I've been having trouble visualizing how to make a good looking RLH with the added "supra baffles". I understand the need to get the "baffle action" down to where the "horn action" falls off. I can also easily foresee a lot of work going into this added baffle, so I thought "Why not incorporate it into the cab itself?". I'm calling it the Tombstone RLH.
I'm no horn designer, so I want to copy the critical horn dimensions from an existing design such as Ron's A126. The following is what I came up with. Note that the added volume directly behind the CC can be used to vary the CC size. It obviously isn't drawn to scale, but the layout is flexible enough to scale the basic folding approach to almost any horn, and get the added benefit of horn pathways that are closer to square than typical constant width RLH's while keeping the construction fairly simple.
Does anyone see any pitfalls that I may not be considering? Is there anything inherently wrong with bifurcating the first 2/3rds of a horn?
I'm no horn designer, so I want to copy the critical horn dimensions from an existing design such as Ron's A126. The following is what I came up with. Note that the added volume directly behind the CC can be used to vary the CC size. It obviously isn't drawn to scale, but the layout is flexible enough to scale the basic folding approach to almost any horn, and get the added benefit of horn pathways that are closer to square than typical constant width RLH's while keeping the construction fairly simple.
Does anyone see any pitfalls that I may not be considering? Is there anything inherently wrong with bifurcating the first 2/3rds of a horn?
An externally hosted image should be here but it was not working when we last tested it.
Interesting idea John. I would like to know how it works out if you build it. Hasn.t created any response - I don't know why. the famous Klipsch corner horn was bifurcated for about two thirds of its length. I had a copy fo the papers he wrote about the design and he didn't seem to think that splitting it caused any problems. I think Dinsdale or one of the other British designers did an ugly looking one that was bifucated in the sixties or seventies. One speaker rear lodaded for the bass with an upward firing mid horn on the other side of the speaketr. I think it was in Wireless World. Designer may have been Crabbe. Hope this helps you make a decision.
jamikl
jamikl
jamikl,
Thanks for the input. I put some dimensions to paper and with a horn somewhere in between the Frugal and A126 horns, I end up with exterior dimensions for the main panel of 80cm high, 22cm wide at the base, 30cm wide at the maximum near the top, and 8cm thick. The mouth will add about 20cm to the back, and the overall size should remain a cute little high WAF horn.
The only change I've made in my plan is to eliminate the triangle centered at the top. I think it would only lead to a less than perfect bifurcation and be more likely to guide HF content into the horn.
I'll report back once I build a pair. My only horn for comparison is the Fostex cab for the 108, which I like alot, but I feel the front mouth is detrimental because it's HF content detracts from the point source sound.
Thanks for the input. I put some dimensions to paper and with a horn somewhere in between the Frugal and A126 horns, I end up with exterior dimensions for the main panel of 80cm high, 22cm wide at the base, 30cm wide at the maximum near the top, and 8cm thick. The mouth will add about 20cm to the back, and the overall size should remain a cute little high WAF horn.
The only change I've made in my plan is to eliminate the triangle centered at the top. I think it would only lead to a less than perfect bifurcation and be more likely to guide HF content into the horn.
I'll report back once I build a pair. My only horn for comparison is the Fostex cab for the 108, which I like alot, but I feel the front mouth is detrimental because it's HF content detracts from the point source sound.
Greets!
Most of the BLH designs of the 50s, 60's were split, not to mention W.E.'s fabulous 1920's 16A 'pancake' compression horn and all the 'W' bins that followed.
Anyway, the quality of the bends determine how much HF the horn will pass as well as how much gets reflected back to the throat, modulating the driver, so its HF corner needs to be fairly low to keep folding simple.
GM
Most of the BLH designs of the 50s, 60's were split, not to mention W.E.'s fabulous 1920's 16A 'pancake' compression horn and all the 'W' bins that followed.
Anyway, the quality of the bends determine how much HF the horn will pass as well as how much gets reflected back to the throat, modulating the driver, so its HF corner needs to be fairly low to keep folding simple.
GM
Tombstone prototypes are under construction. Note that I've gotten away from the original plan of a rear firing mouth and will use the perimeter of the front section to form the mouth.
