Yesterday I made my first k pipe tweeter from some old piece of 1.5" PVC pipe and a cheap p-audio 2" compression driver. This sounded so promising that I kept on tinkering. I found a larger 2.5" pipe and mounted a 4.7" full range driver with a quickly hand cut foam adapter.
The result was quite bad. When I slowly did a manual frequency sweep there I could hear lots of little resonances and crazy didgeridoo noises..
I almost abandoned the experiment but last minute decided to try stuffing. I put some polyfill in the bottom 1/3 of the pipe the result was stunning. No more resonances and only very smooth sound. It almost seems like you could use stuffing as a crossover so you could forgo a lowpass on your midrange pipe.
I also tried some stuffing in the smaller tube but that killed the high end.
If I have some more time I want to measure to verify what I hear. I also like to experiment with different materials. I have a feeling cardboard tubes may sound better than PVC.
Also I will at some point try a very large pipe just to see what happens. Maybe a 6" 5' pipe with a 8" driver and stuffing.........three pipes with a minimal crossover....only highpass filters to protect the drivers.
The result was quite bad. When I slowly did a manual frequency sweep there I could hear lots of little resonances and crazy didgeridoo noises..
I almost abandoned the experiment but last minute decided to try stuffing. I put some polyfill in the bottom 1/3 of the pipe the result was stunning. No more resonances and only very smooth sound. It almost seems like you could use stuffing as a crossover so you could forgo a lowpass on your midrange pipe.
I also tried some stuffing in the smaller tube but that killed the high end.
If I have some more time I want to measure to verify what I hear. I also like to experiment with different materials. I have a feeling cardboard tubes may sound better than PVC.
Also I will at some point try a very large pipe just to see what happens. Maybe a 6" 5' pipe with a 8" driver and stuffing.........three pipes with a minimal crossover....only highpass filters to protect the drivers.
Yes, if used wide BW and/or no stuffing, just some reflection area lining.
Now getting into pipe organ design 'territory'........ 👍 😎
Don't encourage me.....or I may add a Bose wave cannon in stead of a sub
The very large pipe (200cm/4") did not do so well. Without stuffing it is awful, with stuffing better but kind of muffled.
Maybe the pipe is too long. I'll cut off 50cm and try again. Also the driver I used is maybe not ideal. I should find a properly sized driver with very strong motor.
Really have been enjoying the sound of my 1.5" PVC k pipe. Very crisp/immediate/realistic without any coloration.
The 2.5" pipe with weak motor fr driver sounds promising but most definitely cannot keep up with the hf compression driver. SO NOW I FOUND THIS:
A 2.5" exit, 650W, 88.9mm voice coil compression driver. I really don't know a thing about these monster long throw outdoor public address drivers but I would like to try. I have a bunch of bills to pay soon......if I have some money left over I may get one just for the heck of it. I can get one for around 90 bucks. I guess the only country where you could get these cheaper is North Korea. I like the look of that diaphragm. Looks like a ring radiator with total diaphragm diameter of almost 15 cm.... that's insane!
I can see a project with a Klipsch Heritage bass horn with a 2.5"/70cm k pipe doing 300-3000hz and a 1"/23cm k pipe with 18sound nd1tp compression driver doing 3000hz and up.
The 2.5" pipe with weak motor fr driver sounds promising but most definitely cannot keep up with the hf compression driver. SO NOW I FOUND THIS:
A 2.5" exit, 650W, 88.9mm voice coil compression driver. I really don't know a thing about these monster long throw outdoor public address drivers but I would like to try. I have a bunch of bills to pay soon......if I have some money left over I may get one just for the heck of it. I can get one for around 90 bucks. I guess the only country where you could get these cheaper is North Korea. I like the look of that diaphragm. Looks like a ring radiator with total diaphragm diameter of almost 15 cm.... that's insane!
I can see a project with a Klipsch Heritage bass horn with a 2.5"/70cm k pipe doing 300-3000hz and a 1"/23cm k pipe with 18sound nd1tp compression driver doing 3000hz and up.
