Idea? Counterbalancing cones. :)

quickshift · 29th September 2005, 01:29 PM

This would be possible, even easy but is it worth it?

I was thinking about whether it would be beneficial to make a balancing device for drivers.

It would work like this.

A small mass (the same mass as the cone) would be set on a voice coil and mounted on the back of the driver - it would operate in phase but since it would be facing the opposite direction, it would cancel out any effect of the cone moving the cabinet (micro rocking?).

Because it wouldn't be moving any air, it wouldn't need as much power - it would have to match the excursion of the cone and all that.

Is that a daft idea?

mwmkravchenko · 29th September 2005, 01:46 PM

No it is not a daft idea.

There were some good studies on the effect of driver and motor structural born non-linearities. They found that the magnet structure coloured the sound the most. To dampen it they coupled the back of the driver to the enclosure through a resilient mount and it cut down the problem by quite a bit. I think that KEF coupled drivers with a rigid steel rod to do much the same. They were driven as a push pull and the concept was that the rod would help to cancel out the unwanted vibrations much like your idea.

The mass of the object radiating has a lot to do with the length of time it sounds and at what frequency range. A cone has a very small mass when compared to the rest of a driver. The motor structure has much more problems when you start to think about it. Next down the line are the basket and the dust cap. They are all necesary evils in a practical driver.

Mark

quickshift · 29th September 2005, 02:41 PM

Interesting, thank you.

I'm glad it wasn't daft.

I'll see if I can find some info on previous studies.

AndrewJ · 29th September 2005, 04:15 PM

Quickshift,

your idea is not daft, but it is not original either!!
It is true that the major contributor to cabinet vibration is mechanical forces generated by the recoil force on the magnet when the cone moves back and forth. Newtons law " to every action there is an equal and opposite re-action". The forces generated on the cabinet that cause its panels to vibrate from this source are typically more than 10 to 30 times stronger than that due to the internal sound waves.

At KEF, we employed techniques to minimize or cancel this force, either by compliantly mounting the driver to the cabinet, compliantly mounting the magnet to the chassis, or using two drivers with a force cancelling rod.
With properly excecuted design, cabinet vibration can be reduced by 20-30dB, and a lot more cost effectively than by building a more inert cabinet.

The idea of using a counterbalancing weight has been proposed in the past. I believe Sony has a patent on such a technique. The downside is that it halves the efficiency of the driver. You have to drive the additional mass by an extra voice coil, with the additional mass being equal to the cone mass, suspended on matching compliance to the cone / spider compliance.
I read just a couple of days ago that someone has revived this technique on a product that has just launched into the market, but offhand I don't remember who. I will have to search back through all the magazines I have read recently.
However, the double driver idea is a better solution as it typically cancels the reaction force better, and without the loss in efficiency.

regards

Andrew

quickshift · 29th September 2005, 05:23 PM

Thanks for the info Andrew,

I wasn't expecting it to be original if it wasn't daft

- I'll give it maybe 20 years before I may have an original idea on the subject - if indeed there are any original ideas left to have by then

Does it really halve the efficiency? I would have guessed that a lot of the energy goes into moving the air. I thought that maybe a much lower powered system could be used to move the counterweight because it'll be kind of more aerodynamic compared to a cone.

If you do find any info on the new product I would be very pleased if you would let me know what it is.

AJinFLA · 29th September 2005, 06:22 PM

Um, yeah, I think its a great idea

http://www.codrive.com/tech.htm

Cheers,

AJ

AndrewJ · 30th September 2005, 06:37 PM

AJinFLA,

The codrive does not in fact cancel the reaction force of the motor. If you look at the construction of the driver, the force applied to both cones is common, not in opposition, as the two voice coils and cones are mechanically connected together.
The motor system does however cancel even order distortion, because as one coil moves into it's magnet, the other moves out.

Regards

Andrew

AndrewJ · 1st October 2005, 06:31 PM

quickshift,

I found the reference to the counterbalance driver I was thinking of.
It was shown at CEDIA by Sunfire. It is for an in-wall subwoofer they make called the Contrabass Anti-Shake In-Wall Subwoofer.
Unfortunately the only information I have is from an advertisement in the CEDIA daily news.
There is no info yet on their website.
The diagram is too small to fully see what they are doing, but they have two cones plus, they claim, a counterbalance motor, to reduce vibration by 12dB.
I will continue to search for more info.

Andrew

knorke · 2nd October 2005, 08:15 AM

Actually Focal aka JMLab used exactly this technique in one of their flagship models years ago ....

knorke · 2nd October 2005, 08:37 AM

Here are some pictures....

