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?
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?
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?
Have you checked Linkvitz Orion web page?
Re: Re: Re: Reaction Cancelling Compliant Mount
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.
ezkcdude said:
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.
Re: Re: Re: Reaction Cancelling Compliant Mount
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.
ezkcdude said:
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.
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.
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.
Re: Re: Re: Re: Reaction Cancelling Compliant Mount
Just a slight pressure inside the enclosure would displace the cone, it would not work.
I thought you were thinking about inflatable enclosure walls, that would be slightly more possible. But if you think about how much pressure there is in a bicycle tire, and yet it isn`t very hard to compress it just using your thumb.
It would require an enormous pressure to get the walls stiff enough.
There is a long thread about gas filled speakers around here, I don`t remember the name of the thread...
It has been done, the gas makes the enclosure to appear larger acoustically than if it was just filled with air, or smaller depending on wich type of gas you are using.
There is an issue of containing the gas, it would leak through the cone if not contained in a leak proof bag inside.
ezkcdude said:
Just a slight pressure inside the enclosure would displace the cone, it would not work.
I thought you were thinking about inflatable enclosure walls, that would be slightly more possible. But if you think about how much pressure there is in a bicycle tire, and yet it isn`t very hard to compress it just using your thumb.
It would require an enormous pressure to get the walls stiff enough.
gootee said:
There is a long thread about gas filled speakers around here, I don`t remember the name of the thread...
It has been done, the gas makes the enclosure to appear larger acoustically than if it was just filled with air, or smaller depending on wich type of gas you are using.
There is an issue of containing the gas, it would leak through the cone if not contained in a leak proof bag inside.
I wanted to try something simple, no drivers costing thousands of euros, no expensive passive filter components.
The Metronome bipole has some interesting properties:
- Just the bottom and top panels are parallel
- No baffle step compensation required
- Possibility to implement time domain approach by linking the two drivers
For the construction I'm thinking of using two layers of 9mm birchply with a layer of lead (1.32mm thick, used for roof lining ) in between.
Fujitsu Ten is also making speakers using exactly this theory:
TD725SW subwoofer - drivers mounted back-2-back configuration with rigid aluminum coupling shaft.
TD712z Single, full-range driver isolated from egg-shaped cabinet by soft suspension and high mass "anchor" to minimize acceleration of the driver axially.
John Atkinson of Stereophile performed his usual measurements on the TD712z, and had this to say (Jan, 2007):
These guys are doing it, why shouldn't we? I've said in the past I'm never going to buy speakers again...but if I did, these would be on my short list.
TD725SW subwoofer - drivers mounted back-2-back configuration with rigid aluminum coupling shaft.
TD712z Single, full-range driver isolated from egg-shaped cabinet by soft suspension and high mass "anchor" to minimize acceleration of the driver axially.
John Atkinson of Stereophile performed his usual measurements on the TD712z, and had this to say (Jan, 2007):
These guys are doing it, why shouldn't we? I've said in the past I'm never going to buy speakers again...but if I did, these would be on my short list.
ezkcdude said:
The problem I see with this approach is that the drivers are only connected under tension. So when the drivers are pulling against the tension rod the effect will be cancellation of forces. However, when the drivers are pushing in towards the tension rod the same forces do not exist and the only thing countering the forces are the compliant gaskets of the cabinet. So what you have is essentially a system where there is not equal canceling of forces in both directions.
The system must be designed so that it cancels the forces equally in both directions to be effective. Therefore, a different coupling system between the drivers must be used such as a solid bar of stiff material between them. Or if a tensioner is used it must be designed so that it has no slack or backlash in the reverse direction. This would require very high tolerance screw mechanism and bolted from both directions on the ends of the motor housing. How do you get inside? Also, the system must have the practical property of being easy or possible to assemble. And not cover up the vented pole piece which is important for cooling.
Perhaps several aluminum bars about 3/4 - 1 inch diameter running from one driver to the next at the frame mounting holes. Combined with some kind of a non magnetic wrap around clamp that would wrap around the magnets and clamp both drivers together. Add some cooling fins on the clamp and some breathing holes and now you have something. Now you have to have a big hole to access the drivers other than their own holes to assemble it.
The way I see it if you really want this thing to work you have to connect both the motor structures and the outer frames because the frame flexes and vibrates so only connecting the motors will only yield you so much.
Re: Re: Reaction Cancelling Compliant Mount
I agree that the coupling should be rigid to prevent compression axially. I believe the link to the subwoofer in my last post follows this approach. In fact they use aluminum, as you suggest. I'm not sure what you mean when you say "motor"...do you mean magnet? The magnet and frame of a driver are essentially coupled, so if the magnet moves (do to reaction forces), so does the frame. Indeed, the frame will flex more, if it is fixed (bolted) to the cabinet. If the driver is isolated from the cabinet, flexing should be negligible.
Hezz said:
I agree that the coupling should be rigid to prevent compression axially. I believe the link to the subwoofer in my last post follows this approach. In fact they use aluminum, as you suggest. I'm not sure what you mean when you say "motor"...do you mean magnet? The magnet and frame of a driver are essentially coupled, so if the magnet moves (do to reaction forces), so does the frame. Indeed, the frame will flex more, if it is fixed (bolted) to the cabinet. If the driver is isolated from the cabinet, flexing should be negligible.
Planet 10 has long been a proponent of coupling the drivers in bi-poles "to reduce the Newtonian effects," is how I believe he puts it.
A description of my method of coupling for 127E Bi-poles:
http://www.diyaudio.com/forums/showthread.php?postid=530543#post530543
A description of my method of coupling for 127E Bi-poles:
http://www.diyaudio.com/forums/showthread.php?postid=530543#post530543
Re: Re: Reaction Cancelling Compliant Mount
That is not a problem, tension has to work both ways, otherwise the drivers would be pulled together. Something has to resist the tension rod, so when pushing in they will still be coupled.
I thought I would have this same problem with a bipole subwoofer, using threaded rod to couple the two drivers. My fear was once I tighten the threaded rod, what stops the woofer from moving in the opposite direction? The answer is the same thing that allowed me to tighten the rod in the first place, the enclosure. Can't report on the results as it's still a monopole right now.
Dan
Hezz said:
That is not a problem, tension has to work both ways, otherwise the drivers would be pulled together. Something has to resist the tension rod, so when pushing in they will still be coupled.
I thought I would have this same problem with a bipole subwoofer, using threaded rod to couple the two drivers. My fear was once I tighten the threaded rod, what stops the woofer from moving in the opposite direction? The answer is the same thing that allowed me to tighten the rod in the first place, the enclosure. Can't report on the results as it's still a monopole right now.
Dan
Then the driver is not isolated from the enclosure in that case. The brace behind the magnet may help a little, but if the frame is still bolted to the front baffle, the reaction force in the magnet still is transferred directly to the cabinet. Back-to-back (b2b) or single driver suspension+mass (sdsm) are the only two practical ways I can think of to isolate the driver from the cabinet effectively.
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