The sim is what it is. Using a very small woofer maybe pushes the horizontal directivity 1/2 octave higher but you need to balance that against other design considerations like the improvement in the vertical polars with a small woofer and/or a low crossover frequency. It's that old C-C spacing you keep talking about. Woofer dimensions are as important as horn dimensions in that regard.
The way I see it the design process goes something like:
The crossover frequency is determined by the horn, not the woofer. Pick one as low as the horn and the compression driver will allow.
Then pick a woofer that isn't too big for the crossover frequency. Smaller is okay and there's no problem with a 3-way using a 6-8" midrange.
The way I see it the design process goes something like:
The crossover frequency is determined by the horn, not the woofer. Pick one as low as the horn and the compression driver will allow.
Then pick a woofer that isn't too big for the crossover frequency. Smaller is okay and there's no problem with a 3-way using a 6-8" midrange.
I agree with you. I'd like to add, I'm not coming totally from a theoretical perspective. I have used several medium and small format midrange and midwoofers as direct radiators paired with 90° horns. They don't suck, by any means. Some of the smaller mid drivers I've used include JBL 2105, 2115, 2123 and 2012 and from Eminence, the Alpha 8 and 10 and the Delta 10. I've used various crossover frequencies from 200Hz to 2.0kHz, mostly asymmetrical in terms of electrical transfer function.
When using a smaller format midrange or midwoofer, I've always depended on blending to some degree, sort of like what you appear to be advocating here. So I want you to know I'm not entirely against that practice. I've said it before and I'll say it again, you have some wiggle room in the horizontal matching because the two drivers blend. Like you have rightly said, what you don't want is for the directivity to narrow prior to crossover, then widen back up before the horn gains directivity control only to narrow again as frequency rises. As long as the directivity transitions are smooth, that's the most important thing.
All that said, the whole reason I made a midrange horn was because I thought there was a need for one when using these medium size drivers. It provides directivity at lower frequency and also increases sensitivity. I think it makes for a better match between medium format midrange/midwoofers and compression horns. Larger drivers have narrowing directivity and increased sensitivity, but smaller ones don't. A midhorn closes the gap.
Perhaps you'll be happy with an 8" or 10" direct radiating midwoofer paired with a 90° horn. I've made systems that way, lots of them. They aren't bad at all, some were quite good. But I don't think they're as good as a system with a larger midwoofer, for the reasons I've mentioned above (directivity and sensitivity). Try making both kinds of systems, one with a 8" or 10" woofer and another with 12" or 15" woofer, and compare them. Also try a midhorn, see what you think.
When using a smaller format midrange or midwoofer, I've always depended on blending to some degree, sort of like what you appear to be advocating here. So I want you to know I'm not entirely against that practice. I've said it before and I'll say it again, you have some wiggle room in the horizontal matching because the two drivers blend. Like you have rightly said, what you don't want is for the directivity to narrow prior to crossover, then widen back up before the horn gains directivity control only to narrow again as frequency rises. As long as the directivity transitions are smooth, that's the most important thing.
All that said, the whole reason I made a midrange horn was because I thought there was a need for one when using these medium size drivers. It provides directivity at lower frequency and also increases sensitivity. I think it makes for a better match between medium format midrange/midwoofers and compression horns. Larger drivers have narrowing directivity and increased sensitivity, but smaller ones don't. A midhorn closes the gap.
Perhaps you'll be happy with an 8" or 10" direct radiating midwoofer paired with a 90° horn. I've made systems that way, lots of them. They aren't bad at all, some were quite good. But I don't think they're as good as a system with a larger midwoofer, for the reasons I've mentioned above (directivity and sensitivity). Try making both kinds of systems, one with a 8" or 10" woofer and another with 12" or 15" woofer, and compare them. Also try a midhorn, see what you think.
I don't think so but not because of the directivity. A bigger midwoof will have higher sensitivity, better bass performance and lower distortion.
