Yeah as everything is about compromises pushing performance limits needs a lot of work, trade-off between ease and returns. Good sound can be reached multiple ways and its everyones own decision what is good returns.
You can make MEH to cardioid like any similar sized object, add opposite polarity sources to the sides with small delay. Mouth of a waveguide has roughly similar "bafflestep" as similar sized flat baffle would, and the cardioid thing happens from there and below in any cardioid box. Such speaker would be even more complex than simple MEH 🙂
Another option is of course increase size of the MEH, but mouth controlling pattern down to 200Hz and below would need to be big. And I think only reason why cardioid is handy is smaller size and probably the reason you are looking for one. As cardioids lose output the lower the frequency about 2-3 octaves cardioidish bandwidth is fine but any more than that and system sensitivity suffers greatly. Two octaves from 150Hz is 600Hz and you'd need waveguide for MEH to be about perhaps 600-1000Hz in size, perhaps 40-50cm mouth diameter. Too big? ST260 size could make pattern control down to 200-300hz which I think is fine goal already, but it might be tough to fit the drivers inside.
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Seeing @TNT 's picture of a waveguide surrounded by absorption prompts me to ask the question I have had since the interesting work on rear diffraction/reflection effects began. My DIY efforts this far (no speakers yet, though I am chomping at the bit- a TT, DAC, and a tube amplifier) have involved "brute-force" rather than elegant engineering (and more $) to overcome problems that a more skilled designer would approach in a more practical way.
So the options I am considering include building 1) an ATH WG (OSSE) into a soffit wall, 2) An R-OSSE WG protruding through an absorptive wall (rearward termination of the WG against the wall, and 3) free standing with a rear absorptive wall.
Based on all the knowledge y'all have accumulated re. the pros and cons of these waveguides, does one approach stand out as the best or clearly bad?
Thank you for any thoughts.
So the options I am considering include building 1) an ATH WG (OSSE) into a soffit wall, 2) An R-OSSE WG protruding through an absorptive wall (rearward termination of the WG against the wall, and 3) free standing with a rear absorptive wall.
Based on all the knowledge y'all have accumulated re. the pros and cons of these waveguides, does one approach stand out as the best or clearly bad?
Thank you for any thoughts.
You understood to answer to the question it is all about your room and mainly first difractions.
It is not that easy. In my hifi I change a cap at iso value parameter and it is enough to change the tones and soundstage center equilibrium ( well I listen to outside of the triangle... I mean outside of tje triangle peak...bad !
It is not that easy. In my hifi I change a cap at iso value parameter and it is enough to change the tones and soundstage center equilibrium ( well I listen to outside of the triangle... I mean outside of tje triangle peak...bad !
The main reason for me to aim for cardioid is the different tonal (or in a was spacial) balance compared to monopole LF. There is 3-4 dB less energy in the room in the fundamental tone range with cardioid and that is a big difference.
Yeah, that is the theory. And as we know, in theory there is no difference between theory and practice. 😉
But then the woofers need space and if the spacing between the sources to the sides is too big it is not working any more. And there is the problem of the path length from front to side sources. And for 150 Hz the openings in the WG cannot be too small, even less so with a cardioid that has to push some air....
Exactly, that is what you end with. And maybe it might even work. But I do not know how to do it.
In the end I chose my idea because it is actually simple (at least to me 🙂 though it sure does not look that way. 😀 It is one WG in the center and 4 point sources (closed box monopoles) around and behind. Then there are 4 more for cardioid. A MEH is acoustically more complex, way more.
After listening to this I need to brush up on my origami technique to make it a more permanent instalment.
The speaker is a bit special - its placed very close to the walls and it has angled, backfiring basses. So it could very well be that I'm also hear som benefit from reduce reflections / diffraction from the LF part of the speaker. Just wanted to state this as it is not normal to listen to a speaker that have its major output bounced on a wall ;-) - i.e. it might not be the same experience for other with a different setup. I have an intention to do some measures but I need a good and consistent way of taking off and putting back this "scarf".
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The speaker is a bit special - its placed very close to the walls and it has angled, backfiring basses. So it could very well be that I'm also hear som benefit from reduce reflections / diffraction from the LF part of the speaker. Just wanted to state this as it is not normal to listen to a speaker that have its major output bounced on a wall ;-) - i.e. it might not be the same experience for other with a different setup. I have an intention to do some measures but I need a good and consistent way of taking off and putting back this "scarf".
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Indeed looking at the waveguide alone without considering the whole system is not the best idea, but often it is easier and quicker to look at things in isolation first. I think you are probably being overly concerned about vertical nulls. By choosing the correct spacing it is easy enough in most cases to produce a very smooth set of CTA2034 curves, with some care the nulls can be moved to places where they are really quite benign. Coaxial sources are not without their own issues and often one is robbing Peter to pay Paul.
