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Mid-dome directivity mismatch? (Vituixcad simulation)
Mid-dome directivity mismatch? (Vituixcad simulation)
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Old 21st March 2020, 08:27 PM   #1
Arnandsway is offline Arnandsway  Netherlands
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Default Mid-dome directivity mismatch? (Vituixcad simulation)

Hi all,

For a 3-way project I would like to try a mid-dome. I have used the Dayton RS52AN-8 to simulate the response in Vituixcad.
But I run into a problem with the directivity, where I would like your insights on.

To describe troubleshoot the directivity, I will post the procedure I used to come to the results. Imaged from the results can be found below.

First:
1. I used the measurements from Dayton Audio RS52AN-8 | HiFiCompass
2. In Vituixcad --> used SPL-trace to get the .frd file.
3. Simulate half-space response from Enclosure tool in Vituixcad. I used two possible designs. 2 SB17NAC-8 in parallel (2x 6") or a Dayton RS225-8 (8").

4. Simulate off-axis response for the woofers via the Diffraction tool in Vituixcad. A guide can be found here: YouTube
5. As a tweeter I used the Vifa NE19VTS-04, also SPl-traced from the measurements at Hifi-compass. Vifa NE19VTS-04 | HiFiCompass
6. Simulate the speaker response in Vituixcad with EQ and linear-phase XO's. XO's are at 667 hz and 4000 hz.

The result can be seen in the pictures below. I marked the directivity problems in red boxes.
The results is practically the same when I used the infinite-baffle measurements for the mid-dome and tweeter.

Now I wonder, is this problem the result of my procedure or caused by using measurements in a wrong way.

Maybe I don't understand how mid-domes should be used . Anyway, I hope you experienced guys are willing to teach me.
Attached Images
File Type: png middome simulatie directivity probleem.png (199.2 KB, 269 views)
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Old 22nd March 2020, 08:29 AM   #2
Juhazi is offline Juhazi  Finland
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Hi, you show only horizontal off-axis responses. Check also verticals, they will show more directivity in xo area thanks to lobing. Some compensation there.

4-5" cone midrange will have more directivity around 2kHz. My favourite mid-size! Baffle shape and edge contouring will have some effect too.

Zaph doesn't show measured off-axis responses, but I expect them to follow your VCAD sim http://www.zaphaudio.com/ZDT3.5.html
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Old 22nd March 2020, 08:50 AM   #3
Arnandsway is offline Arnandsway  Netherlands
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Quote:
Originally Posted by Juhazi View Post
Hi, you show only horizontal off-axis responses. Check also verticals, they will show more directivity in xo area thanks to lobing. Some compensation there.

4-5" cone midrange will have more directivity around 2kHz. My favourite mid-size! Baffle shape and edge contouring will have some effect too.

Zaph doesn't show measured off-axis responses, but I expect them to follow your VCAD sim http://www.zaphaudio.com/ZDT3.5.html
The link does'nt work for me, unfortunately.

I want to elaborate on the question: What is the ideal usecase for a mid-dome?
Because the mid-dome is very wide in it's passband, let's say 600-6000hz. And so it radiates the same SPL off-axis as front axis.

But a woofer already radiates less off-axis because of it's size.
That's my explanation as to why the simulation does'nt show a good match, i.e. it widens and narrows at the crossover frequencies.

This I don't understand because I believe there are excellent measuring speakers using mid-domes that don't show this behaviour. It makes me think the problem is caused by how I come to this simulated response or how Vituixcad handles domes
I hope you can help me with my thought process.
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Old 22nd March 2020, 03:46 PM   #4
boswald is offline boswald  United States
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Mid-dome directivity mismatch? (Vituixcad simulation)
Sim your mid-dome at 800,900, and 1000hz.
As domes are displacement-limited they are more comfortable crossed closer to 3x fs rather than 2x.
As it happens, this will help match directivity a bit.


You can also calculate the lowest cross for your driver at the max spl you want.
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Old 22nd March 2020, 03:51 PM   #5
Juhazi is offline Juhazi  Finland
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Arnand, please show your baffle and speakers in it as image (screenshot from VCAD)

Yes directivity around W_M xo looks strange, but we don't see angles, is it up to 90?

Zaph ZDT3.5 link works for me in Chrome and MS Edge
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Old 22nd March 2020, 04:09 PM   #6
Arnandsway is offline Arnandsway  Netherlands
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Quote:
Originally Posted by Juhazi View Post
Arnand, please show your baffle and speakers in it as image (screenshot from VCAD)

Yes directivity around W_M xo looks strange, but we don't see angles, is it up to 90?

Zaph ZDT3.5 link works for me in Chrome and MS Edge
Here you go.

The sim is up to 60 degrees yes. It is limited because I use the infinite-baffle measurements SPL-traced from the HifiCompass measurements.
Attached Images
File Type: png diffraction 2x 6 inch.png (60.9 KB, 215 views)
File Type: png diffraction 1x 8 inch.png (58.0 KB, 212 views)
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Old 22nd March 2020, 04:22 PM   #7
Arnandsway is offline Arnandsway  Netherlands
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Quote:
Originally Posted by boswald View Post
Sim your mid-dome at 800,900, and 1000hz.
As domes are displacement-limited they are more comfortable crossed closer to 3x fs rather than 2x.
As it happens, this will help match directivity a bit.


You can also calculate the lowest cross for your driver at the max spl you want.
This only worsens the directivity causing an even bigger dip because of the off-axis response from the woofers.
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Old 22nd March 2020, 05:44 PM   #8
Juhazi is offline Juhazi  Finland
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I did VCAD sims for the double woofers with ideal flat response, and VCAd calculating off-axis at 0, 30, 60 and 90 deg

Looks like using a 2" dome is not a good idea. The volt 3" dome in waveguide should be a fraction better.

A simulation shows response around 3-600Hz much better than indoor measurements!
Attached Images
File Type: jpg arnand vs flat onaxis.jpg (289.7 KB, 181 views)
File Type: jpg arnand flat 0 30 60 90 hor.jpg (251.0 KB, 175 views)
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Old 22nd March 2020, 06:20 PM   #9
Juhazi is offline Juhazi  Finland
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Here is my measured response of a proto with double 8" SS woofers, a 4" Audax HM100 mid and ribbon tweeter with waveguide (Fountek Neo3.5H)

Horizontal response smooth as can be! Wiggles come from recflections indoors- a simulation would look much better!
Attached Images
File Type: jpg 3wdsp spl 0-90deg 12ms 16.jpg (168.5 KB, 50 views)
File Type: png 3whifi 0 30 60¤ 6ms 124.png (82.1 KB, 51 views)
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Last edited by Juhazi; 22nd March 2020 at 06:25 PM.
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Old 22nd March 2020, 06:33 PM   #10
Arnandsway is offline Arnandsway  Netherlands
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Quote:
Originally Posted by Juhazi View Post
I did VCAD sims for the double woofers with ideal flat response, and VCAd calculating off-axis at 0, 30, 60 and 90 deg

Looks like using a 2" dome is not a good idea. The volt 3" dome in waveguide should be a fraction better.

A simulation shows response around 3-600Hz much better than indoor measurements!
Then I wonder. What would be a good usecase for this Dayton mid-dome then?


Which mid-domes would work in a band from 700-4500 hz? I mean that in a sense the directivity does match. That Volt dome is crazy expensive
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