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Old 16th February 2015, 08:23 AM   #261
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Quote:
Originally Posted by nailhead View Post
@cookiemonster:
I had a look on your ABEC model and found out that there is an error in the QTWG Element in Subdomain 1. There is an small area which is not aligned correct. It is the small yellow area in the screenshot. The normal vector is pointing in wrong direction and thus the area is not correctly orientated. This will lead to an error in the simu.

Also the numbers of elemtens and DOFs is quite large, on my computer it would take 2-3hrs to solve the model. Symmetrie would be the way to go, but as I experienced ABEC has (or had?) its problems with symmetry and several (more than one) diaphs included.
For HF only simus I would highly recommend a quarter model, as the actual model has its practical limits to midrange only due to limiting computational time.

Best Regards
Andreas
Thanks Andreas,

I really appreciate that you dig in to find improvement potentials!

Several people have asked me why I don´t use symmetry. The reason is that if you want to split this model up into halves, you will split the Diaphragm representing the CD into two. So far so good, ABEC will handle it when you split an element like that. However, when you mirror the midrange holes, you are doubling the area driven by the LEM model. So if you have on the LEM side a 15mm exit for Driver 1, you will now get 2 15mm exits driven. When you want to investigate coupling, this won´t work. I had a symmetrical model that I sent to Jörg, and he recommended I make it the way it is now. However, when you include the midrange cavities and actual diapgragm into the BEM model, it is possible to mirror and still get the coupling required. I´m not terribly interested in the effect of the CD on the actual midrange diaphragm (imagine a passive radiator), since each element will be given their own amplifier channel and won´t really be influenced like that. But it´s important to see any resonances/reflections by the hole and cavity itself. Once you remove the need for electrical coupling, mirroring becomes possible. When Jörg enables damping on the Baffle element, I will include the woofer diapgragms and chambers into the BEM part of the model too, and then I see no reason to not use symmetry.

There are some bugs when it comes to orientation of normals in the ABEC display. I have reported one, and it was fixed, but I have later seen that there is at least one more. So when in doubt, try for a sanity check. The model as it is now, in my view, passes the sanity check.

For the bug you found: Yes, you are right, i was sloppy when excluding triangles. There are two that need to be removed to make this 100%, 170 and 114.

Elements "QTWG" // use with simplified v7 file
Subdomain=1; MeshFileAlias=HornMesh; Shift=-316.325mm,-316.325mm,-15mm
SwapNormals;
5000 Mesh Exclude 245...250, 8..15, 1...6, 170, 114

Of course, the best way to build this model would be to make a parametric set of nodes rather than importing a mesh file. If somebody volunteers to make an excel sheet or something that generates the triangles required for a QTWG I can include the logic in the Solving.txt. Number of triangles should be fixed, and inputs should be: Diameter of entry, Horizontal Angle and Vertical Angle.
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Old 16th February 2015, 08:28 AM   #262
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Not so much WAF - but at least they don´t need one meter to each wall like my current speakers.

Click the image to open in full size.
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File Type: jpg corner placement.JPG (202.3 KB, 651 views)
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Old 16th February 2015, 01:28 PM   #263
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re'

"For me front chamber volume and port length seem to be related. As you increase front chamber volume the port length needs to be increased to keep the output the same."

definitely true. try port lengths in the range of 1-4 cm that you might get when the sound has to funnel through a solid phase plug as well as the horn wall

I don't disagree with David either. You can model the height of the horn above the floor in AkaBak and Abec or get an approximate result with Jeff Bagby's Diffraction and Boundary Simulator spreadsheet. IMO, the worst case isn't not getting the predicted support, its getting a boundary null in the passband. which is why I would place my woofers outside the horn, D'Appolito style, were it not for how tall the speaker would then have to be.
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Old 16th February 2015, 01:48 PM   #264
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Quote:
Originally Posted by nc535 View Post
which is why I would place my woofers outside the horn, D'Appolito style, were it not for how tall the speaker would then have to be.
I prefer woofers outside the horn as well. The horn can be constructed much smaller and more shallow.

