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105.2 cabinet damping
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T.O. Chef
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PostPosted: Tue Feb 24, 2009 1:24 am    Post subject: 105.2 cabinet damping Reply with quote

Hello all. I've been studying with great interest all of the information posted to date on the Kef 105's ... both the originals and the 105 II's. I have recently acquired some 105 II's that have had only 1 owner (I think), and are completely original (I checked), and do seem to have been very well cared for.
I'm completely reluctant to do ANYTHING to these may in any way compromise them. However, I do see how as Terry pointed out they should benefit from having the wheels removed and a more secure anchoring made to the floor. Especially my wooden ones. I'm thinking spikes and a heavy paving stone, piece of granite, or similar. This, I will do.

Does anyone have any experience though with installing dampening material on the inner walls of the bass cabinets? I'm wondering if there's any sonic merit in this. I note that someone said (was it speaker guru?) that Kef didn't bother with this in the 105 II as the B-300 was isolated from the cabinet in a way the negated the necessity, But ... I can practically see this cabinet vibrate at moderately loud listening levels. Reminiscent of the Celestion ditton 66, that also had no damping material on the inner walls btw.

I have the material on hand, (from Solen Canada). I note that the construction plans for some Kef kits called for this material to be installed in home made cabinets. I also note that there's tons of the stuff in my Cantata's, Ref. 104aB's, Calinda's, and Corelli's.

Thanks. I hope someone has done this (or tried) and can share their experience.
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DrBoar
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PostPosted: Wed Mar 04, 2009 9:54 pm    Post subject: Reply with quote

Crossbraces in the basscabinet will stffen the walls as well as give some damping. Stiff enough they have their resonces above the working range of the cabinet and will then not be set in motion!

Spikes are a bad thing in general and especially on woden floors. With spikes you can put your hand on the floor and feel the vibrations. You might like it but your vibrating floorboards are not a part of the recorded music that you are listening to

http://www.sonicdesign.se/sdfeet.html

Ordinary furniture rubber feet from a hardware store is better than any spikes.

I have seen some claims that spikes work as mechanical diodes directing away vibrations from the speaker (one way). If that is true they have broken Newtons thrird law of motion for the first time since 1687 and will have a Nobel price in the making Laughing
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T.O. Chef
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PostPosted: Thu Mar 05, 2009 1:02 am    Post subject: Reply with quote

Thanks for tossing in DrBoar. Regarding spikes though, I have experienced much better results with the use of the small ones I have on heavy large cabinets such as the Kef Cantata and Ditton 66's. than with no decoupling at all. I mount them pointing straight up BTW, into brass inverted dishes secured to the bottom of the cabinets. Preserving floors and cabinets.

I wonder what degree of isolation the Kef 105 II's wheels provide ... if any at all. Well, rubber furniture feet can be had without much financial pain, so I think I'll see what's out there that has the required aesthetics before delving into the usually very pricey "specialized" stuff as per the link above.

And, I'm pretty sure I don't want to start hammering cross braces into these beautiful cabinets. Even if I knew what the results would be.
The heavy dampening material I have though is almost exactly what one finds in other kef designs and I have to wonder why it was considered unnecessary in the 105.
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SaSi
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PostPosted: Wed Mar 11, 2009 4:28 pm    Post subject: Reply with quote

Better than spikes or rubber feet, I would consider using one or two layers of thick carpet under the enclosures. You can get leftovers for nothing - or next to nothing - and stack 2-3 of those. That worked wonders for a pair of large Wharfedales E90 on a wooden floor.

What is the way "the B300 is isolated from the cabinet" negating the need for bracing or dampening material inside? There is a rubber gasket in the slot on the mounting edge of the basket's face but I can hardly think this is enough for this large woofer.
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ColinR
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PostPosted: Wed Mar 11, 2009 4:40 pm    Post subject: Reply with quote

Quote:
There is a rubber gasket in the slot on the mounting edge of the basket's face but I can hardly think this is enough for this large woofer.


The three B300 mounting bolts go into a threaded bush which is bolted to a ~0.75" dia flexible rubber washer, which in turn is held in an offset triangular mounting plate screwed to the rear of the front baffle.
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T.O. Chef
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PostPosted: Wed Mar 11, 2009 10:28 pm    Post subject: Reply with quote

Yes. There is indeed some wonderful (and I'm sure they were expensive for KEF) mounting hardware for the B-300 in the 105 II. All on the backside and invisible without a mirror. And yes there's a gasket on the back of the driver, but a light touch of the hand on the cabinet at even medium volume confirms that the cabinet resonates quite noticeably. Perhaps this resonance has no audible effect however?
I have an extra set of 6 of those mounting bits btw that were practically being given away if anyone's in need.
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speakerguru
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PostPosted: Thu Mar 12, 2009 8:37 am    Post subject: Reply with quote

T.O. Chef wrote:
but a light touch of the hand on the cabinet at even medium volume confirms that the cabinet resonates quite noticeably.

