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2 way waveguide speaker build ABEC modelling
2 way waveguide speaker build ABEC modelling
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Old 21st January 2021, 02:05 PM   #141
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by mabat View Post
aim...the null(s) in other directions than...the first ...reflections?
The first reflections cover a fairly wide spread, from 40 down to 60 up.
If the C to C is not close then at least one null or peak will inevitably be somewhere in that arc.
Which is basically my point.

The Harman Spinorama work has certain anomalies, for instance only horizontal and vertical measurements are taken, for simplicity.
This works fine for a typical, more or less, axisymmetric source but could potentially be "played" if one pushed response problems into the unmeasured areas.
Similarly it would be possible to push some poor performance into unmeasured vertical directions.
I half suspect the JBL M2 may do this to some extent.
It may improve the published numbers but is unlikely to be without some detrimental effect.

Best wishes
David
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Old 21st January 2021, 02:16 PM   #142
mabat is offline mabat  Czech Republic
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Even if there was a null in that reflection(s) (and I'm still not sure it is inevitable), audibility of such defect (a spectral hole) is generally pretty low. I simply don't consider this as a major issue - that's the trade-off I'm going to accept. I wouldn't accept the degradation of waveguide performance.
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Old 21st January 2021, 11:42 PM   #143
fluid is offline fluid  Australia
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Quote:
Originally Posted by mabat View Post
From my experience, a free standing waveguide can be made somewhat smaller compared to a typical "boxed" one. Think about that
I think about everything you post

Quote:
Originally Posted by tmuikku View Post
I've thought that the bwaslo style DIY MEH which is the easiest one to tackle could be built with better mouth with similar effort, only need to simulate how to bend the panels (kerf bending) to get better mouth termination.
Making anything like this without CNC or 3D printing would be a tall order but it could be done. Something very close to Bill's horn could be simulated in Ath quite easily. I made a mockup of a big one for mark100 some time ago. The sides can be flattened over quite a large area when the profile becomes mostly conical. The down side for conventional construction is that the panels are not completely flat. Terminating a flat sided conical horn properly will make it better but it won't come close to what's possible.

What is interesting in Bill's printed MEH is how he has fed the woofers into the horn. It is quite simple but seems to work remarkably well in measurements. This lends itself more to the rectangular nearly flat sided guides but perhaps something similar could be fashioned for a round one. I probably will look further into this. Some screenshots of it attached.

Quote:
Originally Posted by Dave Zan View Post
The "pile of independent horns" has always looked to me like it would have polars that were also a pile...
of... Hence my scepticism of proposals for a free stand horn.
I don't see that speaker as having anything to do with a freestanding guide.

Anything with spacing more than 1/4 wavelength apart will not sum as a single source. This is a reality for the speaker as I will build it in this incarnation. There will be a vertical split between the woofer and waveguide. This is an arrangement I want to hear and experience for myself.

In a speaker of this size with the crossover being able to be 800Hz possibly down to 500 or 600Hz the requirements are somewhat relaxed and the damage done will be reasonable. I am more concerned about matching horizontal directivity than improving vertical if a choice has to be made.

The best rated speakers in blind listening tests are all vertically split and whilst the coaxial types measure, sum and score better they don't rate better.

There was research done a long time ago by Lipshitz and Vanderkooy
AES E-Library >> Experiments in Direct/Reverberant Ratio Modification
on the effect of directivity changes and holes in the power response from crossover effects. Speaker Dave has cited this research many times and the conclusion is

2 way waveguide speaker build ABEC modelling-power-jpg

Given this and the fact the crossover will be in the region between the speaker being in control and the room taking over makes me less concerned than much is being traded away. Time will tell.
Attached Images
File Type: png bwaslo front.png (270.9 KB, 192 views)
File Type: png bwaslo front z section.png (113.1 KB, 219 views)
File Type: png bwaslo back z section.png (279.9 KB, 194 views)
File Type: jpg L-V-Power.jpg (82.8 KB, 453 views)
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Old 22nd January 2021, 03:40 AM   #144
bmc0 is offline bmc0  United States
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Quote:
Originally Posted by Dave Zan View Post
They won't effect the power response but they will mess up the early reflections response.
The research indicates that this early reflection response is important.
I could be completely wrong since this is mostly just wild speculation on my part, but...

