Taterworks said:
Greets!
Design details?
Anyway, FWIW, the BWC is basically a band-pass alignment and for flattest response these are tuned so that Fb = (Fl*Fh)^0.5. Going back to DJK's 85 Hz Fs driver example which was based on the patent's design info, Fb = 85 Hz and since these are just 1/4 WL pipes, the driver's Fs needs to be = Fb for proper phase summing. Since the long pipe is nominally tuned to ~56.66 Hz and the system at ~42.5 Hz, obviously it's going to have excursion problems if the proper ATCR and BL requirements aren't met, not to mention the patent calls for a high pass filter below the system tuning to protect it.
GM
Cannon
Hello naryb69
I took the just build it approach and took 2 18" woofers and bolted them face to face put 3' of 16" sonotube on one end & 9' on the other. Then I wired the two woofers out of phase and plugged it into a 250 watt amp. Crossed at 40Hz I have to turn it down 8db or everything on the walls will fall. I'm not sure about the voice of God thing but when Darla taps on the fish tank you feel it in your gut.
Hello naryb69
I took the just build it approach and took 2 18" woofers and bolted them face to face put 3' of 16" sonotube on one end & 9' on the other. Then I wired the two woofers out of phase and plugged it into a 250 watt amp. Crossed at 40Hz I have to turn it down 8db or everything on the walls will fall. I'm not sure about the voice of God thing but when Darla taps on the fish tank you feel it in your gut.
Here are a couple pics
in from the end
outside showing the wiring & mounting
from the room- still needs end caps and trim
in from the end
An externally hosted image should be here but it was not working when we last tested it.
outside showing the wiring & mounting
An externally hosted image should be here but it was not working when we last tested it.
from the room- still needs end caps and trim
An externally hosted image should be here but it was not working when we last tested it.
TLs are fun and easy to get right. That's right I said it! EASY! If you take your time the results will show, if you don't have the room for a TL and want to "shrink" it...you better pull the calculator and integration book out because getting right within small spaces is true engineering.
Keep it simple, keep it large and it will pay itself off very quickly!
Keep it simple, keep it large and it will pay itself off very quickly!
Bass Cannon ???
Interesting Link:
http://news.bbc.co.uk/2/hi/science/nature/3087674.stm
As part of the "Ghost" study they built a "Bass Cannon", so follow the links from the BBC Story ...
Interesting Link:
http://news.bbc.co.uk/2/hi/science/nature/3087674.stm
As part of the "Ghost" study they built a "Bass Cannon", so follow the links from the BBC Story ...
I'd call those hypotheses rubbish. After all, if the pipes are responsible for the spiritual 'experiences' people have, how could people have spiritual 'experiences' in modern megachurches with pro sound systems that don't dip below 30 Hz on a good day? Here in the U.S., I've never attended a church that had a pipe organ -- they were either electric organs or no organ at all. It's kind of hard to fit a pipe organ into a contemporary worship service, and yet I've seen plenty of people giving in to spiritual experiences at these types of events. The premise behind the study is goofy, and the idea that people attribute these odd feelings to God instead of the powerful sound of the organ is still an assumption that the boffins seem to have 'slipped in' - they didn't survey people afterward to find out why they think they felt such weird feelings while listening to the music. Whatever you think about religious issues, it seems like a lot of this study's conclusions were simply jumped-to (which is bad science), especially the conclusion advertised by the article's title, that infrasound is responsible for religious experiences.
Certainly as far back as the mid 60's it was well known in scientific circles that infrasonics (sub 20hz and often 15 or less) could instill a sense of awe/fear in a listener. Being infra sonic these sounds could be "snuck" in as they are not actually audible. Aside from full length organ pipes there's very little apart from synthesised music that goes this low on a regular basis and even then, as we are all aware in the subwoofer forum, getting clean sound at sub 20hz is a significant technical challenge.
This study does little more than making a spiritual/god linkage. Organ pipes can go lower than 20hz. Yeah, sure, we knew that, nothing new there. Sub 20hz can produce fealings of fear/awe, again, nothing that wasn't known 3 decades or more ago. Yawn.
Personally, I'd sack the researchers and their supervisors for telling us absolutely nothing that wasn't already on the public record.
Yawn.
They did use what they referred to as a cannon but I suspect it was a 1/4 wave pipe, not a cannon.
This study does little more than making a spiritual/god linkage. Organ pipes can go lower than 20hz. Yeah, sure, we knew that, nothing new there. Sub 20hz can produce fealings of fear/awe, again, nothing that wasn't known 3 decades or more ago. Yawn.
Personally, I'd sack the researchers and their supervisors for telling us absolutely nothing that wasn't already on the public record.
Yawn.
They did use what they referred to as a cannon but I suspect it was a 1/4 wave pipe, not a cannon.
I'd have thought that the two ends of your pipe would come in and out of phase with each other across a broad range with a resulting passband that appears more as two humps with a dip in the middle (although the output even in the dip between those two humps is always more than the raw driver alone would produce). (soo long since i crunched the numbers on this!)
The driver being placed 1/3 of the way along should give a single hump response and if my numbers are right the peak would be at about 70hz. Don't know about secondary peaks lower down, GM is really your man for sims it would seem.
The driver being placed 1/3 of the way along should give a single hump response and if my numbers are right the peak would be at about 70hz. Don't know about secondary peaks lower down, GM is really your man for sims it would seem.
