Alnico magnet, nice price... The Madisound Speaker Store
The problem with these is how to get some bass out of it (Xmax 2mm). It is also impossible to make a box to fit the corner, so why not to use just some good (and cheap) 100-130mm fullrange and make a corner line array bass, xo around 400Hz?
Damn, as I keep on saying this I start to think about reorganizing bookselves in my HT room, to clear out corners... I could use my SEAS coaxials for testing (Xmax 19mm)!
The problem with these is how to get some bass out of it (Xmax 2mm). It is also impossible to make a box to fit the corner, so why not to use just some good (and cheap) 100-130mm fullrange and make a corner line array bass, xo around 400Hz?
Damn, as I keep on saying this I start to think about reorganizing bookselves in my HT room, to clear out corners... I could use my SEAS coaxials for testing (Xmax 19mm)!
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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Do it! Would love to see measurements and what your general impression is.
The 2115 is an LE8T-H less the coating, I believe, and the Alnico LE8T is still the best mids I think I've ever heard, in simple BR boxes. I plan to play more with these interesting, underhung, well-behaved drivers sometime in the future. The slightly higher sensitivity is due to the reduction in moving mass, similar to the LE8T-2 used in some of the Aquarius speakers.
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Not to discount the rest of your post, but I do want to focus on this part.
I think everything is a matter of scale, and specifically that distance to the apex is a matter of acoustic scale. You can expect the source to act as though it were flush as long as it is less than about 1/4λ away. There must be no way for a reflection to be 180° behind, better if it doesn't get past 120-150°. So as long as the source is acoustically close to the boundary, it is not going to create destructive interference.
This gives some leeway with respect to the cabinet position. Of course, the driver must be physically close to the apex. An in-wall blended throat is the obvious best choice, because there is no question then that the source is "acoustically close." But I think a cabinet that is thin or otherwise maintains source location that is acoustically close to the apex provides a useful compromise to a permanent, blended, in-wall installation.
That's a good solution, I agree. In fact, I have found that even light curtains work very well, if the HF waveguide/horn has good horizontal pattern control of approximately 80-90°.
If not, if the tweeter pattern were wider, then I think absorbent material would be really important. In fact, I think if the tweeter pattern were wider, it would be a deal breaker for any sort of non-permanent (free-standing) implementation. Only an in-wall installation prevents the walls from being acoustically distant at HF, so if the tweeter beamwidth isn't narrow enough, that's the only solution that works well.
But as long as the tweeter's horizontal beamwidth is less than 90°, acoustic output at much larger angles (e.g. 150-180°) is highly attenuated. So reflections into the listening area are at quite low levels. Even lower if absorbent foam is installed, as you've suggested.
At angles nearer to the edge of the beam, output isn't attenuated as much as it is at wider angles. In fact, it is as high as -6dB at the edge of the beam. This represents a grazing angle though, and so its effects are limited to people sitting right on the wall. And even that can be easily mitigated with just about anything, light curtains work very well.
It's actually quite stunning. A constant directivity cornerhorn just gets everything right, in my opinion. It's a pity that so few rooms really support this kind of setup, because it sounds amazing.
If not, if the tweeter pattern were wider, then I think absorbent material would be really important. In fact, I think if the tweeter pattern were wider, it would be a deal breaker for any sort of non-permanent (free-standing) implementation. Only an in-wall installation prevents the walls from being acoustically distant at HF, so if the tweeter beamwidth isn't narrow enough, that's the only solution that works well.
But as long as the tweeter's horizontal beamwidth is less than 90°, acoustic output at much larger angles (e.g. 150-180°) is highly attenuated. So reflections into the listening area are at quite low levels. Even lower if absorbent foam is installed, as you've suggested.
At angles nearer to the edge of the beam, output isn't attenuated as much as it is at wider angles. In fact, it is as high as -6dB at the edge of the beam. This represents a grazing angle though, and so its effects are limited to people sitting right on the wall. And even that can be easily mitigated with just about anything, light curtains work very well.
It's actually quite stunning. A constant directivity cornerhorn just gets everything right, in my opinion. It's a pity that so few rooms really support this kind of setup, because it sounds amazing.
