Well, he started by saying he wants to feel it in his chest, but later he said this:
I won't speak for him but I'm guessing he just wants to build something mechanical with the parts (blower) he has on hand that uses his knowledge and skills with servo (or stepper) motors. I think in this case the audio function is secondary to the thrill of the design and build process. But that's just my guess.
I just wish people would stop talking about blowers. Blowers are not going to work for any kind of quality audio. Way too much velocity. I've gone out of my way to talk about this, provide links to a velocity/turbulence limit calculator, and then talk about it some more. It wasn't an issue with the original sonic boom generator (due to it's defined usage as a sonic boom generator) but it won't work for quality audio.
Blowers won't work. You need to use a much lower velocity fan or it's just going to make noise and the whole thing is going to end up in the garbage. Much like my failed rotary sub experiment. https://sites.google.com/site/amateuraudio/projects-1/the-rotary-sub
Using the wrong parts is just the wrong thing to do. I did all the math to select the correct motor size and blade size so turbulence would not be a problem but in the end I didn't use the right parts for the job so I had to abandon the project.
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I read into this a lot about a year ago. I found the design documents from the sonic boom generator, read through the patent several times, and found another approach to this that I didn't think of before.
The math wasn't hard to figure out given enough information. A strange thing I noted was that they to actually have a low frequency roll off, but it is at 6 dB per octave in stead of the usual 12. Cfm requirements are actually pretty modest for a home setting. I figured a 1000 cfm fan would produce 104 dB at 3 Hz in free space. After room gain, that is more than enough.
I worked on some designs for these things,but never actually built anything because I was actually stuck on the controller for the device. I bought an arduino, a stepper motor driver, and a stepper motor, just to see how difficult getting the vane to move properly would be. I ended up getting it to turn the motor based on the position of a pot, but getting it to turn +/- 45 degrees from home at a rate of even a few Hz caused it to lose its position. Cheap hardware was probably the problem, but I didn't have money or sources for better stuff.
I would like to begin testing again, but I lack wood working equipment and and a garage.
The math wasn't hard to figure out given enough information. A strange thing I noted was that they to actually have a low frequency roll off, but it is at 6 dB per octave in stead of the usual 12. Cfm requirements are actually pretty modest for a home setting. I figured a 1000 cfm fan would produce 104 dB at 3 Hz in free space. After room gain, that is more than enough.
I worked on some designs for these things,but never actually built anything because I was actually stuck on the controller for the device. I bought an arduino, a stepper motor driver, and a stepper motor, just to see how difficult getting the vane to move properly would be. I ended up getting it to turn the motor based on the position of a pot, but getting it to turn +/- 45 degrees from home at a rate of even a few Hz caused it to lose its position. Cheap hardware was probably the problem, but I didn't have money or sources for better stuff.
I would like to begin testing again, but I lack wood working equipment and and a garage.
No, these types of air driven devices get more sensitive as frequency decreases, there's no low frequency roll off unless it's inherent to the electronics being used.
That doesn't sound right at all. A 1000 cfm fan should produce way more than 104 db, and 104 db at 3 hz is hardly adequate. It's imperceptible, you won't hear or feel anything except maybe a bit of fan noise.
Yes, they do. They only double the amount of air they move per cycle every octave they go lower. To remain flat they must most four times them amount of air. A well understood principal.
I did mention room gain. At these frequencies expect 15 dB or more gain in room. That 104 dB figure was outside.
Hi Guys
I can fill in some blanks. The sonic boom simulator was a real “loudspeaker” system, it could produce music etc but what it was intended to do was reproduce an “N” wave which is the waveshape of a sonic boom. The flow modulators covered 3-30Hz, BT-7’s 30 to 100Hz, mid bass horns 100-600Hz and compression drivers and horns 600Hz and up (5k being the required upper end).
