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Old 24th July 2013, 12:44 PM   #21
Squeak is offline Squeak  Denmark
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Click the image to open in full size.

Seems slot haven't gone entirely out of style.

Basically what we want is something like this:

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Only with the opposite effect of spreading the sound. IE a concave lens.
Vanes/plade lenses, like above, have been tried many a time before. They might have better efficiency than a slot, but apparently they introduce even more colouration?

Maybe a slot lens made of felt of the right thickness to let lower frequencies through?
Question is how exactly the slot should look like?
A straight slot might work ok with felt.
But maybe some extra holes like in the first pic and the KB lens, and/or a double karlson taper would be needed to get enough venting and spread of the cavity filter effect. They would create some additional diffraction effects that to some degree would counteract the slot. But they might be necessary.
Any ideas?
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Old 24th July 2013, 08:52 PM   #22
Elias is offline Elias  Finland
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Originally Posted by Squeak View Post
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?

Because I gave up using 8" drivers up to 20 kHz They never worked for me that high.

My experimental slot was narrow at the center and widening towards the ends. It did what was expected in diffracting the energy in a wide angle. So it worked

However, there are more to good sound reproduction of high freqs than just directivity.
Liberate yourself from the illusion of two speaker stereo triangle
Dipole Bass vs Monopole Bass Stereophonic Sound from a Single Loudspeaker 3 Speaker Linear Stereo Matrix Wavelets
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Old 24th July 2013, 11:08 PM   #23
Squeak is offline Squeak  Denmark
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Yeah of course, but it is about the only thing wrong with classic FR drivers (if you discount dynamic range).
Still, I'd take a good fullrange over most traditional two or treeways any day. Esp. because of the strained and weird treble.
Room interaction is the name of the game. Tweeter equipped speakers have more than their share of that too though.
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Old 25th July 2013, 12:47 PM   #24
eqjive is offline eqjive  United States
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Default Another approach?

Interesting posts. While different form the single slot for wide HF coverage, there is a description of using multiple slots to control directvity in the white paper here. Check out pages 5 and 6.

White Papers
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Old 25th July 2013, 06:02 PM   #25
Squeak is offline Squeak  Denmark
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It seems to be about reflectors and with compression drivers specifically, not lenses.
But nevertheless an interesting read. Thanks.
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Old 25th July 2013, 07:09 PM   #26
Squeak is offline Squeak  Denmark
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Now THIS is what I'm talking about. ;-)
Esp. this:

Click the image to open in full size.

You could play around with making the side lobes as strong or stronger than the center lobe by making larger holes at the edges of a barrier. This is possibly how the KB slot was meant to work.

Click the image to open in full size.

This is probably also the secret behind Mark Fenlons drivers good directivity. IE he somehow partially defers some of the HF waves at the midpoint of the radius of the diaphragm, probably by some careful mass loading by the thickness of the material.

Last edited by Squeak; 25th July 2013 at 07:21 PM.
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Old 17th August 2013, 02:30 AM   #27
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Regarding the modified KBDiffuser, maybe those holes at the sides are so
badly blended in phase that they don't leak much HF? I'm not so sure the
dumbell ended slot is immune to that either. Its really sort of a radial K
over the dome and cone of the loudspeaker, and might work as well or
better in that shape...

That top picture on #21 also reminds of JBL Aquarius...


No wonder the darn thing looks JBL, the empire strikes again...

Last edited by kenpeter; 17th August 2013 at 02:37 AM.
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Old 18th August 2013, 04:32 PM   #28
Zero D is offline Zero D  United Kingdom
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Originally Posted by Squeak

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.
Hi, you're not alone. See further down for the doughnut info. Here's some similar ideas etc from way back when.

University Diffusicone in the 50's

The "diffuser" element provides dual horn loading of the speaker apex, thus substantially increasing efficiency in the upper frequency range, at the same time affording radial projection and aperture diffusion to assure reception of the speaker's entire range of reproduction irrespective of the listener's location.


I bought the plans for the C40 Harkness folded horn system and proceeded to construct a system. This had a 175DLH horn and lens assembly. This driver was very impressive to look at. The acoustic lens at the front of the horn was a series of perforated steel plates. The plates had a hole in the center which was progressively larger toward the front. This formed the lens. Sound was delayed more at the edges than at the center, creating a more spherical wave front. I measured response out to 15 kHz for this driver.

Citation X speaker system.

The drivers were modified Lowther PM-6 drivers with a canoe shaped whizzer and a few pieces of aluminum foil glued to the main cone. The whizzer covered the range from 2 kHz to 7 kHz. The drivers faced upwards and had a plaster mushroom shaped stabilizer that provided horn loading at higher frequencies. The rear of the cone was coupled to a split, slot-loaded conical horn. Each folded section was 7-1/2 feet long. The slot at the end of the horn was said to reduce phase shift within the horn. Corner placement was not necessary.

My Experience With Sound
Interestingly, University who make Community speakers, had a foam Doughnut model/s over 20 years ago, i seem to remember. Even though the image is poor, this "might" be one of the designs ? The one i saw definately looked like a doughnut, suspended out in front of the throat, by maybe steel rods.

Screenie from here


Those images in Post #21 from the 50's or 60's are a revelation !
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