Wait...I've got it!
Synchronous-Emission Double-Ended Transmission Loudspeaker
The emission of sound from each end of the tube occurs at the same time. ("Synchronous")
The tube has two ends. ("Double-Ended")
It functions more or less as a transmission line. I need to find something different to call it, though, because TL guys may consider it to be an affront to transmission line loudspeaker theory. I don't want to call it Waveguide, because Bose already does that, unless you guys think it's appropriate to call it a waveguide.
- Or -
Output-Summing Dual Transmission Loudspeaker (OSDT?)
Synchronous-Emission Double-Ended Transmission Loudspeaker
The emission of sound from each end of the tube occurs at the same time. ("Synchronous")
The tube has two ends. ("Double-Ended")
It functions more or less as a transmission line. I need to find something different to call it, though, because TL guys may consider it to be an affront to transmission line loudspeaker theory. I don't want to call it Waveguide, because Bose already does that, unless you guys think it's appropriate to call it a waveguide.
- Or -
Output-Summing Dual Transmission Loudspeaker (OSDT?)
Ok, I can't hold it in anymore. I want to build one of these things. I have an orphaned (not one of a pair) RadioShack/Optimus 4" driver that has a Fs of 85 Hz, a Qts of 0.62, and a Vas of 0.10 ft^3. It has a decent mechanical excursion limit, and a nice big magnet. Would it be suitable for a waveguide system like the one pictured in Post #7? Of course, the dimensions would have to be modified for a driver like the one I have. I have some scrap MDF and speaker wire, and I might like building this. I could use it to add some bass to a pair of sealed-box 4" full-range drivers I have. Here's my plan: An OfficeMax store near my house sells cheap three-piece computer speaker systems that have a decent amount of amplification. I could buy one, and then pilfer all useful parts from it, and steal the amplifier from that and then use it to power my creation.
"I use a spacing of 1/4 the total tube length -- as does the Bose Acoustic Wave Music System"
The patent says:
"The separation between openings 28 and 31 is of the order of half the length of the shorter tube between the front of driver 22 and opening 31."
which is 1/8th the total tube length. In the SUMMARY OF THE INVENTION they claim:
"A preferred separation is within the range of one-eighth to one times the length of the path for pressure waves "
This is simply being expedient on their part in making the claim as broad as possible. It covers the Acoustic Wave at 1/8 exit spacing and the Sound Cannon at 1W exit spacing.
The optimum spacing for the smoothest fequency response and the highest broadband gain is 1/2W exit spacing.
"For those of us too dumb to know what the hell you're talking about, could you elaborate?;-)"
I ran a Yahoo search on 'half square antenna' (what a radical idea!) and came up with:
http://www.qsl.net/ka1ddb/20meterhalfsquaredwg.jpg
http://www.cebik.com/hs.html
http://kc5jk.tripod.com//sitebuildercontent/sitebuilderpictures/half-sq-ant.gif
"To get DX angle radiation and gain without the tower and the Yagi, use a HalfSquare. What's a HalfSquare? A HalfSquare is a simple, light, unobtrusive and inexpensive DX gain antenna that you can hang almost anywhere you can put a dipole.
How is it made? Start with a wavelength of wire supported from its ends, and feed it at a point one quarter wavelength from an end. In this form the antenna is called a long wire. It has a decibel or so of gain off its ends and its radiation angle is a little lower than a dipole or Yagi at the same height, but it's no killer DX antenna yet.
Move the support insulators in a quarter wave from each end and let the tails hang down. Bingo! What you have now is a HalfSquare-two quarter wave verticals separated by a half wave horizontal phasing section. By this simple trick you have pushed the takeoff angle down into the serious DX range and you suddenly have nearly an S-unit of broadside gain to boot. As a bonus the feed-point impedance drops to 50 +."
Notice the author mentions that the performance really increases when you have the exits 1/2W apart?
As noted in the Bose patent virtually any spacing from 1/8W (boom box) to 1W (straight cannon) will work, it will just require more equalization to smooth out, and be less efficent.
