There are not enough details on either of those to comment on, but since they both have round throats and rectangular mouths, they both have to have problems. Which is better or worse is hard to tell just from a photograph. I suspect that the radial design has a diffraction slit to be that wide. That's a real no-no in my book.
All good points which were carefully considered when designing the last set of floor monitors I built using a rectangular waveguide.
Building to a specific baffle size only 14.75" tall, 16.25" total including the cabinet walls, the reduction of mouth area using a round wave guide would have required a much higher crossover point than desired for the application.
Had space for a larger round wave guide that could have been crossed as low as desired been available, it would have been considered, but lacking a lathe, not for long
.Art
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Sorry for the late response, but I was out of the country with badd access to the internet.
I do not see what mouth area has to do with the crossover point. I don;t see a connection.
I am retro-fitting a phase plug to a conical horn on an 8" cone intended for use up to 1kHz. The horn was built with the intended throat area at the baffle so I enlarged this and changed the throat entry angle in order to extend it down to the driver cone.
I am in the process of faulting some phase plug designs, ie. the left half shown has been chosen for equal path lengths and the right has been chosen for equal pressure on each side of the ring. I've built the left one but am considering the right one.
With a compression ratio of 3:1, I figure that if the pressure at D, E and F is 0dB then they would add to 9.5dB at the throat, below some frequency... Whereas A, B and C would be at 2.5dB, 0dB and -3.5 dB respectively and would add to 7.5dB of wanted signal and -3.5dB of HOM based on the physical separation of the two entry points against the virtual location of the throat.
With the left phase plug maintained as shown, will this HOM (pair?) cancel itself at the next crossing? Will it continue to increase its path length difference with the main mode and affect lower frequencies? or will it simply be limited to some higher frequency?
On the right side the (average) path length differences before the throat seem to give no problems for two octaves above what I need and would not have the pressure difference. I considered tilting the throat to equalise the path difference from each side of the throat entry but this would seem to be adding an unwanted throat chamber.
Is there any significance to this?
I am in the process of faulting some phase plug designs, ie. the left half shown has been chosen for equal path lengths and the right has been chosen for equal pressure on each side of the ring. I've built the left one but am considering the right one.
With a compression ratio of 3:1, I figure that if the pressure at D, E and F is 0dB then they would add to 9.5dB at the throat, below some frequency... Whereas A, B and C would be at 2.5dB, 0dB and -3.5 dB respectively and would add to 7.5dB of wanted signal and -3.5dB of HOM based on the physical separation of the two entry points against the virtual location of the throat.
With the left phase plug maintained as shown, will this HOM (pair?) cancel itself at the next crossing? Will it continue to increase its path length difference with the main mode and affect lower frequencies? or will it simply be limited to some higher frequency?
On the right side the (average) path length differences before the throat seem to give no problems for two octaves above what I need and would not have the pressure difference. I considered tilting the throat to equalise the path difference from each side of the throat entry but this would seem to be adding an unwanted throat chamber.
Is there any significance to this?
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These are hard questions to answer, they would take a lot of study to calculate.
In general what you want to do is to minimize the path length differences from the various parts of the cone to the horn juncture. It appears that neither of these would do that - something in between would be better. Then you need to consider that the phase plug entrance is at the midpoint of the Fresnel zones so that the amplitude is constant (but is a single slot phase plug this is kind of irrelevant.)
In general what you want to do is to minimize the path length differences from the various parts of the cone to the horn juncture. It appears that neither of these would do that - something in between would be better. Then you need to consider that the phase plug entrance is at the midpoint of the Fresnel zones so that the amplitude is constant (but is a single slot phase plug this is kind of irrelevant.)
Originally Posted by weltersys
the reduction of mouth area using a round wave guide would have required a much higher crossover point than desired for the application.
Art
90 degree horizontal coverage was desired, a baffle area of approximately 10.75" x 5" was available. The rectangular horn used up that area for 53.75 square inches of horn mouth, which resulted in response adequate for around a 1500 Hz acoustical crossover.
A 5" diameter (the largest size available on the small baffle) 90 degree conical horn would only have 19.625 square inches of mouth area, a falling response and little pattern control below about 2400 Hz, a higher crossover than desired for the stage monitor application.
Art
the reduction of mouth area using a round wave guide would have required a much higher crossover point than desired for the application.
Art
A larger diameter round conical horn with more mouth area has a lower cutoff frequency than a smaller horn.
90 degree horizontal coverage was desired, a baffle area of approximately 10.75" x 5" was available. The rectangular horn used up that area for 53.75 square inches of horn mouth, which resulted in response adequate for around a 1500 Hz acoustical crossover.
A 5" diameter (the largest size available on the small baffle) 90 degree conical horn would only have 19.625 square inches of mouth area, a falling response and little pattern control below about 2400 Hz, a higher crossover than desired for the stage monitor application.
Art
As the statement stands here it is not true. Either there are more constraints than you have stated or you misunderstand something.
Since "cutoff frequency" - a term whose usage I deplore - is only applicable for infinite horns, how can the mouth area be a factor at all.
In reality - i.e. exact analysis versus the approximate analysis via the "horn equation" - the mouth area is not a factor at all in the frequency response unless the mouth is sharp and creates a standing wave that augments the LF response (very bad idea). If there is no mouth reflection then the power response is independent of the mouth area. If the mouth is very small then the axial response will fall because of the wider polar response, but square versus round won't make any difference since the "width" and hence the polar aspects, are the same between the two.
