I think the point of coating the aluminium with something is to reduce the plate resonance of the material. These diffusers are meant to change the dispersion pattern of the driver. Felt would dampen the reflections the diffusers are meant to spread out. I am thinking paper on each side would be better because it would be like a very thin and light version of elaminating fiber onto the metal, dampening the resonances inside each small sheet. And I do not like plastic.
Hmmm... I think GM is on to something with making a layered laminate with alternating reflective and damping layers. Aluminum/rubber/aluminum for example. More layers might be better, but the key idea is to do the damping internally to each plate rather than externally. That foam core board stuff that Xkr uses for his boxes might also be good, just not maybe as sturdy as I'd like. Though, with a big sturdy " brush guard" type grille on the front of the cabinet over the lens, maybe the foam or even cardboard would survive long term.
I wondered with the cardboard if there was anything happening internal to each plate, since the corrugations are in the same direction as the sound.. though only rather high frequencies would probably be able to travel thru that airspace, so maybe no audible effect to our ears.
I wondered with the cardboard if there was anything happening internal to each plate, since the corrugations are in the same direction as the sound.. though only rather high frequencies would probably be able to travel thru that airspace, so maybe no audible effect to our ears.
I've been waiting for this to pop up
, Normally this would be preferred, but if the published response is ~accurate, then we'll 'have to agree to disagree' unless the listening position [Lp] is either very close relative to the side walls and/or way off axis to keep first reflections behind the listening positionOf course if one prefers all this added noise to add ambiance due to a very 'dry' [over-damped] room or somewhat offset hearing loss, then by all means use a very resonant metal, even something as resonant as tin.
GM
Listening position is on back wall, room is rectangular with long side being widthwise (speakers are on long wall, opposite couch). Speakers toed in approx 15-20 deg each. Listening area is centered between speakers. Speakers approx 6 ft apart, and about 9 ft from listening area, as dictated by room dims and doorways. Room is certainly not overdamped, but has carpet, soft couches, big coatrack, etc.. Hard wall behind/over couch however. First reflections are evident when the FR speakers are used plainly, but with the lens in place they don't seem to be noticeable anymore. Is that because of the spread, and thus many reflections all timed slightly differently? The spread on my lens is only 60 deg, so still a fairly tight pattern.. for the HF sound anyway.
I made another prototype lens, but this time tried something a bit different than what I've seen. I couldn't see what the very wide plates were doing where the width of the plate was outside of the horn or driver line of sight, other than it's recommended to leave the sides of the plates unobstructed.
So, I shortened them to just the min width to cover the small whizzer, about 4" wide. I also changed the vertext of the angled cutout, where previously I had a ~R 3/8 radius at the vertex, this time I just did a sharp angle - thinking that this would lessen the slight hot spot at the center even more. So 2 changes at once, not too good for scientific experimenting, but short on time and was hoping for the best...
I'll have to get a picture to post up here, but in short it doesn't seem to work as well as the full width version. Dispersion is better than without, but not as good as the full version. The packaging this way is much better I think and could be made stronger/more durable, as well as it being smaller widthwise and potentially easier to tuck into a grille cover (Or, as I had been thinking, maybe even into between the "curtains" of a Karlson K12...)
Jesse
So, I shortened them to just the min width to cover the small whizzer, about 4" wide. I also changed the vertext of the angled cutout, where previously I had a ~R 3/8 radius at the vertex, this time I just did a sharp angle - thinking that this would lessen the slight hot spot at the center even more. So 2 changes at once, not too good for scientific experimenting, but short on time and was hoping for the best...
I'll have to get a picture to post up here, but in short it doesn't seem to work as well as the full width version. Dispersion is better than without, but not as good as the full version. The packaging this way is much better I think and could be made stronger/more durable, as well as it being smaller widthwise and potentially easier to tuck into a grille cover (Or, as I had been thinking, maybe even into between the "curtains" of a Karlson K12...)
Jesse
I am guessing the lens should cover the radiating area fully. Perhaps if there is a sharp crossover frequency at which the main cone stops contributing and the whizzer starts, you could get away with a lens just in front of the whizzer. Otherwise, I would suggest extending the deflector plates vertically to top and bottom of the driver.