This may be a good time to ask a question I've had for some time. Its become the practice in conical horns to add a 2nd flare to combat waistbanding where the horn begins to lose pattern control. But per all my HornResp sims, that 2nd flare causes ripples in the response. When you put a 90 degree horn deep into a corner it shouldn't lose pattern control because of the corner and therefore one shouldn't need a 2nd flare. Is this correct? Although if you did add a 2nd flare, you might be able to use it to cover the gap to the wall. I note Wayne's mid horn doesn't have a 2nd flare....
You are correct. The secondary flare is done to prevent waistbanding, which is caused by mouth diffraction. It is actually a ripple effect, one where the beamwidth vascillates slightly before it opens wide.
You can see this in single slit diffraction of any wavefront - try some of the single slit diffraction applets online to see what I mean.
The constant directivity cornerhorn approach sidesteps this because the walls become the flare, and there is no mouth edge to cause diffraction. It prevents this kind of behavior, more closely resembling an infinite horn, or at least one with a very large mouth.
As an aside, the area expansion of a straight-sided 90° trihedral flare is the same as a 70° square flare.
You can see this in single slit diffraction of any wavefront - try some of the single slit diffraction applets online to see what I mean.
The constant directivity cornerhorn approach sidesteps this because the walls become the flare, and there is no mouth edge to cause diffraction. It prevents this kind of behavior, more closely resembling an infinite horn, or at least one with a very large mouth.
As an aside, the area expansion of a straight-sided 90° trihedral flare is the same as a 70° square flare.
Thanks Wayne.
I want to do a 90 degree horn at ear height in my home theater to obtain a virtual center channel mid screen. For this configuration, the walls only extend the horizontal flares. What do you think the resulting mouth diffraction consequences will be in the verticals?
Perhaps small trihedrals in in the high corners of my home office using small full range drivers....
I want to do a 90 degree horn at ear height in my home theater to obtain a virtual center channel mid screen. For this configuration, the walls only extend the horizontal flares. What do you think the resulting mouth diffraction consequences will be in the verticals?
Perhaps small trihedrals in in the high corners of my home office using small full range drivers....
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There definitely will be diffraction and other aberrations in the verticals. But there are other (more) messy things to deal with there too - like floor and ceiling slap. So you have a handful of things to consider with respect to performance off-axis in the vertical plane, some that can be mitigated and others that cannot.
I almost don't care about waistbanding in the vertical for home hifi. What bothers me more is vertical coverage that's too tall, not too short. I mean, I don't want a laser thin strata, like less than about 30° or so. But that's almost never the problem. The problem is almost always too much vertical spread, not too little.
I personally think the less output directed at the ceiling, the better, especially at high frequency.
I almost don't care about waistbanding in the vertical for home hifi. What bothers me more is vertical coverage that's too tall, not too short. I mean, I don't want a laser thin strata, like less than about 30° or so. But that's almost never the problem. The problem is almost always too much vertical spread, not too little.
I personally think the less output directed at the ceiling, the better, especially at high frequency.
How much is the design of a horn a question of smoothness (low distortion and diffraction) vs constant directivity in your opinion? Will one also suffer to some degree?
The JMLC that we mentioned are definetly not constant, but they seem to be very smooth.
BEM Simulations
I think the issues of trihedral horn in corner aren't with regard to smoothness of response but with where the output is aimed combined with beaming at high frequencies. I can see using one in my 11'x13' home office where I can sit almost directly on axis but I can't see it working in a home theater - except perhaps done as a synergy with a 1" CD at the apex.
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The issue of response smoothness is part and parcel of what this discussion is about - See the very first post of this thread.
But of course, yes, source position does matter. If it's not in the right place, the illusion of realism is smashed. That's one of the reasons constant directivity cornerhorns aren't more popular - Not all rooms are laid out where speakers in the corners would work well. Most aren't, in fact. But for the rooms that are laid out where speakers in the corners will cross axes in front of the listeners, and where the corners are symmetrical and unobstructed, the constant directivity cornerhorn approach gives the best sound I have ever heard.
