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-   -   Redesigning my cabinets. Thoughts? (https://www.diyaudio.com/forums/multi-way/337895-redesigning-cabinets.html)

Mario Pankov 15th May 2019 06:38 AM

Quote:

Originally Posted by 3wayaddict (https://www.diyaudio.com/forums/multi-way/337895-redesigning-cabinets-post5791135.html#post5791135)
How do you think the shape of the midrange chamber will work as diffuser?

The irregular surface creates a diffuser for the soundwave from the back of the cone. in theory, it should scatter it and thus greatly reduce standing wave modes inside the chamber. There are other projects on here that have used this approach and Kharma did try to add internal diffusing planes to scatter the backwave and diffuse it. There is an even better solution but you figure it out yourself :)

3wayaddict 15th May 2019 01:36 PM

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Well, putting more braces in is gonna be difficult but there really isn't much bracing to be added in the first place. They are braced quite well.

It's a fully active tri-amp system with digital crossovers and DSP. The amps are Hypex FA123s which have all this in them. The bass enclosure is a sealed box of 58 L which is the perfect volume for these woofers in an active application because in simulation at 44 Hz the F3 is still as low as these woofers will go in a sealed enclosure of practically any volume but the excursion curve stays flat under 30 Hz which allows to extend the frequency response quite far down with the DSP without the fear of reaching Xmax quickly. In my current enclosures, which also have 58 L bass chambers. I got them to go flat to an F3 of 18 Hz and they can still get louder than one would ever want to play them.
About the woofers, they are two SB-Acoustics Satori WO24P-8s wired in parallel. The midrange is a SB-Acoustics Satori MR16P-4 and the tweeter a TW29B-B.

I have slightly improved the diffuser again. Instead of just square cubes, I made al their sides slanted and all in opposite direction to the one that's on the other side. This makes the entire thing even more irregular. It's a really messy and random shape now.

I know theoretically the perfect diffuser is the exponential absorber found in Lawrence Dickie's speakers and the ones that followed his methods (Bowers & Wilkins Nautilus and 800 series and Vivid Audio speakers) though this is gonna be difficult to replicate to the point where it really effective and though I can't really judge because the resulting sound obviously depends on a lot more. But I think I didn't find the soundstage of those speakers to be quite as great as I like. I think this comes down mainly to the volume of those exponential absorbers. Volume in the Bowers & Wilkins "head" and Vivid Audio tubes is quite restricted, restricting the breath of the midrange.

ICG 15th May 2019 04:09 PM

The different angles do indeed help scatter the reflections more, that's a good approach. However, round/semi-round bumps or completely irregular cuts are even more effective.

You are investing a lot of effort in the enclosures but why aren't you using any constructive method to avoid or reduce the vertical/length resonance in the bass compartment?

3wayaddict 15th May 2019 05:44 PM

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Hmm, good point. Maybe I should split the bass enclosure in two segments, one for each woofer.
Though the woofers will be quite far apart in separate chambers. I think this could make for some phase and timing problems since the lower woofer is much further away from the ear.

3wayaddict 15th May 2019 05:58 PM

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Actually this would be a better implementation of splitting the enclosure in two equal section. Placing the upper woofer on the bottom of the upper section and the lower woofer on the top of the bottom section. This way the will be much closer together. The centre is much further down though. The centre of the two woofers is about 61,5 cm away from the middle of the midrange. 44,2 cm from the middle of the tweeter. Will this be big problem for imaging and phase at a crossover frequency of 300 Hz?

tmuikku 15th May 2019 06:49 PM

You could stairstep the divider to get both drivers up in the cabinet. split the divider in half and add vertical panel in the middle.

ICG 15th May 2019 07:20 PM

I like the look of the two bass drivers on the upper end much better. A divider with a step is possible but introduces resonances/standing waves at two instead of one frequency. Two separate volumes also means two ports (if it will be a BR speaker).

To fight the standing waves, you could alternatively also implement internal absorbers, either in a compartment in the bottom or with tube absorbers. Both take up space/volume, so you have to plan ahead for that.

LineSource 15th May 2019 07:27 PM

3wayaddict,
Have you CAD designed a reference cabinet using plywood flat-panels + multi-hole panel braces + Dickie midrange + baffle with 2"-3" radius edge rounds?

3wayaddict 15th May 2019 07:32 PM

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As I said earlier, it's a completely sealed system. I actually have quite some excess volume in the bass cabinets, which I now have cut of with a simple plate.
I've slightly reworked the bracing. Instead of just that skinny beam along the side walls, there is now an entire vertical brac structure which both increases the stiffness in the width and mainly vertical stiffness. The top and bottom are now connected all the by the braces.

I would also like to have both woofers on top for both sonic and aesthetic reasons (the woofers in the middle actually look even worse than I imagined) and I was also thinking about separating the chamber vertically but I'm also afraid that might bring some standing waves back with it because of the length of the chambers.

tmuikku 15th May 2019 08:32 PM

Build a simple prototype and see if the amount of fiberfill you are going to put in can defeat any standing waves in the passband. Filling in the middle would reduce the lowest standing wave most. Aesthetics is a important thing.


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