What type/brand?
Do you know if it’s only the coils burned?
Is it a rebuildable sub?
Because if it’s not rebuildable there quite hard to rewind.
Do you know if it’s only the coils burned?
Is it a rebuildable sub?
Because if it’s not rebuildable there quite hard to rewind.
hey, ive just been catching up on this thred,
firstly the whole idea is so simple, its suprising that someone dident start making these things sooner. the whole idea of the thing makes such good sence.
a few of the ideas that people have previously sudjested seem good. i did a quick google for variable pitched props, for moddle airplaines and came up with these
http://www.hobby-lobby.com/variablepitch.htm
im in the uk and havent hada a chance to look for a uk source yet, but i think some interesteing tests could be done with these if they solonoides are capable of moving quick enough.
another thing that initaly crosed my mind, a while ago i was looking in to making some hefy flat pannel speakers and came acros some big moving coil flat panel drivers, magnet size not that disimilear from what youd get on a 15" pa driver. but as the coil is designed to be shifing more of a load, and working aganced ( posibly glued) to a hard surface i thought these may be better suted to moving the fan blades.
one last point ( that i can think of atm), i know the design in question runs with the fan blades flat, when there is silence, ie, pitch of the blades modulating around 0% pitch, bit like a audio signal osilating around 0v., would it be an idea to run the blades with a bias, ie (random guess % hear) working between 0% and 10%, biased to 5% (just throwing in random percentages to get my point across) the idea being so that the forces on the blades are alwas in the same direction, rather than alternating, and in my head this would sudjest that they would be "floping" slightly eather way. if they were biased, then this could reduce any fluttering distortion.
i am realy interested in this project, unfortunaly i am currently at uni, away from any DIY facilitys ( its hell, i live on a farm at home, loads of space and tools) so i will not be able to atempt anything, other than maby a 100 mill compute fan, with a small MC driver. i like the idea of this project, because it seems to me it may have uses in the live sound ariea, if it would be posible to get them to operate say up to 100HZ, (it is strange talking about stugling to get a sub to operate up to a high enough freq)
i would be interested in trying out more exotic materials for blades, such as carbon fiber to try and further reduce any distortion caused hear, and reduce the weight that the MC driver has to move.
if any one is still working on this project, let me know what you think of my ideas, and if theres any potentioal there.
cheers
bungle
firstly the whole idea is so simple, its suprising that someone dident start making these things sooner. the whole idea of the thing makes such good sence.
a few of the ideas that people have previously sudjested seem good. i did a quick google for variable pitched props, for moddle airplaines and came up with these
http://www.hobby-lobby.com/variablepitch.htm
im in the uk and havent hada a chance to look for a uk source yet, but i think some interesteing tests could be done with these if they solonoides are capable of moving quick enough.
another thing that initaly crosed my mind, a while ago i was looking in to making some hefy flat pannel speakers and came acros some big moving coil flat panel drivers, magnet size not that disimilear from what youd get on a 15" pa driver. but as the coil is designed to be shifing more of a load, and working aganced ( posibly glued) to a hard surface i thought these may be better suted to moving the fan blades.
one last point ( that i can think of atm), i know the design in question runs with the fan blades flat, when there is silence, ie, pitch of the blades modulating around 0% pitch, bit like a audio signal osilating around 0v., would it be an idea to run the blades with a bias, ie (random guess % hear) working between 0% and 10%, biased to 5% (just throwing in random percentages to get my point across) the idea being so that the forces on the blades are alwas in the same direction, rather than alternating, and in my head this would sudjest that they would be "floping" slightly eather way. if they were biased, then this could reduce any fluttering distortion.
i am realy interested in this project, unfortunaly i am currently at uni, away from any DIY facilitys ( its hell, i live on a farm at home, loads of space and tools) so i will not be able to atempt anything, other than maby a 100 mill compute fan, with a small MC driver. i like the idea of this project, because it seems to me it may have uses in the live sound ariea, if it would be posible to get them to operate say up to 100HZ, (it is strange talking about stugling to get a sub to operate up to a high enough freq)
i would be interested in trying out more exotic materials for blades, such as carbon fiber to try and further reduce any distortion caused hear, and reduce the weight that the MC driver has to move.
if any one is still working on this project, let me know what you think of my ideas, and if theres any potentioal there.
cheers
bungle
Well there you go. The variable pitch props you need are in the link you posted.
Simple enough.
Just need one of their motors or some other hollow shaft motor and some way to push/pull the pitch rod.
