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Multi-Way Conventional loudspeakers with crossovers

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Old 24th April 2018, 04:31 PM   #71
augerpro is offline augerpro  United States
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Thanks Christoph. I'll tighten up the fitment in the next designs. So if I understand correctly, the major improvements to the simmed response are due to: tight dome fitment, and a small 2-3mm step? Where does the crease fit into this? I'm wrestling with Fusion 360 to design that crease, I may just take my Japanese chisels after one I have and measure the results as a quicker way to get some data.

I'm going to send another batch of designs to the printer soon, with more of the larger guides included. Also have the new Dayton RS28A on the way.
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Old 24th April 2018, 10:19 PM   #72
Gaga is offline Gaga  Europe
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Hi Brandon,

My take of the simulations so far: Yes, no gap between the dome/suspension improves the situation - though it will probably not possible to achieve the ideal situation in real live. Still, tighten up the fitment will certainly help.

The step or crease (the 2-3mm for the simulated tweeter) helps, if we have to accept the 'gap' between suspension and waveguide throat. So far I think that the best height of the step (2-3mm in the simulation) depends on (i) the geometry, e.g. height of the dome, (ii) the size of the 'gap' and (iii) the waveguide contour. This means, that the right step height has to be adjusted to a specific tweeter (dome and suspension geometry, the existing gap to the WG throat and the specific waveguide.

Before you print new versions, could you possibly measure the exact height of the SB26ADC dome so I can check back, if my simulation was exact enough? You could simply build the step (or crease) using the existing waveguide VarC and add shims with the correct diameter between tweeter and throat, as you did before.

I'm as well not sure, if the 'step' or crease as simulated is already the best solution. May be a more smooth rounding of the edge (like done in oblate spheroid WGs) work better. I'll simulate this.

However, I think it is good to minimize the gap between membrane/Suspension and WG throat AND to start the WG contour perpendicular to the membrane.

Some simulations to look at that: First a simulation of a flat membrane without gap between membrane and WG throat in the elliptical WG VarC, with and without the 2mm 'step' or crease.

Flat membrane in elliptical WG VarC, no step:
2018-04-23 elliptical WG VarC Flat Membr full -0mm step image 1.png

SPL 0-60:
2018-04-23 elliptical WG VarC Flat Membr full -0mm step SPL horiz 0-60Gr 1.png

Though there is no gap between membrane and WG throat, we still see the 13kHz and 18-20kHz dips.

Does the 2mm 'step' or crease help here?
Flat membrane in elliptical WG VarC with -2mm step/crease:
2018-04-23 elliptical WG VarC Flat Membr full -2mm step image 1.png

SPL 0-60:
2018-04-23 elliptical WG VarC Flat Membr full -2mm step SPL horiz 0-60Gr 1.png

Note, that the situation did not improve basically, i.e. the positive effect of the 2mm step seen before, depends on the membrane geometry and gap to the WG throat.

What happens, if we use the elliptical WG VarC and simulate a membrane, which fulfills the suggested properties, i.e. (i) no gap to the WG throat and (ii) a membrane perpendicular to the contour at the WG throat?

This would look like this:
2018-04-24 Elliptical Waveguide VarC Membran gross rechtwinklig image 1.png

SPL 0-60:
2018-04-24 Elliptical Waveguide VarC Membran gross rechtwinklig SPL horiz 0-60Gr 1.png

Now, this looks promising. Thus I show the horizontal radiation normalized to 0 as well:
2018-04-24 Elliptical Waveguide VarC Membran gross rechtwinklig horiz norm0 1.png

Obviously, we do not have the ideal dome geometry for the WG available.

However, I'd be happy to re-check m simulations with the exact dome/suspension geometry of the SB26ADC and then adjust the best 'Step' height or crease. I'd as well check, if the crease or somehow rounded version of the step works best.

Why did the step/crease work that well for the SB26ADC simulation? I'm not finally clear with that, however, I suspect that the step (bringing the membrane 2mm back) brings the WG contour 'in line' with the emitting dome/suspension, like indicated in this image:
2018-04-25 Elliptical WG VarC SB26ADC membrane -2mm step zoom 1.png

However, this is just a speculation and has to be evaluated still. A simulation with verified dome/suspension contour (including the angle of the dome to the tweeter faceplate) and slightly adjusted WG contour (bringing the contour perpendicular to the dome) and respective step/crease might tell...
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Old 25th April 2018, 01:47 AM   #73
augerpro is offline augerpro  United States
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Quote:
Originally Posted by Gaga View Post

The step or crease
Now I understand the confusion. The step and crease are different things. The crease I'm referring to is in the pic of the Revel speaker, running vertically along the horn wall. It is very slight, I hadn't noticed it before until it was pointed out.