I really doubt that dips in the early vertical reflections are a big problem. Vertical localization is non-existent around the crossover frequency range in question and the reflections are very early. From this, it seems reasonable to conclude that the vertical reflections are perceptually "fused" with the direct sound and not separable by the ear-brain system. So the primary effect of the early vertical reflections is timbre change (this is Toole's conclusion as well, according to his book).

So what degree of spectral coloration can we expect from the crossover null in the floor reflection, for example? I've done some simplistic simulations. First, here are the direct and reflected responses:

2 way waveguide speaker build ABEC modelling-direct_and_reflected-png

Green is coincident, blue and yellow are vertically displaced LR4 and LR6. Reflection delay is 2.6ms for the tweeter. There is 3dB of attenuation for propagation loss and a 4dB shelving filter to simulate the directivity. The floor is assumed to be fully reflective. In the non-coincident examples the woofer leads the tweeter by 0.5ms for perfect cancellation at the crossover frequency. Add the direct and reflected together and you get this:

2 way waveguide speaker build ABEC modelling-summed-png

Purple is coincident and green is LR4. ERB smoothing. The changes in peak/null frequencies makes it harder to distinguish the true difference, so I think a better option is to calculate the RMS average of the direct and reflected responses:

2 way waveguide speaker build ABEC modelling-rms_average-png

We get a ~1dB dip. In reality, you're unlikely to have full cancellation and the dip will also be partially "filled in" by later reflections. So I'm not convinced that fixing the vertical nulls should be a high priority. Feel free to prove me wrong
Attached Images
File Type: png direct_and_reflected.png (23.9 KB, 228 views)
File Type: png summed.png (34.3 KB, 222 views)
File Type: png rms_average.png (28.2 KB, 221 views)
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Old 22nd January 2021, 06:03 AM   #145
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by mabat View Post
Even if there was a null in that reflection(s) (and I'm still not sure it is inevitable)
My back of envelope calculations-
Usual recommendation for crossover frequency is when both sources have similar directivity.
Typically this is around where the horn is λ across and the woofer too.
So a C to C of λ is about the minimum for the obvious layout, use it for simplicity and assume on axis is in phase summation (Linkwitz Riley for example.)
With two sources of same output and λ apart we have a classic interference null at + and - 30 from the on axis.
This is within the limits of the forward directions that are considered by the Spinorama preference score but not in the main window so not very emphasised.
That makes sense to me, such speakers can sound excellent but can perhaps be improved.

Quote:
audibility...is...pretty low. I simply don't consider this as a major issue
Yes, it's not within the main window so audibility should be lower and not a major issue.
But if it could be moved out of the forward window then it wouldn't be even a minor issue.
I certainly wouldn't put noticeable ripple in the main window to remove a small dip in the forward window.
But equally I won't worry about small ripples in the main window to the complete exclusion of cancellation dips in the forward.
I will have to look more carefully at the Harman "Preference Score" to see what they found as a balanced trade-off.

Best wishes
David
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Old 22nd January 2021, 06:32 AM   #146
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by fluid View Post
...This is a reality for the speaker as I will build it in this incarnation.
Like you, I am constrained by the speakers I already have for my current project, also IIRC similar to yours - 1.5" compression drivers and efficient 15" woofers.

Quote:
In a speaker of this size with the crossover..800Hz possibly down to 500 or 600Hz the requirements are somewhat relaxed...
I am more concerned about...horizontal directivity than...vertical if a choice has to be made.
I use a nominal baseline of 666 Hz, it seems appropriate for such a loudspeaker.
And yes, I am more concerned about horizontal too.
But my idea was that for a vertically stacked system a reduction in C to C should help the vertical with minimal impact on the horizontal so it's not a choice that has to be made.

Quote:
The best rated speakers in blind...tests are all vertically split and whilst the coaxial types measure, sum and score better they don't rate better.
Nice news for a vertical speaker owners.
What tests were these?

Quote:
...makes me less concerned..Time will tell.
Yes, as replied to Marcel, I do see this as incremental improvements rather than a major concern.
The only decision I have left is between the classic vertical stacked horn plus woofer, or some sort of MEH or perhaps Bill Waslo'ish slot system.
Thanks for the pics and ideas.

Quote:
Originally Posted by bmc0 View Post
...since this is mostly just wild speculation on my part, but...
Thank you, that's a bit to think about, a proper response may take a while.

