Pulsejet Sound Clip on NPR

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larry cottrill
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Pulsejet Sound Clip on NPR

Post by larry cottrill » Wed Oct 03, 2007 4:42 pm

If you're in the US and are somewhere close to an NPR (National Public Radio) station, you'll be able to hear a short (about 2 minutes) blurb from yours truly at 4:45 PM EDT today, wherein I try to introde the sound of the valveless pulsejet to the listening public. Ha. This is presented as one of their "Sound Clips" mini-features, which are "interesting" sounds recorded by listeners. I have no idea what the final version will be like, as it will be heavily edited down from the ponderous 7 or 8 minute "feature" I recorded.

Sorry for the short notice, but I only learned this morning that they were going ahead with this. I can only hope that the edited version isn't totally stupid. The engine sound itself is from the Lady Anne Boleyn demo video I shot in Jim Russell's studio / workshop. You can find a station near you by going to www.npr.org and clicking on the "STATIONS" link. Then enter your ZIP code in the search window provided.

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APOLOGIES !

Post by larry cottrill » Wed Oct 03, 2007 7:24 pm

Sorry, guys: The email I got from NPR saying they were going to run this “today” came in at about 3:15 YESTERDAY – about half an hour before they were going to run it! I mistakenly thought it had arrived this morning. If you want to hear the clip, here’s a link to the streaming audio; there will be a brief NPR promo message before it plays):

http://www.npr.org/templates/story/stor ... d=14927042

I apologize for the inconvenience caused by my misunderstanding.

Note the use of the word 'Impractical' in the title - needless to say, that is THEIR opinion, not mine! I guess I should have included some gab about what our engines can actually be used for. Aaaargh ...


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Post by metiz » Wed Oct 03, 2007 8:11 pm

haha nice one Larry!
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Larry's speach

Post by hagent » Wed Oct 03, 2007 8:31 pm

That was great Larry!

Nice speach.

Did you get to measure your engine for power and TSFC yet?

Cheers,
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Post by PyroJoe » Wed Oct 03, 2007 9:01 pm

Excellent narrative, enjoyed every second of that hummin' in the background.

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Post by Jim Berquist » Wed Oct 03, 2007 10:51 pm

Great Stuff from you Larry! To bad NPR had to hit it with a wet blanket!

I Liston to them all the time! I don't agree with them more then not!
WHAT TO FRAP, IT WORKED![url=callto://james.a.berquist]Image[/url]

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All Things Considered

Post by Mark » Thu Oct 04, 2007 2:03 am

That was entertaining Larry. A+
Now get to working on something practical, like perfecting a pulsejet powdermilk biscuit, in your Film Noir hat and Guys' Shoes.
You could have thrown in some humorous disinformation. ha
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Post by Jim Berquist » Thu Oct 04, 2007 2:20 am

That's it Mark!!!!!

Powdered Milk Biscuit cooker to be used in Africa! It could also double as a heat source for thermocouples and produce electricity. Hell They would hardily hear it over the gun fire. Good for Goat Ka-Bobs too!



I Know, Not Right!!!!!
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A relationship with a sound

Post by Mark » Thu Oct 04, 2007 10:01 pm

I was listening to other sound bites and came across this simple pipe and brick sound. Not that it was all that astounding, (ha), but having a meter long 25 mm diameter quartz pipe right next to my computer I decided to hold it straight up and down with two fingers and tap it with the rubber coated handle of a pair of pliers.
At certain distances, the sound was dampened in the extreme, almost no resonance, at around 25 cm from the top, I got not only a nice ringing sound but also some kind of overtone more of a high pitched reverberation. Holding it right in the middle, again with just two fingers also produces some of the loudest resonance.
Holding it at the very top makes no sound to speak of. I wonder if a pulsejet would be any louder if you mounted it/held it in certain positions or how important it would be to minimize vibration on your aircraft. Some of my tappings didn't make a lot of sound proportionately/audibly, but did vibrate the quartz pipe and my fingers impressively, so much so that I thought about how a crystal glass finally shatters from "too much sound" .
And what next Larry, Wired Magazine, NPR, ...???
http://www.npr.org/templates/story/stor ... Id=8959480
My quartz tubing, I bought a box of it. This is an eBay photo from the seller.
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larry cottrill
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Re: A relationship with a sound