In earlier testing I assume a wall meeting essentially normal to the diaphragm (perpendicular as you put) would be ideal, but I found steep walls to be generally better.Probably for other reasons related to wavelength vs curve radius of the wall, and whether the flare meets tangent to the baffle surface or not. I can always revisit it though with the large guides.
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Old 26th April 2018, 02:54 AM   #74
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by augerpro View Post
Now I understand the confusion. The step and crease are different...the crease...is in the pic of the Revel speaker...
I was also a bit confused, but could you post the picture?

Best wishes
David
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Old 26th April 2018, 03:51 AM   #75
454Casull is online now 454Casull  Canada
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Marked for later.
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Old 26th April 2018, 05:32 AM   #76
augerpro is offline augerpro  United States
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Quote:
Originally Posted by Dave Zan View Post
I was also a bit confused, but could you post the picture?

Best wishes
David
Post #50
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Old 26th April 2018, 06:06 AM   #77
Gaga is offline Gaga  Europe
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Sorry for the confusion. I may have described things a bit complicated and unclear as a non-native speaker.

Quote:
Now I understand the confusion. The step and crease are different things. The crease I'm referring to is in the pic of the Revel speaker, running vertically along the horn wall. It is very slight, I hadn't noticed it before until it was pointed out.
Yes, with the crease I referred as well to the image of the Revel speaker.

When I'm talking 'step' I refer to the step developing, when I set back the membrane relative to the waveguide throat (here colored yellow):

2018-04-23 elliptical WG VarC Flat Membr full -2mm step image 1a.png

Though the Revel-'crease' is a bit rounded at the transition to the waveguide contour, I suspect that the depths of the Revel-'crease' is roughly in the same range as the 2mm 'step' used for the elliptical waveguide - and does basically the same, i.e. improve radiation.
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Old 26th April 2018, 05:43 PM   #78
augerpro is offline augerpro  United States
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Here:
Q7VyIZj.jpg
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Old 26th April 2018, 06:48 PM   #79
Gaga is offline Gaga  Europe
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Thanks Brandon - now I got the 'crease'! Actually did not see it...

For clarification: The tweeter is set back a bit as well in the Revel waveguide - comparable to the 'step' simulated with your elliptical waveguides.
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File Type: png Revel Waveguide 2.png (22.1 KB, 699 views)
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Old 6th May 2018, 08:39 PM   #80
Gaga is offline Gaga  Europe
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Hi,

A series of new simulations, again around the 'step', i.e. height between tweeter membrane and waveguide-throat.

I did two more changes for this series of simulations, (i) did a slight change to the horizontal waveguide contour and (ii) refined the membrane geometry according to data received from Brandon.

The circle sector used as profile for the waveguide contour was replaced by a spline-profile in order to be more flexible during the profile optimization process to be done later. The horizontal profile used during these simulations looks like this (the vertical profile as not changed at this stage):
2018-05-02 Elliptical WG contour V2 neu SB26ADC Membrane neu V2 horiz contour image 1c.png

The SB26ADC membrane geometry used for these simulations looks like this:
2018-05-01 Elliptical WG Kontur V2 SB26ADC neu Step0-5mm image 1a.png

The image is somehow self-explanatory. The 'step' (yellow) is varied from 0mm to 5mm.

A summary of the simulations is given in the next image:
2018-05-01 Elliptical WG contour V2 spline SB26ADC neu Step 0-5mm 1.jpg

Images at the left side show horizontal radiation normalized to 0, images at the right side show the SPL at different angles from 0 to 60 in 10-steps for steps from 0mm to 5mm.

Again - as simulated for the elliptical waveguide typeC with the somehow simpler SB26ADC membrane geometry before - the 2mm-step seems beneficial for a smooth (although not real constant) directivity.

More on waveguide-throat variants and phase-shield / phase-plug variants later.
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