2 way waveguide speaker build ABEC modelling

[fluid]

I have wanted to build a high efficiency speaker for a long time but something else has always seemed to jump the queue. camplo's 2 way thread and some of the ideas there inspired me to buy a pair of Faital HF146R drivers. I plan to use Faital 15PR400 woofers but I haven't bought these as yet. I found mabat's Ath waveguide tool at the same time and since then I have been trying various different waveguide designs and simulating them with ABEC. mabat's tool makes that very simple in an infinite baffle. To go further and turn that into a free space simulation in an enclosure is a bit more complicated.

I found a design which seems promising and have begun simulating this in an enclosure with various edge treatments to see the effect of those.

The waveguide is difficult to render and show the contour but the attached images should give some idea.

I'll post some more details and images of the simulations to show the sort of output you can get from ABEC. I enlisted the help of DonVK to help me get my head around how to drive it and it is now starting to make some sense.

Although at the moment this project is still quite virtual I do intend to build it in the real world. To that end I have bought a CNC kit which I am in the process of building up. Hopefully it will work well enough to allow me to mill the the majority of the cabinet by CNC.

[nc535]

sounds like fun!

[puppet]

subscibed

BTW, excellent woofer choice.

[fluid]

There has been fun but frustration too It has been a good learning experience.

This is the Horizontal Pressure response of the basic waveguide simulated in an infinite baffle.



This is a good way to compare waveguides to see which ones are worth pursuing further as the waveguide can be modeled with a fairly high degree of accuracy without the simulation taking forever. The number of elements in the model is an important parameter to determine how long the simulation will take. 2500 to 3000 elements usually takes my i7 laptop about 30 to 40 minutes to solve, 4000 somewhere around an hour, 5000 around one hour and 40 minutes.

The size of the elements is also important to make the model accurate and realistic to higher frequencies. The simulation above was done with elements between 5mm at the driver through to 10mm at the mouth. This seems to be a good compromise between time and accuracy.

[puppet]

A little off topic but looking at your waveguide renderings couldn't help but think of stamped copper.

[diyiggy]

Oh Dear, I'm in the same case as the first sentence but wanted to do it with simple 3" cone driver... Compression driver seem more suited. Subscribed . active amps & DSP EQ ?



Yeah Faitals 15PR400 or 15FS520

[AllenB]

Originally Posted by fluid

Horizontal Pressure response

It looks as though much effort went into creating this waveguide. Was all round polars for the square shape the goal, or was it a distributed diffraction oriented design or maybe something else?

[fluid]

Originally Posted by puppet

A little off topic but looking at your waveguide renderings couldn't help but think of stamped copper.

I was trying out the available surfaces in Fusion and the red metal finish seemed to show the contour reasonably well and look quite nice. Reality will likely be more subtle

Originally Posted by diyiggy

Oh Dear, I'm in the same case as the first sentence but wanted to do it with simple 3" cone driver... Compression driver seem more suited. Subscribed . active amps & DSP EQ ?

Yeah Faitals 15PR400 or 15FS520

Cone drivers at the top end tend to limit the overall max spl and dynamic potential and horn loading doesn't change that. A compression driver usually produces a flat wavefront which matches well with an OS or OS derived waveguide. A conical horn is a better match for a driver that produces a more spherical wavefront. mabat's tool can be programmed to show this quite easily.

ABEC would be a good tool to see the effect of the waveguide on the cone driver but it would take a fair bit of effort to get the meshing of the various parts to line up properly. I'll show later why it's important to pay attention to the mesh positioning.

I like the look of the 15FH520 but it's not so easy to get hold of and quite a lot more expensive as I would have to get it from overseas. If TLHP had two in stock a few weeks ago I probably would have bought them. Who knows maybe they will be in stock before I need to buy the woofers.

I will start active with DSP as I am more familiar with that, I might well try a passive crossover if real life measurements make it seem reasonable.

Originally Posted by AllenB

It looks as though much effort went into creating this waveguide. Was all round polars for the square shape the goal, or was it a distributed diffraction oriented design or maybe something else?

There was a fair amount of effort that went into refining the waveguide to the point it is now. I was aiming for a smooth response on and off axis and to have the DI be fairly flat and smooth. The pattern is narrower in the vertical, more than the outline suggests.

I would like to say that I was able to make Ath do exactly what I wanted but that is not the case. The effect of the supershape and the corresponding parameters is not that intuitive and sometimes it's just a happy coincidence. This was close enough to what I was aiming for to move on to the next stage and see what happened.

This is the predicted spinorama style chart from Vituix CAD. The data used for this is from the normalized polars which were normalized to 20 degrees as this is intended to be used in a geddes style setup with the speakers toed in. The listening window (light green trace) is pretty good and the reference axis is dead flat from the normalizing. The DI is pretty flat up to 4k and rises smoothly from there. Predicted in room response is orange hiding behind the early reflections curve in light blue.

[AllenB]

Originally Posted by fluid

The effect of the supershape and the corresponding parameters is not that intuitive

So I see this was a shape in the Ath library, one that reminds me of the JBL M2. IIRC Earl once suggested that the goal with this would have been to create diffraction in consideration of the precedence effect with a pseudo random spread in time and space.

predicted spinorama style chart from Vituix CAD

I could see the benefit of running diagonal polars, and I could also see the spinorama data here as not being on point. What you may be trying to show isn't easy or straight forward as I've watched others attempt to do the same.

[fluid]

This was my first try at a freestanding simulation, it was a total disaster. The model contained 6500 elements due to only being able to use half symmetry and took over 12 hours to solve only to give me complete garbage.

The waveguide did not meet the baffle exactly and the vertices of the waveguide edge, baffle and interface (boundary between the interior and exterior sub domains) were not all aligned.

It doesn't look terrible in the screenshots but a tiny gap or misalignment causes real problems solving for the boundary elements. The results were so bad I didn't save the VACS graph.