gedlee said:
I for one would love to see a thread by yourself on the topic. Particularily proper design of a WG for use with a conventional dome tweeter which is getting very popular but a lack of usable or competently designed waveguides is a real problem right now. Please post a link to such thread so the conversation could carry on there.
Earl,
Any chance you will sell a large WG to the DIY community through your speaker company? I would understand if it is a no, but I think those of us that like to experiment and build on our own would love to have access to a proper WG. They aren't easy to come by and not easy to make, especially larger ones.
Any chance you will sell a large WG to the DIY community through your speaker company? I would understand if it is a no, but I think those of us that like to experiment and build on our own would love to have access to a proper WG. They aren't easy to come by and not easy to make, especially larger ones.
Variac said:
That is a form of an acoustic lens (that is what lenses are in reality, they slow down the speed of light, making the light "bend"). In this case Aleksandar improves the vertical dispersion of his ribbons by "bending" sound in the vertical plane. Edge diffraction (at least for near surfaces) is catered for by serrated front plate.
Note that Dunlavy (and many others, but I think he was first) used star shaped cutout foam/felt in all of his designs. Presumably to aleviate diffraction.
Bratislav
Here's a thread for Earl's use to expound on waveguides:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=103872
See you there Mr. Geddes!
http://www.diyaudio.com/forums/showthread.php?s=&threadid=103872
See you there Mr. Geddes!
Variac said:
Thanks, Variac! I suggested in that thread reprinting the technical postings by Earl - and most certainly Post #1135. This one is solid gold, and the readers of this thread need to read and think about it in depth.
The consequences of multipath distortion from horns (my term, borrowed from RF) are quite sobering. It's the same reason I don't care for line radiators - the blurred arrival times are not correctable by any form of DSP.
I'd also like to direct the reader's attention to the Meyersound paper, Can Line Arrays Form Cylindrical Waves? In a word, no. Summation in air doesn't occur, it happens at the microphone or eardrum.
It should be kept in mind when there are multiple paths from an array of widerange drivers, or multiple paths traversing the interior of a horn, they do not sum in the air-path from emitter to listener.
For a line array, cylindrical waves are not created. It also means the wavefront coming out a horn with HOM's (almost all of them) is not very close to spherical - instead, it is chaotic, with a spatially incoherent wavefront. When a system like this measured, the impulse response looks cluttered, and is also extremely sensitive to small movements of the microphone (or the listener).
When multiple arrivals (that are each individually minimum-phase) are summed at the microphone or eardrum, the summation becomes non-minimum phase. If this exact, microsecond-precise summation could be maintained over a wide angle, then DSP could invert the time distortion and compensate.
However, one unfortunate effect of diffraction is an extreme sensitivity to radiation angle, since the summation at the microphone is nothing more than a collection of multiple paths coming from different sources. The sum-and-differencing, or cancellations, are spatially very small and fine-grained. This means DSP will only work for one very small microphone location, and will worsen the time error everywhere else.
This also reveals why time measurements of line arrays and conventional horns are rarely seen, and published frequency response measurements use 1/3 octave smoothing thirty years after it was abandoned for high-fidelity speakers. The unsmoothed response may prove so chaotic it would be unreadable - unlike direct-radiators.
I'm starting to get an idea why the "sweet spot" of conventional horns is so small, in terms of subjective "coherency". As mentioned many many posts ago, this sweet spot is typically about one listening-position wide, with good-quality sound outside of it, but a noticeable lack of "3-D" presentation and immediacy compared to the "golden" listening location.
Hmmm ... the ribbons are starting to look good, unless treatments like lining the walls of the horn with felt have an effect on the HOM's. Maybe so, maybe not, it might even completely wreck the horn response. As for the baffle, felt-covered mesh is looking interesting from the standpoint of spatially and temporally dispersing the rear-wave. BudP's also experimenting with interesting shapes created with French-curve - we shall see.
Lynn Olson said:
Lynn
Again all quite correct. The chapter in my book on line arrays did not sit well with a lot of people because it derived mathematically exactly what you are talking about. In the near field everything is chaotic and in the far field you get simple a poor spherical wave. Line arrays for large venues makes some sense, but for home listening, the multipath situation does not yield a good impulse response.
