Preference can be for anything but the reasoning here doesn't seem to match up very well with the analysis I have seen on waveguides.
A few things from Earl Geddes http://www.gedlee.com/Papers/Horn Theory reply.pdf
"One can draw a complex set of wave‐fronts on a piece of paper and connect them with a contour, but that does not mean that real sound waves would necessarily follow these drawings. Sound waves have a mind of their own and they will go wherever they want, no matter how much hand‐waving we do. Take for example defining horn shapes based on the assumption that the wave‐fronts propagate with a constant radius. This assumption yields some very nice looking curves and horns. Unfortunately it is a physically impossible for a wave‐front to propagate in such a manner – it violates every concept in physics from Huygen’s Principle to Green’s Theorem. The wave‐fronts in the real device will not follow the wave‐fronts as drawn on the paper. It’s just not that simple."
"You see, in order for a 1P wave to propagate within a 1P device, it has to be excited by a purely 1P source wave‐front. Any other wave‐front will excite Higher Order Modes (HOMs) and the wave propagation will no longer be 1P. In the case of a conical horn (from spherical coordinates) that’s a spherical cap that vibrates radially. Unfortunately such a source device does not actually exist; one could hypothesize making one, but they don’t actually exist today. A dome loudspeaker vibrates axially, not radially, and so it is not 1P. A conical horn on a dome source is not 1P. For the horn in cylindrical coordinates the source must be a radially vibrating cylindrical section, which, once again, does not exist."
"It was in these AES papers that I came to realize the importance of Higher Order Modes (HOMs), as it is precisely these modes that the Horn Equation fails to account for and it is these modes that make true 1P behavior unrealistic. All horns and waveguides in the real world have HOMs. It is the HOMs that create the complex wave motion that prevents us from prescribing it. Whenever we attempt to force the wave‐front to travel a path that it doesn’t want to, it gets back at us by generating HOMs."
In terms of diffraction, mouth reflections and polar uniformity the mouth termination is very important. Don Keele showed this a long time ago in his paper What's so sacred about exponential horns. mabat has done much analysis and simulation through his Ath software in conjunction with ABEC. The waveguides you have used in the Elsinore have progressed into something that satisfies some of these things better but I suspect that more could be done with the termination. An example below of a simulated 50x50 conical horn with and without a Keele style secondary flare. The overall smoothness and polar uniformity increases with better termination.
Thank you for the lesson. But I am quite familiar with Earl Geddes and we have 'met' online and via some PMs.
If you are saying my waveguide design is not perfect, whom am I to argue? It is a compromise, but I had my eye on something that may not have occurred to you? I will leave it at that.
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Not a good waveguide from Scan-Speak below?
If you are saying my waveguide design is not perfect, whom am I to argue? It is a compromise, but I had my eye on something that may not have occurred to you? I will leave it at that.
EDIT:
Not a good waveguide from Scan-Speak below?
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I am not sure what perfect would be and when targeting certain priorities others necessarily fall to the way side. It was more that you said there were no reflections coming back due to the side shape and that there were no HOM's that struck me as an odd claim to make. If you don't want to discuss what you had your eye on that's up to you, I have no desire to create another thorny topic in your thread. I suppose I find it perplexing that you wouldn't want the smoothest impedance transfer from driver to air as you do in the electrical domain as they both make sense to me.If you are saying my waveguide design is not perfect, whom am I to argue? It is a compromise, but I had my eye on something that may not have occurred to you? I will leave it at that.
I know nothing about it other than what it looks like but from a mouth termination standpoint it does not look ideal.
You can read this and also ask the guy who tested it for more info, he's a member here.
You also might be surprised at what you'll find.
https://heissmann-acoustics.de/test-scan-speak-discovery-h2606-920000/
Same thing applies to the older Vifa H25 / H26 tweeters.
No surprises, perfectly fine response except widening ~5kHz and up until at ~10kHz "huge" dip on axis, due to diffraction at the edge.
On axis response is nice flat and it is a fine driver to use as such but this does not mean it could be better off-axis as well. Might be just fine, but not ideal.