For other rooms, I think the DI-matched two-way with flanking subs is the next best thing, a useful compromise that sounds very good too. The flanking subs are helper woofers, much like a 2.5-way or three-way speaker where the woofer is detached. The helper woofer and the woofer in the mains blend in the upper midbass and lower midrange to smooth self-interference from nearest boundaries, much like a truncated array. This is sort of like a multisub configuration, but is primarily done to address the range from 80-150Hz. One or two more distant distributed multisubs can also be used to smooth lower room modes.
Those are my favorite two configurations, and allow me to setup a good sound system in any room.
But of course, yes, source position does matter. If it's not in the right place, the illusion of realism is smashed. That's one of the reasons constant directivity cornerhorns aren't more popular - Not all rooms are laid out where speakers in the corners would work well. Most aren't, in fact. But for the rooms that are laid out where speakers in the corners will cross axes in front of the listeners, and where the corners are symmetrical and unobstructed, the constant directivity cornerhorn approach gives the best sound I have ever heard.
For other rooms, I think the DI-matched two-way with flanking subs is the next best thing, a useful compromise that sounds very good too. The flanking subs are helper woofers, much like a 2.5-way or three-way speaker where the woofer is detached. The helper woofer and the woofer in the mains blend in the upper midbass and lower midrange to smooth self-interference from nearest boundaries, much like a truncated array. This is sort of like a multisub configuration, but is primarily done to address the range from 80-150Hz. One or two more distant distributed multisubs can also be used to smooth lower room modes.
Those are my favorite two configurations, and allow me to setup a good sound system in any room.
Okay, I'm still struggling with the notion of CD horns blended into a corner. It seems superfluous.
In a trihedral corner you are already constrained to 1/8th space which is a d.i. of 9dB, I think. Unless you want even more directional than that, what are the CD horns doing?
For a speaker in the middle of a room the directivity will create a difference between the axial level (aimed presumably at the listener's ears) and the overall reverberent level. This is why we would want to go for a CD system in the first place. As soon as you put the speaker into the corner it is radiating into 1/8th space, but it is behaving much like an omni in the same situation. There may be no primary reflections from the 3 adjacent surfaces, but there is no difference being created between the axial level and the power response (directivity is effectively lost). Unless you design for a d.i. greater than 9 then the horns aren't adding anything.
Am I missing something?
David
In a trihedral corner you are already constrained to 1/8th space which is a d.i. of 9dB, I think. Unless you want even more directional than that, what are the CD horns doing?
For a speaker in the middle of a room the directivity will create a difference between the axial level (aimed presumably at the listener's ears) and the overall reverberent level. This is why we would want to go for a CD system in the first place. As soon as you put the speaker into the corner it is radiating into 1/8th space, but it is behaving much like an omni in the same situation. There may be no primary reflections from the 3 adjacent surfaces, but there is no difference being created between the axial level and the power response (directivity is effectively lost). Unless you design for a d.i. greater than 9 then the horns aren't adding anything.
Am I missing something?
David
A big reason for doing this is to eliminate the reflections from the near boundaries. Your point about the response being the same as an Omni's in the same location is interesting. It would be more telling if you could show me an Omni design that could be made as tight to the corner as a trihedral synergy horn and do equally well at eliminating the near boundary reflections.
I'm not saying it can't be done with an Omni, just saying a horn might be the easiest way to get the same effect. So the horn allows you to use the corners, without boundary reflection nulls. The corner extends the horn so CD extends down below the Schroeder frequency.
So now a large fraction (depending on aspect ratio) of the room is illuminated directly from the corners. The reverberant field is established by reflections from far boundaries. Those are all late reflections and so don't detract from imaging. (Caveat: depending on the height of the corner horn, might have to deal with earlier floor and/or ceiling reflections.)
I hope I got that right, I don't have the background to debate with you but that is the way I understand the theory.
I'm not saying it can't be done with an Omni, just saying a horn might be the easiest way to get the same effect. So the horn allows you to use the corners, without boundary reflection nulls. The corner extends the horn so CD extends down below the Schroeder frequency.
So now a large fraction (depending on aspect ratio) of the room is illuminated directly from the corners. The reverberant field is established by reflections from far boundaries. Those are all late reflections and so don't detract from imaging. (Caveat: depending on the height of the corner horn, might have to deal with earlier floor and/or ceiling reflections.)
I hope I got that right, I don't have the background to debate with you but that is the way I understand the theory.
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