I noticed the larger K tubes really vibrate a lot. Now I wonder if the slot needs to be continuous or if it is ok to have interruptions? If I could leave some connections/slot interruptions it would greatly reduce flexing. I am not very well versed in physics so I have no idea how the slot actually works and if it needs to be 100% continuous.
Erik,
The standard for thread-on PA drivers is 1 3/8" 18 TPI, the exit typically varies between ~5/8" and 1".
A 2.5" thread-on PA driver would be quite unusual, I haven't found any examples of drivers or horns using that size on line.
A ring radiator diaphragm is annular, shaped like a ring, the voice coil located between the inner and outer ring portions of the diaphragm:
The diaphragm you posted is a dome, not a ring radiator like the one above.
The effective radiating area of a dome diaphragm is only that of the voice coil, it's surround outside the voice coil does not count towards it's displacement.
Probably more likely the domes overall diameter is 89.9 mm, it's voice coil in the 50mm/2" range.
That said, 75mm (3") and 100mm (4") phenolic diaphragms are common, with exits from ~25mm (1 3/8") to 50mm (2"), but not thread on.
Do you have a manufacture link to the driver?
Art
This one most definitely is 2.5". This brand sells them in 1.5", 2." and 2.5". In Thailand every street, every village, every temple has public address horns. There is more variety in drivers and they are unfathomably cheap. Some of the horns are humongous. They use a manifold with 4 drivers or one bigger one.
As you can see from the picture the surround probably has a larger surface area than the actual dome. So I guess half of it should be counted towards cone area and it probably has a way longer stroke so it can move a lot of air.
It says voice coil 88.9mm......and the cost 15 bucks 😂
This being Thailand the manufacturer link is not working. For most drivers sold locally here it is impossible to find parameters. If you are lucky they give you sensitivity and a frequency range. To get a feel for the size I made screenshots from a YouTube video.
I just realized these are a perfect diyAudio house style purple 💜
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The output contribution of the surround (if any) would be dependent on the phase plug design.
The convex side of the diaphragm facing the exit is unusual.
Looks like it's excursion would be far greater than any PA compression driver I've ever seen, Id' be surprised if it could make 3000Hz before it's acoustic band pass.
Looks like it could be fun to experiment with!
Until recently I haven't seen anything like this either. I ordered one (there was a sale, I got it for only 75usd) to test because I have no idea about it's sensitivity or usable frequency range.......or it's weight!
I just saw there is even a more powerful 850w version but that would be killing the overkill.
You should review this thread which describes one guys journey setting up and developing his midrange/tweeter Transylvania tubes: https://www.diyaudio.com/community/threads/fieldcoil-k-tube.363723/
I am currently experimenting with a pair of midrange Transylvania tubes - see the attached photo.
I made the Transylvania tubes out of PVC pipe, but if I decide that I want to pursue this pathway further, I likely will experiment with alternate tube materials and configurations.
Retsel
I am currently experimenting with a pair of midrange Transylvania tubes - see the attached photo.
I made the Transylvania tubes out of PVC pipe, but if I decide that I want to pursue this pathway further, I likely will experiment with alternate tube materials and configurations.
Retsel
Attachments
Thanks. I read the whole thread and learned a few valuable things.
Rules of thumb for tube length:
-l10x tube diameter
-¼ wave length of fs/impedance peak
-shorter tubes give wider dispersion than longer ones.
The width of the tube has less influence than expected.
About 20deg tilt seems optimal, more tilt relaxes the sound.
A 2” pipe can play down to 500, 400 or even 300 depending on the driver.
Open cell foam is a good material to damp larger tubes.
Pipe vibration becomes a problem for larger tubes
I intend to roll my own pipes out of a few layers of craft paper and then cover them with fiberglass and epoxy. I will probably make a 3" pipe and a 2.5" to 3" adapter.