Post by larry cottrill » Fri Oct 05, 2007 11:29 am

Mark wrote:I wonder if a pulsejet would be any louder if you mounted it/held it in certain positions or how important it would be to minimize vibration on your aircraft. Some of my tappings didn't make a lot of sound proportionately/audibly, but did vibrate the quartz pipe and my fingers impressively, so much so that I thought about how a crystal glass finally shatters from "too much sound".
Mark, they're two different modes of "ringing". The sound you're getting from your tubes is chiming - vibration of the solid mass (not the air inside), like the sound of door chimes, wind chimes, even "vibes". The ideal point of support is at the 25 percent point, because that's the "nodal point" of any piece that is of uniform cross-section over its whole length. I suppose on some pulsejets the chiming vibration of the shell might have some part in the sound, but it must be a very minor factor due to the high temperature (lack of hardness) in the engine shell.

Perhaps Eric or someone might like to disagree, based on experience from the field. I have been wrong before ...

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Sound

Post by Mark » Fri Oct 05, 2007 11:15 pm

"I wonder if a pulsejet would be any louder if you mounted it/held it in certain positions or how important it would be to minimize vibration on your aircraft." (Me)

You are right Larry about the percentage/contribution of sound the quartz tube chiming would make, it ain't no Liberty Bell. ha
Still, it really gets to vibrating and makes a high pitch. In a way you wouldn't think 1/8 inch thick quartz glass walled tubing could be so "flexible" for want of a better word, like one of the prongs of a tuning fork.
I remember the demonstration of how quiet a string can be when plucked, but if provided a sounding board to enhance the power it is night and day. Maybe we should be attaching our pulsejets to some kind of sounding board, as if they aren't loud enough already. New musical instrument anyone? ha
Anyway, I just thought it interesting how holding the quartz tubing in certain spots completely destroys resonance, just as if you seemingly struck a brick instead of a piece of quartz tubing. On the other hand, the tubing can really make a high pitched ringing, almost sharp to the ears. Thud vs. "howler tube" chiming I guess.
I wonder if the resonance of the pipe walls though amplifies the combustion, passing sound waves up and down tangentially into the criss-cross/back and forth flowing of gases, energizing them? Maybe part of the "stored sound" from the metal pipe excites the fuel/air mixing/burning. I recall seeing the vibration of the fuel particles jiggled out of a metering jet, so that if you dampened the vibration, the atomization of fuel might not be as great and thus the sound output/performance affected indirectly.
To be sure, most of the sound is originating out the tail end and intake and not off to the side, through the walls, I will agree.


http://www.epd.gov.hk/epd/english/envir ... sys_4.html

"A lot of people believe that the characteristic sound of the flute is also affected by the material from which the instrument is made. For instance, instruments made of wood are usually less bright than metal instruments. Different metals are also thought to influence the tone. But this is debatable and has not been proved scientifically."
http://www.knowyourraga.com/bansuri/acoustics.php
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Audio Frequency Radio Waves!

Post by larry cottrill » Mon Oct 08, 2007 12:07 pm

Another NPR SoundClip - radio waves recorded at the South Pole:

http://www.npr.org/templates/story/stor ... d=14300626

Pay close attention to this physicist's description of what happens to the radio signals (from lightning) and the mechanism needed to capture them (almost nothing, just an antenna and an audio amplifier !!!)- now THAT is amazing. This IS NOT an audio modulation of a radio signal (like AM, FM or PM), it IS simply a radio signal propagated at a variety of actual audio frequencies, which are stretched out over time. Unbelievable.

