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?
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?
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
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,
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
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
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.
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,
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
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
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
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
AndrewJ said:
Hi Andrew,
I took a close look at this at CEDIA, and they had the part in the center out of the box. It was sealed so I couldn't see the mechanism inside, but it basically looks like an I-beam, with one of the flat sides mounting flush with the baffle. It is basically a zero acoustic output motor which has been matched to the response of the pair of 10" drivers in the sub. This matching is really the only tricky part of such a design, but can certainly be calculated. As others here have, I had given thought to something like this long ago, and my own conclusion was that if at all possible, it's better to just use a balanced configuration of drivers, as the counterbalance is wasteful of power. Of course today power is a lot cheaper.
I did think it was a clever little design, with the naming being pretty poor taste as the Tom Danley's ContraBass design was in fact one of the references and prior art which forced Bob Carver to re-write the first subwoofer patent related to his "TrueSub." Of course I am biased.
Regards,
Dave,
The Sunfire sub I was discussing was an in-wall design with two front firing subs. Details are not yet on their website.
While I agree that two woofers in bipole mode are the best way of cancelling reaction forces, this configuration is not exactly practical for in-wall applications!!
regards
Andrew
The Sunfire sub I was discussing was an in-wall design with two front firing subs. Details are not yet on their website.
While I agree that two woofers in bipole mode are the best way of cancelling reaction forces, this configuration is not exactly practical for in-wall applications!!
regards
Andrew
For an inwall sub, the Tymphany transducer looks pretty interesting. It manages to pack quite a bit of Sd into a package with shallow depth and force-cancelling design. The medium-size one is only 9 cm deep but has over 500 cm^2 of Sd.
http://www.tymphany.com/pr/LAT_DataSheet.pdf
http://www.tymphany.com/pr/LAT_DataSheet.pdf
wouldn't it be easier to just build a driver directly out of phase with the front driver right at the rear?
this should cancel any vibrations out right?
kinda rediculous (if you ask me) to put any power (towards something that isn't producing sound.
and adding weight to the cabinet is just as dumb if its only gonna change the frequency of the vibration.
this should cancel any vibrations out right?
kinda rediculous (if you ask me) to put any power (towards something that isn't producing sound.
and adding weight to the cabinet is just as dumb if its only gonna change the frequency of the vibration.
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