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Old 4th June 2014, 12:28 PM   #31
IG81 is offline IG81  Canada
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Quote:
Originally Posted by zobsky View Post
I started out with about an 8" long pipe, sketched something approximating a mirrored exponential slot on a piece of paper and transferred the profile to the pipe. I carved the profile using a cut off wheel on my dremel.
Update:
For now, I started the cut about 1/3 of the way along the length. The k-tube for now sounds better than the uncut tube but it still sounds somewhat hollow and resonant. On the plus side, the dispersion is rather good. Using a frequency generator on my phone, the sound seems to pick up around the quarter wave frequency of 400 Hz

I think I need to start the curve earlier and open it out a bit faster and should probably take measurements as I continue to mangle the tube.
Cool! I guess the profile deviates a bit from a half-ellipse but it still looks ballpark to me.

Quote:
Originally Posted by kenpeter View Post
My experience with K-Tubes from 2 inches to 10 in diameter have always
been that they sound better the more and more you cut away until there
is nothing left...
Did you have the same experience with 1" K-Tubes?
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Old 4th June 2014, 01:53 PM   #32
GM is offline GM  United States
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Quote:
Originally Posted by moray james View Post
The double cut away version has less left to right room and tube to tube interaction......
Makes sense to me if I’m visualizing it correctly; a tube has a theoretical ~231.8 deg F6, but bifurcating it with a tapered slot is going to bleed a progressive amount of pressure out, so starts out omni, progressively collapsing into whatever beam-width pattern the tube’s final taper dictates same as any WG. Seems worth pursuing for folks not wanting a really wide ‘sweet spot’.

GM
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Old 4th June 2014, 02:33 PM   #33
GM is offline GM  United States
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Originally Posted by IG81 View Post
As the tube goes from fully-enclosed space to actually terminating, though gradually so...........

I suppose at some point, making it too long will probably require a narrower, more progressive slot..........
Correct, though how much shorter is a function of its acoustical end correction AFAIK, i.e. you will have to calculate its effective final flare, then subtract ~0.613 x the radius of this much larger termination [Am] from the tube’s physical length.

I’ve no clue how to accurately convert a flared cutout along a tube’s length to a flared circular extension to get its [Am] though. Maybe ‘xrk971’ can approximate it in AKAbak like he does the K-slot. Otherwise, your ˝ WL seems a reasonable choice and shorten it if need be.

Agreed, my SWAG is that the longer the tube, the wider its potential BW for a given diameter same as a horn, so calculating a slot taper would be basically no different than designing a tiny exponential horn of the same length, [Am], ergo using a [At] = to a typical ~1/16” wide saw blade, this equates to a ~48,446 Hz cut-off if I did the math right.

GM
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Old 4th June 2014, 02:54 PM   #34
IG81 is offline IG81  Canada
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Quote:
Originally Posted by GM View Post
Correct, though how much shorter is a function of its acoustical end correction AFAIK, i.e. you will have to calculate its effective final flare, then subtract ~0.613 x the radius of this much larger termination [Am] from the tube’s physical length.

I’ve no clue how to accurately convert a flared cutout along a tube’s length to a flared circular extension to get its [Am] though. Maybe ‘xrk971’ can approximate it in AKAbak like he does the K-slot. Otherwise, your ˝ WL seems a reasonable choice and shorten it if need be.

Agreed, my SWAG is that the longer the tube, the wider its potential BW for a given diameter same as a horn, so calculating a slot taper would be basically no different than designing a tiny exponential horn of the same length, [Am], ergo using a [At] = to a typical ~1/16” wide saw blade, this equates to a ~48,446 Hz cut-off if I did the math right.

GM
Thanks for that insight!

Equating the tube to a small horn for analysis is something I've wanted to do ever since I've had my pair of Transylvania. I'm not hip enough on theory to approach this outside of taking comparative measurements. Best I can do is cut a bunch of PVC tubes and see what I can cross-correlate, if anything at all.

I think the effective throat area will always be that of the tube diameter, unless the slot starts really wide right away, which it should not IMO, to keep some loading on the driver. As we move up (out of) the tube, that's where the gradual loss of pressure needs equation to a horn profile and mouth area - unknowns to me.
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Old 10th June 2014, 02:51 AM   #35
zobsky is offline zobsky  India
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Measured the k tube on the midrange compression driver as well as on an eminence psd2002 (more efficient ). Instead of the u-mik and REW on my laptop, I used my iphone , audiotools and the cheap dayton imic

The psd2002 sounds better, despite a higher resonant frequency
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Old 10th June 2014, 11:13 PM   #36
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you could make a 1"ID tube with 5.3" full length slot for comparisons. Eminence's drivers worked well with K-tubes. For some reason (internal flare) IG's Emilar did not mate well. Although patterns may not be a perfect match, I think the little K-tube overall sounds better than CD horn in some applications were `1K5 xover is employed.
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Old 11th June 2014, 01:51 AM   #37
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Originally Posted by freddi View Post
For some reason (internal flare) IG's Emilar did not mate well.
Not certain the throat angle mismatch would account for as large an effect as that dip I got. Looking at certain traces of BMS 4550 on the Tube, there is also a little something, as well as a bit more distortion at that frequency. I'm wondering how the two drivers would compare measured in the far-field, like a good 10' or so, which I can't really do well indoors. I also used D220Ti at first on the tube, but don't think I kept any crossover-less plots of it.
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Old 11th June 2014, 04:10 AM   #38
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5.3" (1"ID) copying Transylvania Power's "The Tube" length is the shortest I tried. For smooth plots there should be little diameter transition. Before going to a totally bare compression driver, try the Weiss lens which mounted on a Type1 Eminence.


Click the image to open in full size.

Weiss "Rocket" patio speaker which used either a Radio Shack 8 or BOFU

Click the image to open in full size.

Last edited by freddi; 11th June 2014 at 04:12 AM.
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Old 11th June 2014, 05:31 PM   #39
zobsky is offline zobsky  India
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Quote:
Originally Posted by freddi View Post
you could make a 1"ID tube with 5.3" full length slot for comparisons. Eminence's drivers worked well with K-tubes. For some reason (internal flare) IG's Emilar did not mate well. Although patterns may not be a perfect match, I think the little K-tube overall sounds better than CD horn in some applications were `1K5 xover is employed.
Okay, I'll try and make something up with a 1" ID tube to compare. The trick will be to adapt it to the larger screw in compression driver.
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Old 11th June 2014, 05:34 PM   #40
zobsky is offline zobsky  India
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Quote:
Originally Posted by freddi View Post
5.3" (1"ID) copying Transylvania Power's "The Tube" length is the shortest I tried. For smooth plots there should be little diameter transition. Before going to a totally bare compression driver, try the Weiss lens which mounted on a Type1 Eminence.


Click the image to open in full size.

Weiss "Rocket" patio speaker which used either a Radio Shack 8 or BOFU

Click the image to open in full size.
A bit off topic, but looking at the rocket speaker, .. that's a sealed speaker with a K-slot waveguide. Is that the same as the old Magenetar Klam subwoofer? I've got a dozen 12" subwoofers (with Qts about 0.7 and low Fs )lying around (long story ...) as well as pair of low Qts pyle PYM 1298 and I'm wondering if they would be suitable in a Klam bass module, and what the upper and lower bound of a Klam design would be.
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Last edited by zobsky; 11th June 2014 at 05:44 PM.
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