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A patent is only as good as the claims. The idea of a rotary speaker is not new and I imagine any claims would be to some particular method/design ideas not the basic principle. As phoenix gold manufactured the cyclone which operates on the same principle back in the 90's. I did a search on Thigpen's name and came up with nothing on the rotary sub. Of course that wouldn't include anything that was pending. Generally pending status is granted after provisional patent application is made and only lasts for a year the full patent is developed and applied for. So if it has been under patent pending status for over a year there is a good chance there is no legal protection status. Of course there are circumstances where things could be dragged out, but that's typically how it goes.

Even if the device was protected as intellectual property that doesn't prevent you from making one for yourself or improving on it. It only prevents you from offering it for sale, and then only if the inventor issues a cease desist letter.
 

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No not at all. Actually your version of the device could be totally "different" and you could be sued for infringement. It's all dependant on what the claims are and how they're worded/written. For example, if one of bruce's claims was regarding using a specific material for a component then regardless of how you made made your verision you could not use that material (more complicated than that but you get the idea). Also say he claimed the manufacturing method of stamping for the fan blade, then you cannot use the stamping method for any material.

Often the most desired claims are material or manufacturing method becasue this makes for a very broad exclusion of others especially if you do it right and use optimal materials and methods for components. In this case it wouldn't do any good to claim fan blades made of gold because anyone else could easily patent the use of say aluminum since it's cheaper and gives a better cost advatage. Same is true with custom machined parts. For mass appeal you would want to claim a basic manufacturing process such as plastic molding.

Of course if he made the basic claim of a variable pitch rotary device for use as a transducer. you couldn't make anything like it without infringing. but again like I said before his rotary woofer is not novel, it's an old idea that just has never made it to market. I would suspect a challenger could win a case regarding a claim such as that, but then who wants to waste time and money fighting in the courts.

That's another point too, all patents do is give the inventor the right to exclude other from offering what you claim for sale or importing it. There's no law against copying anything and it's up to the inventor to defend his property rights without any help from the gov't. So even if you decided to directly copy Thigpen's design and mass market the contraption, it would be up to him to fight you in court and foot the bills from his pocket (or his assignee's). Of course most often a deal is struck in the way of a royalty agreement where you would pay some amount to use the idea. These types of agreements are really only a gentlemen's way of saying I won't sue you.
 

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Looks like SoundSplinter and CSS are current Shack supporters. If you guys want to guilt them into offering me a high Bl motor assembly without a basket or cone for sale, then I would continue the project. I have no interest in trying to dissect an existing driver. All I need is a linear 10mm, but more doesn't hurt.

Also, it would be wise to not even consider trying to sell a finished product rotary sub, just come up with a DIY design that works, and post how you got there. Others can build it if they are interested.
 

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Steve,

You'll probably need the basket attached since the spider is uusally attached to the frame. Also a given motor may not be as linear once the surround is removed. Most of the compliance is contributed by the spider but the surround adds some, so the motor won't operate the same without it.

Also you'll need a driver with a pole vent large enough to pass the fan shaft also or machine a custom back plate. It would be sweet to cut a pocket in a back plate that would accept a bearing.
 

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Not sure why I would want the basket - I'd have to cut off the spokes then.

Remember that there needs to be a bearing inside the voice coil as well, allowing the flange to rotate freely while still being attached to the voice coil. So a larger voice coil diameter helps.
 

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Steve powerful motors are readily available all over the place. For example just hit up robotunderground for an assortment. Car audio guys sell them all of the time.
 

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Newbie here, if I am not mistaken all we need to do is move a significant amount of air and at the same time create a frequency within it. Wouldn't it be easier to use a squirrel cage blower like in a furnace to move the air? and then you would just have to create some kind of movable blade type device to create the frequency within the airflow? Insults are welcomed. :rubeyes:
 

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Steve,



Also you'll need a driver with a pole vent large enough to pass the fan shaft also or machine a custom back plate. It would be sweet to cut a pocket in a back plate that would accept a bearing.
Unless you were to put the control mechanism in front of the fan blade rotor contraption...then you wouldn't need it to fit over the fan shaft. It would just need to be in line with the shaft.
 

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How about a co-axial contra-rotary woofer, there a two three-blade rotors turing in opposite directions, with this speaker wolud be more powerful in relation to diameter, the faster rotational speed wloud increase the number of turns per cycle and extend the frequency response.
 

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The rotational motion of the blades isnt what produces frequencies. The only job of the rotary motion is to shift lots of air to efficiently reproduce very low frequencies.
 

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The rotary motion amplifies the sound, but more rotations per cycle means greater amplification, co-axial cotra-rotary design would shift more air relative to blade diameter, the smaller diameter and higher rotational speed would therefore extend the frequency response. Futhermore one of the fans would covert the tangetinal airflow from the other into axial flow.
 

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The rotary motion moves air. With zeros degrees of blade pitch you would get virtually no sound as no air would be moved. The variation in pitch causes a variation in the amount of air moved which in turn causes a variation in amplification. The amount of pitch needed for a given spl output would of course be dependant the rotational speed of the fan, and as with multiple drivers in a traditional system, more fans would mean less pitch (excursion) required for any given output level. The RPM of the blades in in effect the equivalent of the size of the cone used in a traditional system.

Looking into your proposed deign more, how would you mount your fans, side by side or one in front of the other. It sounds like your suggesting one in front of the other, and contra rotating fans are generally used where you would place fans together in this fashion. If they were side by side they would not need to spin in opposite directions, and do you think that whether or not the airflow being tangential or axial would make a difference to the sound output from the woofer? Surely, as long as its shifting a tonne of air anyway it would work fine. Obviously, as with any design, you would need to construct it to produce the spl's you require with relative ease, so you need to figure out how much air you potentially need to move. The good thing about a rotary woofer though is that you could experiment with increasing the fan speed to increase output.
 

