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ajc9988
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image
image

So, with it mostly the rest of the way modeled.

 

Edit:

image

Fixed the sub hole in the image and added the port slot on the bottom. Wouldn't want to forget that!

For the upper chamber, I did 2 window cross going left to right, then vertical up and down the back, with the vertical ones and the window ones interlocking. 4 braces in the upper chamber may be overkill, but it will also help to control anything coming from the sub below.

 

Edit: that moment when you realize when you make the cut list that your design calls for 14 sheets of plywood to make 4 speakers, each speaker will likely weigh 220-250 lbs, and that you use about 86% of the 14 sheets (excluding further shaping the braces).


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ajc9988
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So, updating the design. Turns out, if you instead reduce the plywood to 0.5" from 0.75", add in 1" of rockwool in both compartments, you wind up with 1/10 the displacement from the pressure (using 120dB, which is 20 Pascals or 0.0029007548 PSI) versus doing the extraordinary bracing. This also reduces greatly the weight.

Tower 05in w rockwool FRvsMode
Tower 05in w rockwool
Towers Freq vs Magn displacement

First two are the new design, the third one is the old design.

image

There are cutouts to allow the braces to slide into each other, then glue into place, including having cutout blocks to hold the vertical left to right brace in after it is slid into its final placement. I have enough room in the upper chamber to cover the exposed bracing with dacron. I probably will do the same for the bottom. I also kept the insulation cut back enough that it will not interfere with the port flow of air.

@nixem - we should pick up the topic of material use, etc., here, rather than in DSP.

This takes 14 sheets of 24x48x1in rockwool insulation to cover both chambers. Approx. cost (for what I can find at the moment) including shipping = $210.

Edit: The current design, the FEA displacement may actually be higher than reality. When clicking to apply the pressure load to the bare portion of the walls at the bottom by the vent, the program applied that much pressure to the entire wall, instead of the portion of the wall, meaning it is overestimating pressure on the parts of the walls covered by the insulation. So, I might run it again in a bit to try without pressure at those points.

But, the last analysis took up nearly 500GB for the tower alone. So, definitely a space hog. lol.


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Nixem
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@ajc9988 

Great work! 👍


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kanaaudio
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@ajc9988 Looks amazing!


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123Toid
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@ajc9988 

Killing it!

https://www.youtube.com/123toid


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ajc9988
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@kanaaudio @123Toid @Nixem - also, to clarify, the $200 in insulation is to build 4 enclosures, not a single enclosure (around $120 for the insulation, then $80 to have it shipped), which then is $50 per. I used a constrained layer with cheap 1/4" gym rubber mats for the vent shelf and the separator between the upper and lower chambers (partly with the vent to reduce resonance from the air passing through it since you cannot use insulation and need to avoid insulation being too close to the vent; whereas for the separating chambers is to further reduce vibrations not handled by the insulation from either chamber). I figure that would be around $34 to do all 4 with rubber. For Dacron, that could be $40-80, give or take, depending on the quality of polyester/dacron/PET used and local availability and shipping. So I estimate around $300 for all insulation and damping materials for all 4 speakers.

But, this shows why many speaker companies use 3/8" to 1/2" materials for their boxes, because so long as there is enough bracing (which there is less benefit to bracing from my studies than seen on 3/4", although for constrained layer damping, I saw more benefit from 1/2" on both sides with a constrained layer than 3/4" on both sides or 3/8" on both sides) and there is insulation, you can damp more than thicker material and bracing alone. Constrained layer damping is in between the effectiveness of bracing alone and insulation. As such, insulation should be leaned on the heaviest in designs, with CLD used judiciously in cases where it would do better than insulation at damping or when insulation cannot be used for one reason or another (or when using it in conjunction with insulation makes sense). Using bracing alone can help (for example, non-braced 2'x4'x0.5" had 0.06in displacement with no bracing, whereas the 2'x4'x0.75" had 0.02" displacement without bracing; a simple cross (meaning one vertical brace intersecting a horizontal brace forming a cross shape, except centered) brought the 0.5" sample down to around 0.016" displacement, but the 0.75" sample was brought down with the same type of brace to the 0.006" displacement. Doubling up the thickness of the brace by gluing two braces together does add more to 0.75" samples (so 1.5") than doing so with the 0.5" samples (1"). As such, the thinner the material being worked with, you have diminishing returns on trying to increase bracing thickness to compensate.

The insulation also damped the clear ringing (looking like a rising sun shape) on the original design. This would likely have shown up in final testing after built, with a wider (lower) Q effect in that range, rather than the much higher Q, very short duration modes seen in the recent design with insulation. That means it will be much less audible, if at all, in the final design. This almost makes me wonder if an FEA was done on speakers identified to have a port resonance or box resonance (sometimes called ringing), that then the ringing could be identified by modeling speakers for reviews (although the cost and time to run FEAs on items for review does not justify any ROI of doing the analysis, so interesting thought that we could possibly visualize the data that currently is hard to show in testing data for frequency response through looking at displacement vs frequency in FEA, but that any cost to do so means we won't see it outside of published studies, potentially).

I just find the data interesting to understand why speaker manufacturers do what they do.


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