10kHz is 3,4cm long and there is secondary sound source in opposite polarity on-axis, which makes the dip. This calculates there is about 3,4cm distance from source center to edge where diffraction happens and it makes opposite polarity secondary source which makes strong interference on-axis, destructive at this wavelength. And there is boost on-axis one octave below this, where wavelength is double that and path length to edge is half wavelength making constructive interference. As the interference is visible on the frequency responses it means there is secondary sound source, diffraction. Make smooth roundover / termination for the mouth, remove the edge, and now one would have nice response all around, no secondary sound source, no interference.
On axis response is nice flat and it is a fine driver to use as such but this does not mean it could be better off-axis as well. Might be just fine, but not ideal.
10kHz is 3,4cm long and there is secondary sound source in opposite polarity on-axis, which makes the dip. This calculates there is about 3,4cm distance from source center to edge where diffraction happens and it makes opposite polarity secondary source which makes strong interference on-axis, destructive at this wavelength. And there is boost on-axis one octave below this, where wavelength is double that and path length to edge is half wavelength making constructive interference. As the interference is visible on the frequency responses it means there is secondary sound source, diffraction. Make smooth roundover / termination for the mouth, remove the edge, and now one would have nice response all around, no secondary sound source, no interference.
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Still outstanding though IMHO.
I also have two of the other drivers that Heismann Acoustics tested, namely Vifa XT25 and SSpeak D2604 mounted on a Monacor WG and for some reason almost always prefer my Vifa H25 for most of my projects.
Speaking about ideal I would say Beyma AMT fits that criteria quite alright, but not when price is mentioned.
But who am I to argue.
Yes, all this could be moot if its not audible and what not. Definitely very handy to get standard sized package straight from manufacturer. And as you say the response is quite nice. But, if one is after sublime sounding system then there is no reason to neglect this as its not too difficult to come up with better waveguide, and they are easy and cheap to make even. So, there is no need to argue, just something that perhaps people have not paid attention to until recently when we suddenly have had chance to make any waveguide profiles and simulate them easily. Its among first observations from anyone who tries to simulate waveguides that without mouth termination the response is not as nice as it can be. Audibility is another thing but there is about no penalty factor in some mouth termination.
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The D2604 on WG300 shows the point about a smoother mouth termination, but there is obviously more to what maybe preferred than directivity alone. I find it hard to believe that if the same tweeter is used that anyone would end up preferring a waveguide with variable directivity and more diffraction over one with less and smoother directivity, stranger things have happened though.
I am not going to engage with textbook jockeys. They can have their opinions, but the waveguide design is not going to change. I have my reasons and I will simply state them and leave it at that:
My waveguide was made to maximise 'gain' at 3KHz with this particular tweeter, that was my design choice. It comes down to priorities and mine are distinctly different from most designers
I maximise what I can do to lower distortion on the current side. Could this waveguide be changed to improve things on the acoustic side? Perhaps, but I actually consider that less of a priority. The tweeter we have now with that waveguide and that particular crossover has been confirmed to have unbelievably low distortion, confirmed by incredibly critical listeners here in Australia and New Zealand and elsewhere.
If the Purifi tweeter works out to be suitable, and I am definitely hoping that it will be, then the promised possibility of them allowing us to design our own waveguide to suit, then that option may become available with the ULD version of Elsinores. That will then be a ULD Mk2 perhaps. In the meantime, I have around 100 plus of the current waveguides here and they are not going to be thrown away. That waveguide was conceived back in 2013 in time for the Mk6 design and also suitable for Mk5, this was at a time the waveguides were made by Joel Wesseling in Canada. I then decided to invest quite a few thousand dollars and get 200 more. Later on, that order was repeated. So I have gone through 300 plus waveguides plus those made by Joel. Before that, some were made in MDF and square MDF panels by Steve Zobec here in Australia. They were the ones that had the modeling done. Fundamentally it has not changed since with 400 plus waveguides out there?
They still do the job.
Below is the designed off-axis response I am looking for. Note the elevated response above the light blue line, this elevated response is due to this waveguide design.
I pretty much ignore the on-axis response with this tweeter. The Elsinores are designed to be listened to at 10-20° off axis.