Best wishes
David

Last edited by Dave Zan; 22nd January 2021 at 06:41 AM.
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Old 22nd January 2021, 07:39 AM   #147
fluid is offline fluid  Australia
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Quote:
Originally Posted by Dave Zan View Post
But my idea was that for a vertically stacked system a reduction in C to C should help the vertical with minimal impact on the horizontal so it's not a choice that has to be made.
I think we are all agreed that reducing the distance is a good goal so long as nothing else is compromised significantly to get there.


Quote:
Originally Posted by Dave Zan View Post
Nice news for a vertical speaker owners.
What tests were these?
The Harman blind listening tests, the Salon 2 is still the preferred speaker to my knowledge of all those tested and the M2 is very close but appeals to a different audience. They both fall in the statistically difficult to separate category of the top performers.


Quote:
Originally Posted by Dave Zan View Post
The only decision I have left is between the classic vertical stacked horn plus woofer, or some sort of MEH or perhaps Bill Waslo'ish slot system.
Thanks for the pics and ideas.
Bill's method is simpler than I thought so I too am giving greater consideration to that as another option in the future.

Quote:
Originally Posted by Dave Zan View Post

I will have to look more carefully at the Harman "Preference Score" to see what they found as a balanced trade-off.
I don't really understand the fascination with the preference score. The basic tenets of the research were obvious before the metric and the score is not to be taken literally from my reading of it. Seems to be a simple way to know if you are in the ball park rather than a target. The Salon 2 does not score awesomely well but it is still widely considered their best speaker.
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Old 22nd January 2021, 08:12 AM   #148
tmuikku is offline tmuikku  Finland
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Yeah the vertical nulls probably affects more to the localization or other qualities of the speaker than listening window sound or frequency response or how to describe it, I don't know if it is an issue, maybe not but still Listening distance would affect.

A MEH would allow a bigger waveguide that could control directivity down to Schroeder frequency and as point source wouldn't care much about listening distance. If there wasn't any reflections and diffraction at the speaker nor too much off-axis anomalies I'd guess the speaker disappears completely localization wise. But as said it is much more work to design and fabricate. Still I think it is the ultimate sound radiating physical object one can make with controlled directivity. At least there is the promise since more compromises seem to be in favor of audio and the trade offs are in time, money and size. Never heard one and my stacked multi-way sounds good so, just speculating Carry on

Last edited by tmuikku; 22nd January 2021 at 08:31 AM.
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Old 24th January 2021, 08:53 AM   #149
fluid is offline fluid  Australia
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I have been getting to grips with the 4.7 version of Ath trying to design a freestanding guide.

This one from mabat is my target (it is a 1" guide where I will be using 1.4"). Of all the options I have seen this to me seems optimal.

2 way waveguide speaker build ABEC modelling-report_flat-png

I've developed four pretty decent options, all different. Sadly combining the best parts in one seems like a tall order and after 100 or so simulation runs I'm getting burned out trying.

I've run my best effort from bmc0's code through Ath to generate the same report to compare.

I have attached a slowed down gif and separate files for those who like to see either.

The directivity is very constant with bmc0's it's much bigger and I didn't notice the 1200Hz bump as much when simulating to 600Hz. Test2 has smooth curves but is a 60deg window, Test4 is perhaps the closest to what I want. What I like in all of them is that the directivity gives up gently and doesn't just fall in a heap.

2 way waveguide speaker build ABEC modelling-ath-reports-gif
Attached Images
File Type: png report_flat.png (110.9 KB, 149 views)
File Type: gif Ath Reports.gif (354.2 KB, 153 views)
File Type: png bmc0.png (127.9 KB, 4 views)
File Type: png Test1C.png (130.2 KB, 5 views)
File Type: png Test2C.png (131.8 KB, 4 views)
File Type: png Test3C.png (129.4 KB, 5 views)
File Type: png Test4C.png (129.3 KB, 5 views)
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Old 24th January 2021, 10:06 AM   #150
fluid is offline fluid  Australia
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For the MEH fans here is a Faital 6RS140 woofer in a 2 litre box which seems like it could be constructed as part of the back of the waveguide. Relatively simple cone shape to model.

2 way waveguide speaker build ABEC modelling-6rs140-raw-gif


and again with a little bit of Flattening EQ

2 way waveguide speaker build ABEC modelling-6rs140-gif
Attached Images
File Type: gif 6RS140 raw.gif (34.3 KB, 147 views)
File Type: gif 6RS140.gif (34.1 KB, 148 views)
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