds on the bass drivers, refreshed the ferrofluid on the tweeters, and obviously they now have a new matched pair of midrange drivers.

(I was able to source a new old stock Kube 200 for them as well, box was still sealed)

The rosewood cabinets were rough, but fortunately there were only a couple of small flaws the went through the veneer. I'm a hobbyist woodworker so I was able to correct all of the flaws. Cabinets then received some sealer and pore filler, then 5 coats of laquer.

This was certainly one of the more rewarding projects I've done, I can't believe the sound of these little things. You KEF folks did an outstanding job on these, they wound up replacing my vandersteen 2ce signatures.
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audiolabtower
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Joined: 06 Jan 2009
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PostPosted: Thu May 10, 2018 11:32 pm    Post subject: Reply with quote

What a great story, and a fine way to restore a speaker the original designers and makers spent a great deal of effort on.
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oldandintheway
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Joined: 16 Mar 2018
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PostPosted: Thu May 10, 2018 11:37 pm    Post subject: Reply with quote

What an fantastic result! Well done.
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