A picture of the first single valve prototype and the wall of stuff facing the old house;
The Worlds Largest Basshorns
Two of 6 modulators, taken in the Servodrive speaker shop at Intersonics with me and the TEF machine.
http://cdn.avsforum.com/b/b9/b94533c6_vbattach180970.jpeg
The “what for”;
http://pdf.aiaa.org/preview/1993/PV1993_4430.pdf
While loudspeakers are not normally required to replicate a signals waveshape, that was key to making a sonic boom that behaved like the real thing. Back when NASA had an active manned space program and plans for a space plane, one big problem was going to be it’s sonic boom signature which was much lower in frequency and power than normal . Intersonics was a NASA contractor already doing acoustic levitation but this project was actually refereed to the speaker division by JBL. This is back when I met Art too, he was one of our customers on the speaker side.
Anyway, this was also the first project the levitation side of the company worked on with the loudspeaker side.
I couldn’t think of a practical way to do this job, 132dB down to 3 Hz on the outside of a building was a pretty steep hill. Around MSFC in Huntsville there were a number of towers with large exponential horns on them. On inquiring, it was explained that at Redstone arsenal next door, when they developed the Saturn 5 rocket engine that several times when they were testing it, the LF sound reflected of a temperature layer and came back down 20 miles away breaking windows etc. After several occurrences, they put remote microphones all around the area and before testing the rocket, they would turn on the horns. If they didn’t hear the horns in the remote mics, it was ok to test.
These were Flow modulators made by LTV ling co and each required a 300Hp diesel air compressor to power it. They made them ranging from 2000 to 10,000 acoustic Watts as I recall. This was what I called a “class A valve” which meant it was half open with no signal and the signal modulated it from that (open or closed etc). While these could also operate to DC, the “small” problem was that the air noise they made was only about 10 or 12 dB down from full signal output.
My solution was to GREATLY lower the pressure and velocity AND to use a much larger push pull bridged valve. With no signal, the air velocity is all within the loop, the valve in either extreme position directs the full flow out one face and in on the other. A position sensor on the valve was feedback to the servomotor system moving it and the flow vs position was plotted and served as a correction curve.
A problem being outdoors was there is no room gain and to reach the target at 3Hz from 2 meters required a fan source that had about 50 cu mtrs sec and needed 12 X 5hp fans to produce. The only solution to the back wave I could think of was simply to place the house at one exit and move the opposite phase far enough away. To allow the flow to expand uniformly instead of forming a free jet within the exit, a tapered section following the graph I found in a Thermodynamics text book dealing with jet and rocket engines.
To be clear, if this had been coupled into the old test house at one end, I am absolutely sure we could have brought it down with very little effort, we did damage even from outside just fooling around.
For the DIY’rs, work out what pressure is a safe target. Even 2 lb’sq foot is WAY WAY too much at very low frequencies if you wish to keep your home /drywall seams intact, multiply the pressure times the area of your ceiling for example.
The Matterhorn;
One of my last projects at the Servodrive spinoff was to rough out a design for something the military wanted. After I left, that was apparently built and tested. At the new company, I was approached to take another shot at whatever this was.
After some design work using a Tapped horn, I had estimated the entire thing could be could be built within / on a single shortie freight container which is a large size reduction and that it could be powered by only about 20-30Kw AND at a fraction of the price.
This estimate hit a nerve I guess because then they wanted to have the rights to anything invented in the process.
Mike said nope, we will keep the Tapped horn, build it on our dime and sell them to you, they said ok, they would need a dozen or so.
I did a sneaky thing, since this was going to run 24hr a day for days on end, I designed it to go down much lower than needed. This put a large impedance rise across the band that it would be used in and that minimized the I^2Xrdc heating, no more air chillers needed etc.
Anyway some testing was completed and it appeared to do what was required (I put some margin in the design) but shortly after the change of administration, the project was stopped, our contacts were not happy either.
I never did find out what this was for and while some kind of an acoustic toilet plunger for caves in a hot part of the world seemed logical, that doesn’t require low distortion or an ability to modulate frequency over a narrow band.
We did end getting back and keeping the Matterhorn and the Tapped horn patent was eventually granted.
Something goofey like that did make decent press which helped offset the effort. There has been discussion about “an entertaining use” for it although there damage to the grass moving at half time it is the concern.