A lot can happen to an electromagnetic wave on its way from here to there. Everybody "knows" that more distant galaxies are seen red shifted far more than near ones because they are moving away faster. But nobody actually knows any such thing - it's just the easiest model to visualize that makes physical sense. Just like it makes sense that you would need a radio receiver to hear lightning thousands of miles away.

One time I helped a friend of mine set up a homebuilt FM antenna, made from plans in a magazine - kind of a big vertical array, mostly made of wood, with copper tubing elements. When we got it up there, I suggested on a lark that we ought to hook the indoor end of the twinlead up to his nice little Heathkit oscilloscope "to see if we can detect anything". Based on my "vast experience" in ham radio, I thought all we would see was a tiny blurry smear stretched across the scope face. Instead, it came alive with gyrating, pulsing waveforms, as transitory as lightning but clearly distinguishable. I wouldn't have believed it till I saw it. And with the sensitivity of that big array, the signals were many times greater amplitude than what I would have imagined. (He got great FM reception, too, though it was highly directional, of course.)

I figured out one time a simple way to make a powerful loop antenna, though for some reason I never got around to trying it. What you would do is make a 6- to 8-foot diameter loop of that unshielded multi-wire telephone cable (or any color-coded multi-wire cable, unshielded). At the bottom gap, where the two ends come close together, you would choose an insulation color at one end and solder the wire to a DIFFERENT color at the other end. For example, if the wires were single colors, you might join:
- Black to Brown
- Brown to Red
- Red to Orange
- Orange to Yellow
- Yellow to Green
- Green to Blue
- Blue to Violet
across the gap. This would leave you with an unused Black lead at one side of the gap and an unused Violet lead at the other (to connect your twin-lead to), with eight complete turns of wire going clear around (just a flat, giant inductance coil). Note that some telephone cable has 30 or 40 wires with various color stripe combinations, so your loop could be MUCH more powerful than my simple 8-color example! Such a loop is highly directional, naturally - you can use it as a 'direction finder' to locate transmitting stations around your area. I doubt that it would perform well at high frequencies like TV or FM radio, but it would certainly be a cheap and simple radio toy to play around with. Who knows what 'whistlers' you could pick up - ha!

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Re: Sound

Post by larry cottrill » Tue Oct 09, 2007 4:09 pm

Mark wrote:"A lot of people believe that the characteristic sound of the flute is also affected by the material from which the instrument is made. For instance, instruments made of wood are usually less bright than metal instruments. Different metals are also thought to influence the tone. But this is debatable and has not been proved scientifically."
http://www.knowyourraga.com/bansuri/acoustics.php
Mark -

There is actually a simple explanation for this. Assume that you have a metal flute and a wooden one with exactly the same internal dimensions and hole size, etc. The acoustics of air in the pipe will be virtually identical. What you'll find, however, is that the chiming frequency of the metal flute is much higher than that of the wooden flute. So, I think that "chiming" of the metal instrument (even when held in the hands) is excited by the higher frequencies (and higher harmonics of the low ones) and augments these frequencies. A simple experiment would verify this: The metal flute could be gripped gorilla-like while playing it, deadening its chiming ability (instead of the rather delicate way the instrument is normally held) - or some deadening material could be wrapped around it temporarily. This should prove whether or not the "bright" aspect of the sound comes from the vibration of the metal itself.

Note that the most ancient organ pipe design is a long wooden box. Even when pipes are made of metal, it is usually something pretty soft (sheet tin) to prevent the pipe "ringing". It's possible that some "bright" voices (e.g. trumpet) are or have been made from harder metal, but I don't know that - just speculating that it might have been tried. Shaping the voices of organ pipes is one of those arcane design skills that barely manages to survive in the modern world, like Samurai sword making. I have always thought that hand-crafting a set of organ pipes would be great fun - I have seen some really beautiful tin ones, just recently.

L Cottrill

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