I have always opted for the "point source with constant directivity" approach in all my designs. I want a single apparent acoustic source, but use in a small room dictates higher directivity. As far as I know this can only be achieved with a waveguide. A waveguide with no HOM and mouth diffraction will be very close to a point source with directivity.
I should also like to point out here, as I have many times before, that OB systems are not CD, except at thier lower frequencies (where radiation efficiency is poor) when the directivity is very wide - 180 degrees. This is of course their advatage over monopoles - they have LF CD at 180 degrees instead of CD at 360 degrees. That extra factor of directivity is a big thing in its favor. But all too soon the OB starts to become directional and then it is no longer CD.
I have long wanted to use an OB for the range just below the waveguide for just the reason that it gives a significant improvement in directivity over the closed box. Very attractive. But the complexity of making this work gets to be problematic and the end result in my paper studies has been complications in crossovers and more drivers required and soon things don't look so attractive.
I have always been attracted to simplistic designs that work rather than complexity. What could be more simple than a two way? And two-way and OB just don't seem to be in the cards.
That squares well with some of the guesses I made earlier ... notably that the "airiness" of line arrays and large multicell horns actually comes from the many decorrelated time delays. My guess though is that the time windows involved are crucial here w.r.t. how objectionable the effect is. The very early horn reflections in small HF horns >900 Hz, a.k.a. HOMs, seem to be most objectionable, while the much more delayed arrival times from line arrays, and dipole rear waves, especially in the midrange, seem to please quite a few people - basically they constitue an acoustic "spatializer" without electronic wizardry.
I for once have lived with my DIY OB's for many years now and find the naturalness of the midbass quite without par - but it is hard to tell whether this is due to the dipole radiation pattern per se or the absence of any re-radiated acoustic energy through the cone, which seems to be a major problem with boxes. I don't find the necessary EQ and multi-amping a real problem, many conventional monitors are built just the same, electronic X-O and EQ, and integrated bi-amping.
From my experience the radiation pattern of actually built dipoles works very well in practice and gives a very natural feeling especially off axis, even far off axis. Ironically it is on-axis that I see room for improvement: due to the presence of full on axis rear radiation, but limited lateral radiation, there always seems to be more depth than width to the sound when sitting in the sweet spot. For this reason I suspect a cardioid that maintains its pattern over a wide range might be the optimal solution, but this is not easy to achieve. A cardioid would also be the perfect candidate for mating with a waveguided HF unit.
Finally another question to Earl Geddes: there is some body of evidence that even in small rooms, reflections are actually a good thing and necessary for natural sound impression, as long as the time delay is >1.5 ms and ideally in the 10-15 ms range (Linkwitz, Griesinger etc are in this camp). Linkwitz mentions that ribbons might give their spacious impresssion specifically because of very good HF lateral dispersion. This would call for wide dispersion patterns. Lynn leans towards a ribbon now, me I target a 120 degree waveguide, and dipole/cardioid radiation pattern. What is your opinion on this, compared to the more conventional 90 degree pattern of a typical HF horn?
I for once have lived with my DIY OB's for many years now and find the naturalness of the midbass quite without par - but it is hard to tell whether this is due to the dipole radiation pattern per se or the absence of any re-radiated acoustic energy through the cone, which seems to be a major problem with boxes. I don't find the necessary EQ and multi-amping a real problem, many conventional monitors are built just the same, electronic X-O and EQ, and integrated bi-amping.
From my experience the radiation pattern of actually built dipoles works very well in practice and gives a very natural feeling especially off axis, even far off axis. Ironically it is on-axis that I see room for improvement: due to the presence of full on axis rear radiation, but limited lateral radiation, there always seems to be more depth than width to the sound when sitting in the sweet spot. For this reason I suspect a cardioid that maintains its pattern over a wide range might be the optimal solution, but this is not easy to achieve. A cardioid would also be the perfect candidate for mating with a waveguided HF unit.
Finally another question to Earl Geddes: there is some body of evidence that even in small rooms, reflections are actually a good thing and necessary for natural sound impression, as long as the time delay is >1.5 ms and ideally in the 10-15 ms range (Linkwitz, Griesinger etc are in this camp). Linkwitz mentions that ribbons might give their spacious impresssion specifically because of very good HF lateral dispersion. This would call for wide dispersion patterns. Lynn leans towards a ribbon now, me I target a 120 degree waveguide, and dipole/cardioid radiation pattern. What is your opinion on this, compared to the more conventional 90 degree pattern of a typical HF horn?