And, also guessing, the width of the commercial variants if probably no coincidence, is this perhaps necessary in relation to wavelengths of the lowest frequency required? Just thinking out loud, if you manipulate/delay the soundwave to a certain effect, you probably want to do that for the entire wavefront. Not just the middle bit.
From the brochure stuff I've read so far, these lenses don't seem too deep, but wiiiiiiiide. Maybe those circular perforated plate lenses are better if width is a concern?
And, also guessing, the width of the commercial variants if probably no coincidence, is this perhaps necessary in relation to wavelengths of the lowest frequency required? Just thinking out loud, if you manipulate/delay the soundwave to a certain effect, you probably want to do that for the entire wavefront. Not just the middle bit.
From the brochure stuff I've read so far, these lenses don't seem too deep, but wiiiiiiiide. Maybe those circular perforated plate lenses are better if width is a concern?
What about making a variation on plate diffusers shaped like a fan with notches on the blades?
Would be more complicated, but just wondering if it's been done before.
Edit:
sbcrx007: you mean like the sealed K-coupler "Klam"/"Clam" boxes?
Edit2:
GM: I do not like resonating aluminium. Steel alloys can have a nice sound, brass is wonderful.
Would be more complicated, but just wondering if it's been done before.
Edit:
sbcrx007: you mean like the sealed K-coupler "Klam"/"Clam" boxes?
Edit2:
GM: I do not like resonating aluminium. Steel alloys can have a nice sound, brass is wonderful.
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Ivo, I forgot to snag a picture, sorry. I've only read that the plate spacing limits the upper effective frequency of the lens, but it's entirely possible that the width has an effect on what the lower limit is. For the Fane 12" FR, it's really only the peaky stuff up at the top end of the graph that needs dispersed.
Re: wavefront delay, I don't think the difference in arrival time is probably much at all - not sure if it would be perceivable to anyone. The path length is only 1.65" longer thru the lens. For my narrow lens, part of my thought was just to limit how much "punch" I'm blocking that should be emanating from the main cone.
The perforated plate design is probably wayyy more flexible in terms of how you control the dispersion, since you can control both horizontal and vertical dispersion that way. In my mind, there's also a danger of "muddying up" the sound more since it has to bounce around inside that type of lens more than the angled plate design. Mostly I haven't tried it yet because I didn't have any perforated steel grille material laying around.
Just a bunch of assumptions and suppositions for now though... more reading to be done, and need to catch that fellow Freddy recommended. I had found a document by Dr. Geddes that seemed to have some math in it for calculating some angles, but it was a bit hard to follow without a background in that sort of thing. If it's permitted, I could probably dig that up and post it - it was an AES publication from long ago.
Jesse
Edit:
Kaffi, I'm having a hard time picturing what you mean with a fan blade design..? The existing designs clearly had a lot of research done on them back in the day, I'm not sure how much room for improvement there is without reinventing the wheel, so to speak...
I meant the K12 and K15 boxes that Freddy loves, that have the "curtains" out front and the driver mounted back behind them.
Re: wavefront delay, I don't think the difference in arrival time is probably much at all - not sure if it would be perceivable to anyone. The path length is only 1.65" longer thru the lens. For my narrow lens, part of my thought was just to limit how much "punch" I'm blocking that should be emanating from the main cone.
The perforated plate design is probably wayyy more flexible in terms of how you control the dispersion, since you can control both horizontal and vertical dispersion that way. In my mind, there's also a danger of "muddying up" the sound more since it has to bounce around inside that type of lens more than the angled plate design. Mostly I haven't tried it yet because I didn't have any perforated steel grille material laying around.
Just a bunch of assumptions and suppositions for now though... more reading to be done, and need to catch that fellow Freddy recommended. I had found a document by Dr. Geddes that seemed to have some math in it for calculating some angles, but it was a bit hard to follow without a background in that sort of thing. If it's permitted, I could probably dig that up and post it - it was an AES publication from long ago.
Jesse
Edit:
Kaffi, I'm having a hard time picturing what you mean with a fan blade design..? The existing designs clearly had a lot of research done on them back in the day, I'm not sure how much room for improvement there is without reinventing the wheel, so to speak...