But a 3-way can have lower distortion yet. Horn-loading the midrange of a 3-way is a good idea but then you space the drivers farther apart and the vertical polars aren't as good. I don't think you can build a mid horn big enough to give any real directivity at mid frequencies without mucking up the vertical polars.
Speaker design is all about tradeoffs and there are lots of ways to skin the proverbial feline.
Concentrating on one or two design parameters is tunnel vision and that's been my point all along.As just noted by Neo Dan over at AVS, the sub-$10 QSC horns we're all raving about didn't exactly come out of the blue. Mark Engebretson has been working for them since 2005 and he's got some horn-design skills -- DDS 10" waveguide among others.
http://www.qscaudio.com/press/press_releases/archive/2005/03_05/01Mark.htm
http://www.qscaudio.com/press/press_releases/archive/2005/03_05/01Mark.htm
As with all things, loudspeaker design often requires balancing competing priorities. That's been my position too - not to optimize one trait at the expense of others. For example, I would never build a controlled directivity loudspeaker that had a vertical null closer than 20° from the forward axis. You don't have to, there are ways around it if you simply care to employ them. Another is, as I said, and I think now that you agree with me, the larger woofers provide better matching of both directivity and sensitivity. These are sort of synergistic design efforts as I think most good things are.
Along the same lines, I think midhorn design for indoors use is decidedly different than outdoors. Outdoors, you need large mouth area both for proper acoustic loading and for directivity control. But indoors, you can't possibly achieve directivity control at the low end (below about 200Hz) even if the horn is large enough because room modes take over. So you can undersize the horn and use driver blending instead, overlapping the woofer with the midrange to smooth the sound field. Try this approach sometime.
I've built three-way constant directivity designs both ways - with a direct radiating mid and with a horn loaded mid - and I like the horn loaded version better. I keep CTC spacing down because the midhorn mouth height is only 12". It has good vertical control at the top of its passband and, like I said, the bottom is in the modal region, where directivity takes on a whole new meaning. The lower end blends with the woofer, reducing the floor bounce self-interference notch that would otherwise be present with mids up off the ground. It's basically the same approach as the multisub configuration but the blending is at the upper end of the modal range.
Most of my designs are like that, with a particular component or subsystem chosen because it offers a handful of balanced priorities. Rarely do I ever make a design choice that focuses on one acoustic property only.
Along the same lines, I think midhorn design for indoors use is decidedly different than outdoors. Outdoors, you need large mouth area both for proper acoustic loading and for directivity control. But indoors, you can't possibly achieve directivity control at the low end (below about 200Hz) even if the horn is large enough because room modes take over. So you can undersize the horn and use driver blending instead, overlapping the woofer with the midrange to smooth the sound field. Try this approach sometime.
I've built three-way constant directivity designs both ways - with a direct radiating mid and with a horn loaded mid - and I like the horn loaded version better. I keep CTC spacing down because the midhorn mouth height is only 12". It has good vertical control at the top of its passband and, like I said, the bottom is in the modal region, where directivity takes on a whole new meaning. The lower end blends with the woofer, reducing the floor bounce self-interference notch that would otherwise be present with mids up off the ground. It's basically the same approach as the multisub configuration but the blending is at the upper end of the modal range.
Most of my designs are like that, with a particular component or subsystem chosen because it offers a handful of balanced priorities. Rarely do I ever make a design choice that focuses on one acoustic property only.
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Joined 2003
The thing that still concerns me with the asymmetric sims is the rather dramatic change in vertical polar response from the octaves below about 1k to the octaves above 2k. The change within the area from 1k-2k may be smooth but, in the broader picture, the change appears very abrupt relative to the overall spectrum.
For all of the good reasons mentioned by many, I may eventually try an asymmetric horn...but also spend time looking at vertical polar response below the crossover region. Easiest might be two mid/bass drivers stacked vertically, perhaps with the physically lower driver rolled off a little below the top one. Even two 15" drivers will fit below an asymmetric horn.