ScottG said:
AFAIK It's quite impossible to do it in Akkabak (but I'm no expert), howerver each CFD (computational fluid dynamics) code solving the Navier-Stokes equations should do the trick. However the boundary layers are always difficult. Maybe someone with more experience could comment on that.
edit: and don't start on turbulence makes it even more difficult
MBK said:
I don't think that many would agree with your 1.5 ms lower limit, but I think that everyone would agree with the 10-15 ms one. After the initial time gap behind the direct wave of about 10 - 15 ms, IMO there should be as many reflections as possible - as much reverberation as possible, which is why all of my rooms are so live. But in a small room it is very difficult to get low energy density in the 1 - 10 ms. region with a very high density of reflections after 10 ms without a very narrow directivity on the loudspeakers.
Plot this out a on a piece of paper sometime and you will see what I mean. The narrower the directivity the lower the 1 - 10 ms energy. But once the revereberant field start to build, then the directivity is not an issue anymore because its simply the power response of the loudspeaker that dictates the response.
Think the situation through very carefully and you will see that if one wants a dead zone after an initial diffraction free direct sound, then narrow directivity ( < 90 degrees) is the only option as wider directivity just builds up the reverberant field sooner. And wide non-CD - like a ribbon - is just not going to yield what I am looking for.
Point taken about the reverberant field and power response, as well as the 10-15 ms being the ideal "gap".
I have actually thought the delayed reflection issue through before. The problem is that to generate high apparent source width (soundstage, ASW) you need decorrelated delays coming roughly from the source direction, so overall reverberation won't help: you still want some clues from the side walls.
Here, the calculation works out depending on speaker placement. In general it can work in a typical living room if speakers are positioned along the long side of the room. For instance, for speakers/listener in an 8 ft or 2.4 m equilateral triangle configuration, putting the speakers >5.5 ft or 1.65 m from the front wall and >6 ft or 1.8 m from the side walls, gets you a minimum sound path distance (direct to reflected) of ca. 3.3 m or 11 ft, for roughly 10 ms delay. That would require minimum room dimensions of just 8+2*6=20ft wide and 5.5+ca.2+sofa depth say 2.5 ft=10 ft deep.
So I still believe fairly wide lateral dispersion will help the impression of spaciousness, especially ASW, and under the condition that boundary distances are respected, it can be made to work in typical living rooms while keeping optimal intelligibility.
I have actually thought the delayed reflection issue through before. The problem is that to generate high apparent source width (soundstage, ASW) you need decorrelated delays coming roughly from the source direction, so overall reverberation won't help: you still want some clues from the side walls.
Here, the calculation works out depending on speaker placement. In general it can work in a typical living room if speakers are positioned along the long side of the room. For instance, for speakers/listener in an 8 ft or 2.4 m equilateral triangle configuration, putting the speakers >5.5 ft or 1.65 m from the front wall and >6 ft or 1.8 m from the side walls, gets you a minimum sound path distance (direct to reflected) of ca. 3.3 m or 11 ft, for roughly 10 ms delay. That would require minimum room dimensions of just 8+2*6=20ft wide and 5.5+ca.2+sofa depth say 2.5 ft=10 ft deep.
So I still believe fairly wide lateral dispersion will help the impression of spaciousness, especially ASW, and under the condition that boundary distances are respected, it can be made to work in typical living rooms while keeping optimal intelligibility.
MBK said:
If the room is only 10 ft. wide front wall to back wall, what about the reflection off of the back wall. How can this possibly be 10 ms. of delay difference? I don't see how what you are saying can be so. Only if you are ignoring the wall behind the listener, but then you are making a big mistake. An early reflection from behind you is very disturbing. I put the wall behind me back by about 10 feet at least. My room is twenty feet long and the listener is in the center.
Correct, the listening position also has to be a minimum of 5 or 6 ft off the back wall. So that now requires a minimum room size of 20 ft wide and 15-16 ft deep, with speakers along the long wall. I completely forgot about the back wall when I recalculated these values (maybe because my own listening position also is in the middle of the room).
