Rockin' the KaZba Dipole (K aperture Z-baffle Dipole)

[xrk971]

Yes, beautiful LaScala - is that simply 12/15 scale then?

 

[CLS]

Hi X,

Your KaZba dual 8 indeed sounds tight and snappy in the bass. Somewhat light-balanced for my taste, though. I think there's much more to play with the aperture's contour and EQ...

 

[bolexsbm]

that LS is adorable - where are its corner and -10dB points? are your drivers 8" or 6"? I don't think PWK's little bast$rd (LB76) could play as well (?) bolexsbm - have you tried cone K-dispersed tweeter? (or maybe a piezo with K-aperture?) I know the K-tube is "king of tweeters" - lol (but true over a certain range with good compression drivers)

Thanks for the kind words, guys.
I know this is the KaZba thread, so I'll try to be be brief...

freddi - I'm a newbie, and when it comes to the technical terminology, what I don't know is a lot. (it doesn't help that it's mainly in English either. LOL)
So if you will kindly explain what your question means(maybe in a another thread?) I'll try my best to find an answer for you.
(does the -10db point mean where the sound 'stops'? I think maybe it's around 31.5hz... )

It has 8 inch drivers instead of 'normal-for-it's-size' 6 inch drivers.
(It was a real pain to cram the 4 of them all in there...)

I haven't tried the cone and the piezo for the K-tweeter. (Just the fullrange tweeter that came out of couple of computer speakers - i.e. not optimal, I know) Trying to get a decent compression driver for the tube...


xrk - Yes, it is just simply scaled down from 15 to 12.

As for the KaZba, what kind of drivers do you feel are suited for this design? Are ones suitable for OB's better than 'normal' fullrangers?

If one were to use the W frame instead, then does it make sense to use normal K-aperture in the front, and use the double K(or RJ aperture?) at the back? What do you think? Is it doable?

 

[freddi]

my apologies - your English grasp and use is better than mine
"F3" is the half power point on the downwards LF slope and F10 is -10dB which is sometimes considered to sound "half as loud" as the 0dB reference

here is my Peavey FH1 outdoors in the middle of a small yard. Its just about the same as a Klipsch La Scala or Belle having a 110Hz -3dB point. Indoors and against a wall. this will improve. You can see the initial rolloff is ~12dB per octave then increases to ~18dB per octave.

 

[xrk971]

Bolexsbm,
Your command of English is quite amazing - I thought you were a native English speaker living in Korea.

So a LS normally uses qnty 4 x 6in drivers? What driver are you using? Which plans did you base your scaled design from? Do you have a link?

Regarding TS params suitable for KaZba: it could be OB high Qts drivers but with addition of aperture you want a strong motor so moderate Qts around 0.4 to 0.6 is better. Larger xmax, and preferably driver with linear motor and shorting rings. Something like RS225-8 can work too.

 

[freddi]

Klipsch's original La Scala uses 1-15" speaker with 3"x13" throat - most have K33 spec of moderate qts - midhorn = K400 with K55 driver, tweeter = K77 (like EV T35) - the Peavey above is pretty much the same other than 2 more cubic feet and better bracing. DJK some time ago noticed the upper horn chamber could add enough rear chamber volume to vent - that along with treating it like a 6th order reflex with Q=2 boost at ~1.03*fb gave it some low bass. I've not kept up with DJK's 4X8" push pull.

http://www.hifisentralen.no/forumet...c/1089d1335551849-diy-klipsch-la-scala-ls.jpg

 

[bolexsbm]

Thanks, guys.

freddi - No apology needed! Thanks for the explanation(x2). A friend of mine made a simple measurement of the LS cab in my room with a Synergy horn experiment on top about a year ago.

I guess the graph can tell you much more than I can.
(The hollow portion below 450hz is the LS - obviously. LOL)


xrk - The original LS uses a 15" driver, and djk PPSL mod uses four 8 inch drivers loaded in a manifold(plenum) instead of the 15. So I figured, if 8" for 15, that must mean 6" for 12! (But that was just my 'newbie thinking', and I went with 8 inch drivers anyway... )

Anyway, here is the thread that introduced me to PPSL, if you're interested.

https://community.klipsch.com/index.php?/topic/142855-ppsl-vented-lascala/

As for the driver, I'm using Korean 'Sammi' woofers. Didn't know too much about T/S params at the time - and not much has changed since then... - so I just tried to find the one with the closest spec with the ones that djk recommended.

 

[IG81]

Four 8" drivers will have comparable cone area to one 15"-16" nominal frame driver. Does your PPSL plenum have compression, meaning smaller area than total Sd for your 4 drivers? Cool horn in any case and the measurement is about what I'd expect.

 

[bolexsbm]

Cool horn in any case and the measurement is about what I'd expect.