The anti-vibration mounts reduce the mechanical coupling from chassis to cabinet but the acoustic coupling (direct air pressure to the cabinet walls) remains. The mounts only work for a range of frequencies. At very low frequencies they tend towards rigid and at high frequencies the rubber losses prevent perfect de-coupling. If you want to see how much difference the mounts make, you can short circuit them by jamming something solid between the chassis rim and the baffle, then see how much the cabinet vibration increases.
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T.O. Chef
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PostPosted: Thu Mar 12, 2009 10:25 am    Post subject: Reply with quote

Hmmm. Well Speakerguru, I don't think I want to see / hear what the effect of no decoupling would be as I'm sure KEF incorporated these into the design for very good reason.
It leaves me to wonder if the cabinet resonance that exists is also "part of the design". Could we say that the cabinet resonance is this way intentionally tuned contributing to the overall response curve?
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speakerguru
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PostPosted: Fri Mar 13, 2009 8:42 am    Post subject: Reply with quote

T.O. Chef wrote:
It leaves me to wonder if the cabinet resonance that exists is also "part of the design". Could we say that the cabinet resonance is this way intentionally tuned contributing to the overall response curve?


No it wasn't. A delayed resonance will never be the same as an intended lift in direct radiated response. There just comes a time when you can't pile any more cost into the design or you won't sell any. This is where a DIYer has the advantage. He/she can add as many belts and braces as they want.
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T.O. Chef
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PostPosted: Fri Mar 13, 2009 10:42 am    Post subject: Reply with quote

Ah. Well then, so the decision by kef to not use internal damping material in the 105 II was likely driven by the cost factor, and it is possible that an improvement in bass response could be realized with the addition of this. The cabinet resonance resulting from the driver would / does add a degree of colouration that can be somewhat tamed in this way?
I suppose it can't hurt to try, and as mine will be apart anyway for a professional application of clear finish to the cabinets I will install some and report later on its merits.
I must say .. I'm a bit surprised no one has chimed in with their experience trying this.
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ColinR
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PostPosted: Fri Mar 13, 2009 11:04 am    Post subject: Reply with quote

Quote:
I'm a bit surprised no one has chimed in with their experience trying this.


I imagine it's a case of those "who tinker" with sheets of lead to line their cabinets are sitting smugly, whilst the rest of us are sitting and enjoying the music Very Happy .
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T.O. Chef
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PostPosted: Fri Mar 13, 2009 3:29 pm    Post subject: Reply with quote

Oh well.
Ignoring the cynical and condecending remarks, thanks to all who shared their thoughts.
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proffski
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PostPosted: Mon Mar 16, 2009 7:00 pm    Post subject: Reply with quote

T.O. Chef wrote:
Ah. Well then, so the decision by kef to not use internal damping material in the 105 II was likely driven by the cost factor, and it is possible that an improvement in bass response could be realized with the addition of this. The cabinet resonance resulting from the driver would / does add a degree of colouration that can be somewhat tamed in this way?
I suppose it can't hurt to try, and as mine will be apart anyway for a professional application of clear finish to the cabinets I will install some and report later on its merits.
I must say .. I'm a bit surprised no one has chimed in with their experience trying this.


Adding extra mass and or increasing rigidity?
Lead lining sounds fine, but what happens once the panel starts moving, it will take longer to stop... Small areas probably will benefit see how you go.
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proffski
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PostPosted: Mon Mar 16, 2009 7:01 pm    Post subject: Reply with quote

T.O. Chef wrote:
Ah. Well then, so the decision by kef to not use internal damping material in the 105 II was likely driven by the cost factor, and it is possible that an improvement in bass response could be realized with the addition of this. The cabinet resonance resulting from the driver would / does add a degree of colouration that can be somewhat tamed in this way?
I suppose it can't hurt to try, and as mine will be apart anyway for a professional application of clear finish to the cabinets I will install some and report later on its merits.
I must say .. I'm a bit surprised no one has chimed in with their experience trying this.


Adding extra mass and or increasing rigidity?
Lead lining sounds fine, but what happens once the panel starts moving, it will take longer to stop... Small areas probably will benefit see how you go.
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man standing in a bucket and trying to lift himself up by the handle.
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audiolabtower
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PostPosted: Tue Mar 17, 2009 5:44 pm    Post subject: Reply with quote

proffski wrote:
Lead lining sounds fine, but what happens once the panel starts moving, it will take longer to stop...


a VERY good point from proffski. Cost would have been a consideration but not the main one in their (at that time) top speaker because they put all the research into the mounts which were carefully designed not to transmit to the cabinet if torqued exactly right.

The whole BBC thin wall + damping philosophy was to keep the resonances out of the critical mid range and push them lower down with lower Q. High mass can have high Q resonances which are much more deadly to sound quality.
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