Paul
For all of the good reasons mentioned by many, I may eventually try an asymmetric horn...but also spend time looking at vertical polar response below the crossover region. Easiest might be two mid/bass drivers stacked vertically, perhaps with the physically lower driver rolled off a little below the top one. Even two 15" drivers will fit below an asymmetric horn.
Paul
You said you were concerned by the "rather dramatic change in vertical polar response from the octaves below about 1k to the octaves above 2k". I ask you though, are you concerned because of philosophical/intellectual reasons or because you think it actually sounds bad?
Every DI-matched two-way loudspeaker has omnidirectional coverage at low frequency that grows increasingly directional as frequency goes up. We talk like these speakers are CD, when in reality, they are not. They have collapsing directivity up to the crossover point in both horizontal and vertical planes. The goal of this type of loudspeaker is to have smooth transitions in directivity rather than to change abruptly, and also to have constant coverage, where possible, in the upper frequency band.
If the loudspeaker is properly designed, directivity transitions smoothly in the horizontal plane, for a 90° horn it goes from 360° down low to 90° above crossover. Likewise, the pattern collapses in the vertical but the nulls "squish" it a little further, usually to something in the range of 40° to 60°, at least in the better loudspeakers. When an asymmetrical horn is used, the coverage pattern remains at this angle through the high frequencies. To me, this is the goal. The alternative is to allow the pattern to open back up above the crossover region, which I think is undesirable.
I cannot see any benefit from output at tall vertical angles, as it only serves to increase ceiling slap. Would you prefer to allow this in the tweeter range, just because the speaker has no vertical control at the frequencies where the direct radiating woofer operates?
If you think about it, the same can be said of the horizontal as well. Directivity collapses from 360° to 90° in the horizontal. Why the reluctance to collapse vertical directivity a few more degrees, to 40°-60° or so? The nulls will force that upon you anyway, so I like to use a horn with about the same coverage angle.
I mean, to me, I certainly agree that it would be better to have CD through the whole audio band, which is one of the design goals in the Pi cornerhorn. It achieves CD in the horizontal plane through the whole band, from the Schroeder frequency (about 200Hz, depending on the room), not just from 1kHz onwards like most DI-matched two-ways. You can definitely hear the difference, for one thing there is NO side reflection at all.
The verticals are a little different though. I suppose if you had a real strong midrange reflection coming from the ceiling, that would be annoying. I also imagine that is possible in some rooms, in which case I would probably look at using an array, which is the only other thing I know of that can control vertical directivity besides a very large horn. But what I've regularly found is that the annoying problem is a ringing sound that comes from the 5kHz to 15kHz region. That's what I call ceiling slap.
Maybe others have different experience, but I've been in a lot of rooms over the years, from homes to hotels to businesses and I regularly find the same sorts of acoustical problems. One of the most common is an HF ringing sound. To test it, I always clap my hands. Many rooms have that tinitis sound ringing, comes right back at you from the ceiling. That's what I call ceiling slap, easy to avoid using a tweeter with reduced vertical coverage. Some rooms also sound reverberent to me, a box like sound in the lower midrange. This is room modes, best dealt with using damping and or placement. The only rooms I ever really find with a lot of annoying midrange reflection are built like bathrooms (sound like singing the the shower) and they have hard smooth walls, usually tile or plaster sometimes concrete or brick. People setting up sound systems in basements have this problem. In that case, false walls are important to damp the sound. They're so lively that directional speakers don't even help them.
Every DI-matched two-way loudspeaker has omnidirectional coverage at low frequency that grows increasingly directional as frequency goes up. We talk like these speakers are CD, when in reality, they are not. They have collapsing directivity up to the crossover point in both horizontal and vertical planes. The goal of this type of loudspeaker is to have smooth transitions in directivity rather than to change abruptly, and also to have constant coverage, where possible, in the upper frequency band.