And a pseudo coax can yield to a directivity which fits perfect to a horn with narrow dispersion. I'm working on such a project at the moment. Still waiting for the right horn (40° x 40°) to arrive, but the prototype is promising. And its depth is only 20 cm.

Click the image to open in full size.

Click the image to open in full size.
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File Type: png image001.png (34.5 KB, 357 views)
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Old 16th February 2015, 01:52 PM   #265
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CookieMonster:
You had a long and productive day yesterday!

Is that what your finished design will look like? I had to look twice to see whether it was a photo or a rendition, but ultimately the emptiness of the room was the giveaway

My 90 degree corner horns tuck more tightly into the corner than yours but when I put them up on their Jubilee-like base bins, they are still hard to miss. Nothing one can do about the fact that size matters.

Are you going to extend your mesh to include the room? I guess that would/should be a separate simulation...nice that ABEC can do that too.

Jack
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Old 16th February 2015, 02:11 PM   #266
Flaesh is offline Flaesh  Russian Federation
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Quote:
Originally Posted by FoLLgoTT View Post
I prefer woofers outside the horn as well.
Hi!
Cool directivity pattern!
What is xover frequency and drivers\horn sizes in this prototipe?..
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Old 16th February 2015, 02:38 PM   #267
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Quote:
Originally Posted by Flaesh View Post
Cool directivity pattern!
What is xover frequency and drivers\horn sizes in this prototipe?..
Thanks! I hope it will be still as good with the 40° x 40° horn.

At the moment I use a 1" horn (Limmer 022, 75° x 45°) and 4" midrange drivers. Crossover point is at 1,8 kHz. The front of the enclosure is 50 x 50 cm. Of course the prototype lacks the bass section, yet. When I make progress I will open a new thread about this concept.

Last edited by FoLLgoTT; 16th February 2015 at 03:01 PM.
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Old 16th February 2015, 08:05 PM   #268
bwaslo is offline bwaslo  United States
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Quote:
Originally Posted by cookiemonster77 View Post
Not so much WAF - but at least they don´t need one meter to each wall like my current speakers.

Click the image to open in full size.
Cookie, those look nice. You can improve the WAF of course by adding a grille across the horn. And I think that some SOs would actually prefer larger speakers against the walls to less large ones that sit out 4 feet into the room!
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Old 16th February 2015, 08:30 PM   #269
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Default rear chamber implementation issues

Hi CookieMonster:
Today I measured my 4FE35 in a sealed chamber. Its made from PVC pipe fittings with 3.5" internal diameter, a good match to the seating rim provided on the driver for mounting to the front of a baffle. I'm making a similar chamber with a mailing tube for the 3FE25s

When building it, I was concerned that the response would be affected by the magnet (2.8" dia.) almost completely filling the pipe, that the driver wouldn't see or feel the cavity in back of the mirror. The measurements show that this is indeed the case. I calculate .54L volume, which should yield a peak at (Fbox) of 232 Hz but instead get a peak at 345-365 Hz (two diff measurements). This tune corresponds to box volume of .15L but I imagine what I really have is a bandpass system with a port between two chambers.

I thought I would pass along the caution because the fit in a 3" mailing tube for the 3FE25 is even tighter and could impact what you are doing. I'm hoping you are motivated to model the chamber in ABEC as I'm not there yet in terms of being able to do it myself. I'm waiting for the glue to dry on the 3FE25 chamber and will have a measurement on it before long.

I've attached the horn resp sim results and a screen shot from REW of a clos mic measurement. In the HR, the grey trace is for a .54L chamber and the black is the chamber volume adjusted to match the peak frequency in the measurement. Note the nasty resonances as well.

Jack
Attached Images
File Type: jpg 4fe35 Dir Rad HR sim.jpg (52.1 KB, 27 views)
File Type: jpg 4FE35 Clos Min in .54L sealed.jpg (99.7 KB, 25 views)
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Old 16th February 2015, 08:31 PM   #270
agent.5 is offline agent.5  United States
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Quote:
Originally Posted by cookiemonster77 View Post
Not so much WAF - but at least they don´t need one meter to each wall like my current speakers.

Click the image to open in full size.
Looks great. Where is/are the subwoofer(s)?
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