Indeed, although the speakers in his simulated room were pretty far from the "walls". One has to be careful to generalize his conclusions to all small rooms.
If a speaker is placed closer to the walls, the rear wall may introduce audible colouration (just like the floor reflection in some cases). Side wall reflections may introduce image shift/blurring or perhaps colouration (very early reflections).
The side wall reflection is something that may depend on personal taste. Image shift/blurring is a negative aspect for some, while others may find the effect to be pleasantly spacious. The majority seems to like it.
Even though the spatial aspects of room reflections can be positive, the masking of comb filtering by multiple reflections might be the biggest advantage. Minimizing possibly harmful reflections (i.e. floor) while preserving other reflections might be the best approach.
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I once heard a Beolab 5 and it was one of the worst listening experiences I've ever had. They were placed close to the front wall but far away from all other walls (>5-10ms).
I've never heard them, but I could imagine that the positioning close to the front wall might have been a problem (in my experience it is with most speakers). I've also seen some measurements of the speaker once. While it has wide horizontal directivity, it is far from smooth. The tweeter seems to have a wider directivity than the midrange. Can't be good.
Directivity of the Beolab might also be just a little too wide. Markus, what was the main problem for you, colouration or lousy imaging?
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All of that. I couldn't even say what exactly was wrong because everything was wrong. And it didn't even sound spacious. I got better spaciousness from two side-firing 3" fullrange driver.
I remember that, yes. Yet, the level of first order reflections is very well perceivable as stonger or less ASW or spaciousness. I am just experiencing that live with the two versions of my omni. So that point is subject to preference.
I should have said increased ratio of direct/reflected sound. That does exist.
Just in case someone's interested how a FRS8 performs in a "180° horn" (10° steps, red is 0°, blue is 90°):
Attachments
I knew would come up with something like thisBut the back of the driver is then enclosed and it is a halfspace radiatior ?
Currently it's an open baffle. Just testing something Tom mentioned here http://www.diyaudio.com/forums/mult...ce-back-into-loudspeakers-12.html#post3145624
I'm sure everyone was expecting something little bit more than FRS8 in a cardboard dipole when "horn experiments" were mentioned
Life is tough. Hope it hasn't been to much of a disappointment
Markus,
I would like to see where anyone would call a flat baffle a horn in any traditional sense? Yes there have been actual horn waveguides that have attempted to have 180 degree radiation but commonly that required an extremely narrow vertical dispersion pattern that made them very limited in use. I could think of a couple of ways to use a vertically firing device that could be either a 180 degree or 360 degree radiation pattern with much great vertical dispersion patterns. What you are showing is simply a cardboard dipole as far as I am concerned.
I would like to see where anyone would call a flat baffle a horn in any traditional sense? Yes there have been actual horn waveguides that have attempted to have 180 degree radiation but commonly that required an extremely narrow vertical dispersion pattern that made them very limited in use. I could think of a couple of ways to use a vertically firing device that could be either a 180 degree or 360 degree radiation pattern with much great vertical dispersion patterns. What you are showing is simply a cardboard dipole as far as I am concerned.
haha i like that 'horn', although why the FRS8? Price? I generally like Visaton drivers, but not their fullrangers.
Ive got some FRS5X and theyre for tweeter duty, but their frequency response is at least fairly flat in the important ranges.
If I had room, id try a good dipole. Upfiring omnis sound awful in my room, and im not sure that those inverted cone reflector types may be TOO narrowed in radiation vertically.
Like ive said, too often, the ribbon worked a treat. Its waveguide loaded and the published specs show -3dB at 10 degrees vertical off axis at 10khz. Id guess thats somewhere in between a dome and the reflector things.
Id argue, without being au fait with it all, that a similar vertical pattern would be desireable but at a much lower point, say 2khz.
Is that even possible?
Ive got some FRS5X and theyre for tweeter duty, but their frequency response is at least fairly flat in the important ranges.
If I had room, id try a good dipole. Upfiring omnis sound awful in my room, and im not sure that those inverted cone reflector types may be TOO narrowed in radiation vertically.
Like ive said, too often, the ribbon worked a treat. Its waveguide loaded and the published specs show -3dB at 10 degrees vertical off axis at 10khz. Id guess thats somewhere in between a dome and the reflector things.
Id argue, without being au fait with it all, that a similar vertical pattern would be desireable but at a much lower point, say 2khz.
Is that even possible?
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What is a horn, is a flat baffle a horn too?
If one asked “what does a horn or waveguide do”, most would answer that it raises the efficiency of the driver and / or it confines the radiation to an angle set by it’s ridged walls or boundaries.
It the case of impedance transformation, one finds horns have a “high pass” corner to that transformation and that is based on the rate the area increases as one moves away from the source.
For an exponential horn which has a constant rate of expansion, one finds that for a 30hz horn, the area must not expand any faster than doubling every 24 inches or so while at 300Hz, it is 1/10 of that or doubling every 2.4 inches.
The synergy and unity horns depend on that factor because if you examine the rate of expansion, one finds that at the apex the expansion is very rapid, or suited only for high frequency horn loading while further from the apex, the expansion progressively slows so that one can couple into the horn and have horn loading to a much lower frequency than one would see if limited to the horn apex.