If the loudspeaker is properly designed, directivity transitions smoothly in the horizontal plane, for a 90° horn it goes from 360° down low to 90° above crossover. Likewise, the pattern collapses in the vertical but the nulls "squish" it a little further, usually to something in the range of 40° to 60°, at least in the better loudspeakers. When an asymmetrical horn is used, the coverage pattern remains at this angle through the high frequencies. To me, this is the goal. The alternative is to allow the pattern to open back up above the crossover region, which I think is undesirable.
I cannot see any benefit from output at tall vertical angles, as it only serves to increase ceiling slap. Would you prefer to allow this in the tweeter range, just because the speaker has no vertical control at the frequencies where the direct radiating woofer operates?
If you think about it, the same can be said of the horizontal as well. Directivity collapses from 360° to 90° in the horizontal. Why the reluctance to collapse vertical directivity a few more degrees, to 40°-60° or so? The nulls will force that upon you anyway, so I like to use a horn with about the same coverage angle.
I mean, to me, I certainly agree that it would be better to have CD through the whole audio band, which is one of the design goals in the Pi cornerhorn. It achieves CD in the horizontal plane through the whole band, from the Schroeder frequency (about 200Hz, depending on the room), not just from 1kHz onwards like most DI-matched two-ways. You can definitely hear the difference, for one thing there is NO side reflection at all.
The verticals are a little different though. I suppose if you had a real strong midrange reflection coming from the ceiling, that would be annoying. I also imagine that is possible in some rooms, in which case I would probably look at using an array, which is the only other thing I know of that can control vertical directivity besides a very large horn. But what I've regularly found is that the annoying problem is a ringing sound that comes from the 5kHz to 15kHz region. That's what I call ceiling slap.
Maybe others have different experience, but I've been in a lot of rooms over the years, from homes to hotels to businesses and I regularly find the same sorts of acoustical problems. One of the most common is an HF ringing sound. To test it, I always clap my hands. Many rooms have that tinitis sound ringing, comes right back at you from the ceiling. That's what I call ceiling slap, easy to avoid using a tweeter with reduced vertical coverage. Some rooms also sound reverberent to me, a box like sound in the lower midrange. This is room modes, best dealt with using damping and or placement. The only rooms I ever really find with a lot of annoying midrange reflection are built like bathrooms (sound like singing the the shower) and they have hard smooth walls, usually tile or plaster sometimes concrete or brick. People setting up sound systems in basements have this problem. In that case, false walls are important to damp the sound. They're so lively that directional speakers don't even help them.
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Catapult's sims indicate it's "abrupt" with symmetrics, as well. Without the vertical nulls, one might argue that the asymmetric is LESS abrupt in the vertical....
The term "waveguide" has been applied to horns that provide constant directivity using a flare that doesn't require diffraction for waveshaping. I believe it was Geddes that made this definition, a specialized subset of constant directivity devices using a catenary flare profile to reduce diffraction.
I often think the additional limitations on word usage are nonsense used by academics (often in an effort to bolster credibility). i.e. marketing blather intended to market the concept by a specific individual (..rather than marketing for profit).
Simply put:
A waveguide (for sound) is any mechanism used to control a sound wave's dispersion pattern. i.e. a sound-*wave* *guide*.
A horn (for sound reproduction) is any physical mechanism used to provide additional *gain* (or increased sound pressure level), for a particular direction.
All horns derive gain by trading a larger radiation pattern for increased gain, which results in increased directivity. Because of this all horns *are* waveguides. On the other hand not all waveguides are horns. EX. A waveguide could be derived by *absorbing* sound to control the sound-wave's radiation with no significant increase in sound pressure level.
..or at least that's the way I perceive it.
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Joined 2003
Haven't heard a direct a/b comparison between two otherwise similar designs, so philosophical/intellectual. I believe a smoother change in vertical polar response spread over a broader frequency range would tend to produce a smoother reverberant field...less "hey I'm a speaker, look at me".
