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Old 19th April 2004, 10:29 AM   #1
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Default Flexible mounting of drivers?

I recall 25 years ago there was a move to have drivers secured to their boxes with fairly soft or flexible mountings. I think that this was stressed in one of Seigfried Linkwitz's early DIY designs and I've recently seen an Italian design on the TNT site that has the tweeter suspended with chords. What is the current thinking on this issue? Has anyone tried a comparison between rigid and flexible mounting?
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Old 19th April 2004, 11:38 AM   #2
sreten is offline sreten  United Kingdom
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Deeply unfashionable for bass/mids though still used for tweeters.

To get round the fashion problem some drivers are made with
decoupled magnet systems which achieves similar results,
though I've never seen these sorts of drivers for sale.

The principle is still going strong though, see the B&W white papers
on their top speakers for midrange / tweeter decoupling schemes.

sreten.
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Old 19th April 2004, 03:19 PM   #3
sobazz is offline sobazz  Denmark
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So flexible mounting of bass/midrange drivers is bad, or? You suggested blutacking my tweeters. I'm curious if there may be an improvement in doing it with the bass/midrage drivers, too.
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Old 19th April 2004, 04:17 PM   #4
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Decoupling the bass drivers from the box will give a huge drop in bass performance.

There is an impedance mismatch in the woofer, between the voice coil / cone assembly, and the magnet / basket assembly. (It might also be called a damping factor, I'm not sure.) When the voice coil pushes, all it's pushing against is a magnetic field from the magnet structure, and if the magnet structure's weight is close to the weight of the cone assembly (not likely) then the magnet and basket will move back and forth in the opposite direction of the cone, reducing performance.

So, for bass drivers, it is a Good Idea to mechanically couple them to the heaviest thing you can; thus, people really like speaker cabinets made of thick MDF, heavy woods, marble, corian, concrete...
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Old 19th April 2004, 05:09 PM   #5
Variac is offline Variac  United States
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It does seem that speaker makers with mid/high "pods" such as B&W and TAD are decoupling them from the bass box.

From poking at these speakers, it seems to me that the flexibility is less than you might think ie it takes a pretty firm push to make the pod flex much. I suspect that the pod assembly weighs enough that it forms a pretty solid reference for the cones.

Any way, IMHO there seems to be a "flexy pod mounting of mid and tweeter fashion appearing...."
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Old 19th April 2004, 07:53 PM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by sobazz
So flexible mounting of bass/midrange drivers is bad, or? You suggested blutacking my tweeters. I'm curious if there may be an improvement in doing it with the bass/midrage drivers, too.
Blutacking is not flexible mounting, its used to improve the
mechanical coupling of various parts not to isolate them.

Can be use to good effect on bass drivers chassis to
"tie" them to the baffle if the frames are thin steel.

sreten.
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Old 19th April 2004, 09:04 PM   #7
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The idea of isolating the driver from the cabinet was popularised by KEF back in the eighties. I gave many demonstration of the benefits of the technique in reducing cabinet colouration and have used the technique many times since, most recently for Pioneer and TAD.
It is not really true that the bass is greatly diminished. The ratio of cone to magnet/chassis mass is typically greater than 100:1, so even if the driver is hung on a string and freee to move, the magnet moves 100 times less than the cone, and so the effect on the cone motion is less than 1%, or 0.09dB.
Additionally, this motion is an exact facsimile of the cone motion.
In contrast when the driver is mounted to the box the magnet canb at some frequencies move more than when freely suspended, since the box is a resonant system. Strange but true.
I have the measurements to show this. I have written a white paper on this subject, which I will post if I can find a way. If not, e-mail me and I will send a copy to those who are interested.

Andrew

p.s. I think I will have to split the file into two parts for posting.
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Old 19th April 2004, 09:29 PM   #8
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Well my white paper is a word document, so I cannot post it (Unless anyone can tell me how to get it posted).
Anyone interested in it will have to e-mail me.

regards

Andrew
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Old 19th April 2004, 09:33 PM   #9
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It's not so much the relative mass of the driver vs. cone as the resonant frequency of the mass of the driver aginst the compliance of the decoupling medium. This frequncy would need to be outside the FR of the driver. This is more difficult to accomplish in the bass region.
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Old 19th April 2004, 09:34 PM   #10
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Quote:
Originally posted by AndrewJ
Well my white paper is a word document, so I cannot post it (Unless anyone can tell me how to get it posted).
Anyone interested in it will have to e-mail me.

regards

Andrew
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