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Old 19th July 2013, 02:48 PM   #11
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I am sure JBL did a stack of perforated plates with circular frustrum.
But did they try perforated plates with slot frustrum? I think they had
some preference for a wavy maze of plates for horizontal dispersion,
so we never got to see perforated plates in that application.

I'm just saying the modified KB diffuser looks to work on the same
principle? But its only one perforated plate, and holes are silly huge.
I don't know how much we trade-off here by keeping it simple...

Last edited by kenpeter; 19th July 2013 at 03:05 PM.
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Old 19th July 2013, 04:21 PM   #12
xrk971 is online now xrk971  United States
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You might want to see how a K-slot affects directivity in a simulation of the mini Karlsonator with and without a K-aperture here: A Speaker that Kicks Butt in Large Spaces
It makes a big difference at mid range of 500 Hz.
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Old 19th July 2013, 09:16 PM   #13
Squeak is online now Squeak  Denmark
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500 Hz to 2000 kHz is seldom where there's problems with directivity IME.
I'd be much more interested in something that could give a bit more uniform directivity for the 5000, to perhaps all the way to 16000 kHz region.

The KB and Karlson slot looks to have much the same thing going on. IE they are straddling the line between doing a narrow opening to simulate a smaller driver and still allowing the other frequencies to "get out", without too much filtering and congested coloured sound.
The KB slot could be viewed as approximately the same thing as the Karlson slot only stylized.

I'd be very interested to hear whether they really work as intended. And how much colouration they cause.

I've been thinking of another variation and simplification/generalization on the theme, although not confined to mainly work horizontally: A torus (doughnut) shape suspended flat in front of the driver.
This would avoid any sharp edges, it would also avoid much of the sharply defined cavity and be stiffer.
It would still have a narrow central opening and a peripheral opening.
No doubt this has been done before. Anyone know about it?

Last edited by Squeak; 19th July 2013 at 09:18 PM.
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Old 19th July 2013, 10:13 PM   #14
IG81 is offline IG81  Canada
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Squeak, I don't know if it's been done, but I gotta say I've thought of similar embodiments before. Getting better dispersion up to ~2kHz is good IMO, as it'll broaden an 8" or 10" woofer's dispersion to meet up a tweeter with similar pattern. Any higher and the slot gets tighter, too much choke, hence the "flying donut" lens idea.

Not exactly the same, but Altec had a "coaxial" driver that was a small horn suspended over the dustcap to try and amplify whatever came out of there. Of course throat coupling will be poor, as it might be with a diffusor, but it must have worked to a certain extent?
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Old 19th July 2013, 10:24 PM   #15
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by Squeak View Post

I've been thinking of another variation and simplification/generalization on the theme, although not confined to mainly work horizontally: A torus (doughnut) shape suspended flat in front of the driver.
This would avoid any sharp edges, it would also avoid much of the sharply defined cavity and be stiffer.
It would still have a narrow central opening and a peripheral opening.
No doubt this has been done before. Anyone know about it?
I am a little confused as to the arrangement. The axis of the donut is coaxial with driver? And you mean a round donut like the type we eat not a flat disc with a hole in it?
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Old 19th July 2013, 10:42 PM   #16
Squeak is online now Squeak  Denmark
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Quote:
Originally Posted by xrk971 View Post
I am a little confused as to the arrangement. The axis of the donut is coaxial with driver? And you mean a round donut like the type we eat not a flat disc with a hole in it?
Yeah. To reference something i can find a picture of, just like the cantilever support on the Axiom 80:
Click the image to open in full size.
Only thicker and rounder.
Or it could be any toroid shape that is better suited. A torus is just close enough and relatively easy to find or make in styrofoam for example.
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Old 20th July 2013, 01:09 AM   #17
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Quote:
Originally Posted by IG81 View Post
Not exactly the same, but Altec had a "coaxial" driver that was a small horn suspended over the dustcap to try and amplify whatever came out of there. Of course throat coupling will be poor, as it might be with a diffusor, but it must have worked to a certain extent?
I've KTubed over the dustcap to some success, but its damn hard to make that
a permanent fixture... And it does need about 1/4 or more inches of clearance.
Not for want of hitting the cap, but just cause it sounds better that way.
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Old 23rd July 2013, 04:25 PM   #18
Elias is offline Elias  Finland
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Quote:
Originally Posted by eqjive View Post
Using diffraction slots over a cone transducer to achieve very wide horizontal coverage? Can anyone comment on or refer to experience, threads, papers, etc about this sort of thing?

The general consensus is that diffraction of sound is associated with bad sound quality - but in this case would that hold true?

I'm looking to explore the pros and cons of a full range speaker concept that would use a slot over a single cone to offset increasing directvity with increasing frequency.

Long ago I did some tests with diffraction slot on 8" fullrange driver. It was simple piece of thick cardboard which I encarved with knife

The result: It works.

However, be prepared for severe on-axis level drop at high frequencies. This is because the energy is redirected to wider angle than originally. Simple energy preserving law So if you initially have flat on-axis at high freqs, after the slot it'll be down to -10 ... -20 dB.

For a driver having heavily rising freq response, diffraction slot maybe a good idea.
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Old 23rd July 2013, 06:15 PM   #19
Squeak is online now Squeak  Denmark
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Thank you for your post!
If it worked, how come you're not using it now?

I too did some experiments, but as said above came to the conclusion that there was too much colouring going on, but that was with a simple straight 2 slot.
Was your slot "alternatively" shaped or was it wider?
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Old 23rd July 2013, 06:29 PM   #20
paulfx is offline paulfx  United States
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Hmm, reminds me of the Electro Voice Acoustic Lens, found on the Interface:A circa 1973

They had an equalizer that went with the set but I don't know if they boosted the highs as well as the bass.

It seems that to scale this up to a full range size, a non-rigid material should be used. How about a donut made of loosely-woven yarn on a needlepoint hoop? The yarn would be very fuzzy so as to block the highs yet the midrange would blow through.
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