That is not what I suggested. I stated my concern for the asymmetric, and offered a possible system improvement I would consider if/when I try an asymmetric. Two midbass drivers to narrow vertical directivity to more closely approximate the horn vertical/horizontal pattern. Narrower vertical response in the midrange might alleviate my concern with the horn...trying to work with you and the asymmetric here
I am not at all opposed to reduced vertical polar response...I favor reduced floor and ceiling bounce. I simply believe the reduction should be spread smoothly over as broad a range as practical. The horizontal certainly doesn't collapse in an octave!
They are all Horns
I would call any device (Geddes included) to adapt and/constrain the output of a sound radiating surface to free air. Some are just trying to distance themselves from others some how some way.
I'm sure the terminology is adapted from microwaves ...Waveguide> A device that constrains or guides the propagation of electromagnetic radiation along a path defined by the physical construction of the guide. Electromagnetic waves may propagate in space, as radio waves, but for many purposes waves need to be guided with minimum loss from the generating point to a point of application.
Horns in microwaves would be a subset of waveguides. A specialized one to match impedance and directivity or coverage in free air. http://www.arww-rfmicro.com/html/13100.asp?S=3
I would call any device (Geddes included) to adapt and/constrain the output of a sound radiating surface to free air. Some are just trying to distance themselves from others some how some way.
I'm sure the terminology is adapted from microwaves ...Waveguide> A device that constrains or guides the propagation of electromagnetic radiation along a path defined by the physical construction of the guide. Electromagnetic waves may propagate in space, as radio waves, but for many purposes waves need to be guided with minimum loss from the generating point to a point of application.
Horns in microwaves would be a subset of waveguides. A specialized one to match impedance and directivity or coverage in free air. http://www.arww-rfmicro.com/html/13100.asp?S=3
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Actually, the horizontal pattern collapses at exactly the same rate as the vertical. It's just that the vertical is pinched a smidge more because of the nulls. By approximately 1.5kHz, the pattern will have narrowed to 90° in the horizontal, best case for a speaker like this would be 60° in the vertical, maybe more like 40°, depending on driver/horn dimensions and crossover. The only real debate is what to do above the crossover frequency - open back up to 90° using a round horn or remain 40° - 60° using an elliptical or rectangular horn.
About directivity below the crossover frequency, from what you're saying, it looks like we must think pretty much along the same lines. I prefer more control at lower frequency where possible, and the way I've done that is to use the room's corners as 90° "waveguides". It's simple and effective, basically using the largest acoustic device in the room to set the pattern. This works very well all the way down to the Schroeder frequency, so you get the most unform coverage possible. It would be the perfect solution, the only problem of course being that you are limited to corner placement and that isn't ideal for all rooms, maybe not even most. The next best thing to me is a DI-matched two-way with flanking subs. Either way, run multisubs to smooth the sound field below the Schroeder frequency.
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Joined 2003
Wayne,
The whole point of my post was to suggest another possible way of achieving a midrange polar pattern better matching the polar pattern of an asymmetric horn. So we aren't debating anything except perhaps the definition of "collapse"...a nit in the overall scheme of things.
Agree on distributed flanking subs. The system I'm finishing up includes a vertical line of three subs on both sides of each LCR..."planar bass array".
Paul
The whole point of my post was to suggest another possible way of achieving a midrange polar pattern better matching the polar pattern of an asymmetric horn. So we aren't debating anything except perhaps the definition of "collapse"...a nit in the overall scheme of things.
Agree on distributed flanking subs. The system I'm finishing up includes a vertical line of three subs on both sides of each LCR..."planar bass array".
Paul
Yeah, that's cool. I wasn't trying to pick any nits - there's plenty of that on these audio discussion forums. I just wanted to point out that the pattern collapse rate is the same in the vertical and the horizontal and also to remind everyone how much directivity increase is required for matching. Maybe you already knew that but I wasn't sure.
Many people think loudspeakers like these are CD in the horizontal, but they're not. Of course, if the speaker is positioned in a corner of the room, the walls constrain the pattern down low. That's an easy way to provide CD all the way down to the Schroeder frequency, if the room has the right layout to take advantage of this.