A bit further off-axis 30° is blue, note 3KHz it is still at the peak:
This is what I wanted and I think this must have been back in 2011-12 and I did not have any fancy software on hand. To this day I am still satisfied by what it does.
My waveguide was made to maximise 'gain' at 3KHz with this particular tweeter, that was my design choice. It comes down to priorities and mine are distinctly different from most designers
I maximise what I can do to lower distortion on the current side. Could this waveguide be changed to improve things on the acoustic side? Perhaps, but I actually consider that less of a priority. The tweeter we have now with that waveguide and that particular crossover has been confirmed to have unbelievably low distortion, confirmed by incredibly critical listeners here in Australia and New Zealand and elsewhere.
If the Purifi tweeter works out to be suitable, and I am definitely hoping that it will be, then the promised possibility of them allowing us to design our own waveguide to suit, then that option may become available with the ULD version of Elsinores. That will then be a ULD Mk2 perhaps. In the meantime, I have around 100 plus of the current waveguides here and they are not going to be thrown away. That waveguide was conceived back in 2013 in time for the Mk6 design and also suitable for Mk5, this was at a time the waveguides were made by Joel Wesseling in Canada. I then decided to invest quite a few thousand dollars and get 200 more. Later on, that order was repeated. So I have gone through 300 plus waveguides plus those made by Joel. Before that, some were made in MDF and square MDF panels by Steve Zobec here in Australia. They were the ones that had the modeling done. Fundamentally it has not changed since with 400 plus waveguides out there?
They still do the job.
Below is the designed off-axis response I am looking for. Note the elevated response above the light blue line, this elevated response is due to this waveguide design.
I pretty much ignore the on-axis response with this tweeter. The Elsinores are designed to be listened to at 10-20° off axis.
A bit further off-axis 30° is blue, note 3KHz it is still at the peak:
This is what I wanted and I think this must have been back in 2011-12 and I did not have any fancy software on hand. To this day I am still satisfied by what it does.
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I'd prefer your opinion without the belittling insults
Seems like you take discussion or comment as criticism, nowhere was it suggested that your waveguide didn't meet it's design goals or needed to be dumped for something else. It was your claim of it having no HOM's is what I questioned.
I am surprised why anybody should be insulted. Why? That is exactly what I was trying to avoid. So less said about that the better and sorry if I got my defense guard up.
Anyway, looking at that response, the dip around 5KHz is actually a characteristic of the tweeter itself and not the waveguide, so between 3KHz to 10KHz, the waveguide is actually fairly smooth (as long as it is not dead on axis). There really isn't that much to complain about, and since this is a 10-11 years old design, it is still delivering. And there is nothing out there off-the-shelf that is any better. Not for my purposes.
All I am saying is that I am very happy with it and others are welcome to have a different point of view.
If it is the textbook jockey remark, then I am sorry but they always have a go at me. I am after results much more than just theory. Fair enough?
Anyway, looking at that response, the dip around 5KHz is actually a characteristic of the tweeter itself and not the waveguide, so between 3KHz to 10KHz, the waveguide is actually fairly smooth (as long as it is not dead on axis). There really isn't that much to complain about, and since this is a 10-11 years old design, it is still delivering. And there is nothing out there off-the-shelf that is any better. Not for my purposes.
All I am saying is that I am very happy with it and others are welcome to have a different point of view.
If it is the textbook jockey remark, then I am sorry but they always have a go at me. I am after results much more than just theory. Fair enough?
That is fair and reasonable. I suppose I see theory and particularly analysis or simulation as a useful way to work out how to get a good result, rather than a separate entity.
When it's time to design a new waveguide, just call upon the forum to help out. It cannot hurt to get exactly what you want and have it optimized at different angles as well. They can be simulated and optimized using software and these tools have become available to us DIY crowd and are in active use by more and more people. Luckily it goes further than textbook only, as we have seen many practical results. Lets move forward together...
A good paper about distortions https://acoustics.ippt.pan.pl/index.php/aa/article/view/1780/pdf_255 for someone who is new to current drive
Hello Joe,
I am assuming that the tweeter plots in your post were made with a voltage source amplifier.
I also observe that both you and GedLee listen with your speakers toed in.
Me Too.
I also think of you as more artist than "textbook jockey".
Thanks DT
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