Simple enough.
Just need one of their motors or some other hollow shaft motor and some way to push/pull the pitch rod.
Tom Danley did some designs like this. They were called Servo-Valve loudspeakers, and developed air movement in each direction by using a four-way valve with a servo-motor operating a lightweight panel to divert the air flow. A fan operating with a constant speed provided the airflow, and at zero output, the valve was oriented so that no air movement was produced. Something about ungodly amounts of information at 3 Hz was mentioned.
Attachments
hi,
had a play with panomaniac's sujestion of driving a computer speaker with a amp, i used a 22nanofarad cap. the fans span up, using a fair amount of power tho, ( i was using 200wrms, from a pa amp) cranked to about 3/4 to get the fan to go, and very little sound came out, just what sounded like it was coming from the coils insde vibrating. then more power made my cap explode, they dont smell good.
the pic below is a realy bad diagram (drawn in word for lack of anything better to use) to try to explain how i intend to make my vaiable pitch prop. feed back would be cool.
some things i dident mention on the diagram, i beleve the shafts to the fan blades should be holow and eather bent, or cut and glued/solderd/welded at the cranks. idealy i beleve they should be made from carbon fiber to be stiff and light, but i dont beleve ill be able to get access to any to test this. ill prob use small copper pipe or some kind of plastic.. i also think the blades should be made out of carbon fiber for the same resons. might have to resort to glass fiber though.
had a play with panomaniac's sujestion of driving a computer speaker with a amp, i used a 22nanofarad cap. the fans span up, using a fair amount of power tho, ( i was using 200wrms, from a pa amp) cranked to about 3/4 to get the fan to go, and very little sound came out, just what sounded like it was coming from the coils insde vibrating. then more power made my cap explode, they dont smell good.
the pic below is a realy bad diagram (drawn in word for lack of anything better to use) to try to explain how i intend to make my vaiable pitch prop. feed back would be cool.
some things i dident mention on the diagram, i beleve the shafts to the fan blades should be holow and eather bent, or cut and glued/solderd/welded at the cranks. idealy i beleve they should be made from carbon fiber to be stiff and light, but i dont beleve ill be able to get access to any to test this. ill prob use small copper pipe or some kind of plastic.. i also think the blades should be made out of carbon fiber for the same resons. might have to resort to glass fiber though.
Attachments
bungle69er said:
You meant drive a computer Fan right? You were driving the fan with an amp? How did you keep the AC biased to only one polarity of voltage? What frequencies were you feeding the fan?
For the physics behind this implementation, I think the rate at which the fans slow down would be the limiting factor for how high in frequency the fans would be able to reproduce pressure waves. (Assuming the fans don't accept a voltage in the other direction)
By having fans that have an rpm sensor and combining it with some sort of computer generated signal correction, you could feed the computer the input signal, and the computer would send a biased and corrected signal to the amplifier powering an array of fans. If all the fans were the same, you could assume the rotation speed of one fan would be true for all fans and the approximation would be good enough.
Finding low voltage fans would also help with the amplifier. Anyone know the impedance of an electric motor coupled with a fan?
Hey Bungle.
Glad to hear you tried the computer fan idea. Sorry you blew up your cap!
Problem was, your cap was much, much too small. Like 100K times too small. You made yourself a high pass filter that was not letting much low frequency thru at all. No wonder you needed 200W.
It's hard to say what the "impedance" of the computer fan is - but they seem to vary from about 24 to over 300 ohms. So you would want a cap of 220uF to maybe 2200uF or more.
Your 22nF is not going to let those low frequencies thru. It's a high pass filter with a -3dB point maybe as high as 28Khz - or higher. Not so great for a subwoofer. 😉 You don't need the cap unless you want to add DC bias to the fan.
FYI, if you want to build a fan subwoofer, you need a baffle of some kind. Otherwise the rear wave will come around and cancel out the front wave. The fan woofer shown in this thread is installed in the attic for an infinite baffle. You could also use a window.
Glad to hear you tried the computer fan idea. Sorry you blew up your cap!
Problem was, your cap was much, much too small. Like 100K times too small. You made yourself a high pass filter that was not letting much low frequency thru at all. No wonder you needed 200W.
It's hard to say what the "impedance" of the computer fan is - but they seem to vary from about 24 to over 300 ohms. So you would want a cap of 220uF to maybe 2200uF or more.
Your 22nF is not going to let those low frequencies thru. It's a high pass filter with a -3dB point maybe as high as 28Khz - or higher. Not so great for a subwoofer. 😉 You don't need the cap unless you want to add DC bias to the fan.
