I think that it is like a lot of things. You have to solve the big problems before you can detect changes to the smaller ones. I am sure that with older devices the resonances and HOMs from the horns acoustics would mask any such effects from its mechanics. Clean up the acoustics and then the mechanics becomes the major issue.
The extreams seem to work best:
either a simple circular section OS horn (with lips) that operates nearly aberration free;
or more recently,
the JBL/QSC which I suspect is chaotically dismembering the wave front entering the horn to get the wide pattern spread.
Performance of the designs in between seem to me to be mediocre in performance.
WHG
either a simple circular section OS horn (with lips) that operates nearly aberration free;
or more recently,
the JBL/QSC which I suspect is chaotically dismembering the wave front entering the horn to get the wide pattern spread.
Performance of the designs in between seem to me to be mediocre in performance.
WHG
Great observation.....and it's one of the reasons ultra light ribbon membranes get such a bad rap.......slap em on a vibrating baffle with dynamic cones is like asking for a tattoo while on a whitewater rafting trip.........not good. My WG/CD builds have all been seperate enclosures for the HF and concentric layers of MDF with resin fill for the waveguides.......a bit extra work but worth the effort IMO.
FWIW, I theorize HOMs are exascerbated resonant wavelengths by underdamped structure. A ring is a ring is a ring with all their harmonic beauty......or not. Lol
......and yes, to my ears the M2 guide is the finest WG/ horn I've yet heard with the 15" Summa a close second only trailed an edge by the QSC.
But for me, there's still a bit of something special about damped HiFi drivers and properly used ribbons that even the most elaborate horn based Pro driver system can't achieve. Can't put my finger on it and certainly haven't been able to identify it with measurements but in a quiet dedicated small listening space at reasonable levels the Hifi alignment is my preference to date. Still working on it though.
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SInce HOMs exist even if the walls are infinitely rigid, I don't think that your hypothesis can be correct. Agree that a resonant flimsy waveguide could also create HOM's they clearly can exist even in a perfectly rigid one.
Since there are less than six sets of 15" Summa's (that I personally built and tested) I would be curious to know where you heard them. That design is now a decade old and I am sure that the NS-15 - the finest speaker that I have ever made and/or measured - would give the M2 a run for its money. I am going to finally replace my ancient Summa prototypes with NS-15's. They are the first speakers that I have considered doing that. (By the way those old Summa's will go cheap when compared to the NS-15 or even what they sold for originally.)
good empirical practice tho. then you knew for certain what was crapola in the design.
the horn i damped was still crapola but less so with the damping
Errata
Should read JBL/ICW (M2) for the aggressive design implementation of this technology.
Should read JBL/ICW (M2) for the aggressive design implementation of this technology.
Attachments
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Am I right in thinking that a change in aspect will produce diffraction within the waveguide when the radius of the cross section around the expanding dimension is greater than 1/4 wavelength, and that the termination radius will be partly eclipsed from this by the waveguide wall, resulting in side lobes outside the main pattern as well as some internal reflection?
I propose, (actually I've been caught up on this idea and would rather just put it to bed if need be), that if the corners lead the expansion with respect to the change in aspect, the reflections will be directed further from the listening position, and the side lobes might optionally be absorbed at the mouth.
I propose, (actually I've been caught up on this idea and would rather just put it to bed if need be), that if the corners lead the expansion with respect to the change in aspect, the reflections will be directed further from the listening position, and the side lobes might optionally be absorbed at the mouth.
This waveguide makes me think what I've written above. I've been trying to trade it off as a fix to an exaggeratedly narrow central vertical directivity without over increasing the directivity index, while also acting as a sacrificial part of the expansion to pass across to, for example, the central side walls when starting to terminate them in the hope that diffraction will be more localised around the side panels. So far I'm just finding it a mess.
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With the waveguide I'm working on, a 1.7:1 aspect (eg 16x9.25) will hold from the throat with 90x60 straight walls for at least the first 20cm of axial length. This might be worth moving closer to.
However vertical directivity is normally controlled by the height of an array, and more commonly a horn throat for a narrow vertical is made higher than it is wide.
Are these two connected or could I go with the wider shorter aspect? If it's a matter of their respective fH, I can probably cross that, but the top and bottom would need to be axially longer which is a concern. Are these the only constraints/downsides?
[By the way is it also fair to say the criteria for the throat being sufficiently small for a given higher frequency... to compare a dimension across the throat of a waveguide and the waveguide angle leading from it, to a circular free radiator of that diameter, and its nartural directivity (ie that it be at least as wide)?]
However vertical directivity is normally controlled by the height of an array, and more commonly a horn throat for a narrow vertical is made higher than it is wide.
Are these two connected or could I go with the wider shorter aspect? If it's a matter of their respective fH, I can probably cross that, but the top and bottom would need to be axially longer which is a concern. Are these the only constraints/downsides?
[By the way is it also fair to say the criteria for the throat being sufficiently small for a given higher frequency... to compare a dimension across the throat of a waveguide and the waveguide angle leading from it, to a circular free radiator of that diameter, and its nartural directivity (ie that it be at least as wide)?]
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Allen - I am sorry but I am just finding it difficult to visual what it is you are asking. It seems to me that you are talking about a basically diffraction device, which works quite differently than a waveguide. What happens when the cross section aspect changes is not really known, but I suspect that it would generate some non-axisymmetric HOMs (which can exist, but are not an issue in an axisymmetric waveguide.)