Assuming a loss-less tube: "providing a nominal 6 db increase in sensitivity compared to the same driver in the infinite baffle. "
The patent says:
"The separation between openings 28 and 31 is of the order of half the length of the shorter tube between the front of driver 22 and opening 31."
which is 1/8th the total tube length. In the SUMMARY OF THE INVENTION they claim:
"A preferred separation is within the range of one-eighth to one times the length of the path for pressure waves "
This is simply being expedient on their part in making the claim as broad as possible. It covers the Acoustic Wave at 1/8 exit spacing and the Sound Cannon at 1W exit spacing.
The optimum spacing for the smoothest fequency response and the highest broadband gain is 1/2W exit spacing.
"For those of us too dumb to know what the hell you're talking about, could you elaborate?;-)"
I ran a Yahoo search on 'half square antenna' (what a radical idea!) and came up with:
http://www.qsl.net/ka1ddb/20meterhalfsquaredwg.jpg
http://www.cebik.com/hs.html
http://kc5jk.tripod.com//sitebuildercontent/sitebuilderpictures/half-sq-ant.gif
"To get DX angle radiation and gain without the tower and the Yagi, use a HalfSquare. What's a HalfSquare? A HalfSquare is a simple, light, unobtrusive and inexpensive DX gain antenna that you can hang almost anywhere you can put a dipole.
How is it made? Start with a wavelength of wire supported from its ends, and feed it at a point one quarter wavelength from an end. In this form the antenna is called a long wire. It has a decibel or so of gain off its ends and its radiation angle is a little lower than a dipole or Yagi at the same height, but it's no killer DX antenna yet.
Move the support insulators in a quarter wave from each end and let the tails hang down. Bingo! What you have now is a HalfSquare-two quarter wave verticals separated by a half wave horizontal phasing section. By this simple trick you have pushed the takeoff angle down into the serious DX range and you suddenly have nearly an S-unit of broadside gain to boot. As a bonus the feed-point impedance drops to 50 +."
Notice the author mentions that the performance really increases when you have the exits 1/2W apart?
As noted in the Bose patent virtually any spacing from 1/8W (boom box) to 1W (straight cannon) will work, it will just require more equalization to smooth out, and be less efficent.
Assuming a loss-less tube: "providing a nominal 6 db increase in sensitivity compared to the same driver in the infinite baffle. "
"Ok, I can't hold it in anymore. I want to build one of these things. I have an orphaned (not one of a pair) RadioShack/Optimus 4" driver that has a Fs of 85 Hz, a Qts of 0.62, and a Vas of 0.10 ft^3. It has a decent mechanical excursion limit, and a nice big magnet. Would it be suitable for a waveguide system like the one pictured in Post #7? "
Post #7 just shows a 1/4W trans line. The Sound Cannon would have about 6dB more output and less cone motion, very important where small drivers are used.
For a computer desk system it is quite easy. Use a 20" long by 3" dia pvc pipe in front of the cone. Make a little box for the drver and pipes to fit into. The box hold the driver and acts like a 90* elbow. The box would be at the back left (or right) corner of the desk. A second pipe 40" long goes across the back of the desk into a 90* elbow, and then to the front through another 20" pipe. The whole thing can be hung to the underside of the desktop with a couple of strap hangers, or you could hang it on the wall.
Post #7 just shows a 1/4W trans line. The Sound Cannon would have about 6dB more output and less cone motion, very important where small drivers are used.
For a computer desk system it is quite easy. Use a 20" long by 3" dia pvc pipe in front of the cone. Make a little box for the drver and pipes to fit into. The box hold the driver and acts like a 90* elbow. The box would be at the back left (or right) corner of the desk. A second pipe 40" long goes across the back of the desk into a 90* elbow, and then to the front through another 20" pipe. The whole thing can be hung to the underside of the desktop with a couple of strap hangers, or you could hang it on the wall.