I meant the K12 and K15 boxes that Freddy loves, that have the "curtains" out front and the driver mounted back behind them.
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Oh. so you meant the real Karlson type boxes, and not the "Klam"? The Klam is just a sealed box, and the front of the driver is in a sort of front chamber with those curtains you mention. As far as I have intertpreted things, it's the curtains that is the "K-coupler", and there are speakers around with k-coupler pipes on compression drivers even, seems like a pretty versatile design.
The Klam would probably be an application then too I guess, I just don't know too much about it. And it's really only worth thinking/talking about if the lens plates still work if they are shortened considerably width-wise. You could even place a lens right inside the K-aperture or coupler and have the lens plates go right out to meet the curtain edges, so there would just be a neat looking louvered section in the center. It would look killer, but I've no idea if it would sound good at all!
fwiw, Karlson's klams from the little KR5 Rocket to APX/Oliver Phase III and AP100 (assume "Magna Clam" were vented - whether effective or not = ? The little Rocket used a weak motor radio speaker. Oliver's Phase II used an alnico magnet 10" guitar speaker. AP100 used an Altec 421 15" speaker and a K-tube.
A cardboard mini klam front with typical angles of 30-40 degrees, suspended in front of the whizzer would deflect highs downwards and spread them - how smoothly = have to decide "by ear". It would be worth 10 minutes of time to make and try one.
A cardboard mini klam front with typical angles of 30-40 degrees, suspended in front of the whizzer would deflect highs downwards and spread them - how smoothly = have to decide "by ear". It would be worth 10 minutes of time to make and try one.
it would disperse "something" and have some downwards or upswards direction property. The power response of fullrange drivers can leave a big hole above 3K. You wouldn't want the paper klam very wide - maybe try like your mini plate lens - if its garbage, well at least you know.
I think the angle in K's illustration (hacked) below was 30 degress elevation - you could try 40 making the aperture steeper and top plate shorter.
I used a 40 degree mini klam on a one inch format compression driver (slot facing "down" as in that drawing - oddly it seemed to pretty much kill output above the flat upper part.
A. Weiiss' patent image shows a 40 degree version - don't know if the cone speaker was really used or just for illustration
- his product had a metal lens for a one inch format Eminence compression driver. I'm guessing that lens was about 1.25" square where it mounted over the compression driver's exit. Story goes that lens/driver in a system was evaluated and rejected as
it sprayed highs everywhere (vs THX controlled spec)
http://patentimages.storage.googleapis.com/pages/US5943431-1.png
I think the angle in K's illustration (hacked) below was 30 degress elevation - you could try 40 making the aperture steeper and top plate shorter.
I used a 40 degree mini klam on a one inch format compression driver (slot facing "down" as in that drawing - oddly it seemed to pretty much kill output above the flat upper part.
A. Weiiss' patent image shows a 40 degree version - don't know if the cone speaker was really used or just for illustration
- his product had a metal lens for a one inch format Eminence compression driver. I'm guessing that lens was about 1.25" square where it mounted over the compression driver's exit. Story goes that lens/driver in a system was evaluated and rejected as
it sprayed highs everywhere (vs THX controlled spec)
http://patentimages.storage.googleapis.com/pages/US5943431-1.png
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Like this? Is this also an acoustic lens?
Yes, that was what I assumed someone must have made sometime.
Edit:
Here it is on the speaker units:
2x SIEMENS Klangfilm 10" COAX speaker - ACOUSTIC LENS | #135558015
Edit2:
A bit OT, but never heard of Kinap Lomo before, looks nice:
KINAP LOMO speakers 11" 25GD-18-22 KLANGFILM FULL-RANGE USSR 4pcs | eBay
Edit3:
Nice square lenses from Japan, not too expensive for the pair:
JBL 2308 / L91 TYPE Kenrick Sound Acoustic Lens pair SET NEW From Japan | eBay
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This is very similar to what I expected, you are interested in spreading out the high frequency sounds that come from the wizzer, not the lower frequencies that come from the main cone.
I read some paper about circular diffusers, but it seemed to be for focusing sound of 100khz, so a bit higher up than I can hear.
I read some paper about circular diffusers, but it seemed to be for focusing sound of 100khz, so a bit higher up than I can hear.
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