Acoustic wave canon
Does any body have an idea how to build a bass canon (like the bose)
We could explain the theory to you, but the big question here is:
>>> Why? <<<
If you want a tubular subwoofer with a lot of output, try the SVS line of subwoofers.
Well-known in the Home Theater market for providing the best bass for the best price.
I'll admit that I don't know the theory behind the Wave Cannon but I do know that it takes a lot of equalization for it to give decent output. This means operating the driver closer to its maximum tolerances than usual.
The SVS subs, on the other hand, require no EQ and use no artificial bass boost, but still produce large amounts of earthmoving bass. They also are good at integrating, and they are known to be very "musical" as far as subs in their class are concerned.
Or you could go to the far reaches of extreme base and build this little item.
There was once an article in Speaker Builder dealing with a waveguide subwoofer.
There was also an article in JAES about modeling of horns etc using cylindrical and conical sections where there is an example using the same topology that the B**e device uses.
I will try to find the articles.
This thingie is actually something like the TL equivalent to a double-chamber bass reflex enclosure. The ratio of the tube lengts is 1:3.
I think Mr. Bose has a strong affinity for using heavily resonant devices to get strong bass response cheaply - with questionable quality IMHO.
As far as I can recall the Bose cannon can be approximated by placing a long stroke driver (Peerless 8 ohm XLS 10 inch perhaps would be good) 1/4 of the way down a 6m long pipe.
I'll need to crunch the graphs again to look at the predicted response but from memory it was fairly flat (peaks and troughs less than +/-2dB ) from around 18Hz up to about 90.
Not sure what all this talk of eq is, my predictions based on phase summations of the outputs didn't seem to indicate that it'd be that bad (as resonant pipes go).
The cannon was developed more as a means of getting significant LF sound pressure into theatres more than as a high fidelity beast I think but I'm keen to have a go at it myself.
I"ll be back in touch once I've crunched some numbers.
Couple of Bose patents. First, what looks like his latest version of his radio.
Note the patent number if you want details at the US Patent Office website. Don't forget to download one of their image viewers. IE 5 will drive you nuts trying to download one of them.
21A is where the speaker goes. 24 is the polyester stuffing the Line is stuffed with. I think 31 is where the other speaker is mounted, and the same thing is repeated beneath this drawing-two levels, as it were.
Now this might be for the thing you might think is the "Cannon". From the patent itself:
"United States Patent 4,628,528
Bose , et al. December 9, 1986
Pressure wave transducing
A loudspeaker driver has its front surface adjacent one end of a low loss acoustic waveguide and its rear surface adjacent to one end of a second acoustic waveguide that is one third the length of the first. The other openings of the waveguides face air and couple acoustical energy substantially uniformly over a relatively broad range of frequencies extenting into the bass frequency region. An equalizer includes a notch filter so that the frequency response of the equalizer below a bass cutoff frequency is sufficiently low to prevent audible distortion."
I think the long tube is between 1/4 and 1/2 the wavelength of the F3 frequency aimed for, and the short tube behind is 1/3 the length of the long tube. It might not be clear from ther illustration, but both ends are open to the air.
Here is another page from the patent. Again, note the patent number. There does indeed seem to be an equalizer involved, which schematic is included below.
Hope this helps.
Incidentally, in no way does the reproduction of these pictures mean that you can actually legally build this. You should check with Bose Corporation for legal permission. I include excerpts from this patent only for informational purposes-for you to gain some idea of how these things might work.
Actually, as a private individual and not for resale I'm fairly sure that there's nothing to stop you building whatever you want.
There was an article in a pro audio magazine (Connections I think it was) in about 1995 that dealt with the phase/wavelength theory behind the cannon (worked out independantly by them with no input from Bose based upon the length of the original tube) and provided plans for a DIY version.
Re eq, it looks like it's only a bandpass cct to stop really low end from overdriving the unit and a lowpass to tailor it into a system. Pretty much the same as any sub amp I've ever seen. Nothing new there.
Personally I think the long straight pipe is better than the labyrinthine version and the wave radio may well be stretching the physics to near breaking point. IMO Bose have always been pretty heavy on the EQ to try and get the response that is quoted. (Look at the output from a 901 equaliser) (Eeeuurrkk!)
A driver with pipes on either side with one that's 3 times longer than the other corresponds with my call of earlier that you put the driver 1/4 of the way along the 6m tube. Just a different way of saying the same thing. 3/4 is 3 times as long as 1/4.
The filter shown is of course a very ordinary Sallen-Key 2nd order highpass filter ( i.e. for subsonic protection).
If one wants to build such a device he really doesn't need to ask Mr. B**e if he is allowed to do so.
And there are more elegant foldings possible than Mr B@$* suggests (why do I never get this Name posted correctly !?) in his patents.
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