For a simpler system an in baffle waveguide like Tritonia would match quite well with a pair of woofers above and below. Similar to one of bwaslo's small syn designs or similar in layout to one of nc535's ideas
https://www.diyaudio.com/community/...-wall-or-corner-placement.337956/post-6618160
There is a lot of directivity control both horizontal and vertical that can be realised from the placement of the woofers, still in that sort of quasi coax way. The side woofers can still be used.
It really isn't complicated and ideally there would only be one cavity for which the end forms the slot, but it is not straightforward to construct.
A bigger single woofer behind would be easier to optimize the cavity with and probably suffer less the sort of diffractions you saw in your simulations..
Anything that is not explicitly accounted for in the simulation, the phase plug, junctions between devices, woofer chassis etc. including anything nearby the speaker, yes. The point is that some simulation methods can make some diffractive effects appear worse than they are in reality. My own simulation of a synergy port suffered the same issues. Everything being treated as a fully reflective surface, when in reality they are not. Circsym with high mesh resolution is going to highlight things even more.
Including a woofer enclosure.
WG response - horizontal, vertical:
A direct comparison of the WG alone and with the enclosure (horizontal polars):
(There are obviously some numerical defects on HF - a higher-resolution mesh would surely help.)
WG response - horizontal, vertical:
A direct comparison of the WG alone and with the enclosure (horizontal polars):
(There are obviously some numerical defects on HF - a higher-resolution mesh would surely help.)
Here's the code and the updated exe.
https://at-horns.eu/ext/ath-4.9.0-pre-230115.zip
Feel free to increase the mesh resolution. I just wanted to keep the number of elements under 4000.
https://at-horns.eu/ext/ath-4.9.0-pre-230115.zip
Code:
Mesh.Quadrants = 14
BEE = {
Height = 500
Radius = 130
Depth = 250
YOffset = -370
ZOffset = 40
; mesh resolution: top-front, top-back, bottom-back, bottom-front
Resolution = 10,20,50,50
}
Mesh.ThroatResolution = 8
Mesh.MouthResolution = 10
Mesh.RearResolution = 15Feel free to increase the mesh resolution. I just wanted to keep the number of elements under 4000.
I could not agree more. I was rather happy with my result of a CD in WG with rounded back all on its own.
But then I found out that combining two isolated parts might not work at all the way one would expect it.
I expected some interference especially in this arrangement where every disturbance would sum up on axis because of the symmetry, but I did not expect what I got.
The results for a woofer box beneath a freestanding WG look much more benign, but interference is still obvious and much stronger than most of the differences between different ways of termination or lip form that are frequently discussed here.
I just wanted to point that out: Keep an eye on the full system!
In what way do you want to optimise the cavity with a single woofer when the best way to improve the interference seems to be to "fill" the cavity?
I would really be interested. I did not follow this idea after I saw the result with the rounded cylinder because my simulations showed that improvement was easy to get with a) rounding/sloping the front of the cylinder into a cone or sphere and b) with „filling“ the space behind the WG. So I arrived at this boxfish design with the WG as „mouth“.
I quoted the graph from Dmitrij_S to show that the polars of the woofer might work out, but I am just not good enough with ABEC to check that.
About the (vertical) nulls, you might be right, I am a bit obsessed with that. But on the other hand reflection from floor and ceiling are the first ones of the early reflections most of the time and nulls right in the mid range do not seem to be the best idea. Sometimes one reads tips like "use a thick carpet", but I am not yet convinced.
And these nulls are always connected with a DI peak and I am not convinced that those are a good feature either ;-)
I think we are all pretty aware of that. The above system (#11,449) is the current culmination of my work in this area (i.e. reasonably sized high-quality speakers), and also what I would still opt for, aware of all its limitations.
- A bit more higher-resolution data:
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Thank you so much for this. Great work again. This looks very nice indeed.
About the awareness, I wrote my post after there where some posts about inspecting 0.25 dB ripple in the FR/DI curves to optimise further when on the other hand hardly any results for complete systems were shown. At least it was my impression.
It may be as important (or more so) to optimise the top of the woofer enclosure as you did with making it cylindrical than to adjust tmax by some percent.
The higher resolution graphs are for the identical system? It looks like the WG is placed a bit higher, or is it only the perspective?
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Worth pointing out because creating crossover conditions is still an open topic and one that many struggle with.
Yes, it's a bit higher, just a coincidence. I leave a more thorogh analysis for the reader 🙂
- What I want to try next is to cut some holes into the LF enclosure behind a midrange diaphragm and make it "open-back".
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That's not true, you can have a flat DI (i.e. flat both direct sound and the total radiated power) even with non-coincident sources. That all depends on the crossover.
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If I won't come up with something better in the meantime, this is going to be my design, I think I've been showing it already.