29th September 2005, 01:29 PM	#1
quickshift diyAudio Member Join Date: Jun 2005 Location: West London	Idea? Counterbalancing cones. :) This would be possible, even easy but is it worth it? I was thinking about whether it would be beneficial to make a balancing device for drivers. It would work like this. A small mass (the same mass as the cone) would be set on a voice coil and mounted on the back of the driver - it would operate in phase but since it would be facing the opposite direction, it would cancel out any effect of the cone moving the cabinet (micro rocking?). Because it wouldn't be moving any air, it wouldn't need as much power - it would have to match the excursion of the cone and all that. Is that a daft idea?

29th September 2005, 01:46 PM	#2
mwmkravchenko diyAudio Member Join Date: Jan 2002 Location: Perth Canada	WHeres the Draft? No it is not a daft idea. There were some good studies on the effect of driver and motor structural born non-linearities. They found that the magnet structure coloured the sound the most. To dampen it they coupled the back of the driver to the enclosure through a resilient mount and it cut down the problem by quite a bit. I think that KEF coupled drivers with a rigid steel rod to do much the same. They were driven as a push pull and the concept was that the rod would help to cancel out the unwanted vibrations much like your idea. The mass of the object radiating has a lot to do with the length of time it sounds and at what frequency range. A cone has a very small mass when compared to the rest of a driver. The motor structure has much more problems when you start to think about it. Next down the line are the basket and the dust cap. They are all necesary evils in a practical driver. Mark __________________ Mark

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29th September 2005, 02:41 PM	#3
quickshift diyAudio Member Join Date: Jun 2005 Location: West London	Interesting, thank you. I'm glad it wasn't daft. I'll see if I can find some info on previous studies.

29th September 2005, 04:15 PM	#4
AndrewJ diyAudio Member Join Date: Sep 2001	Quickshift, your idea is not daft, but it is not original either!! It is true that the major contributor to cabinet vibration is mechanical forces generated by the recoil force on the magnet when the cone moves back and forth. Newtons law " to every action there is an equal and opposite re-action". The forces generated on the cabinet that cause its panels to vibrate from this source are typically more than 10 to 30 times stronger than that due to the internal sound waves. At KEF, we employed techniques to minimize or cancel this force, either by compliantly mounting the driver to the cabinet, compliantly mounting the magnet to the chassis, or using two drivers with a force cancelling rod. With properly excecuted design, cabinet vibration can be reduced by 20-30dB, and a lot more cost effectively than by building a more inert cabinet. The idea of using a counterbalancing weight has been proposed in the past. I believe Sony has a patent on such a technique. The downside is that it halves the efficiency of the driver. You have to drive the additional mass by an extra voice coil, with the additional mass being equal to the cone mass, suspended on matching compliance to the cone / spider compliance. I read just a couple of days ago that someone has revived this technique on a product that has just launched into the market, but offhand I don't remember who. I will have to search back through all the magazines I have read recently. However, the double driver idea is a better solution as it typically cancels the reaction force better, and without the loss in efficiency. regards Andrew

29th September 2005, 05:23 PM	#5
quickshift diyAudio Member Join Date: Jun 2005 Location: West London	Thanks for the info Andrew, I wasn't expecting it to be original if it wasn't daft - I'll give it maybe 20 years before I may have an original idea on the subject - if indeed there are any original ideas left to have by then Does it really halve the efficiency? I would have guessed that a lot of the energy goes into moving the air. I thought that maybe a much lower powered system could be used to move the counterweight because it'll be kind of more aerodynamic compared to a cone. If you do find any info on the new product I would be very pleased if you would let me know what it is.

29th September 2005, 06:22 PM	#6
AJinFLA Banned Join Date: Feb 2005 Location: Tampa	Um, yeah, I think its a great idea http://www.codrive.com/tech.htm Cheers, AJ

30th September 2005, 06:37 PM	#7
AndrewJ diyAudio Member Join Date: Sep 2001	AJinFLA, The codrive does not in fact cancel the reaction force of the motor. If you look at the construction of the driver, the force applied to both cones is common, not in opposition, as the two voice coils and cones are mechanically connected together. The motor system does however cancel even order distortion, because as one coil moves into it's magnet, the other moves out. Regards Andrew

1st October 2005, 06:31 PM	#8
AndrewJ diyAudio Member Join Date: Sep 2001	quickshift, I found the reference to the counterbalance driver I was thinking of. It was shown at CEDIA by Sunfire. It is for an in-wall subwoofer they make called the Contrabass Anti-Shake In-Wall Subwoofer. Unfortunately the only information I have is from an advertisement in the CEDIA daily news. There is no info yet on their website. The diagram is too small to fully see what they are doing, but they have two cones plus, they claim, a counterbalance motor, to reduce vibration by 12dB. I will continue to search for more info. Andrew

2nd October 2005, 08:15 AM	#9
knorke diyAudio Member Join Date: Dec 2004 Location: Eichstetten	Actually Focal aka JMLab used exactly this technique in one of their flagship models years ago ....

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