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Old 12th January 2003, 06:06 AM   #31
Wizard of Kelts
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The SoundEasy/BoxCAD suite costs $250, so it would be advisable to find someone with the program to help you out on any project that runs into money.

If there were any equations, somebody with more math ability than myself could use Excel or some other spreadsheet to graph things for free. But the patent does not appear to contain equations. I'll re-check, though.

Incidentally, from the promotional literature that Bose itself supplies, I see no evidence that the Sound Cannon, despite it's provacative name, provides any more bass output than a bass reflex enclosure one half it's volume.
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Old 13th January 2003, 01:39 AM   #32
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Default Re: My idea for a Wave Cannon Project

Quote:
Originally posted by BAM
Say I wanted to build a Wave Cannon using the MCM 55-1854 4" aluminum woofer.....

For an F3 of 56 Hz (above the Fs of 54.1 Hz), how long should I make the 2.5" pipe?
(What I'm asking is, could someone calculate a 1/4-wave for me, or tell me how to calculate it for myself? We haven't covered sound in my physics class yet.)
Sound travels at the rate of 770 miles per hour or so. Slightly slower above sea level. For planes, Mach 1 is the speed of sound, Mach 2 is twice the speed of sound, etc. I believe Mach was the fellow who figured out the speed of sound.

Anyhow, 770 miles per hour figures into 13,500 inches per second. So the wavelength of 1 Hertz is 13,500 inches.

To find the wavelength of any frequency, simply divide 13,500 by that frequency. So the wavelength of 54 Hz is (13,500/54), which is 250 inches.

That is how we find the wavelength of any frequency. However, here we have a speaker with an Fs of 54 and want to find what size tube we need for it. I shall go by the patent-I never built one of these things.
Quote:
From the Bose patent
The free air resonant frequency of the loudspeaker driver may be chosen to be that at which the length of the longer of the tubes is a half wavelength..
250 inches is the wavelength of of 54 Hz, the resonant frequency of our speaker. That is supposed to be twice the wavelength of The Long Tube. So The Long Tube is supposed to be 125 inches.

However, The Long Tube is only 75% of the total length of the enclosure. And the total length of the enclosure is 1/4 wavelength of the lowest frequency.

So, we divide 125" by .75, and we find the total length of the tube is 166.66 inches. That is the length of a quarter wavelength of the lowest frequency we are trying to reproduce. So, we multiply the tube length by 4 to find the wavelength of F3. 166.66 inches X 4 = 666.6 inches-the wavelength of F3.

To find F3, we simply divide 13,500 inches by 666.6 inches, and we get 20.25 Hz. That should be the F3 of the speaker in the Cannon enclosure.

Don't forget, the length of the total enclosure is 166.6 inches, or 13.9 feet long. Are you sure you will be able to fit this into your dorm room?

Again, I am just going by what the patent says, or what my interpretation of the patent is.
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Old 13th January 2003, 01:56 AM   #33
Wizard of Kelts
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If you are making the tubes a diameter of 2.5", then the circular area of the tubes is 4.9 sq in, and the volume is 816 cubic in, or 47% of a cubic foot. Not bad.

That is if it works. The patent seems to give us guidelines, but not formulas like the ported box uses.

There is the further issue of the ability of a 4" speaker to procduce hearable bass at 20 Hz. I doubt it-the speaker simply cannot move sufficient amount of air, even enhanced by the tube. A ported box enhance the air moving capability of a speaker by four. Even is the Sound Cannon is twice as great as the ported box, you will still fall woefully short.

In it's Sound Cannon going down to 25 Hz, Bose seems to think a 12" woofer with a half inch excursion is necessary. That speaker moves 43 cubic inches of air. Even if your 4" has an excursion of .25"-which it probably does not-you are only moving 1.75 cubic inches of air. And you are trying to go lower than the Bose Cannon!

Why not aim for a Sound Cannon going down to 50 Hz? The tubes will only be 40% as long, and you have a much better chance of getting hearable bass out of it.
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Old 14th January 2003, 12:54 AM   #34
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Oops
I think I may have sent the wrong signal.

I didn't want to go down to 25 Hz. I just wanted it to go down to 50 Hz.
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Old 14th January 2003, 06:48 AM   #35
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I finally found the SB articles dealing with this device.

It was back in 1995 (thats why it took me so long to find it: I had to fight my way up to the attic).
It was in issues 6 (page 8) and 7 (page 18), was written by G.R. Koonce and titeled "The waveguide path to deep bass". Unfortunately there is a third part as well, which might be the most interesting of them all, and which I don't own (it was very hard to find "Speaker Builder" in central Europe, the only European place I've seen it so far was in the newspaper department of Tower Records in London).

Regards

Charles
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Old 14th January 2003, 07:41 AM   #36
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Phase Accurate:

Well, we certainly would appreciate whatever info comes from the first two parts of the article. Rght now, things are a little sketchy, just going by the patent.
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Old 14th January 2003, 07:54 AM   #37
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BAM:

The point of my previous post was that your MCM speaker with the 54 Hz Fs wouldn't be able to be used in a Cannon going down to only 50 Hz.

I am just going by my interpretation of what the patent says. I could well be mistaken, but here goes.

We want to know what the Fs of the speaker would be if it was to be used in a Sound Cannon that has an F3 of 50 Hz.

The tubes, both front and back added together, should be a quarter wavelength of 50 Hz. The wavelength of 50 Hz is (13,500/50) = 270 inches. So a quarter of that equals 67.5 inches. The two tubes together should be 67.5 inches long.

The Long Tube should be 3/4 of that length. So The Long Tube should be 50.6 inches long-let us round off to 50 inches.

The wavelength of the resonant frequency of the speaker should be twice the length of The Long Tube. That would make it 100 inches.

13, 500 inches divided by 100 inches yields a frequency of 135 Hz. So to build the enclosure you are speaking of, find a speaker with an Fs of 135 Hz, and have the tube behind it be 50 inches long, and the tube in front of it be 17.5 inches long.

Again, this is just going by the patent, as best as I can understand it.
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Old 14th January 2003, 07:15 PM   #38
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So I could build the 13-foot line but not expect the greatest results? What would become of that little driver if I put it in and asked it to go down to as far as it would go? Would it tear itself apart trying to do 20Hz or would it just be a long line that is still only any good down to 50 Hz?
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Old 14th January 2003, 10:18 PM   #39
Wizard of Kelts
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Quote:
Originally posted by BAM
So I could build the 13-foot line but not expect the greatest results?

What would become of that little driver if I put it in and asked it to go down to as far as it would go?

Would it tear itself apart trying to do 20Hz or would it just be a long line that is still only any good down to 50 Hz?
Don't know. My guess is that things would be no worse than if you put it in a sealed box or ported enclosure that would allow it to go down to 20 Hz. You would be building a long line that would not get used to it's full potential, but if that is what you want to do, go ahead. It's only going to be 2.5" diameter PVC pipe anyway, so I guess it would be relatively easy to snake around the room.

For what it is worth, I believe a major Japanese audio maker once made a five inch speaker in a ported container about a third of a cubic foot, and it was flat down to 30 Hz. Nobody ever reported anything about the speaker tearing itself apart.
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Old 21st January 2003, 09:11 PM   #40
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http://www.geocities.com/kreskovs/basscannon.html

Found this study done by John K's website. Seems to be what your looking for.
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