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Old 10th January 2003, 12:09 AM   #21
Wizard of Kelts
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The patent continues:

"Increasing the B1 product causes the peaks in response at the edge of the band (for which the tube length is an odd multiple of a quarter wavelength) to increase similar to the effect of increasing the ATCR. Thus, a low ATCR may be partially offset by using a higher B1 product. Furthermore, a higher B1 product decreases the sensitivity in midband where the length of the longer tube is a half wavelength. Preferably the B1 product is selected to help provide a more uniform response. For a given geometry of cone and tubes B1 is preferably selected such that the response at the frequency corresponding to .lambda./4 of the large tube is comparable to the response at the frequency corresponding to .lambda./2 of the large tube."

Now, I know this much-Bl product is related to Qts. That is to say, all other things being equal, a speaker with a higher Bl product has a lower Qts. Also, Qts is a measure of speaker damping, I believe, with the lower Qts having a higher damping.

To check if your Qts is too low, perhaps you should attach a resistor in series with the woofer. If the response smooths out, then a higher Qts woofer is in order. The response will come down because of the resistor in any event-it is the ratio of peaks to valleys that the higher Qts hopefully will help.

If the response does smooth out, then experiment around with resistors and putting a smaller tube inside the larger tube. You might need a different woofer.
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Old 10th January 2003, 12:36 AM   #22
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This illustration is something that might be used to fit a thinner tube into both sides of the Cannon.

Of course, if worse comes to worse, you can always cut some of the tube off, put a couple of vent holes in it, mount the woofer in front of one end, plug up the back end, and make it a reflex tube sub a la Hsu.
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Old 10th January 2003, 12:43 AM   #23
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Bl is the power of the motor in a speaker, and is a product of the number of turns in a voice coil, and the flux density of the magnetic field. If I remember correctly that is!
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Old 10th January 2003, 03:24 AM   #24
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Thinking about Drew's configuration with the Peerless XLS and the 18 foot long pipe.

If I understand the patent correctly, a twelve foot pipe would require a speaker with an Fs of 63 Hz.

An 18 foot pipe Sound Cannon would have a rear pipe that is three quarters as long as that-13.5 ft. Double that length is 27 ft. The frequency with a 27 ft wavelength is 41.6.

An 18 ft long Sound Cannon would therefore require a speaker with an Fs of 41.6 Hz or so, if I read the patent correctly.

Peerless makes four XLS models. Two 12 inchers, two 10 inchers.
The Fs for each is, respectively, 18 Ha, 18 Hz, 28 Hz-and 39.4 Hz.

The XLS speaker with the 39.4 Hz Fs would appear to be a good fit for an 18 ft long Sound Cannon. However, it is not a 12 incher, it is a 10 incher.

If Drew can find that article, I would wonder-was it perhaps the XLS 10 incher that was the basis for the Sound Cannon?

I am just speculating here.

PS: SoundEasy-BoxCad, a pay loudspeaker modeling program, can simulate a Sound Cannon enclosure. Now if anyone has that software, please jump right in this conversation.
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Old 10th January 2003, 09:10 PM   #25
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Default More questions

If I use sewer elbows to smoothly bend the tube around a corner, would that cause any problems?

Also, it looks as though you are only designing a subwoofer with a tube on one side of the woofer. What about the Wave Cannon, which has tubes over both sides? Or do you just compute the total length and put the driver a third of the way up the tube?

Does this increase SPL or diminish it?
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Old 11th January 2003, 12:53 AM   #26
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BAM:

No, I am computing a configuration for both sides with a tube. the tube in back is The Long Tube, and is 3 times the length of The Short Tube in front.

The wavelength of the resonant frequency of the driver whould be twice the length of the The Long Tube. Or, if you do the math, it should be 1.5 times the length of both tubes put together.

Both tubes put together should be about a quarter wavelength of the lowest frequency you want reproduced.

Put the driver about one quarter the way up the tube, not a third. At least, that is how Bose designed it-I don't what happens if you put the driver one third the way in.

Incidentally, some transmission line enclosures are designed for the driver to be one third of the way up the length of the tube. What would happen with this configuration-one tube in front, one in back-I don't know.

Even after reading the patent, we have lots of unanswered questions.
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Old 11th January 2003, 05:09 AM   #27
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I René,

I suppose you are from Montreal or somewhere near. Tu parles francais? I am sure you bought this speaker at Addison or Maddison. I have somewhat a good experience with Max pentivents speakers and the one you bought is meant for a small enlcosure. You should have received a spec sheet with the speaker. There are recommend enlcosure volumes and everything you need to know on the speaker. And for this speaker specificaly I don't think you will get deep and loud bass. Not powerful enough.
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Old 11th January 2003, 10:00 PM   #28
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From memory, originally the magazine article suggested using one of the Response brand drivers from Jaycar in Australia.

I don't have the article, it was one I thumbed through in the newsstand. (guilty as charged!) Because I was interested I kept notes of overall pipe length, distance ratios etc.

General reports on the response units are that although they function ok, they aren't the last word in driver quality.

The 8 ohm Peerless 10 inch xls has a better reputation, higher power handling, lower fs etc, etc,etc and a much better built structure if the 12 inch xls I've seen is anything to go by.

________________________________________

Re putting the driver one third of the way along the tube...
the back wave from the driver is opposite in phase to the front wave.

draw a sine wave with a negative peak starting at one side of the driver and have it do 1/2 a wavelength so it produces a positive peak level with the end of the short tube
Now start off a positive peak sine wave of the same frequency in the long tube but here it has a full wavelength's distance to propagate. It'll end up at the positive peak at the end of the tube.

Now sum positive peak from the rear of the short tube with the positive peak from the rear of the long tube...

BOOM!!!

Of course, using a 6m pipe then if you wanted to take someone's teeth out at 85hz it could be fun. And if you had the space for a 24m pipe....

In a nutshell, placing the driver a third of the way along causes mighty big peaks and troughs in the response.

________________________________________

As far as using smooth curves to bend the pipe I see no reason why not. Dr Amar and friends absolutely punish the smoothness of the path in things like the wave radio. (likely to the detriment of the sound due to backwaves IMHO) A straight pipe will be better.

Drew
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Old 12th January 2003, 05:36 AM   #29
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Default My idea for a Wave Cannon Project

Say I wanted to build a Wave Cannon using the MCM 55-1854 4" aluminum woofer. (this woofer has a nice low frequency range - all the way down to 50 Hz.)

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.)

I will build this during the summer I think, or next Christmas, powered by a 15W/channel (@ 4ohms) amplifier kit from Parts Express. I could make the wave cannons to hang on the underside of my loft in my dorm room and then make little satellites to be where they can point right at me for music in bed.
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Old 12th January 2003, 05:47 AM   #30
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BAM:


Considering the various things that are unknown here, I would suggest getting an inexpensive 4" and testing. I will do the math for the speaker you specified tomorrow-getting a little late for involved calculations tonight.

I would think the best bet is to find someone who has bought the SoundEasy program, which calculates these things. They even mention the Sound Cannon in the promotional literature.
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