Earl,
I never compared a square horn to a round horn.
I compared a 90 degree horizontal coverage rectangular waveguide with a mouth approximately 10.75" x 5" to a 5" diameter mouth waveguide also of 90 degrees.
Using the same driver, the former will have more on axis response than the latter to a lower frequency, which is the desired outcome, hence the shape that was chosen for the particular application.
Art
Art
I still don't agree.
Your statement "A larger diameter round conical horn with more mouth area has a lower cutoff frequency than a smaller horn." is incorrect.
You seem to have changed the discussion to "I compared a 90 degree horizontal coverage rectangular waveguide with a mouth approximately 10.75" x 5" to a 5" diameter mouth waveguide also of 90 degrees." In the later case you are not comparing apples to apples.
I still don't agree.
Your statement "A larger diameter round conical horn with more mouth area has a lower cutoff frequency than a smaller horn." is incorrect.
You seem to have changed the discussion to "I compared a 90 degree horizontal coverage rectangular waveguide with a mouth approximately 10.75" x 5" to a 5" diameter mouth waveguide also of 90 degrees." In the later case you are not comparing apples to apples.
I'm not sure I'm familiar with this but are the Fresnel zones directed by the relative phase at the inner and outer entry points and even for a single slot plug, responsible for maintaining (or setting) the wavefront shape providing that the walls follow?
Gedlee,
I am confused as well.
Please explain, why most, if not all, literature on horns talks about truncation of the horn as introducing ripples into the low end frequency response.
Are waveguides that much different in the way they handle the LF response compared to a "conventional" horn?
Earl,
You are correct, I'm not comparing apples to apples, I'm comparing a 90 degree horizontal coverage rectangular waveguide with a mouth approximately 10.75" x 5" to a 5" diameter mouth waveguide also of 90 degrees.
Both would fit on the baffle space available, but the larger waveguide has good horizontal pattern control to a lower frequency, and more output to a lower frequency than the smaller circular waveguide, both of which are good things for the intended usage.
I'm not sure how that has "changed the discussion", the only comparison I made was the one above.
Art
Its far too complicated to get into in detail here, but the Fresnel zone concept is well documented in one of my patents. Patents are available for free (United States Patent and Trademark Office) so this is a good source of information.
As I said, in a single slot plug the Fresnel zone concepts don't really apply and all that matters is that the channels be as close to equal as possible.
As I said, in a single slot plug the Fresnel zone concepts don't really apply and all that matters is that the channels be as close to equal as possible.
Yes, truncation causes ripples if the mouth is not dealt with. Waveguides and horns are both identical in this respect. I don't know where you are getting the idea that I said that they weren't. You have to understand that all waveguides are horns, but not all horns are waveguides. So a question like "Are waveguides that much different in the way they handle the LF response compared to a "conventional" horn?" doesn't really have an answer because, in this context, they are the same thing.
I objected to the statement "A larger diameter round conical horn with more mouth area has a lower cutoff frequency than a smaller horn." It was incorrect when it was stated and its still incorrect. I don't understand why everyone keeps wanting to change the discussion - maybe to avoid having to admit that this statement is wrong?
N.B.
When signal wavelength is much longer than horn dimensions, the horn becomes acoustically transparent. In this setting horn parameters become irrelevant. For the larger horn this will occur at a lower frequency. Conical horns and their derivatives exhibit low order high-pass filter characteristics in their frequency pass bands.
WHG
When signal wavelength is much longer than horn dimensions, the horn becomes acoustically transparent. In this setting horn parameters become irrelevant. For the larger horn this will occur at a lower frequency. Conical horns and their derivatives exhibit low order high-pass filter characteristics in their frequency pass bands.
WHG
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This is news to me. I'd be interested in seeing some research on that. Can you point us to some. Any clues would be welcome.
Earl,
All horns are also wave guides, though other than radially symmetrical conical horns they do not guide sound waves consistently with frequency.
Assuming the same wall angle, a conical horn with a larger diameter (which by definition also has more depth and mouth area) will have a lower Fc as well as pattern control to a lower frequency than a smaller diameter horn.
Granted, when using a decent driver and a conical horn roughly the diameter of the woofer Fc is not a concern, but it does not negate the fact it exists.
Art
Picture a conical horn of some defined angle. Now double its length. Its mouth area has increased, but the cutoff frequency remains unchanged. The lower edge of its pattern control has gotten greater, but that's not what the statement said. It said "A larger diameter round conical horn with more mouth area has a lower cutoff frequency than a smaller horn." which is clearly untrue.
And, if the length of the two conical horns being compared is held constant, but the mouth area of one is greater, then the one with the greater mouth area will have the higher cutoff (and wider coverage angle), not the other way around.
As far as waveguides versus horns, you guys need to read my explanation on my website. You may not like it, but that is beside the point. Its how I see the issues and this thread is titled "Geddes on Waveguides".
And, if the length of the two conical horns being compared is held constant, but the mouth area of one is greater, then the one with the greater mouth area will have the higher cutoff (and wider coverage angle), not the other way around.
As far as waveguides versus horns, you guys need to read my explanation on my website. You may not like it, but that is beside the point. Its how I see the issues and this thread is titled "Geddes on Waveguides".