Thanks, IG81! That's very reassuring to know.

I don't know the exact compression ratio on the plenum/SD, but I guess it's gotta be pretty high, considering that I had to make it very small to fit it in there.

So when I was getting the plans ready, I wanted to know if this was possible at all, so looked for some clues regarding the issue. And I found this post by djk at 'A Thread for those interested in PPSL enclosures' thread.

- "...DJK, what's the smallest slot you have made?"

My first prototype was 3.24:1, later I switched to 2:1 for convienence of construction.

I was alarmed at how much pressure I was getting with the first prototype, but in retrospect it was nothing in comparison with a typical compression driver and its 10:1 compression ratio.

NP in his slot-loaded OB speaker measured a 2.78dB gain with a 3:1 ratio. I have not tried to verify this with my PPSL. -

So after reading this, I kinda assumed that I was OK(could be wrong, but...), and just went for it...

 

[xrk971]

Qts of KaZba dual 8in

if the aperture plates are permanent, then you might extend the slot towards the top - maybe as a narrowing slit - I don't think it would have a big effect on response - might get worse - its an unknown as your KaZba is a fresh idea.

X - what is the Q of this KaZba? - you can run an impedance sweep and read it as would free-air parameter (I think)

Freddi,
Here is the impedence sweep of the KaZba (green) compared with a single driver (blue). The KaZba cabinet brings the fs from 39Hz down to 31Hz! That is surprising and means that there is an air mass loading going on. Qts is about 0.69 vs o.53 for bare driver. The squiggly business from 100-200Hz may be K-aperture vibration and buzz that is audible. Need to stiffen it and use foam gasket to absorb motion from pressure.

If I remove the two K-apertures (yellow), we see that the absence of the apertures shifts fs up to 35Hz and decreases Qts to 0.58. The wiggles are definitely caused by the apertures.

 

[freddi]

nice Qt! plus a substantial drop in fs = cool - -if this can be translated predictably to larger KaZba - then there will be a new configuration for the hobbyist. Is Qt similar with wings removed?

 

[xrk971]

nice Qt! plus a substantial drop in fs = cool - -if this can be translated predictably to larger KaZba - then there will be a new configuration for the hobbyist. Is Qt similar with wings removed?

Is Qt similar with wings removed?

I knew you would ask, see previous post and again shown below. yes...

Without K-aperture fs is 35Hz, with 31Hz and Qts goes from 0.57 to 0.68.

It sure is nice when there is a measurable effect to changing the acoustic boundaries and loading.

 

[freddi]

Good ! many thanks - are larger KaZba practical with regards to response, improved polars, etc.? I think they should work for some single drivers with moderately high Q

 

[xrk971]

I was thinking that an OB dipole box that can drop the fs from 39Hz to 31Hz is pretty cool. I was getting a solid 30Hz response and thought that might be a room mode - but it seems intrinsic to the speaker now. I think adding anothe FC layer and some bracing strips or support dowels for the wings might cure the vibrations in the 100-200Hz range.

 

[CLS]

I think it's the similar effect of air mass loading as slot loaded.

For the vibration on the wings, how about these?

 

[bolexsbm]

Wow! Solid 30Hz response from an OB dipole box? With two buyout 8 inch drivers? That's impressive!

Maybe you should set up a website and start a business, xrk!


CLS - The sketch on the right looks fun!
Will it work with some other figures? I'm thinking of small circles side by side, increasing numbers and/or size as we go to the bottom.

If this works, then will it be possible to make K-apertures by just punching enough holes with a few different sized hole saw?

 

[CLS]

haha...

That holey panel is more or less inspired by this: http://www.diyaudio.com/forums/multi-way/244508-monster-massive-4.html#post4142642

 

[xrk971]

That holey panel (except think rectangular holes) is how I model a K aperture in Akabak.

If this works, then will it be possible to make K-apertures by just punching enough holes with a few different sized hole saw?

Yes.

 

[Greg B]

Well I'm getting to this update a little late. Sounds like the KaZba was a big success. Congrats!! I was pretty sure it was going to work. I'll have to listen to the clips later at home.

AFA stiffening the panels: you could always be ridiculous and lay them up with some carbon fiber. Normally I make fun of people who use carbon in speakers, but in this case it makes sense, because it can be done with minimal tools and workshop. All you really need is scissors, gloves and an old squeegee -- and lots of newspaper for the floor...

 

[Greg B]

I've tried differently sized holes a couple times for Fulmer style terminated TL's and TQWT's. Works just fine for that. It'd be interesting to see how well it might work for front radiation. Diffraction is going to be an issue. There might be some clever way to combine it with acoustic lenses to achieve a cohesive wavelaunch, either the perforated disk or slat/louver type lenses.