I would think that this or similar had been thought of before, but I haven't seen it; though to be frank 'til recently I thought little about directivity. (But I do have some ribbons that I want to employ to their best, and many other technical challenges . .
I may have overlooked a fundamental of waveguides and/ or directivity theory, but just in case:
To improve vertical dispersion, waveguides on the sides of ribbons, forward of the their side axes, that reflects some of the wide horizontal dispersion inwards, and up and/ or down.
I have no idea how large the waveguides should be, or if they would be better flat or curved etc.
To get the 'correction' best for the room/ listener/ system would require adjustment. Waveguides could be mounted close to the ribbon on pivots, starting with them e.g. about 30 degrees forward of the ribbon's side axes. By reducing horizontal dispersion, much of it bouncing off side walls, image width would probably decrease, but image 'specificity' increase.
The key idea: the waveguides would be divided in two horizontally, with the upper part, folded back, diverting sound up. The % of the waveguide folded up, depending on how much energy you want to divert up. I would think usually more than half, with typical directivity focused on a listener who is seated, but wants more even response when standing or walking around.
If the split of the waveguides' upper and lower parts is hinged, the amount of diversion up or dowm could be fine tuned.
Any merit?
I may have overlooked a fundamental of waveguides and/ or directivity theory, but just in case:
To improve vertical dispersion, waveguides on the sides of ribbons, forward of the their side axes, that reflects some of the wide horizontal dispersion inwards, and up and/ or down.
I have no idea how large the waveguides should be, or if they would be better flat or curved etc.
To get the 'correction' best for the room/ listener/ system would require adjustment. Waveguides could be mounted close to the ribbon on pivots, starting with them e.g. about 30 degrees forward of the ribbon's side axes. By reducing horizontal dispersion, much of it bouncing off side walls, image width would probably decrease, but image 'specificity' increase.
The key idea: the waveguides would be divided in two horizontally, with the upper part, folded back, diverting sound up. The % of the waveguide folded up, depending on how much energy you want to divert up. I would think usually more than half, with typical directivity focused on a listener who is seated, but wants more even response when standing or walking around.
If the split of the waveguides' upper and lower parts is hinged, the amount of diversion up or dowm could be fine tuned.
Any merit?
Ummm... no.
First off, that's not a waveguide in the linked site.
That's a cheezy way to change the effective length of the ribbon with respect to frequency. Foam isn't terribly effective, but it might help some.
At higher freqs only the open area radiates, but then the level is also dropped due to the absorption of the other 2/3 of the ribbon not radiating (if the absorption works).
They tapered the wedges to try to make the ribbon "change size" wrt freq.
A waveguide is a sort of horn. This is not a sort of horn.
A waveguide will do nothing to improve the vertical dispersion of a ribbon, but it could control the horizontal directivity, and or pop up the energy at or below the F3 point...
_-_-bear
First off, that's not a waveguide in the linked site.
That's a cheezy way to change the effective length of the ribbon with respect to frequency. Foam isn't terribly effective, but it might help some.
At higher freqs only the open area radiates, but then the level is also dropped due to the absorption of the other 2/3 of the ribbon not radiating (if the absorption works).
They tapered the wedges to try to make the ribbon "change size" wrt freq.
A waveguide is a sort of horn. This is not a sort of horn.
A waveguide will do nothing to improve the vertical dispersion of a ribbon, but it could control the horizontal directivity, and or pop up the energy at or below the F3 point...
_-_-bear
The longer ribbons (about 5" long) like the Aurum Cantus G3, Fountek Neo2.0, and similar are the ones with more limited vertical response if you just use one. These ribbons need to be at ear level for best results.
The shorter ribbons (3" long) I have used such as the A-C G2 or G2si, Fountek Neo3.0 and similar have enough vertical dispersion so that they sound OK at listening distances in normal situations.
I wouldn't think that any attempt to use waveguides and such would be successful with any of these ribbons. The ribbon element is already embeddedd somewhat so you'll quickly screw up their horizontal dispersion. All of the ribbons mentioned above have exceptional wide horizontal dispersion and sound great when used properly.
The shorter ribbons (3" long) I have used such as the A-C G2 or G2si, Fountek Neo3.0 and similar have enough vertical dispersion so that they sound OK at listening distances in normal situations.
I wouldn't think that any attempt to use waveguides and such would be successful with any of these ribbons. The ribbon element is already embeddedd somewhat so you'll quickly screw up their horizontal dispersion. All of the ribbons mentioned above have exceptional wide horizontal dispersion and sound great when used properly.
I can't point to empirical data on these, but at the frequencies in question, I believe the foam wedges may be quite effective at widening vertical coverage.
Depending on the formulation and pore size, the foam will supply not only absorbtion but also a form of physical acoustic delay proportional to its thickness (actually slowing the speed of the sound passing through it), creating a lensing effect much like the perforated metal "potato masher" lenses on the front of some vintage horns.
Bill F. said:
Whilst Bear is right that they are a little cheesy(I kinda like 'em though) there's no denying they are effective. So your right Bill, I've seen with and without the foam and the results aren't subtle confirming that the foam is indeed effective.
