Hara said:
Yep, derivative of cos(x) is -sin(x). If you graph them together and look think of them as input signal and blade pitch you can see what I'm getting at. OTOH, nobody seems to have mentioned this before, so I may be totally off my rocker.
I don't think it would be a phase shift. I don't have the vocabulary to describe it, but it's kind of an inversion of what a speaker usually does. Your voltage/current source description may be apt.
Also, I finally took the time to read completely through this thread and the one over on AVSForum where Bruce posts and I didn't have any great insights. Bruce posted some interesting comments, but nothing earthshattering from a construction perspective. I'll quote the comment I thought was the most interesting, but if you haven't already read it the thread has a few good parts:
Just a quick update. I was curious about the idea of using computer hard disk internals as an option for control of blade pitch. I took apart an old drive (80Mb Western Digital) stripped out the platters and left the spindle stepper and the voice coil head mechanism.
To get an idea of how quickly it can move I feed it a 60Hz sine signal with 12v peaks. With this input signal the heads move a distance of about a quarter inch, or around 8 degrees of a circle. Unloaded it consumes around 200mA. I haven't measured the static force it generates, but it is considerable (attempting to hold it still by hand is mostly futile).
I didn't have time to set up a signal generator to try other frequencies or to hook it to an audio amp, but I'll give that a try later. I'd also like to measure the impedance to see how it looks for connecting them directly to an audio amp.
I think that this idea has some merit, the voice coil assemblies are small and strong, easily available, and could be affixed directly to the blade axles, avoiding any mechanical linkages. They could either be provided with a centering mechanism (spring) to work like a speaker, or they could be servo controlled by a microcontroller (possibly useful if mis-matched assemblies are to be used).
It might also be possible to increase the magnetic flux across the voice coil by stacking additional magnets into the gap, thereby increasing the available torque .
The primary drawback is the rotational distance that the motor assembly provides, which isn't very large, nowhere near the 90 degrees used by Bruce. Possibly multiple ways to address that.
To get an idea of how quickly it can move I feed it a 60Hz sine signal with 12v peaks. With this input signal the heads move a distance of about a quarter inch, or around 8 degrees of a circle. Unloaded it consumes around 200mA. I haven't measured the static force it generates, but it is considerable (attempting to hold it still by hand is mostly futile).
I didn't have time to set up a signal generator to try other frequencies or to hook it to an audio amp, but I'll give that a try later. I'd also like to measure the impedance to see how it looks for connecting them directly to an audio amp.
I think that this idea has some merit, the voice coil assemblies are small and strong, easily available, and could be affixed directly to the blade axles, avoiding any mechanical linkages. They could either be provided with a centering mechanism (spring) to work like a speaker, or they could be servo controlled by a microcontroller (possibly useful if mis-matched assemblies are to be used).
It might also be possible to increase the magnetic flux across the voice coil by stacking additional magnets into the gap, thereby increasing the available torque .
The primary drawback is the rotational distance that the motor assembly provides, which isn't very large, nowhere near the 90 degrees used by Bruce. Possibly multiple ways to address that.
noah katz said:
Sorry, I just realized you were referring to your previous post:
noah katz said:
I'm coming back
My access to a machine shop last year didn't work out, so I've been putting off the project. But I'm getting back into it. Here's a teaser pic for ya'll.
I will post more hopefully tomorrow.
My access to a machine shop last year didn't work out, so I've been putting off the project. But I'm getting back into it. Here's a teaser pic for ya'll.
I will post more hopefully tomorrow.
OK xplod, you've have left us in a teased state for over a year now...
Has anyone done any DIY fan subs?
Has anyone done any DIY fan subs?
i'm also looking for a good system to do this DIY or find an alternate company making them for less than $25,000.... its been a few years already but it seems like nothings popping up. anyone hear of new developments?
anyone... anyone... ?
It's such a cool concept/method that I would really love to see someone attempting it.
It's such a cool concept/method that I would really love to see someone attempting it.