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The rotary motion moves air. With zeros degrees of blade pitch you would get virtually no sound as no air would be moved. The variation in pitch causes a variation in the amount of air moved which in turn causes a variation in amplification. The amount of pitch needed for a given spl output would of course be dependant the rotational speed of the fan, and as with multiple drivers in a traditional system, more fans would mean less pitch (excursion) required for any given output level. The RPM of the blades in in effect the equivalent of the size of the cone used in a traditional system.
The amount of pitch needed depends mainly on the revolutions per cycle (revolution in relation to the frequency).

Looking into your proposed deign more, how would you mount your fans, side by side or one in front of the other. It sounds like your suggesting one in front of the other, and contra rotating fans are generally used where you would place fans together in this fashion. If they were side by side they would not need to spin in opposite directions, and do you think that whether or not the airflow being tangential or axial would make a difference to the sound output from the woofer? Surely, as long as its shifting a tone of air anyway it would work fine. Obviously, as with any design, you would need to construct it to produce the spl's you require with relative ease, so you need to figure out how much air you potential need to move. The good thing about a rotary woofer though is that you could experiment with increasing the fan speed to increase output.
If you have two fans side by side, there is still no reason to spin them in the same direction. It's a simple fact that the blades are always moving perpendicular to the airflow at all times, unlike any component in a pure cone driver speaker, so it makes sense (to me) that blades should spin in opposite directions. With Contra-rotary fans, the amount of pitch needed for a given sound output is less relative to the diameter, and a co-axial design would more compact than a tandem design. As for whether the airflow should be axial or radial, well that depends. Yes you can experiment with increasing fan speed, but it seems to me that you may as well have two smaller diameter fans as smaller diameter fans are more suited to higher rotational speed, with more needed to provide a given power output, co-axial mounting provide the best packaging and least turbulence.
 

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The amount of pitch needed depends mainly on the revolutions per cycle (revolution in relation to the frequency).
Of course, but like with larger cones, you move more air with a cycle you need less excursion. Less required excursion = lower distortion.

If you have two fans side by side, there is still no reason to spin them in the same direction.
The only argument against that I can see is that for a DIY'er, you would need to make 2 sets of opposite handed parts, possible making it more complicated than it needs to be for a first time outing.

It's a simple fact that the blades are always moving perpendicular to the airflow at all times, unlike any component in a pure cone driver speaker, so it makes sense (to me) that blades should spin in opposite directions. With Contra-rotary fans, the amount of pitch needed for a given sound output is less relative to the diameter, and a co-axial design would more compact than a tandem design. As for whether the airflow should be axial or radial, well that depends. Yes you can experiment with increasing fan speed, but it seems to me that you may as well have two smaller diameter fans as smaller diameter fans are more suited to higher rotational speed, with more needed to provide a given power output, co-axial mounting provide the best packaging and least turbulence.
This seems to me to border on the small multi driver array vs singular larger driver arguments you see in DIY subwoofery. I cant honestly see the gains paying off when a singular 8" diameter fan or so can provide all the output you require (or so it seems looking at comments on the net about rotary woofers). Larger fans can rotate slower for a given amount of moved air volume meaning reduced fan noise, but on the flip side, a smaller diameter fan will require a less strong motor and the pitching blades with present less load to that motor.

I have to go and strip out a 750 mm diameter fan this week than can move over 6 cubes per second, maybe I should experiment with that :devil:
 

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The goal of this was a fairly simple DIY project. As with other threads regarding the same endeavour it gathers steam and then stops due to manufacturing and in some cases design complication which generally = $$$.

A contra-rotating fan setup with concentric shafts could be small and compact but the mechanics would be extremely complex. You'd have to be a rocket surgeon to figure it out unless you had a CAD/CAM setup and a nice CNC mill and lathe and shop. First of all you have to have the reversing mechanism and a hollow shaft/set. Then you have to have linkages that operate 180 degrees out of phase....or do you? This would be an extremely complicated setup. I can't imagine working all of that out and I'm generally really comfy with machine design. I guess you could make it simple with two VC drives wired out of phase but my inkling is that you just amped up the cost and complexity for little gain. The only thing I can see this effectively accomplishing is eliminating the vortice shed a single blade set would have.

Also one thought would be the noise the counter blades would produce. According to some of fan design info I read a while back a large portion of the generated noise is due to the chopping action of the fan, i.e. around the blade passing frequency. Introducing another set of blades in the opposite direction would probably exaggerate this noise and also force it into a higher frequency band that you might be more sensitive too.

since it's meant to be an audio device large and slow moving is the best route. no good to have something that does 1Hz if you can't hear or feel it over the self noise.
 

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Steve would have to chime in but I doubt it. I think he found the choke point is the actuation. Steve ran into issue with having a VC modded with Fi and and a motor is terribly complicated to design from the ground up even the proper FEA. I did find that there's a handful of companies that offer off the shelf VC style linear actuators that would work with the idea, thus circumventing having a manufacturer do you a favor, but the real issue is cost. I contacted a couple of these companies and a VCLA with similar force characteristics as a high BL sub runs between $900-1500 plus there's some additional machining designing to do to incorporate it.

This definitely isn't a trivial project in knowledge, mechanics, or money. I think it would be somewhat easy to come up with with a mockup type device that technically "works", but actually creating a workable transducer with any agreeable acoustic capability is really difficult for DIY.
 
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