The radiation angle of the horn is set by it’s dimensions and wall angle. The first person to recognize that and supply a “rule of thumb” was Don Keele in his landmark paper;
http://www.xlrtechs.com/dbkeele.com/PDF/Keele (1975-05 AES Preprint) - Whats So Sacred Exp Horns.pdf
When you examine the math or measure the horn, one finds there is no demarcation between a flat baffle and straight walled horn, they all behave according to the rate of expansion and wall angles vs frequency.
If one places a piston source that is less than ¼ wl in diameter on a flat baffle, it radiates a simple interference free pattern that is about 180 degrees. This extends for the “pattern loss” frequency at the low end described by Don Keele up to the point that the source begins to have it’s own directivity.
The maximum size one can have for the source and still “fill out” the entire horn wall angle is the same or similar thing which governs the size of the “airy disk” in telescope optics, it is set by the variation in phase angles from the center to edges.
Best,
Tom Danley
If one asked “what does a horn or waveguide do”, most would answer that it raises the efficiency of the driver and / or it confines the radiation to an angle set by it’s ridged walls or boundaries.
It the case of impedance transformation, one finds horns have a “high pass” corner to that transformation and that is based on the rate the area increases as one moves away from the source.
For an exponential horn which has a constant rate of expansion, one finds that for a 30hz horn, the area must not expand any faster than doubling every 24 inches or so while at 300Hz, it is 1/10 of that or doubling every 2.4 inches.
The synergy and unity horns depend on that factor because if you examine the rate of expansion, one finds that at the apex the expansion is very rapid, or suited only for high frequency horn loading while further from the apex, the expansion progressively slows so that one can couple into the horn and have horn loading to a much lower frequency than one would see if limited to the horn apex.
The radiation angle of the horn is set by it’s dimensions and wall angle. The first person to recognize that and supply a “rule of thumb” was Don Keele in his landmark paper;
http://www.xlrtechs.com/dbkeele.com/PDF/Keele (1975-05 AES Preprint) - Whats So Sacred Exp Horns.pdf
When you examine the math or measure the horn, one finds there is no demarcation between a flat baffle and straight walled horn, they all behave according to the rate of expansion and wall angles vs frequency.
If one places a piston source that is less than ¼ wl in diameter on a flat baffle, it radiates a simple interference free pattern that is about 180 degrees. This extends for the “pattern loss” frequency at the low end described by Don Keele up to the point that the source begins to have it’s own directivity.
The maximum size one can have for the source and still “fill out” the entire horn wall angle is the same or similar thing which governs the size of the “airy disk” in telescope optics, it is set by the variation in phase angles from the center to edges.
Best,
Tom Danley
Tom,
I think that this is a stretch of the term. In the case you are sighting then we can call just about anything a horn. Why not call a cone driver a horn then as it technically meets your definition by producing wavelengths that are smaller than the cone diameter and could qualify. All you seem to do is confuse the issue with that statement. I am not going to start calling an infinite baffle a horn, not going to go there. In that case I can call your Synergy horn a baffle with an apparent concave contour. Your definition is more than stretching what is traditionally considered a waveguide or horn lens. With your definition the word loses all meaning.
I think that this is a stretch of the term. In the case you are sighting then we can call just about anything a horn. Why not call a cone driver a horn then as it technically meets your definition by producing wavelengths that are smaller than the cone diameter and could qualify. All you seem to do is confuse the issue with that statement. I am not going to start calling an infinite baffle a horn, not going to go there. In that case I can call your Synergy horn a baffle with an apparent concave contour. Your definition is more than stretching what is traditionally considered a waveguide or horn lens. With your definition the word loses all meaning.
I think it's you that's confusing the issue here - where is the baffle when there is only the driver by itself with no baffle ?
It's only by having the baffle wider than the driver that you get the effects of a waveguide. A constant directivity waveguide works because the source of radiation - the driver, is a lot smaller than the mouth of the wave-guide, and so it is with the size of a driver on a flat baffle, and the size of that baffle. The same relationships apply.
Whether you like the terminology or not doesn't really change things - a large baffle (eg significantly larger than the driver itself) does indeed work like a constant directivity waveguide with a DI of 3dB and a radiation angle of about 180 degrees from the baffle step frequency up to the frequency where the driver itself starts to beam.
It boosts the on axis response above the cut-off (eg baffle step) frequency and reduces it beyond 90 degrees off axis. It boosts the on axis response less at high frequencies where the driver is starting to beam, exactly like a waveguide would when the driver is beaming and not illuminating the waveguide walls (here, the baffle) fully.
By constraining solid space to 180 degrees it also increases the radiation resistance the driver sees (above the baffle step frequency) giving a 3dB increase in efficiency. (Combined efficiency and directivity gains give a total on axis increase of up to 6dB)
A small driver on a large baffle can maintain a near constant 3db DI over a wide frequency range - the bottom end frequency limit depends on the baffle size, the top end limit on the drivers effective piston diameter.
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