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Old 24th May 2008, 02:23 PM   #1
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Default Reaction Cancelling Compliant Mount

A friend and myself were talking about how to decouple the driver frame from the cabinet. Basically, everyone should know that the force driving the voice coil has a reaction force that pushes the magnet in the opposite direction. Since the frame is bolted to the cabinet, the only solution to eliminating coloration due to this transfer of energy is adding mass to the cabinet. Ok, nothing new here.

So, my friend had this idea that instead of rigidly fixing the frame to the cabinet (i.e. baffle), we would increase the mass of the driver (magnet/frame) and try to isolate the frame from the cabinet - thus, eliminating this coloration. Ok, so we thought about different ways to do this. The first idea I had was to hang the driver using bungee cords. This seems impractical, no? Next, I thought one can attach a spring axially to the back of the magnet and couple that to the back of the cabinet - this would essentially create an axial "suspension" system.

This morning, in doing some more research on the topic, I stumbled across what seems to me the most practical solution, which is almost embarassingly simple to implement: Reaction Cancelling Compliant Mount, which has been done by Vivid Audio. Of course, they charge an insane amount of money for these speakers. The idea is really simple. Mount the two drivers in a back-to-back configuration, such that the magnets are directly coupled through a very stiff tensioner element. In this configuration, the two forces cancel. This was like a Eureka! moment for me. It's so obvious. I should point out, that clearly the speaker is now acting as a bipolar, and it is not clear to me whether that is an advantage or disadvantage.

So, has anyone here tried this or even thought about this problem before? It seems like 99.9% of speaker designs simply assume the driver is mounted to the baffle, and the cabinet must be massive to reduce coloration. With the isolation technology, now the cabinet does not need to be so massive. This is a tremendous advantage. Although this company is charging insane amounts of money for these speakers, in theory, the mass of the cabinet (and thus, a large part of the cost) should become a non-issue. Why this hasn't become widespread is beyond me. Thoughts?
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Old 25th May 2008, 02:34 PM   #2
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Nobody has opinions on this?
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Old 25th May 2008, 02:48 PM   #3
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Because it involves more complicated calculation and more complicated cabinetwork. Most of the commercial speaker manufacturers are not going to bother because your average audiophile aren't going to hear or pay attention to the difference. It's a lot easier to attract people with “diamond clad silver capacitors” and “platinum fadudle babkis tweeter”
Have you checked Linkvitz Orion web page?
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Old 25th May 2008, 03:12 PM   #4
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Default Re: Reaction Cancelling Compliant Mount

I think it`s a good idea, great for subwoofers (not a fan of bipolar mid and high).
Nothing new here, I`ve seen it before. I think KEF did something similar years ago.

The cabinet still needs to be stiff.
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Old 25th May 2008, 03:19 PM   #5
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Default Re: Re: Reaction Cancelling Compliant Mount

Quote:
Originally posted by Peter M.


The cabinet still needs to be stiff. [/B]

Stiff is good, but mass is essentially taken out of the equation. Actually, I believe one could construct an inflatable subwoofer. Very stiff - but low mass. How's that for a novel idea?
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Old 25th May 2008, 04:51 PM   #6
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Default Re: Re: Re: Reaction Cancelling Compliant Mount

Quote:
Originally posted by ezkcdude



Stiff is good, but mass is essentially taken out of the equation. Actually, I believe one could construct an inflatable subwoofer. Very stiff - but low mass. How's that for a novel idea?

Novel, but complicated to make and probably no real improvement compared to a stiff balsa/foam core or nomex honeycomb covered with fibreglass or carbonfibre, (if you really need it light weight). Very high pressure air would be needed i think.
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Old 25th May 2008, 05:01 PM   #7
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Default Re: Re: Re: Re: Reaction Cancelling Compliant Mount

Quote:
Originally posted by Peter M.



Novel, but complicated to make and probably no real improvement compared to a stiff balsa/foam core or nomex honeycomb covered with fibreglass or carbonfibre, (if you really need it light weight). Very high pressure air would be needed i think.

I guess it doesn't make sense, then, because you'd affect the cone displacement.
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Old 25th May 2008, 05:02 PM   #8
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Default Re: Re: Re: Reaction Cancelling Compliant Mount

Quote:
Originally posted by ezkcdude



Stiff is good, but mass is essentially taken out of the equation. Actually, I believe one could construct an inflatable subwoofer. Very stiff - but low mass. How's that for a novel idea?
I don't know about the inflatable subwoofer idea (But could inflating with different gases produce large variations in performance? e.g. like speaking after inhaling Helium?). But, if bi-polar is to be avoided, maybe it would be worth considering having the second driver coneless, possibly with a spring/mass/damper setup to simulate a cone, to try to keep the mechanical cancellation more accurate. Or, alternatively, maybe an electronic network could derive the 'canceller' driver's signal from the active one's signal. Or maybe even a MEMS accelerometer (or something) and some electronics could be used to drive the canceller unit.

Just some food for thought. I haven't really thought about how to do any of this, or whether or not it would be worth doing.
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Old 25th May 2008, 05:05 PM   #9
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You might want to take a look here:

Time Domain


I'm going to build a pair of Metronome bipoles with FostexFE126E drivers. I'm thinking of using a wedge that can be pushed between the drivers by means of some bolts.

BTW If you're looking for very stiff and light material, look for birchply for airplane construction. 6mm thick sheets have 12 layers and are absolutely fault free.
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Old 25th May 2008, 06:06 PM   #10
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Quote:
Originally posted by Gerrit Boers


I'm going to build a pair of Metronome bipoles with FostexFE126E drivers. I'm thinking of using a wedge that can be pushed between the drivers by means of some bolts.

I'll be very interested to see how that works for you.
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