The basic idea is to take the Frugelhorn and add an extension to greatly enlarge the mouth, similar to the effect of the Frugel deflector, but probably more controlled. To retain the overall theme of efficiency in size most of the perimeter of the main cab will be part of the panels forming a horn mouth greater than 3000 cm2 (up to 4k cm2 if I ignore edge diffraction, which I might be able to get away with to some extent since the baffle is 11" wide). These cabs shouldn't suffer ill effects too much with near wall, corner, or placement well into the room due to the mouth size and orientation.
The guts of front section are pictured below. Note that a small panel to prevent interference between the operation of the 2 throats isn't installed. To give you an idea of scale, they are 90cm x 28cm x 9cm (3ft x 11" x 3.5") externally. The back plate will increase the width and height, but they are prototypes. In shareable form I'll be able to shrink the height quite a bit by using some of the CC which is way too large right now at about 3.5L.
Note the ease of construction so far, and I'll probably mod the layout to minimize angled cuts when I shrink the height, leaving only a few angled cuts to form the rear segments, or at least focus on standard 90's and 45's.
Also, these are looking way too much like tall skinny baby coffins, so I need another name to avoid the negative connotations. Any input is welcome. In the meantime, my fingers are crossed regarding the sound. While I've covered a lot of bases in theory, as Ed always reminds me, good sound means a lot more than theory.
The basic idea is to take the Frugelhorn and add an extension to greatly enlarge the mouth, similar to the effect of the Frugel deflector, but probably more controlled. To retain the overall theme of efficiency in size most of the perimeter of the main cab will be part of the panels forming a horn mouth greater than 3000 cm2 (up to 4k cm2 if I ignore edge diffraction, which I might be able to get away with to some extent since the baffle is 11" wide). These cabs shouldn't suffer ill effects too much with near wall, corner, or placement well into the room due to the mouth size and orientation.
The guts of front section are pictured below. Note that a small panel to prevent interference between the operation of the 2 throats isn't installed. To give you an idea of scale, they are 90cm x 28cm x 9cm (3ft x 11" x 3.5") externally. The back plate will increase the width and height, but they are prototypes. In shareable form I'll be able to shrink the height quite a bit by using some of the CC which is way too large right now at about 3.5L.
Note the ease of construction so far, and I'll probably mod the layout to minimize angled cuts when I shrink the height, leaving only a few angled cuts to form the rear segments, or at least focus on standard 90's and 45's.
Also, these are looking way too much like tall skinny baby coffins, so I need another name to avoid the negative connotations. Any input is welcome. In the meantime, my fingers are crossed regarding the sound. While I've covered a lot of bases in theory, as Ed always reminds me, good sound means a lot more than theory.
An externally hosted image should be here but it was not working when we last tested it.
To get rid of the nasty implications, just make them rectangular, leave the bends as internal and fill the voids with sand.
If you paint them jet black, you can call them Monoliths... not original but it could work wonders with ape-like friends
Hope it works well. I'm in the search of new homes for my 108s too...
Gastón
If you paint them jet black, you can call them Monoliths... not original but it could work wonders with ape-like friends
Hope it works well. I'm in the search of new homes for my 108s too...
Gastón
They look fantastic John!
and maybe not so hard to build. I have some FE126e's which could work. keep us posted.
I'd love to make a tastless dead baby joke...but i probably shouldn't.
Could be made to look a bit like Zu duids maybe as per ghpicard's suggestion. I think the shape looks like a skate or surfboard.
Regards Philip
and maybe not so hard to build. I have some FE126e's which could work. keep us posted.
I'd love to make a tastless dead baby joke...but i probably shouldn't.
Could be made to look a bit like Zu duids maybe as per ghpicard's suggestion. I think the shape looks like a skate or surfboard.
Regards Philip
Thanks Philip,
These are just first tries, so I'll probably go shorter and closer to rectangle when I use some of the CC for early portions of the horn. I'm going to finish the 2 out differently to see which works best, the original plan (rear exit) or the mouth(s) around the cab, and compare them to my Frugels and Fostex's.
I think I can finish out the horns no problem. My biggest sticking point now is how to deflect/dissipate HF in the CC with using absorbant in order to prevent reflections back at the cone. This is very problematic in the Fostex cab with flat service behind and close to the driver. In my Frugels I solved the problem very well with deep V shapes behind the driver, but I had excess depth to work with there. With these I don't have much depth to work with, so I'll probably have to use a circular plate behind the driver with bevelled edges to deflect them away and dissipate them using V shapes elsewhere in the CC. I have over 1.5 liters to fill up anyway.