Yup...the Bose WC is essentially a 1/4WL TL tuned to 35Hz. (8 feet) with a shorter tube of a length that is half of the "real" TL part...4 feet. So, 8 feet+4 feet=12 feet. It's very simple. Use that method to determine tube lengths, an Sd of about the driver's and use a HP@20Hz or so to limit driver excursion and you've got a Bose WC. Of course, you could apply EQ too, but you shouldn't need to with a properly designed loudspeaker.
"Assuming a loss-less tube: "providing a nominal 6 db increase in sensitivity compared to the same driver in the infinite baffle. "
Is this a quote frome the patent? A plain ol' TL should provide at least that much output, shouldn't it? And I thought BRs where s'posed to be IB + 12dB @ LF.
Can the pipe be tuned higher than Fs? How 'bout lower? Any TL gurus (guri? gurisi? gurotsi? whatever) out there?
Considering room effects, maybe it doesn't matter if the FR goes all to hell (or (more to the point) LA skyline, for that matter) so long as there is increased extension...
Is this a quote frome the patent? A plain ol' TL should provide at least that much output, shouldn't it? And I thought BRs where s'posed to be IB + 12dB @ LF.
Can the pipe be tuned higher than Fs? How 'bout lower? Any TL gurus (guri? gurisi? gurotsi? whatever) out there?
Considering room effects, maybe it doesn't matter if the FR goes all to hell (or (more to the point) LA skyline, for that matter) so long as there is increased extension...
fortyquid:
"So could I just make a pipe 1/4W of my target F3, higher than the native Fs of the driver would dictate?"
That is what I did. My driver has an Fs of 28Hz indicating a 1/4W tuning of 14Hz.
I used a more conservative tuning of 19Hz to lessen the chance of a "hole" where the subs crossover to the mains at 80Hz.
Even at 19Hz tuning, the short pipe is tuned to 56Hz -- pretty low for an 80Hz crossover.
I wouldn't go much below 20Hz tuning.
With room gain you'll probably be wasting power on subsonics.
"So could I just make a pipe 1/4W of my target F3, higher than the native Fs of the driver would dictate?"
That is what I did. My driver has an Fs of 28Hz indicating a 1/4W tuning of 14Hz.
I used a more conservative tuning of 19Hz to lessen the chance of a "hole" where the subs crossover to the mains at 80Hz.
Even at 19Hz tuning, the short pipe is tuned to 56Hz -- pretty low for an 80Hz crossover.
I wouldn't go much below 20Hz tuning.
With room gain you'll probably be wasting power on subsonics.
Boseo:
"Yup...the Bose WC is essentially a 1/4WL TL tuned to 35Hz. (8 feet) with a shorter tube of a length that is half of the "real" TL part...4 feet. So, 8 feet+4 feet=12 feet. It's very simple. Use that method to determine tube lengths, an Sd of about the driver's and use a HP@20Hz or so to limit driver excursion and you've got a Bose WC. Of course, you could apply EQ too, but you shouldn't need to with a properly designed loudspeaker"
Actually it is 9' (31Hz tuning) and 3' (94Hz tuning).
"Yup...the Bose WC is essentially a 1/4WL TL tuned to 35Hz. (8 feet) with a shorter tube of a length that is half of the "real" TL part...4 feet. So, 8 feet+4 feet=12 feet. It's very simple. Use that method to determine tube lengths, an Sd of about the driver's and use a HP@20Hz or so to limit driver excursion and you've got a Bose WC. Of course, you could apply EQ too, but you shouldn't need to with a properly designed loudspeaker"
Actually it is 9' (31Hz tuning) and 3' (94Hz tuning).
DJK:
"Ok, I can't hold it in anymore. I want to build one of these things...."
1. Buy a 12' piece of 3" pvc pipe, and two 3" "closet" collars
2. Buy 4 x 2" bolts and nuts
3. Cut the long tube to 78" (42 Hz tuning)
4. Cut the short tube to 25"
5. Wire the 4" driver and sandwHich it between the two collars
6. Bolt the collars together with 2" bolts and nuts.
7. Plug the tubes into the collars
8. Snake wire out of short tube
WATCHOUT!