Many people think loudspeakers like these are CD in the horizontal, but they're not. Of course, if the speaker is positioned in a corner of the room, the walls constrain the pattern down low. That's an easy way to provide CD all the way down to the Schroeder frequency, if the room has the right layout to take advantage of this.
I still tend to call low-diffraction CD horns (OS, PS, quadratic, whatever) as "horns" instead of the now oft-used term "waveguides".
A "waveguide" used in RF work is a transmission line made in the form of a duct. It is the conductor of microwaves and is usually a straight pipe. It may be terminated at the end with a "horn antenna", if the signal is to be propagated some distance through open space. So to me, the word "horn" is still most appropriate.
I guess I don't really care if we invent a new lexicon for audio, starting to use the word "waveguide" for a specialized subset of horns. Some would have the term used to describe only one flare profile, which may be more restrictive than necessary. To me, this is sort of like making a unique word definition for "spheres that are exactly 12.2cm diameter", setting them apart from all other spheres. On the other hand, I can see most people take "waveguide" to mean a sort of adjective/noun combination, where the word describes the purpose, a "guide of waves". Like Scott said, that can be pretty much anything from a Mantaray horn to a low-diffraction CD horn to a beam-steered array. The term is diluted to the point it is meaningless. It seems to me it has become a marketing catch-phrase more than anything else.
I really think most of us interested in this thread have gravitated towards loudspeakers with horns having uniform directivity and low diffraction. That draws us towards certain flare shapes, OS, PS and quadratic horns. They're conical or radial horns with radiused throats that match the driver exit angle. Most would prefer a radiused mouth edge, but that may be sometimes optional, depending on horn size (i.e. an infinite or really big horn doesn't need it as much as a smaller horn does). There are some details that we can examine and kick around, but I think most of us here agree that these are desirable traits.
The thing I think we have disagreed on is the aspect ratio, whether axi-symmetry is inherently better or if asymmetry is more desirable for home hifi. I am firmly in the asymmetrical camp, as most people know, specifically 90x40 to 90x60. I would have never guessed anyone interested in this kind of loudspeaker would consider any other configuration. I believe most others are now looking in this direction too because it is pretty clear that it has the potential for making loudspeakers capable of providing a much more usable pattern.
A "waveguide" used in RF work is a transmission line made in the form of a duct. It is the conductor of microwaves and is usually a straight pipe. It may be terminated at the end with a "horn antenna", if the signal is to be propagated some distance through open space. So to me, the word "horn" is still most appropriate.
I guess I don't really care if we invent a new lexicon for audio, starting to use the word "waveguide" for a specialized subset of horns. Some would have the term used to describe only one flare profile, which may be more restrictive than necessary. To me, this is sort of like making a unique word definition for "spheres that are exactly 12.2cm diameter", setting them apart from all other spheres. On the other hand, I can see most people take "waveguide" to mean a sort of adjective/noun combination, where the word describes the purpose, a "guide of waves". Like Scott said, that can be pretty much anything from a Mantaray horn to a low-diffraction CD horn to a beam-steered array. The term is diluted to the point it is meaningless. It seems to me it has become a marketing catch-phrase more than anything else.
I really think most of us interested in this thread have gravitated towards loudspeakers with horns having uniform directivity and low diffraction. That draws us towards certain flare shapes, OS, PS and quadratic horns. They're conical or radial horns with radiused throats that match the driver exit angle. Most would prefer a radiused mouth edge, but that may be sometimes optional, depending on horn size (i.e. an infinite or really big horn doesn't need it as much as a smaller horn does). There are some details that we can examine and kick around, but I think most of us here agree that these are desirable traits.
The thing I think we have disagreed on is the aspect ratio, whether axi-symmetry is inherently better or if asymmetry is more desirable for home hifi. I am firmly in the asymmetrical camp, as most people know, specifically 90x40 to 90x60. I would have never guessed anyone interested in this kind of loudspeaker would consider any other configuration. I believe most others are now looking in this direction too because it is pretty clear that it has the potential for making loudspeakers capable of providing a much more usable pattern.
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