I've read repeatedly that absorbant in the CC is harmful to a horn's sound. I think the resulting change in the compliance of the air/absorbant combo is harmful to the horn's function. I've long speculated that the sonically destructive HF bouncing around in the CC can be dissipated using rigid surfaces in special shapes. That way the air volume in the CC retains its normal compliance. The results I'm getting with my Frugels supports this theory.
These are just first tries, so I'll probably go shorter and closer to rectangle when I use some of the CC for early portions of the horn. I'm going to finish the 2 out differently to see which works best, the original plan (rear exit) or the mouth(s) around the cab, and compare them to my Frugels and Fostex's.
I think I can finish out the horns no problem. My biggest sticking point now is how to deflect/dissipate HF in the CC with using absorbant in order to prevent reflections back at the cone. This is very problematic in the Fostex cab with flat service behind and close to the driver. In my Frugels I solved the problem very well with deep V shapes behind the driver, but I had excess depth to work with there. With these I don't have much depth to work with, so I'll probably have to use a circular plate behind the driver with bevelled edges to deflect them away and dissipate them using V shapes elsewhere in the CC. I have over 1.5 liters to fill up anyway.
I've read repeatedly that absorbant in the CC is harmful to a horn's sound. I think the resulting change in the compliance of the air/absorbant combo is harmful to the horn's function. I've long speculated that the sonically destructive HF bouncing around in the CC can be dissipated using rigid surfaces in special shapes. That way the air volume in the CC retains its normal compliance. The results I'm getting with my Frugels supports this theory.
I think Fostex themselves would agree with you, given they sell those plastic HP reflectors for this purpoise. Over priced for what they are, and almost certaily less well-built than yours, but I hear from several quarters, including Terry Cain, that they work exceptionally well, so there's certainly something in it.
The thing is, I don't want to just diffuse the HF, I want to dissipate it. If you've ever built a tall pyramid shaped box with the driver mounted in the base, they don't need damping. Just a little stuffing at the point and the sound turns into heat there, but the lower frequencies which are only in pressure form, not wave form, are unaffected.
Ron knows someone with the software to model what shapes and dimensions are required to absorb different frequencies, but apparently it has military applications, so the info can't be shared.
In this case, I have just over 7cm of depth, so there's not much room behind the driver. The approach I will try is to reflect them away from the driver and then disspate them, so they don't come back to be reflected right back to the driver.
In my Frugels, I'm seriously considering using concrete to get the shape I want, since I don't have a removeable front plate to build it out of wood, although the blocks do work quite well and with them wedged in there, the CC panels are quite dead.
Ron knows someone with the software to model what shapes and dimensions are required to absorb different frequencies, but apparently it has military applications, so the info can't be shared.
In this case, I have just over 7cm of depth, so there's not much room behind the driver. The approach I will try is to reflect them away from the driver and then disspate them, so they don't come back to be reflected right back to the driver.
In my Frugels, I'm seriously considering using concrete to get the shape I want, since I don't have a removeable front plate to build it out of wood, although the blocks do work quite well and with them wedged in there, the CC panels are quite dead.
Ron knows someone with the software to model what shapes and dimensions are required to absorb different frequencies, but apparently it has military applications, so the info can't be shared
Well i can say this: Its all about sound, its all about space, its all about pressure in the strangest place.
In reality most do not realize that its a multi frequency action. Most think of a BLH in just the sense of the lowest frequency (Fc).Its when you introduce different frequencies (wavelengths) that the action becomes much more complicated. Different wavelengths being sent thru a changing flare rate react differently
than a singular wave at a given frequency
, this is apparent in both the TL(Martin showed us this) and the horn action.
I have been critized in the past for looking at it from a pressure standpoint, but in any sound wave its nothing more than an alternating positive and negative pressure with the baseline of the difference as being the ambient pressure.
When a higher frequency wave encounters a given loading it attenuates at a greater rate than a lower frequency. The shape/volume( at each point of the expansion) of the expansion determines the loading. Every time you bend the pressure front you attenuate the sound but at a different rate for different frequencies.
ron
Well i can say this: Its all about sound, its all about space, its all about pressure in the strangest place.