Best,
Tom
I can fill in some blanks. The sonic boom simulator was a real “loudspeaker” system, it could produce music etc but what it was intended to do was reproduce an “N” wave which is the waveshape of a sonic boom. The flow modulators covered 3-30Hz, BT-7’s 30 to 100Hz, mid bass horns 100-600Hz and compression drivers and horns 600Hz and up (5k being the required upper end).
A picture of the first single valve prototype and the wall of stuff facing the old house;
The Worlds Largest Basshorns
Two of 6 modulators, taken in the Servodrive speaker shop at Intersonics with me and the TEF machine.
http://cdn.avsforum.com/b/b9/b94533c6_vbattach180970.jpeg
The “what for”;
http://pdf.aiaa.org/preview/1993/PV1993_4430.pdf
While loudspeakers are not normally required to replicate a signals waveshape, that was key to making a sonic boom that behaved like the real thing. Back when NASA had an active manned space program and plans for a space plane, one big problem was going to be it’s sonic boom signature which was much lower in frequency and power than normal . Intersonics was a NASA contractor already doing acoustic levitation but this project was actually refereed to the speaker division by JBL. This is back when I met Art too, he was one of our customers on the speaker side.
Anyway, this was also the first project the levitation side of the company worked on with the loudspeaker side.
I couldn’t think of a practical way to do this job, 132dB down to 3 Hz on the outside of a building was a pretty steep hill. Around MSFC in Huntsville there were a number of towers with large exponential horns on them. On inquiring, it was explained that at Redstone arsenal next door, when they developed the Saturn 5 rocket engine that several times when they were testing it, the LF sound reflected of a temperature layer and came back down 20 miles away breaking windows etc. After several occurrences, they put remote microphones all around the area and before testing the rocket, they would turn on the horns. If they didn’t hear the horns in the remote mics, it was ok to test.
These were Flow modulators made by LTV ling co and each required a 300Hp diesel air compressor to power it. They made them ranging from 2000 to 10,000 acoustic Watts as I recall. This was what I called a “class A valve” which meant it was half open with no signal and the signal modulated it from that (open or closed etc). While these could also operate to DC, the “small” problem was that the air noise they made was only about 10 or 12 dB down from full signal output.
My solution was to GREATLY lower the pressure and velocity AND to use a much larger push pull bridged valve. With no signal, the air velocity is all within the loop, the valve in either extreme position directs the full flow out one face and in on the other. A position sensor on the valve was feedback to the servomotor system moving it and the flow vs position was plotted and served as a correction curve.
A problem being outdoors was there is no room gain and to reach the target at 3Hz from 2 meters required a fan source that had about 50 cu mtrs sec and needed 12 X 5hp fans to produce. The only solution to the back wave I could think of was simply to place the house at one exit and move the opposite phase far enough away. To allow the flow to expand uniformly instead of forming a free jet within the exit, a tapered section following the graph I found in a Thermodynamics text book dealing with jet and rocket engines.
To be clear, if this had been coupled into the old test house at one end, I am absolutely sure we could have brought it down with very little effort, we did damage even from outside just fooling around.
For the DIY’rs, work out what pressure is a safe target. Even 2 lb’sq foot is WAY WAY too much at very low frequencies if you wish to keep your home /drywall seams intact, multiply the pressure times the area of your ceiling for example.
The Matterhorn;
One of my last projects at the Servodrive spinoff was to rough out a design for something the military wanted. After I left, that was apparently built and tested. At the new company, I was approached to take another shot at whatever this was.
After some design work using a Tapped horn, I had estimated the entire thing could be could be built within / on a single shortie freight container which is a large size reduction and that it could be powered by only about 20-30Kw AND at a fraction of the price.
This estimate hit a nerve I guess because then they wanted to have the rights to anything invented in the process.
Mike said nope, we will keep the Tapped horn, build it on our dime and sell them to you, they said ok, they would need a dozen or so.
I did a sneaky thing, since this was going to run 24hr a day for days on end, I designed it to go down much lower than needed. This put a large impedance rise across the band that it would be used in and that minimized the I^2Xrdc heating, no more air chillers needed etc.