The question I still have is how important is a uninterrupted slot? Vibrations in large tubes could be greatly reduced if the tube is not completely cut through. Is there anyone with enough understanding of the principals or a way to model it who can indicate if slot interruptions are OK and how big/numerous these interruptions can be before it starts to hurt performance?
I can also try craft paper - fiberglass - rubber sheet - fiberglass
-or-
craft paper - fiberglass - cork - fiberglass
I am hoping I can cover 150-4000hz with my large mid pipe. That would even open up the possibility of just using 1st order crossovers.
For the bass I am working on a open baffle H frame with pentagon shapes for 2x 15" drivers. The baffles will have Karlson style slits to reduce resonances.
But first I need a few weeks to finish my OB line arrays.....
The question I still have is how important is a uninterrupted slot? Vibrations in large tubes could be greatly reduced if the tube is not completely cut through. Is there anyone with enough understanding of the principals or a way to model it who can indicate if slot interruptions are OK and how big/numerous these interruptions can be before it starts to hurt performance?
I can also try craft paper - fiberglass - rubber sheet - fiberglass
-or-
craft paper - fiberglass - cork - fiberglass
I am hoping I can cover 150-4000hz with my large mid pipe. That would even open up the possibility of just using 1st order crossovers.
For the bass I am working on a open baffle H frame with pentagon shapes for 2x 15" drivers. The baffles will have Karlson style slits to reduce resonances.
But first I need a few weeks to finish my OB line arrays.....
Depends on its design BW, i.e. low frequencies are transparent to them, so will begin 'speaking' with harmonics once ~ a WL long, so best to use just one if possible.
For example, a 1st approximation and ignoring any pipe end correction; a 2" dia. pipe x 24" slit will have a ~13543.3/pi/2 = ~2155.5 Hz dia., 13543.3/4/24 = 141.1 Hz slit, so its mean = (2155.5 x 141.1)^0.5 = ~551.4 Hz is where you want to place a brace and fine tune its location from there.
That would work out to be roughly at the 1/3 length of the tube right?
What about multiple small braces so it is almost like a grill? If a larger pipe (3"x30") that isn't playing the top two octaves aren't the waves too long to see a few 1/4" braces? Or will they themselves cause diffraction?
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I did a little experiment to see if I could determine if my PVC tubes produce resonances. I used an AP on my phone (Spectroid) which does provide an estimate of the frequencies the phone hears. I suspect that the program is pretty limited by the mic on the phone, although the middle-most frequencies are probably OK. So I knocked on the PVC pipe with my knuckle and held my phone up to the tube and the rapping produced a sound in the 800 to 100 hz range. As it turns out I do have a frequency peak at ~1000 hz when I do a frequency sweep of the midrange transvylvania tube with a Stereophile CD and Rat Shack db sound meter, so maybe they are related.
Retsel
Retsel
Correction: that knuckle knock test on my midrange PVC transylvania tube produce sound in the 800 to 1000 hz range....
That Reinout guy, whose experiments were documented by the thread of posts I referenced, made transylvania tubes out of plastic and metal fused together to reduce resonances. Cardboard is inherently more inert, and would be a better choice than PVC, although composites would be a good choice as well.
That Reinout guy, whose experiments were documented by the thread of posts I referenced, made transylvania tubes out of plastic and metal fused together to reduce resonances. Cardboard is inherently more inert, and would be a better choice than PVC, although composites would be a good choice as well.
I made a small, medium and large tube and at every step the vibrations exponentially increases. In my thick wall pvc 4" pipe you can see the vibrations with the naked eye. A pipe is a very strong shape but the slot disconnects the shape and it almost becomes like a spring.
So the most elegant solution would be to not create a spring like shape to begin with.
But if this is not possible because it turns out there are good reasons to keep the slot uninterrupted we need to create a better shape. I would then progressively thicken the tube from the slit edge towards the back of the tube. I. The same way as engineers progressively taper cantilever beams.
Trying to achieve it just by using more advanced materials or material combinations instead of addressing the inherent shape weakness seems to me like an uphill battle.
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