Redesigning my cabinets. Thoughts?

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Hello,

Not an ultimate concept this time (even though it's quite close).

A while ago (December) I built my active tower speakers. Because didn't setup the crossovers properly they now get quite harsh and overly bright with anything that isn't superiorly recorded "audiophile" music. Obviously I could mostly fix all of this by just resetting the crossovers, which I will eventually, but I'm in my finals right now, almost done with school and I'll have about 4 months of vacation. 2 of which I'm at home. So I have lots of time to do whatever I want and earn quite a bit of money.
My current cabinets I have worked my a s s of to design and built and it's not a bad design by any means but it's far from perfect. It's all square both for the outside and inside (except for the midrange chamber). There's some pretty bad diffraction going on with the current baffles and even though they weigh over 60 kg each, are constructed out of 1" thick high-density MDF and have lots of bracing in them, the cabinets aren't as stiff as I would wan't. The sides, despite the bracing, are vibrating quite a bit, and the entirety of the cabinet of course.

So I'm rebuilding my cabinets. They will have curved sides for extra stiffness, eliminating standing waves and minimal diffraction consequences. And it will be modular. The tweeter, midrange and woofers will each have their own separate little box which are then stacked on top of each other. This again reduces standing waves and resonances in the cabinet and the separate enclosures can be decoupled by putting soft felt in-between the separate boxes. This way the midrange and tweeter don't pick up any vibrations of the woofers. This should greatly increase clarity and spaciousness. And also, I don't have to rebuild the entire cabinet when for example I want to change tweeters.

Because of the curved edges, the cabinets will be constructed by stacking layers of 1" MDF. This also allows for easier and stronger bracing. And instead of 1", the walls of the woofer enclosure will be a little over 1-1/3" thick for extra stiffness. There will also be a small beam of an additional 1" thick walking over the middle of the sides from top to bottom. So the woofer enclosures should be a lot heavier and stiffer.

The for the midrange chamber. The thing that IS great about my current enclosures and that pretty much makes the entire speaker as good as it is, is the internal design of the midrange chamber. It has these big defusing shapes in it. With the current design it's made by stacking MDF plates with bigger and bigger diameter holes in them. Because of the oval shape of the wall with this design, that's a lot harder to do. So instead I've come up with this. amongst the walls there's cubes that get bigger and bigger towards the top and bottom of the box and with every layer the cubes on the left sides stick out a little further than on the right side, and then the cubes on the right side stick out a little further than on the left side on the next layer. This should make for a GREAT diffuser, probably even better than in my current enclosures, especially in combination with the curved walls.
 

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This design should make for extremely minimal cabinet coloration. With the crossovers properly setup using the nice new laptop which I'm gonna buy instead of having to borrow my parent's all the time and being time restricted, this should make for something truly phenomenal.
 
1" mdf is a great start to a very solid cabinet, can't you reach in the driver holes and add some bracing?

You may be overestimating the sonic gains you will achieve by decoupling cabinet sections and reducing diffraction. Compared to the crossover being right, thats small fish. I'd set up the crossover perfectly before making such a heroic box. You may decide during that process that you want a different driver somewhere.
 

ICG

Disabled Account
Joined 2007
Indeed, build a test enclosure first.

The mid-high enclosures got a different size and there are flat surfaces sticking out - not a good idea! That will give you reflections (-> unlinear response) and uneven dispersion. either round it off greatly or use the same size and shape there. You didn't plan for avoiding length standing waves.

The assembly/gluing of the layers will be a PITA. To improve that, make 2 bores in each layer, at the same location on each one, from top to bottom and stick metal rods into it, that way they will always line up perfectly. You can remove the rods later. You should probably make the straight baffle boards removable, that way you can swap for a different board for other drivers.

The speakers will be very heavy. Did you plan for any feet? To get the speakers off of the ground will help a lot regarding the room impression.
 
You`re getting closer to a very good enclosure. The planes below and above the offset tweeter will create frequency response irregularities. A better way to offset it would be to either have these chamfered/rounded to a large radius (if the design allows it), or to put the tweeter in a waveguide which offsets it and saves all the trouble with the complex box design. Some, like the Visaton WG148R and the Monacor WG300 will offset it just right for a typical 6-7" woofer (small adjustment may be required, like a slight tilt but will be really small).

The sharp internal diffusors will be hard to machine, unless its laser cut and will have worse effect than round pattern (wave-like) which allso happens easier to machine. It can even be done at home with a router template and a quality router.
 
What do you mean exactly with bracing in the driver holes?

I know it's al about the crossover. But I'll be rebuilding them anyway. Because yes the crossover is the most important, but that doesn't mean a better enclosure isn't better. And I know the difference won't be like going from the Focal Chorus 716 to the Grand Utopia EVO but I know for a fact that the cabinet will make an improvement, and I now I'll have the time and money to do so, I want to make every improvement I can to the speakers physically as well.

Yes the speakers will be very heavy. I'm just guessing around 80 kg each looking at the what my current speakers weigh and the amount of wood used to construct them. But I don't worry about weight. In fact, from a sonic perspective, the heavier, the better. And for moving them around they also won't be that much more difficult because of the modular design. I will be putting them on feet. I've got spikes that should be able to hold them just fine.

Putting rods through the sides might indeed make thing easier. I'm gonna try to do that.

The tweeter won't be offset. The modular design is not meant for time alignment like with Wilson Audio speakers. The modular design is purely meant for decoupling and not having to rebuild the entire cabinets would I want to change drivers. Time alignment is handled in the DSP.

I already had another design of the midrange diffuser. Similar but just smooth curves instead of cubes but I thought it might not be effective enough. I'll look back at that design and might come up with something different. The proper diffusing in the midrange chamber really is from upmost importance. You keep bragging about the crossover which is definitely also very important but to my experience the treatment of the midrange chamber seriously is just as important, and I'm not over exaggerating. Seriously, I've done some experimenting with different shapes of the midrange chamber and amount of damping and it seriously makes the entire speaker.
 
"What do you mean exactly with bracing in the driver holes?"

In the cabinet you are using now. If you can reach inside, and place braces. Pieces of wooden curtain rod can be used as braces. Difficult to place and secure, but possible. 2 months doesn't sound like long to optimize a crossover, let alone build and finish a cabinet that complex. Remember to multiply your estimate of how long it will take you by 3. (that's just how it seems to go).
 
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 :)
 
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.
 

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ICG

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Joined 2007
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?
 
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.
 

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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?
 

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ICG

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Joined 2007
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.
 
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.
 

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