FYI, if you want to build a fan subwoofer, you need a baffle of some kind. Otherwise the rear wave will come around and cancel out the front wave. The fan woofer shown in this thread is installed in the attic for an infinite baffle. You could also use a window.
hi,
tried the computer fan again with a 2200micro farad cap ( btw i realised i made a mistake, i was using a 22micro farad before not nano farad) and the fans wouldn’t spin up at all. i decided to use a dc bias of 8 volts ( just a convenient transformer i had around) and then i managed to get the fans speed to modulate, but ony at around 0.25 hz and then i realised, how slow computer fans are at starting up, when you plug them in to there full 12V. i don’t believe the motor in a computer fan is powerful enough, relative to how heavy the fan is to get any kind of transient response, maybe it could follow a LF test sine wave but i doubt it would go above a few Hz.
Interesting test though.
Does any one else hear think that the principle of a fan sub has potential for PA systems? if one could be made with the moving parts light enough to work up to 100hz. It seems to me that the efficiently of this idea is greater than that possible with a normal pistonic driver, as far as the amplifier power needed anyway. Is this because there is better acoustic impedance matching between the fan blades and the higher-pressure air, than there would be between a pistonic driver and air?
Cheers..
bungle
tried the computer fan again with a 2200micro farad cap ( btw i realised i made a mistake, i was using a 22micro farad before not nano farad) and the fans wouldn’t spin up at all. i decided to use a dc bias of 8 volts ( just a convenient transformer i had around) and then i managed to get the fans speed to modulate, but ony at around 0.25 hz and then i realised, how slow computer fans are at starting up, when you plug them in to there full 12V. i don’t believe the motor in a computer fan is powerful enough, relative to how heavy the fan is to get any kind of transient response, maybe it could follow a LF test sine wave but i doubt it would go above a few Hz.
Interesting test though.
Does any one else hear think that the principle of a fan sub has potential for PA systems? if one could be made with the moving parts light enough to work up to 100hz. It seems to me that the efficiently of this idea is greater than that possible with a normal pistonic driver, as far as the amplifier power needed anyway. Is this because there is better acoustic impedance matching between the fan blades and the higher-pressure air, than there would be between a pistonic driver and air?
Cheers..
bungle
The probable reason why your computer fan experiment isn't working is because the fan itself is electronically commutated. It isn't just a straight motor with brushes and a commutator ring -- there is circuitry which identifies the input voltage and energizes the coils in sequence to produce rotation. Tom Danley used "servomotors".
BAM said:
Ah Ha! Good to know. Are all computer fans like that?
But considering the mass of the spinning blades, maybe it would never work fast enough. As mentioned in an earlier post.
Yes, pretty much every computer fan is electronically commutated. I think AC-powered muffin fans might also be electronically commutated. Take a look at small hobby motors, though. One could be connected by a belt to a servo-controlled vane in an air path, like the Danley design. The small inertia might make a hobby motor quite useful for this. They can usually only withstand 1.5 volts, though, so low power is what's happening there. It might be possible to blow out the coils with more power than that.
I recommend in the future after the proof of concept stage is done is to add some sort of signal modifying feedback section because I would expect the blade angle to pressure/flow rate to be non-linear. Because the frequency is so low, I don't think the sensors would need to be that expensive. The blade pitch motors could be powered by non-audio grade op amps.
For proof of concept for the variable speed fan idea, you can use those portable battery powered fans. Those should have a voltage range of from 1v to 9v. You can find those at the 99cent store.
For proof of concept for the variable speed fan idea, you can use those portable battery powered fans. Those should have a voltage range of from 1v to 9v. You can find those at the 99cent store.
Here are some detail about that "sub" I posted on dBdrag forum
http://audioforum.termpro.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=8;t=025544
Doc
http://audioforum.termpro.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=8;t=025544
Doc
cool chears Doctorbas,
those pics of the inner workings look not disimilear to what i had in mind, allthough surly by making the shafts and crank linkage things outa what looks to be aluminium there limiting there higher end output by the weight and therefore the speed that the mecanisum could change direction.
i beleve if all the moving parts that the VC will have to move should be as light and stiff as posible that the unit would be able to cover the freqency range simmiler to that of say an 18" bass driver used in live sound systems, but obviously with extended low end responce.
idealy i think the shafts and cranks shoud me produced out of carbon fiber rods, or at least holow tubes of alu.