Bear was thinking about it like I originally did ie. progressive attenuation of HF along the extremes of the ribbon. Whereas you correctly state that sound passing through the foam gets delayed in relation to that which is unimpeaded. So you get an offset in the time domain where the frequencies on the extremes of the ribbon are less likely to create the typical line source characteristic.
There are downsides of course but my pair of RAAL's should arrive within the week and I'll be testing with and without the foam to see just what happens, what improves and how this relates to overall performance.
Based on the similarities in design between the RAAL and the Aurun Cantus G3, (and the cheapness of creating the foam wedges), I might just have to try this.
The G3s have a measured (on the website) 15+dB drop-out at 10 degrees off vertical at 15kHz - where the RAALs have 15dB drop-out at 20 degrees off vertical at 15kHz.
I'm not going to hack out the saw edge baffle though.
The G3s have a measured (on the website) 15+dB drop-out at 10 degrees off vertical at 15kHz - where the RAALs have 15dB drop-out at 20 degrees off vertical at 15kHz.
I'm not going to hack out the saw edge baffle though.
Dear Action Man
My sick wife wants me to accompany her watching Little Miss Sunshine, but it's not on http://www.metacritic.com/ so is it good?
DEELIMNAS!
In my part of the world, Clarke Rubber is closed, so it's onto the to do list . .
My sick wife wants me to accompany her watching Little Miss Sunshine, but it's not on http://www.metacritic.com/ so is it good?
DEELIMNAS!
In my part of the world, Clarke Rubber is closed, so it's onto the to do list . .
The foam thingy can also be regarded as an acoustic lens since it will also delay the sound a little depending on thickness.
A very similar idea for increasing the horizontal (not much difference than doing it turned around by 90 degrees) dispersion has been posted on this forum be me (Years ago) !
Regards
Charles
A very similar idea for increasing the horizontal (not much difference than doing it turned around by 90 degrees) dispersion has been posted on this forum be me (Years ago) !
Regards
Charles
Grumpy_Git
I had seen the Little Miss Sunshine billboard and thought it was another corny family movie, probably aussie.
But you're right, I loved it! By the end I was in tears of laughter.
BTW, Bear and Jim
Thanks for warning me off the red herring of waveguides for this aim!
I imagine the acoustic delay from foam is small, but very subtly negative.
Charles
www.diyaudio.com/forums/showthread.php?s=&postid=489763&highlight=#post489763
Experimenting is sounding more appealing
Cheers
I had seen the Little Miss Sunshine billboard and thought it was another corny family movie, probably aussie.
But you're right, I loved it! By the end I was in tears of laughter.
BTW, Bear and Jim
Thanks for warning me off the red herring of waveguides for this aim!
I imagine the acoustic delay from foam is small, but very subtly negative.
Charles
www.diyaudio.com/forums/showthread.php?s=&postid=489763&highlight=#post489763
Experimenting is sounding more appealing
Cheers
It will be a little bit of both: The speed of sound within a medium is dependant (amongst other things) on 1/SQRT(density). And it willl also present some increase in path length the way it is done within the classic acoustic lens:
http://www.jblpro.com/pub/obsolete/4320.pdf
Regards
Charles
http://www.jblpro.com/pub/obsolete/4320.pdf
Regards
Charles
To be more clear, I should say the sound waves passing through a given thickness of open-cell foam traverse it slower than they would the same distance of open air.
A sound wave can be thought of in terms of fluid flow. The complex structure of open-cell foam forces the fluid flow to make many tiny deviations from its axis of travel which add up to a net delay.
Edit:
Beat me to the punch, Charles.
A sound wave can be thought of in terms of fluid flow. The complex structure of open-cell foam forces the fluid flow to make many tiny deviations from its axis of travel which add up to a net delay.
Edit:
Beat me to the punch, Charles.
I have heard good examples of foam increasing the effective distance a wave has to travel, i have used it in horns and while the top end is attenuated somewhat the horn does appear to be bigger and longer than it really is (it will support a noticably lower wavelength). I so no reason why this wont work and my offer to lend Shin my Fountek Neo3s is now retracted until I get chance to try this out
Yes, I agree, the foam wedges will also serve somewhat as an acoustic lens. Being open cell foam. But they also absorb and are lossy.
Looking at the site's curves for the on/off axis response I was not terribly impressed with the results. They are not as good as the old JBL "potato masher" referred to here, imho.
Perhaps better than nothing?
Old idea... not new, fwiw.
Some Japanese company is copying a patented ribbon design - that has been discussed here as well- it has a slit down the middle and being somewhat "square" in aspect ratio, it does well in both axes...
Ribbons, ribbons everywhere...
_-_-bear
Looking at the site's curves for the on/off axis response I was not terribly impressed with the results. They are not as good as the old JBL "potato masher" referred to here, imho.
Perhaps better than nothing?
Old idea... not new, fwiw.
Some Japanese company is copying a patented ribbon design - that has been discussed here as well- it has a slit down the middle and being somewhat "square" in aspect ratio, it does well in both axes...
Ribbons, ribbons everywhere...
_-_-bear
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