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Old 4th October 2005, 05:17 PM   #1
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Default Servo rotary subwoofer!

in an effort to produce the ultimate subwoofer with huge excursion, very low FS for HT use... and tons of output off of little power to around 10hz (looking for on the order of 120db at 10hz with this in dipole) I've come upon geo's rotary sub

http://www.betteraudio.com/geolemon/servoproject/

the idea is awesome and would easy produce massive stable excursion, very low fs if you wish and probably could be made to work well in dipole

so I modeled this up in CAD tell me what ya think

the Kevlar panel in the cylinder is 25" wide and would be within .1" to the sides of the cylinder...

the panel is also 40" tall... so around 12x40 effective cone area if I understand this design correctly....
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Old 4th October 2005, 05:18 PM   #2
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Old 4th October 2005, 05:23 PM   #3
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Old 4th October 2005, 06:26 PM   #4
cowanrg is offline cowanrg  United States
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need some servo motors? i have a few hundred. some big 1.5HP ones, and some smaller more realistic ones...
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Old 4th October 2005, 07:18 PM   #5
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maybe we'll see

I was trying to model specs in BB6... granted it's questionable trying to get a rotary's specs from a pistonic program

but ideally I want a 7hz Fs with this design, around 3000cm2 of Sd, as much Xmax as I can get, Mms around 2000g, CMS <.25mm/N and BL below 14 N/A.... I guess this would be applying this to a pistonic speaker... so I dunno about this design

I'm looking for a QTS of around .9 and a Fs around 7hz I guess those are the only true specs I care about
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Old 4th October 2005, 08:51 PM   #6
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realistically a QTS around .9, Fs around 15hz and MMs at least 1000g is all that I want as far as specs (Mms is the least I think I can get while keeping a very strong cone)....

I dunno about everything else... it seems a very low Cms is needed to do this.... below 0.1 mm/N...
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Old 4th October 2005, 08:55 PM   #7
johnnyx is offline johnnyx  United Kingdom
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Have you got suitable servo drives for the motors? It seems a very expensive way of doing it, but interesting. I wonder what would happen if I fed an audio signal into our test servo drive at work; would it be happy to go back and forward rapidly for fractions of a revolution. It uses an optical encoder for positional feedback, and this works at all speeds, but I'm not sure how it would react to an audio signal over fractions of a revolution.

I'm sure I saw an ad for a system that used a servo controlled fan to move lots of air at low frequencies, but I forget details about it; maybe it's the one you described.

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Old 4th October 2005, 08:57 PM   #8
cowanrg is offline cowanrg  United States
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i think you should throw something together out of cardboard just to see how it all works, then worry about the fine details.

so the concept is that you hook up an AC signal from an amp to a servo motor and it turns in frequency with the signal? but it needs a "return" mechanism to make it pulse, otherwise it just turns in one direction?
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Old 4th October 2005, 09:01 PM   #9
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Quote:
Originally posted by johnnyx
Have you got suitable servo drives for the motors? It seems a very expensive way of doing it, but interesting. I wonder what would happen if I fed an audio signal into our test servo drive at work; would it be happy to go back and forward rapidly for fractions of a revolution. It uses an optical encoder for positional feedback, and this works at all speeds, but I'm not sure how it would react to an audio signal over fractions of a revolution.

I'm sure I saw an ad for a system that used a servo controlled fan to move lots of air at low frequencies, but I forget details about it; maybe it's the one you described.




no different design... basically what happens is the motor tries to spin the the kevlar panel but the tortion bar (not very stiff) sends it back to rest position... I know the fan you're talking about though

I need to know how much BL the design can stand so I can choose the motor strength... a design I'm quite happy with has a BL around 30 N/A... but this is in BB6

but I would like really efficent motors... which is basically what a servo motor is... it's not really as expensive as you think.... maybe for a huge 1.5 HP monster it would be... but not this design me thinks
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Old 4th October 2005, 09:03 PM   #10
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~cownrg

that's the tortion steel mechanism Geo designed... it would work quite well as a suspension and allow you to fully control the suspension stiffness by steel thickness and/or adjusting distances of the pads...

it's like the last pictures on the page

I believe the idea is two servo motors...

one side of the cone would always be going forward and to rest position and the other side would always be going back and to rest position...

at least this is the only way that makes sense... it's a bipolar speaker in theory
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