if the responce of this driver could be rased then i beleve it could have a fairly large impact in live sound, where the non hi fi ness of it would not matter, but its low end and potentioaly high SPL would be benaficial.
will be home home next week so will start to colect the materials for a proto type,
if anyone knows supplyers of carbon fiber rods in the uk, the links would be apreiciated.
cheers
matt
www.bungleproductions.co.uk
those pics of the inner workings look not disimilear to what i had in mind, allthough surly by making the shafts and crank linkage things outa what looks to be aluminium there limiting there higher end output by the weight and therefore the speed that the mecanisum could change direction.
i beleve if all the moving parts that the VC will have to move should be as light and stiff as posible that the unit would be able to cover the freqency range simmiler to that of say an 18" bass driver used in live sound systems, but obviously with extended low end responce.
idealy i think the shafts and cranks shoud me produced out of carbon fiber rods, or at least holow tubes of alu.
if the responce of this driver could be rased then i beleve it could have a fairly large impact in live sound, where the non hi fi ness of it would not matter, but its low end and potentioaly high SPL would be benaficial.
will be home home next week so will start to colect the materials for a proto type,
if anyone knows supplyers of carbon fiber rods in the uk, the links would be apreiciated.
cheers
matt
www.bungleproductions.co.uk
Sweet bungle69er !!
I hope i will see some pics of your prototype!
I wanted to built a prototype too, at Sherbrooke Univercity where i work, I have all cnc, lathe, mills and other stuff to built every parts.. but i quit that job in the next week ... I will join my girlfriend at Quebec city cause i found a new job in optical ingeneering R/D.. that mean less machinist job and more optical alignment..
And i loose all those advantages about mecanics workshop, but i will bult my own workshop with future salary increase...
anyway, good luck! i will stay connected about your project!
Doc
I hope i will see some pics of your prototype!
I wanted to built a prototype too, at Sherbrooke Univercity where i work, I have all cnc, lathe, mills and other stuff to built every parts.. but i quit that job in the next week ... I will join my girlfriend at Quebec city cause i found a new job in optical ingeneering R/D.. that mean less machinist job and more optical alignment..
And i loose all those advantages about mecanics workshop, but i will bult my own workshop with future salary increase...
anyway, good luck! i will stay connected about your project!
Doc
Oooh interesting
I though about this a while ago. I would look at the Volt radial drivers for a motor (www.voltloudspeakers.co.uk), if you pull the basket off, you are left with a 10mm hole through the motor and the motor has the magnet spider and VC as once unit. Monacor do a small 6.5" 'raptor' sub which has an odd double spider arrangement that I thought may be worth a look (quite cheap too IIRC). I think model airplane and rocket builders use quite a lot of carbon fibre rod and tube, model car builders also have a good range of small 'rose joints' or rod ends for making the moving assembly.
I'd be very interested in how you get on.
I though about this a while ago. I would look at the Volt radial drivers for a motor (www.voltloudspeakers.co.uk), if you pull the basket off, you are left with a 10mm hole through the motor and the motor has the magnet spider and VC as once unit. Monacor do a small 6.5" 'raptor' sub which has an odd double spider arrangement that I thought may be worth a look (quite cheap too IIRC). I think model airplane and rocket builders use quite a lot of carbon fibre rod and tube, model car builders also have a good range of small 'rose joints' or rod ends for making the moving assembly.
I'd be very interested in how you get on.
Just a thought...
I remember hearing about these mobile units that were used in the '30's; they consisted of a motor-trike with a box on the rear that contained a largish horn loudspeaker. I suppose this was early eventing type gear - dunno whether anyone else has come across them? The relevant point here is that the major form of amplification used was pneumatic; the engine ran a compressor line that was fed directly into the throat of the horn, thus boosting the (naturally aspirated
!?) output.
Just wondering whether combining this technique with Hayden's idea ( http://www.diyaudio.com/forums/showthread.php?postid=1036694#post1036694) might pay dividends. Any thoughts?
I remember hearing about these mobile units that were used in the '30's; they consisted of a motor-trike with a box on the rear that contained a largish horn loudspeaker. I suppose this was early eventing type gear - dunno whether anyone else has come across them? The relevant point here is that the major form of amplification used was pneumatic; the engine ran a compressor line that was fed directly into the throat of the horn, thus boosting the (naturally aspirated
!?) output.Just wondering whether combining this technique with Hayden's idea ( http://www.diyaudio.com/forums/showthread.php?postid=1036694#post1036694) might pay dividends. Any thoughts?
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