I'm very rusty on it. Posted the original maths in post 41 I think in May of 03.
Pipe is in the roof at my place in storage at the moment but isn't hooked up at present.
I originally crunched it all on graph paper and summed the outputs from the front and rear of the driver at particular wavelengths.
Pipe is in the roof at my place in storage at the moment but isn't hooked up at present.
I originally crunched it all on graph paper and summed the outputs from the front and rear of the driver at particular wavelengths.
Starting point: (As I remember it)
You have a pipe of X length and a pipe of 3X length.
At any given frequency, these pipes will correspond to a certain proportion of a wavelength.
What this means is that they introduce a small delay before the wave is able to propagate into the room, thereby having the result that the position through the cycle of the sine wave for the frequency being produced will not cancel as it would if you had the driver on a bipole flat baffle where the + wave and the - wave combine to produce a null, and do not sum as they would if you had a sealed 2 driver dipole, but rather, produce a response where the output from the ends of the tubes come in and out of phase with each other as frequency changes.
When I say "a small delay", in practice you're looking at 4.5m of delay on the long side of the pipe even if you make a cannon that is very large. If 340m represents one second of delay then 34m represents 100ms and 3.4m represents 10ms so we're looking at a delay of around 15ms before the output is heard. At bass frequencies, this is pretty much negligible as far as I'm concerned.
In order to do my original number crunching I took that the sine of 90 was +1, the sine of 180 and 36 were null points and the sine of 270 was -1 and drew these graphically. Then I side shifted the wave calculations by 90 degrees so that I could have my zero point at +1 corresponding to 100% of forward radiation when the driver was making full excursion.
I could then calculate where on the 100% - 0 - -100% - 0 - +100% waveform the lengths 1.5 and 4.5 metres as a proportion of the waveform would be placed and what the output at the ends of the tubes.
You should end up with a set of data that says: (I'm plucking % numbers from thin air with no calcs so ignore the actual values)
50Hz,
output at short tube +0.78%
output at long tube -0.13%
sum = 65% of full output
40 hz
30hz
Once you've combined the values, you can ignore the resultant + or - sign. A full pressure backwave is just as loud as a full pressure front wave, the + and - is only there for the purpose of caluclating if the waves will add or subtract from each other.
You should then be able to graph a predicted frequency response of the output.
Hope that made some sense.
Got to get to a working bee.
Type more later amd feel free to ask q's. I'll try to help if I can
drew
You have a pipe of X length and a pipe of 3X length.
At any given frequency, these pipes will correspond to a certain proportion of a wavelength.
What this means is that they introduce a small delay before the wave is able to propagate into the room, thereby having the result that the position through the cycle of the sine wave for the frequency being produced will not cancel as it would if you had the driver on a bipole flat baffle where the + wave and the - wave combine to produce a null, and do not sum as they would if you had a sealed 2 driver dipole, but rather, produce a response where the output from the ends of the tubes come in and out of phase with each other as frequency changes.
When I say "a small delay", in practice you're looking at 4.5m of delay on the long side of the pipe even if you make a cannon that is very large. If 340m represents one second of delay then 34m represents 100ms and 3.4m represents 10ms so we're looking at a delay of around 15ms before the output is heard. At bass frequencies, this is pretty much negligible as far as I'm concerned.
In order to do my original number crunching I took that the sine of 90 was +1, the sine of 180 and 36 were null points and the sine of 270 was -1 and drew these graphically. Then I side shifted the wave calculations by 90 degrees so that I could have my zero point at +1 corresponding to 100% of forward radiation when the driver was making full excursion.
I could then calculate where on the 100% - 0 - -100% - 0 - +100% waveform the lengths 1.5 and 4.5 metres as a proportion of the waveform would be placed and what the output at the ends of the tubes.
You should end up with a set of data that says: (I'm plucking % numbers from thin air with no calcs so ignore the actual values)
50Hz,
output at short tube +0.78%
output at long tube -0.13%
sum = 65% of full output
40 hz
30hz
Once you've combined the values, you can ignore the resultant + or - sign. A full pressure backwave is just as loud as a full pressure front wave, the + and - is only there for the purpose of caluclating if the waves will add or subtract from each other.
You should then be able to graph a predicted frequency response of the output.
Hope that made some sense.
Got to get to a working bee.
Type more later amd feel free to ask q's. I'll try to help if I can
drew
Getting closer I think
Took your numbers and used them, in used them in the XL sheet that I was working on, it's in inches.
Noticed you used the COS instead of SIN as was used in a post a few months ago, and was wondering about how to add the 90 and 180 degree shift where needed
Maybe we could come up with a basic spread sheet others could use
Took your numbers and used them, in used them in the XL sheet that I was working on, it's in inches.
Noticed you used the COS instead of SIN as was used in a post a few months ago, and was wondering about how to add the 90 and 180 degree shift where needed
Maybe we could come up with a basic spread sheet others could use
My suggestion would be to grab a sheet of graph paper and draw at least one set of sine waves overlaid on the tube for a particular frequency so you have an understanding of what you're trying to achieve before producing big wads of spreadsheet.
I'll try and draw up a pic in the next few days but I can only upload it from work and sick children mean that I won't be there till Thursday at the earliest (and will have backlog work to catch up on).
I'll try and draw up a pic in the next few days but I can only upload it from work and sick children mean that I won't be there till Thursday at the earliest (and will have backlog work to catch up on).
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