Do not overdrive or you will get nasty slapback (CLACK CLACK CLACK). That is why Bose uses a notch filter.
"Ok, I can't hold it in anymore. I want to build one of these things...."
1. Buy a 12' piece of 3" pvc pipe, and two 3" "closet" collars
2. Buy 4 x 2" bolts and nuts
3. Cut the long tube to 78" (42 Hz tuning)
4. Cut the short tube to 25"
5. Wire the 4" driver and sandwHich it between the two collars
6. Bolt the collars together with 2" bolts and nuts.
7. Plug the tubes into the collars
8. Snake wire out of short tube
WATCHOUT!
Do not overdrive or you will get nasty slapback (CLACK CLACK CLACK). That is why Bose uses a notch filter.
What is shown in Post #7 is actually a design from a bose product that I think I have seen once on eBay. I do not remember what it was for, though. I think they made a larger one for a pro subwoofer or something. It is indeed a Wave Cannon design, simply folded. Note that the location of the driver is such that when it is mounted, the front of the cone fires into a shorter tube, and the rear wave goes into the longer tube. that is why there are two terminuses (termini?) and no extrenal driver hole. I will need to examine that design to try and get an idea of how the line length is.
Here are the fundamentals of Wave Cannon theory as I understand them: Design a tube that is 1/2 the wavelength of the Fs of the driver. This will be the longer tube. Then design a tube that is 1/4 the wavelength of the driver Fs. This will be the shorter of the two tubes. The direction of the driver does not matter. The ratio of cone cross-sectional area to driver Sd is 0.5<x<1.0 with a ratio of 0.5 generating the flattest response and the ratio of 1.0 generating the greatest peaks in output at either end of the frequency band. (much like a 6th-order bandpass, hmm?) The terminus of each line should be spaced on the exterior of the enclosure at least 1/8-wavelength of driver Fs to prevent booming and exaggerated output phasing problems. I'm not sure about that last one, that's just what I gathered here in these last few posts. Driver Fs seems to be the only relevant parameter, but a Qts in a band between 0.5 and 0.3 is more preferable.
Here are the fundamentals of Wave Cannon theory as I understand them: Design a tube that is 1/2 the wavelength of the Fs of the driver. This will be the longer tube. Then design a tube that is 1/4 the wavelength of the driver Fs. This will be the shorter of the two tubes. The direction of the driver does not matter. The ratio of cone cross-sectional area to driver Sd is 0.5<x<1.0 with a ratio of 0.5 generating the flattest response and the ratio of 1.0 generating the greatest peaks in output at either end of the frequency band. (much like a 6th-order bandpass, hmm?) The terminus of each line should be spaced on the exterior of the enclosure at least 1/8-wavelength of driver Fs to prevent booming and exaggerated output phasing problems. I'm not sure about that last one, that's just what I gathered here in these last few posts. Driver Fs seems to be the only relevant parameter, but a Qts in a band between 0.5 and 0.3 is more preferable.
BAM:
"1.0 generating the greatest peaks in output at either end of the frequency band. (much like a 6th-order bandpass, hmm?) "
My cannon has an ATCR of close to 1 as does the $2,700 Bose Acoustic Cannon.
I based my descision on Jon Risch's outstanding TL guidlines at Planet10's t-linespeakers.org. It sounds nothing like a 6th-order bandpass.
Please check DrewP's very positive comments of his cannon -- who also has an ATCR of close to 1.
"1.0 generating the greatest peaks in output at either end of the frequency band. (much like a 6th-order bandpass, hmm?) "
My cannon has an ATCR of close to 1 as does the $2,700 Bose Acoustic Cannon.
I based my descision on Jon Risch's outstanding TL guidlines at Planet10's t-linespeakers.org. It sounds nothing like a 6th-order bandpass.
Please check DrewP's very positive comments of his cannon -- who also has an ATCR of close to 1.
I really think you are on to something here...