A more directional speaker won't help with the back wall issue though, or would it?
I must say, I've read much of this very thoroughly. It is passionate and technical but I've got one question:
How many of you even have a listening room that is 20 x 16?
I live in a home that I built a room that is 20 by 26 (520 sq feet). I know this is quite large compared to most homes. Mine is worth well over $1M. I also know the average, to above average, home has no such rooms of this size so I'm a little confused.
How many homes are there where the dwellers are willing to have their chairs/listening station 6-10 feet from the back wall? Not to mention speakers 3-5' from the front wall. I mean really, give me a break here, I love audio but to position furnishings in a way that destroys the functionailty of the room, there is something wrong here. A stereo that is worth X (let's say the speaker system is worth $25k) in a room that is 520 sq feet at $150 a foot, let's see, that comes out to a little less than $80k. Not to mention a normal home dependent upon such living quarters.
How do any of you justify screwing up your living quarters this way? Or, is this merely a theoretical discussion that has no pragmatic applications? Who does this to their home? Gees, I'll bet you're not married? This appears hardly practical in any form.
If I am even somewhat right this kind of discussion is mute. It's just not going to happen unless you're wealthy enough to have a dedicated room or you over run your wife.
Look, all this is fine. Find a way to work your magic in a normal listening room, then you'll have the golden egg.
How many of you even have a listening room that is 20 x 16?
I live in a home that I built a room that is 20 by 26 (520 sq feet). I know this is quite large compared to most homes. Mine is worth well over $1M. I also know the average, to above average, home has no such rooms of this size so I'm a little confused.
How many homes are there where the dwellers are willing to have their chairs/listening station 6-10 feet from the back wall? Not to mention speakers 3-5' from the front wall. I mean really, give me a break here, I love audio but to position furnishings in a way that destroys the functionailty of the room, there is something wrong here. A stereo that is worth X (let's say the speaker system is worth $25k) in a room that is 520 sq feet at $150 a foot, let's see, that comes out to a little less than $80k. Not to mention a normal home dependent upon such living quarters.
How do any of you justify screwing up your living quarters this way? Or, is this merely a theoretical discussion that has no pragmatic applications? Who does this to their home? Gees, I'll bet you're not married? This appears hardly practical in any form.
If I am even somewhat right this kind of discussion is mute. It's just not going to happen unless you're wealthy enough to have a dedicated room or you over run your wife.
Look, all this is fine. Find a way to work your magic in a normal listening room, then you'll have the golden egg.
Room diffusion
There was a series of article in Audio magazine about the Hass effect with respect to room acoustics. The initial reflections should not be <8ms after the initial inpluse That is while an OB should be 4ft drom the nearest reflective surface.
Earl is right the more diffuse the reflected soundfield the better.
IMO RPG is the leader in the acoustic design of listening spaces using architectural components. Not a real high WAF though. Their components can do a great job optimizing a rooms behavior.
http://www.rpginc.com/research/index.htm
There was a series of article in Audio magazine about the Hass effect with respect to room acoustics. The initial reflections should not be <8ms after the initial inpluse That is while an OB should be 4ft drom the nearest reflective surface.
Earl is right the more diffuse the reflected soundfield the better.
IMO RPG is the leader in the acoustic design of listening spaces using architectural components. Not a real high WAF though. Their components can do a great job optimizing a rooms behavior.
http://www.rpginc.com/research/index.htm
I am a bit confused here. This is pretty much the size of just a two-car garage. I've seen many homes in the US with roughly that size living rooms, and none cost $ 1 Mio. Not to mention my "own", actually rented place, in land-strapped Singapore - my living room measures (edit) 13x22 ft and with wife and kid I still manage to place the speakers roughly according to these principles, not perfect but roughly. And I have seen living rooms in the ubiquitous public housing estates here that were larger than that.
Placement issues and WAF sure are a matter of personal compromises. But one can't quite ignore some laws of physics and the psychoacoustics involved. In other words, it's one or the other.
Earl's design, the Summa, addresses the issue specifically for small rooms, especially for the distances to the side walls, along with a specific placement recommendation IIRC. But even using the SUmma I suppose you'd have to place the backwall 4-5 ft behind your listening position for optimal results - or use absorbers/diffusers on that wall.