Help with my first box design. - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 10 Old 10-18-2019, 05:10 AM - Thread Starter
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Help with my first box design.

https://subbox.pro/en/design/?bt=1&b...&pa=150&pp=100


I have decided to go with Dual FiCar HT3 subs. Still toying on what to power these with. Per FiCar (super awesome customer service btw), they suggested 6 cft sealed boxes and this is what I came up with. The depth is only 22 ish inches which mirrors my JTR that I have currently.



My question is about bracing. How much? What shaped? Where do I place them?
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post #2 of 10 Old 10-18-2019, 06:10 AM
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Originally Posted by ratm View Post
https://subbox.pro/en/design/?bt=1&b...&pa=150&pp=100


I have decided to go with Dual FiCar HT3 subs. Still toying on what to power these with. Per FiCar (super awesome customer service btw), they suggested 6 cft sealed boxes and this is what I came up with. The depth is only 22 ish inches which mirrors my JTR that I have currently.



My question is about bracing. How much? What shaped? Where do I place them?
Those are really nice looking subs!

I would reconsider the choice of sealed. Here's why:

WinISD models of that sub with 1000w input.

12 Cubic foot tuned to 18hz and 6 cu. ft. sealed. The sealed only has more output below 13hz, but at tuning, ported has 12 dB more output.

Room gain will close that gap some, and if size is a constraint, then you will be able to add more power for more output with the sealed sub.

Some more info such as what you are using for an amp and what your desired/max box sizes would be will help to nail down a good box design.

But for starters, you should download WinISD and try modelling a bit. Use this thread and BTH's method for entering parameters:
https://www.avsforum.com/forum/155-d...to-winisd.html
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post #3 of 10 Old 10-18-2019, 06:41 AM - Thread Starter
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Thank you for modeling that. A couple of things. I plan on building 4 of these. 2 right now for my front stage and 2 in the future nearfield(ish). I am not looking for crazy SPL. In fact, maybe once or twice a year will I be alone in my house to crank it to reference level. Plus I just want to go the sealed route.

That said, (and forgive my noobness), but I noticed that you entered the Fsc @ 34.49 hz. The specs on the HT3 say the FS is 21.2 hz for sealed. Are they the same thing? Also, how does that graph change by modeling 2 subs? And finally, isnt QTC .707? or does that change with the driver?
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post #4 of 10 Old 10-18-2019, 07:29 AM
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Quote:
Originally Posted by ratm View Post
Thank you for modeling that. A couple of things. I plan on building 4 of these. 2 right now for my front stage and 2 in the future nearfield(ish). I am not looking for crazy SPL. In fact, maybe once or twice a year will I be alone in my house to crank it to reference level. Plus I just want to go the sealed route.

That said, (and forgive my noobness), but I noticed that you entered the Fsc @ 34.49 hz. The specs on the HT3 say the FS is 21.2 hz for sealed. Are they the same thing?
They are not. https://www.diymobileaudio.com/forum...54-post53.html

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Originally Posted by ratm
And finally, isnt QTC .707? or does that change with the driver?
Changes in box size for a given driver affect Qtc.

As you are not after high SPL you'll likely be just fine with the HT3s in 6cuft (net) sealed boxes. And if there comes a time down the road that you do want high SPL you can make new boxes for them.

Sub builds: Yet another Infinity 1260 build | Twins! | Modified V.B.S.S. build | UM12-22 builds | AV stand and sealed UM18s

Speaker builds: DIYSG HTM-10 build | DIYSG Volt-6 build | DIYSG Fusion-8 builds
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post #5 of 10 Old 10-18-2019, 07:40 AM - Thread Starter
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Originally Posted by smcmillan2 View Post
They are not. https://www.diymobileaudio.com/forum...54-post53.html



Changes in box size for a given driver affect Qtc.

As you are not after high SPL you'll likely be just fine with the HT3s in 6cuft (net) sealed boxes. And if there comes a time down the road that you do want high SPL you can make new boxes for them.
Or just add more sealed. Which is the plan for equal dispersion. Side note, referencing the above graph, how many db's would I add if it was modeled with duals? Or is it already modeled with duals and I'm just too dumb to notice that.
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post #6 of 10 Old 10-18-2019, 07:54 AM
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Or just add more sealed.
Sorry, should have said "higher SPL in the 15 - 50Hz range" (the difference in the ported vs. sealed graphs scottvalentin posted). That knee on the ported graph shows quite a bit more in that range, but of course the box is twice the size too.

Quote:
Originally Posted by ratm
Side note, referencing the above graph, how many db's would I add if it was modeled with duals? Or is it already modeled with duals and I'm just too dumb to notice that.
Might be duals, Scott would have to answer that. Doubling the cones should give you ~3dB increase, but the curve remains the same.

Sub builds: Yet another Infinity 1260 build | Twins! | Modified V.B.S.S. build | UM12-22 builds | AV stand and sealed UM18s

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post #7 of 10 Old 10-18-2019, 08:14 AM - Thread Starter
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Quote:
Originally Posted by smcmillan2 View Post
Sorry, should have said "higher SPL in the 15 - 50Hz range" (the difference in the ported vs. sealed graphs scottvalentin posted). That knee on the ported graph shows quite a bit more in that range, but of course the box is twice the size too.



Might be duals, Scott would have to answer that. Doubling the cones should give you ~3dB increase, but the curve remains the same.
Sweet. Back to part of my original question. How do I figure out bracing in this box? It cant be random.
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post #8 of 10 Old 10-18-2019, 10:08 AM
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Sweet. Back to part of my original question. How do I figure out bracing in this box? It cant be random.
It can be, mostly in regards to style. Window, spine, stick, etc. Personally I try to make sure no panel section within 10" is without some type of bracing. Combination of window and spine braces.

Others duplicate what they see in commercial offerings, such as:
https://www.parts-express.com/denovo...seri--300-7079
https://shop.gsgad.com/collections/m...eight-shipping

Sub builds: Yet another Infinity 1260 build | Twins! | Modified V.B.S.S. build | UM12-22 builds | AV stand and sealed UM18s

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post #9 of 10 Old 10-18-2019, 11:17 AM
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Sweet. Back to part of my original question. How do I figure out bracing in this box? It cant be random.
Every 6-8" try to have some type of cross bracing, for the areas that prevent cross bracing, use angle bracing and wall to wall material.
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post #10 of 10 Old 10-18-2019, 02:33 PM
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Originally Posted by smcmillan2 View Post
Sorry, should have said "higher SPL in the 15 - 50Hz range" (the difference in the ported vs. sealed graphs scottvalentin posted). That knee on the ported graph shows quite a bit more in that range, but of course the box is twice the size too.



Might be duals, Scott would have to answer that. Doubling the cones should give you ~3dB increase, but the curve remains the same.
Sorry I was away from the computer since the AM.

I just modeled ONE driver. Keep in mind the SPL levels shown are at 1 meter (I think), so the level at the listening point will be lower.

The FS you were reading above is the FS of the sealed box system, same as the QTC being .67 as a system with that driver in that size box.

The advice on bracing is good - every 8-10" have some form of cross or window bracing, front to back, side to side, and some top to bottom, etc. Even just some 2X4's work well.

With 4 of these units in sealed boxes, you will have a LOT of headroom assuming they are sufficiently powered, so you could EQ them very flat in room to very low frequencies. So you may be perfectly happy with them sealed. As @smcmillan2 says, if you aren't happy, you could then build ported boxes to get the output you need.

Good luck!!
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