DJK:
"I use a spacing of 1/4 the total tube length -- as does the Bose Acoustic Wave Music System
The patent says:
"The separation between openings 28 and 31 is of the order of half the length of the shorter tube between the front of driver 22 and opening 31."
which is 1/8th the total tube length. In the SUMMARY OF THE INVENTION they claim:
"A preferred separation is within the range of one-eighth to one times the length of the path for pressure waves "
This is simply being expedient on their part in making the claim as broad as possible. It covers the Acoustic Wave at 1/8 exit spacing and the Sound Cannon at 1W exit spacing.
The optimum spacing for the smoothest frequency response and the highest broadband gain is 1/2W exit spacing."
I stand corrected sir...
The separation between openings (center-to-center) to total tube length of my cannon is 13% ( 30" / 240" ).
The separation between openings (center-to-center) to total tube length of the Bose Wave System is 17% ( 14" / 84" ).
But here is the rub...
Shouldn't we really be using the mid-point in Hz of the cannon's operating range, and using that for the optimum distance?
In my case that would be 37Hz ( ( 19Hz + 56Hz ) / 2 ) or 7.5 feet.
In the case of the Acoustic Cannon it would be 4.5 feet, and 28 inches for the Wave System.
It turns out that this would always be 1/3 the total length, or 1/2 the length of the long tube (straight math).
Please bear with me. I am a dunce when it comes to electronics theory...
DJK:
"I use a spacing of 1/4 the total tube length -- as does the Bose Acoustic Wave Music System
The patent says:
"The separation between openings 28 and 31 is of the order of half the length of the shorter tube between the front of driver 22 and opening 31."
which is 1/8th the total tube length. In the SUMMARY OF THE INVENTION they claim:
"A preferred separation is within the range of one-eighth to one times the length of the path for pressure waves "
This is simply being expedient on their part in making the claim as broad as possible. It covers the Acoustic Wave at 1/8 exit spacing and the Sound Cannon at 1W exit spacing.
The optimum spacing for the smoothest frequency response and the highest broadband gain is 1/2W exit spacing."
I stand corrected sir...
The separation between openings (center-to-center) to total tube length of my cannon is 13% ( 30" / 240" ).
The separation between openings (center-to-center) to total tube length of the Bose Wave System is 17% ( 14" / 84" ).
But here is the rub...
Shouldn't we really be using the mid-point in Hz of the cannon's operating range, and using that for the optimum distance?
In my case that would be 37Hz ( ( 19Hz + 56Hz ) / 2 ) or 7.5 feet.
In the case of the Acoustic Cannon it would be 4.5 feet, and 28 inches for the Wave System.
It turns out that this would always be 1/3 the total length, or 1/2 the length of the long tube (straight math).
Please bear with me. I am a dunce when it comes to electronics theory...
The separation between openings (center-to-center) to total tube length is becoming a real-world design nightmare (for me, anyway)
Have you tried designing 50% of total tube length? It’s pretty hairy. Where would you put it?
How does 25% of total tube length work? That's much more doable.
Also, doesn't ROOM EFFECT far outweigh this separation-between-openings issue (and ATCR for that matter) in terms of raggedness?
There has been much interpretion of vague patent mumbo jumbo but has anyone actually done the math?
Bose's contention that an ATCR of 1 causes problems is in total disagreement with Jon Risch's guidelines (and with my real-world listening experiences).
How MUCH worse is an ATCR of 1, an opening distance of 1/8?
My two cents – from long term real-world listening is that it is not a major issue (like ROOM EFFECT).
Have you tried designing 50% of total tube length? It’s pretty hairy. Where would you put it?
How does 25% of total tube length work? That's much more doable.
Also, doesn't ROOM EFFECT far outweigh this separation-between-openings issue (and ATCR for that matter) in terms of raggedness?
There has been much interpretion of vague patent mumbo jumbo but has anyone actually done the math?
Bose's contention that an ATCR of 1 causes problems is in total disagreement with Jon Risch's guidelines (and with my real-world listening experiences).
How MUCH worse is an ATCR of 1, an opening distance of 1/8?
My two cents – from long term real-world listening is that it is not a major issue (like ROOM EFFECT).
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