Rockin' the KaZba Dipole (K aperture Z-baffle Dipole) - diyAudio
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Old 7th March 2015, 11:24 AM   #1
xrk971 is offline xrk971  United States
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Default Rockin' the KaZba Dipole (K aperture Z-baffle Dipole)

Here is an idea that I have been toying with for a dipole with really uniform dipole polar responses in the mid and higher frequency regions. Much of this was Freddi's inspiration and we got to thinking that given very uniform polar response that a K-aperture provides, what if we use this to enforce a sort-of slot loading on an open baffle or SLOB? Many people like the sound of a dipole, and have used various means to make the bass units more compact (H baffle, W baffle, SLOB, etc). Adding these enclosures around the baffle to enhance bass starts to affect how the dipole nature of the higher frequencies behave, making them less of a dipole.

To remind you of what a K-aperture can do for polar response, take a look at the data from the XKi (5dB variation over 45 deg off axis up to 10kHz):

Click the image to open in full size.

So here is the general concept of the Karlson-aperture Z-baffle dipole, or KaZba Dipole. The Z configuration provides a couple of advantages: angles the driver relative to the K-aperture to reduce resonances, makes the structure stiffer with a big inherent brace, allows the mounting of a second driver in push-pull to reduce 2nd order suspension hysteresis harmonic distortion, and just plain looks cool.

Click the image to open in full size.

So this can be implemented with a pair of full range drivers of any size really, but since we want some semblence of real bass, I am going for 8in drivers. I will be using woofers for the prototype - I am picking some relatively low cost units and so found these buyout 8in units from PE (5 mm xmax, 88dB, 8ohms, is not bad and moderate Qts and $10 ea - the price is right) http://www.parts-express.com/wfr800g...8-ohm--299-343. To this, I will add a whammy of an upper end dipole - where it makes all the difference: a Heil ESS AMT. The Heil AMT is a world-class tweeter that is almost full range, able to go as low as 600Hz. I will probably cross at about 750Hz in a 2-way. The KaZba, hopefully, will provide a nice wide bandwidth and smooth response up to well past 1kHz and be an excellent match. The woofers will be driven in parallel so sensitivity should be about 94dB at 2.83v.
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File Type: png kazba-sketch1.png (155.0 KB, 1463 views)

Last edited by xrk971; 7th March 2015 at 11:29 AM.
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Old 7th March 2015, 07:08 PM   #2
freddi is offline freddi  United States
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KooL! - - I'd like to understand the general effects as the overall structure's depth and volume is reduced and for fullrange buffs, a list of common drivers to try as proof of concept.

my super rough cardboard baffle had a Boss 6x9" - subjectively it improved with a rear inverted aperture. The little Boss 6.5" (BRS65), available for $10 shipped has good Q for folded baffle work - subjectively it has a character typical of polycone where there's less detail than some paper - but its $10

also, on my baffle, the fullrange was positioned where the aperture and the aperture depth to baffle was greatest - but that was only around 2" back at the very bottom as overall depth was perhaps 4.5"

besides the large AMT, do you have a low cost option for the tweeter section? it could be just one tweeter - or a bi-pole arrangement.

you could block the "rear" aperture temporarily with cardboard for a response measurement - not sure what useful info it would tell but I like weird situation graphs - Karlson's klams had front volume about the same as rear chamber.

Last edited by freddi; 7th March 2015 at 07:12 PM.
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Old 7th March 2015, 07:50 PM   #3
tubo is offline tubo  Philippines
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im very interested. can't wait to hear about the results
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Old 7th March 2015, 08:09 PM   #4
djn is offline djn  United States
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So the back chamber is not open to the front? I've been playing with the Ess amt for years and to my ear they are very thin sounding anywhere below 5khz.
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Old 7th March 2015, 08:32 PM   #5
xrk971 is offline xrk971  United States
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ESS Heil AMT (15 lb variety) is perhaps the best driver from 700Hz to 20kHz IMO. Not thin at all. I measure solid 100dB sensitivity at 2.8volts. Power limited at 40 watts though.

Back chamber open back K aperture. They share a baffle mount board.
It is an OB.
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Old 7th March 2015, 09:11 PM   #6
nesha is offline nesha  Serbia
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Visaton WS25 E 10" Paper Cone Woofer 8 Ohm

Even better candidate... 10" ,Qts=1.4 ,Fs=34Hz, Xmax=5mm, 29$ ... But I don't think you are going to get that 94dB/W ... 15"Alpha on 20" OB gives 90dB, in H frame even less...
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Old 7th March 2015, 09:51 PM   #7
freddi is offline freddi  United States
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a $10 Boss 6.5" with a cheap helper tweeter rolled on around 8KHz might be fun for a one-driver 4ohm version - a paper K-tube could be tried on the tweeter


Boss 6.5 - Boss 6x9 Dayton PA130
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Old 8th March 2015, 01:51 AM   #8
xrk971 is offline xrk971  United States
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Before making a big one for the dual 8 inchers, I am building a small prototype in FC for the TC9FD, called the mini KaZba. This will not have any bass as it is scaled way small, but will give me some practice in the construction and also to model it in Akabak so that I can optimize the chamber volumes and Karlson aperture cross sectional areas for optimum performance.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

There is a lot of air pressure - need to double up layers as it is rattling now...
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File Type: png mini-kazba-photo-1.png (450.1 KB, 1098 views)
File Type: png mini-kazba-photo-2.png (419.3 KB, 1099 views)
File Type: png mini-kazba-photo-3.png (244.1 KB, 1087 views)
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Old 8th March 2015, 05:16 AM   #9
djn is offline djn  United States
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OK, now I see what you did.
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Old 8th March 2015, 07:02 AM   #10
xrk971 is offline xrk971  United States
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Default Added bracing and some stuffing

I added lots of little 90deg corner angles to brace the walls and reduce rattling and vibrations. I also doubled up the K-aperture with two sheets of FC glued together. This worked pretty well, and then added some fiberglass stuffing behind the magnets of the drivers to help absorb some chamber reflections.

Click the image to open in full size.

How does the dipole work? In a dipole box this small, there is not enough of a baffle distance to get any bass - there is some but it starts falling off below 200Hz. The K-aperture combined with the chamber reflections and some of the bracing is creating a lot of dips in the response. I took some polar data and the box seems to be doing its thing, frequency dips, notwithstanding. What is there, is following what I expected for the polar response from a K: uniform over 5dB up to 45 deg off axis up to about 10kHz. The dipole effect can be seen with a fairly uniform 20dB attenuation at 90deg off axis. The data shown is at 0.5m with a gate of 1ms before and 4ms after for a resolution of 200Hz and stuff above 400Hz is good.

Click the image to open in full size.

Here is the impulse response from the 0 deg case:

Click the image to open in full size.

Here is the harmonic distortion from the 0 deg case:

Click the image to open in full size.

This quick FC study is giving me some good lessons learned for the real build with the 8in drivers. I tried listening to this speaker, and it sounds surprisingly good with the some female vocals and jazz despite the several deep notches in the response. What is good is the uniformity of the sound as I walk around the room, or behind it. Just directly to the side, the response is very low as expected.
Attached Images
File Type: png kazba-tcc9fd-polar.png (145.1 KB, 1064 views)
File Type: png kazba-tcc9fd-ir.png (44.5 KB, 1049 views)
File Type: png kazba-tcc9fd-hd.png (120.6 KB, 1050 views)
File Type: png mini-kazba-photo-4.png (468.8 KB, 1067 views)

Last edited by xrk971; 8th March 2015 at 07:05 AM.
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