If you have a free air speaker under light power with a guitar and you wiggle the string, even on a cheap instrument it will pick up the lowest you can wiggle the string, as demonstrated by the driver movement, and why wouldn't it?
Also, the infrasound may add an extra airiness and almost a wave of sorts for the rest of the information to be carried on, which already happens to a degree. With the nature of "real" infrasound, however, I do not believe any sound technology piece has ever really created it, becuase it would travel for blocks if not miles and make some people sick, quesy, etc, and I just don't see that happening. Niagara's Fury at Niagara Falls has six (6) rotary woofers installed as part of a 4 dimensional show that even includes water being sprayed on you. I've never been to it.
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Speakers or strings wiggling does not mean they are producing sound at an audible level.
That said, bumping a condenser microphone can put out significant VLF output, it annoys me that many news programs don’t bother to HP voice microphones, I hear (and see on an RTA) recorded unintended bumps and air handling noises down at 20 Hz and below all too frequently.
Low frequency sound does have the ability to diffract around fairly large objects, so it will travel further than high frequency sound of the same SPL level.
That said, it still falls at 6 dB per doubling of distance.
If your VLF output (say at 10 Hz) was 100 dB at 10 meters from the source, that level would be only 76 dB at 160 meters, 6240 feet, a bit over a mile away.
Put that source in a closed building, and the level may be 20 or more dB lower.
Tom Danley has made blower (fan) driven devices with lots of low frequency output down to 3 Hz.
Here is some information in his own write, circa 1998:
“In my work developing transducers at Intersonics Inc, I have built
devices and systems to produce high sound levels at both ends of the
spectrum. One sonic boom simulator supplied to BBN could produce 163 dB
at 5 HZ (in a concrete bunker) and could remove windows and doors from
there frames and fixtures.
Another sonic boom simulator (3 way system called "speakers from hell"
on "beyond 2000" TV show) had the displacement of an 8 foot by 12 foot piston
moving 18" peak to peak, the system could produce >132dB on the outside wall
of an old house from 3HZ to 5KHZ.
This is about 2 lb pressure acoustic pressure per sq ft and with a sine
wave at 3 HZ, made the middle of the wall move 8-10 inches in and out
and "house parts" frequently would fall off (I thought we broke the
house at one point when there was a loud crash from the crawl space so
we stopped "teasing" the house with the oscillator).
In testing, I intentionally experienced many slow TEF sweeps from 28
down to 3 HZ at full intensity (cause I'm a bass sicko) with never the
need to change underwear. Certainly there was a strong feeling of relief
when it stopped but it had no other Ill effect. BTW at 3 HZ the
threshold of audibility is about 125 dB so at 132 dB 3 HZ IS audible! I
felt fairly safe exposing myself to this as I had found a very good book
on the subject called "Infrasound and Low Frequency Vibration" edited by
W. Tempest, published by Academic press.
Regards,
Thomas Danley”
If you are interested in available technology that can produce serious VLF output at an affordable cost, check out Josh Ricci’s Gjallerhorn.
http://www.diyaudio.com/forums/subwoofers/189784-gjallerhorn.html
Post #52 has charts, #53 plans, #61 Josh offers more detail to those interested.
Art Welter
LOL! Man, I'd love to build something capable of doing this. Imagine how easily it would reproduce "sane" levels if it's capable of detaching your wall studs from the foundation.
That's OK Bart we know there might be a slight exaggeration in there somewhere but what the hey, makes a for a good campfire story. 😉
That "story" has no exaggeration, and there were college students paid to live in the hell house to study the effects the noise had.
Tom has also made an acoustical levitator, which I find even more interesting than simply deflecting walls.
Bart, they don't know the quality of Belgium brick housing over there, which possibly would be qualified as 'heavily fortified bunker'
Well, I honestly didn't think it would actually come to this but if you know something about building construction you'd know this is more than just a little exaggeration. I think when Tom used the term "I thought we broke the house once" he kind of gave it away, don't you? 🙂
To have a complete wall move 10", you would have to have woofers that can move several feet back and forth... I won't be responding at this subject anymore, I have my limits unlike your woofers. 😉
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