In reality most do not realize that its a multi frequency action. Most think of a BLH in just the sense of the lowest frequency (Fc).Its when you introduce different frequencies (wavelengths) that the action becomes much more complicated. Different wavelengths being sent thru a changing flare rate react differently
than a singular wave at a given frequency
, this is apparent in both the TL(Martin showed us this) and the horn action.
I have been critized in the past for looking at it from a pressure standpoint, but in any sound wave its nothing more than an alternating positive and negative pressure with the baseline of the difference as being the ambient pressure.
When a higher frequency wave encounters a given loading it attenuates at a greater rate than a lower frequency. The shape/volume( at each point of the expansion) of the expansion determines the loading. Every time you bend the pressure front you attenuate the sound but at a different rate for different frequencies.
ron
Ted Jordan's membrane absorber...
John you could try playing with these. Ted Jordan published an article years ago in Wireless World I think.
Amembrane absorber is a simple device to make. You take a cabinet panel and place a four sided frame of strapping around the outside edges, the strapping can be 3/4" or higher. Then you place damping material into the inside space such that it extends higher than the top edge of the strapping (the damping material must loft above the strapping) then you install a plastic film skin over top of the strapping. The film and the frame (made up by the strapping) must be air tight and you want some tension on the film.
What you end up with is an air tight membrane absorber. Air pressure inside the cabinet presses on the membrane which in turn presses on the damping material (fiberglass for example) and as the fiberglass moves it generates friction and so turns the energy of the pressure front into heat. The neat part is that it does not stop there. Since the "system"" is a closed one (ie. sealed air tight) the compressed air trapped inside the absorber pushes back and the process is repeated. So for a given amount of damping material you get a lot more loss and I believe that the usable band is also extended (but don't quote me on this). You do need to account for the volume of the absorber but as to how much I am not too sure (probably not a lot and it also probably will vary with frequency.
Something else you might consider trying is to fill your cavity with Pearlite. You need to pass the Pearlite through a sive to loose the small particles and the dust and you also need to place the Pearlite into a bag of sorts (Pantyhose would do). I think that filling a thin plastic film bag would also do but not everyone agrees with me there. In an event the Pearlite is an exceptional damping material (best I have ever used). KEF published a journal paper on using active charcoa as a damping medium. Sorry I don't have a reference. Pearlit is very similar to charcoal and is actually a bit more porus bet of all it is clean to use/handle and is very cheap to buy. Give it a shot and see what you think. I have found the pearlite to be superior to long fiber wool. Regards Moray James.l
John you could try playing with these. Ted Jordan published an article years ago in Wireless World I think.
Amembrane absorber is a simple device to make. You take a cabinet panel and place a four sided frame of strapping around the outside edges, the strapping can be 3/4" or higher. Then you place damping material into the inside space such that it extends higher than the top edge of the strapping (the damping material must loft above the strapping) then you install a plastic film skin over top of the strapping. The film and the frame (made up by the strapping) must be air tight and you want some tension on the film.
What you end up with is an air tight membrane absorber. Air pressure inside the cabinet presses on the membrane which in turn presses on the damping material (fiberglass for example) and as the fiberglass moves it generates friction and so turns the energy of the pressure front into heat. The neat part is that it does not stop there. Since the "system"" is a closed one (ie. sealed air tight) the compressed air trapped inside the absorber pushes back and the process is repeated. So for a given amount of damping material you get a lot more loss and I believe that the usable band is also extended (but don't quote me on this). You do need to account for the volume of the absorber but as to how much I am not too sure (probably not a lot and it also probably will vary with frequency.
Something else you might consider trying is to fill your cavity with Pearlite. You need to pass the Pearlite through a sive to loose the small particles and the dust and you also need to place the Pearlite into a bag of sorts (Pantyhose would do). I think that filling a thin plastic film bag would also do but not everyone agrees with me there. In an event the Pearlite is an exceptional damping material (best I have ever used). KEF published a journal paper on using active charcoa as a damping medium. Sorry I don't have a reference. Pearlit is very similar to charcoal and is actually a bit more porus bet of all it is clean to use/handle and is very cheap to buy. Give it a shot and see what you think. I have found the pearlite to be superior to long fiber wool. Regards Moray James.l
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