Anyway some testing was completed and it appeared to do what was required (I put some margin in the design) but shortly after the change of administration, the project was stopped, our contacts were not happy either.
I never did find out what this was for and while some kind of an acoustic toilet plunger for caves in a hot part of the world seemed logical, that doesn’t require low distortion or an ability to modulate frequency over a narrow band.
We did end getting back and keeping the Matterhorn and the Tapped horn patent was eventually granted.
Something goofey like that did make decent press which helped offset the effort. There has been discussion about “an entertaining use” for it although there damage to the grass moving at half time it is the concern.
Best,
Tom
Tom,
After seeing the massive staging set up and struck during half time, moving a container off and on seems fairly trivial- I'd like to see how they move all that stuff so fast more than the entertainment usually placed on the stage.
You mention the flow modulators made by LTV ling co. had air noise only 10-12 dB below the output level.
What was the air noise SPL of the Sonic Boom Simulator when playing "music" or sine waves compared to the "N" wave it was designed for?
Art
all,
the chest feel = disco punch is 60 - 120Hz, right - use some 18"s, push at 500 - 1000W per driver plus some boost at around 90Hz. Easy. But that has NOTHING to do with Infrasonic.
The infrasonic blower has been one of my ideas over years. But never built due to limited time resources. Simply use one blower to blow into the room through a pipe / hose. Use another hose to let the overpressure exit. No sucker or anything required. Then modulate the blower power by a kind of valve. That is it. The valve is the tricky part plus the noise from the fan. It is not true that you would then get only one half wave, you get BOTH half waves plus a slightly elevated DC room pressure that you will not notice since it is static DC. Like moving some floors by an elevator the pressure changes but soon after 1 minute you will be fully acclimatized. Do not worry about any THD or the like. worry about the fan noise reduction only and the valve mechanic design. that is the difficult part.
the chest feel = disco punch is 60 - 120Hz, right - use some 18"s, push at 500 - 1000W per driver plus some boost at around 90Hz. Easy. But that has NOTHING to do with Infrasonic.
The infrasonic blower has been one of my ideas over years. But never built due to limited time resources. Simply use one blower to blow into the room through a pipe / hose. Use another hose to let the overpressure exit. No sucker or anything required. Then modulate the blower power by a kind of valve. That is it. The valve is the tricky part plus the noise from the fan. It is not true that you would then get only one half wave, you get BOTH half waves plus a slightly elevated DC room pressure that you will not notice since it is static DC. Like moving some floors by an elevator the pressure changes but soon after 1 minute you will be fully acclimatized. Do not worry about any THD or the like. worry about the fan noise reduction only and the valve mechanic design. that is the difficult part.
Blackhawk sound
My understanding of the Thigpen rotary sub is it operates more like helicopter blades, using the change in pitch angle rather than any valving to create low frequency sounds.
It runs at constant RPM and has no valving at all, but the blades can rotate on their mounts in the hub changing the angle of the blade.
Can they do this over part of the rotation and move back to nominal position in one revolution like a helicopter blade, I don't know.
How would one DIY this, I don't know.
Anyway, I do not think that shop vacs and blowers with high speed valves could work the same way.(be as effective)
my 0.02
which may be very wrong
Dave
My understanding of the Thigpen rotary sub is it operates more like helicopter blades, using the change in pitch angle rather than any valving to create low frequency sounds.
It runs at constant RPM and has no valving at all, but the blades can rotate on their mounts in the hub changing the angle of the blade.
Can they do this over part of the rotation and move back to nominal position in one revolution like a helicopter blade, I don't know.
How would one DIY this, I don't know.
Anyway, I do not think that shop vacs and blowers with high speed valves could work the same way.(be as effective)
my 0.02
which may be very wrong
Dave
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Yes, this is how it works. They do use parts originally designed for helicopters.
http://news.softpedia.com/news/Are-...minent-Technology-TRW-17-Says-YES-66257.shtml
http://www.rotarywoofer.com/howitworks.htm
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