Maybe include some drawings to illustrate your questions.
Maybe include some drawings to illustrate your questions.
I've used mortite and liquid nails for subfloors. Stole the latter idea from Geddes. Both are available at Home Depot.
I think mortite probably works better, but I tend to use liquid nails because I have concerns about mortite delaminiating. It's probably not something I need to worry about, I've nevery actually *seen* it delaminate, it just seems like liquid nails is more permanent.
just run a search like this in google:
site:diyaudio jbl m2
There's tons of discussions of it here. There's a pic on the previous page. As far as I can tell, the M2 is basically an evolution of the biradial constant directivity horns from forty years ago, but with the addition of a rather clever diffraction slot. But it's still a diffraction slot.
For a simple technique (a better technique would involve expensive materials not readily available) I would use liquid nails and glass cloth (ala fiberglass). Something within the bed of massive adhesive is required to dissipate the vibrational energy. Just adding mass is somewhat effective, but not nearly as effective as adding damping through some form of constrained rigid filler. I use glass beads, but again, not readily available.
ICW Design Issues
View the throat of an ICW as a short cylindrical segment deeply castellated by quadratic slots that lead abruptly to the four corner trenches in the horn face. (There could be more radially disbursed I suspect.) Then imagine how a acoustic wave might behave to those boundary conditions while diffracting around them and eventually radiating away from the horn face. In my estimation, the resulting process is sufficiently chaotic that there are no prominent HOM's formed to be heard; but somehow, in the far field, a broad wave front of uniform pressure emerges. The patent that covers this design, does not reveal details of the transformation process that is taking place, nor does it disclose why the wave spread is not bandwidth limited even when signal wavelength becomes comparable to and much smaller than, horn throat dimensions. I think for good reasons this information was withheld. Until process details become evident, successful design variants of this horn will remain in the realm of serendipity and trade secrets. WHG
View the throat of an ICW as a short cylindrical segment deeply castellated by quadratic slots that lead abruptly to the four corner trenches in the horn face. (There could be more radially disbursed I suspect.) Then imagine how a acoustic wave might behave to those boundary conditions while diffracting around them and eventually radiating away from the horn face. In my estimation, the resulting process is sufficiently chaotic that there are no prominent HOM's formed to be heard; but somehow, in the far field, a broad wave front of uniform pressure emerges. The patent that covers this design, does not reveal details of the transformation process that is taking place, nor does it disclose why the wave spread is not bandwidth limited even when signal wavelength becomes comparable to and much smaller than, horn throat dimensions. I think for good reasons this information was withheld. Until process details become evident, successful design variants of this horn will remain in the realm of serendipity and trade secrets. WHG
HF Horn Flex and Ringing Issues
To mitigate the former for an existing horn, why not isolate it in its own sub-enclosure? For the remaining HF flex, bond external ribs across the bending modes of the horn body.
For the latter, a typical characteristic of Aluminum horns, we applied layers of vehicle body under-coat to suppress the ringing.
WHG
To mitigate the former for an existing horn, why not isolate it in its own sub-enclosure? For the remaining HF flex, bond external ribs across the bending modes of the horn body.
For the latter, a typical characteristic of Aluminum horns, we applied layers of vehicle body under-coat to suppress the ringing.
WHG
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WHG,
I agree that some of these suggestion on how to dampen and stiffen a horn are just not effective. If I had to reinforce a fiberglass horn or even a cheap plastic horn would be to bond some wood ribs on the back side. You really don't have to cover the entire surface to stiffen the structure or the raise the resonant properties of the horn surfaces. One trick it to use asymmetric placement of the stiffeners, this helps to spread any remaining resonances so they don't add together. If I was just looking for a cheap damping material i would look for some of the low density foam you find in the hardware store. As long as it is a rigid foam that will not only stiffen the structure but damp at the same time. Let it dry and you can sand it and shape it. You can add more layers, they will bond well and make the shape whatever you like.
I agree that some of these suggestion on how to dampen and stiffen a horn are just not effective. If I had to reinforce a fiberglass horn or even a cheap plastic horn would be to bond some wood ribs on the back side. You really don't have to cover the entire surface to stiffen the structure or the raise the resonant properties of the horn surfaces. One trick it to use asymmetric placement of the stiffeners, this helps to spread any remaining resonances so they don't add together. If I was just looking for a cheap damping material i would look for some of the low density foam you find in the hardware store. As long as it is a rigid foam that will not only stiffen the structure but damp at the same time. Let it dry and you can sand it and shape it. You can add more layers, they will bond well and make the shape whatever you like.
Hi Patrick,
Yes, I have seen a lot of discussion about JBL M2 horn, but I have understood that You have made a horn like M2 but with different size or shape, so if it is the case, please show us some pictures. As I have understood in M2 design, it seems that exponential surface law flare is maintained applying diagonal "Karlson Koppler" V-shape surface expansion.
There are not so many real technical info about M2, so if You have something please 'distribute' to us.
regards
ivica
Yes, I have seen a lot of discussion about JBL M2 horn, but I have understood that You have made a horn like M2 but with different size or shape, so if it is the case, please show us some pictures. As I have understood in M2 design, it seems that exponential surface law flare is maintained applying diagonal "Karlson Koppler" V-shape surface expansion.
There are not so many real technical info about M2, so if You have something please 'distribute' to us.
regards
ivica