18" DIY Subs for Dedicated Theater Help - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 18 Old 01-13-2020, 01:43 PM - Thread Starter
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18" DIY Subs for Dedicated Theater Help

Hello.

I have been following along on AVS for a long time, but don't post much. I recently became interested in building some DIY subs for my dedicated home theater. I quickly realized that I am in over my head on the design aspect.

I have a dedicated room that is approximately 18’6”L x 10’8”W x 7’6”H. There is a 12” riser for the back third of the room. The room is decoupled and has double drywall with green glue.

The available space at the front of the room for subs between the LCR speakers and below the screen frame is approximately 41”L x 21”H. I have a door on the wall to the left of the screen that will only allow an approximately 20” depth for that space, but the right side could have a larger depth.

I would like to build two subs utilizing the UM18-22 driver and tuned to approximately 18Hz. I would prefer ported, but if I have to go sealed due to the available space I am open to it.

I have an NX6000D to power the subs.

Would someone be willing to help me design boxes?

Thanks,

Zack
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post #2 of 18 Old 01-13-2020, 04:03 PM
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Is this 2 spaces that are 41x21, as in one between center and right and one between center and left? Or just a single 41x21 opening?

If its 2 separate spaces, I think you could get close to a mini Marty sized box. If the two share that space you will likely have to go sealed.
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post #3 of 18 Old 01-13-2020, 07:01 PM - Thread Starter
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Quote:
Originally Posted by BlueGhost View Post
Is this 2 spaces that are 41x21, as in one between center and right and one between center and left? Or just a single 41x21 opening?



If its 2 separate spaces, I think you could get close to a mini Marty sized box. If the two share that space you will likely have to go sealed.
Thank you for the reply.

It is two separate spaces. One between left and center and the other between right and center.

I can't fit the standard Marty (on its side) sizes due to the height limitation.

I'll post a picture later to provide better perspective.

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post #4 of 18 Old 01-13-2020, 07:28 PM
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If you were to use every inch, and assuming 3/4" material with an 18hz tune … you are left with a 7cu/f box, side port (left or right side) 2"x19.5" and 41" length. You'll get a peak 27ms at 14hz so you can lower this number dramatically with a HPF. Ultimately you have a total of 8.3 cu/f internal to play with and that includes the port, driver and bracing.

The response doesn't look too terrible either, the excursion doesn't go above 22mm until you feed it 1800 watts but by then your port will be limiting you a lot.
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post #5 of 18 Old 01-13-2020, 08:36 PM - Thread Starter
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Here are some pictures of the front of the room for reference.

In order for the door on the left to open 90 degrees, the sub on the left can't be more than approximately 20" deep.

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post #6 of 18 Old 01-13-2020, 08:37 PM - Thread Starter
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Quote:
Originally Posted by Trimlock View Post
If you were to use every inch, and assuming 3/4" material with an 18hz tune … you are left with a 7cu/f box, side port (left or right side) 2"x19.5" and 41" length. You'll get a peak 27ms at 14hz so you can lower this number dramatically with a HPF. Ultimately you have a total of 8.3 cu/f internal to play with and that includes the port, driver and bracing.



The response doesn't look too terrible either, the excursion doesn't go above 22mm until you feed it 1800 watts but by then your port will be limiting you a lot.
Would the construction be similar to a mini Marty on its side just with smaller dimensions?

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post #7 of 18 Old 01-13-2020, 09:09 PM
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18" DIY Subs for Dedicated Theater Help

Quote:
Originally Posted by kcazretsof View Post
Would the construction be similar to a mini Marty on its side just with smaller dimensions?

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Yes, slightly more narrow/longer than a mini Marty.


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Last edited by Trimlock; 01-13-2020 at 09:22 PM.
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post #8 of 18 Old 01-14-2020, 08:04 AM - Thread Starter
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Quote:
Originally Posted by Trimlock View Post
Yes, slightly more narrow/longer than a mini Marty.


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When I plug in the dimension with the port configuration you recommended into the Marty spreadsheet, I come up with the attached. Does this look right?
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post #9 of 18 Old 01-14-2020, 08:56 AM
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I’ll have to look at it when I get home, but it does look fine.


Actually it looks like you put in the internal dimensions into the external. Do you intend to use the entire space available?


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Last edited by Trimlock; 01-14-2020 at 12:14 PM.
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post #10 of 18 Old 01-14-2020, 04:44 PM - Thread Starter
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Quote:
Originally Posted by Trimlock View Post
I’ll have to look at it when I get home, but it does look fine.


Actually it looks like you put in the internal dimensions into the external. Do you intend to use the entire space available?


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There is exactly 41" between the center and mains on each side. I reduced the box to 40" to leave a little bit of room between them and the sub.

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post #11 of 18 Old 01-14-2020, 04:52 PM
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Oh ok, I’ll rerun the sim later but the box tuning shouldn’t be too bad. You’ll lose a few db down low and the port will increase a tad.


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post #12 of 18 Old 01-14-2020, 06:05 PM - Thread Starter
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I measured again and I think I can squeeze in a 21"-22" depth and not affect the door too much.

So 40"L x 21"H x 21"D or 40"L x 21"H x 22"D.

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post #13 of 18 Old 01-14-2020, 06:06 PM
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I’ll base the sim on an external 40x21x21 frame.


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post #14 of 18 Old 01-14-2020, 08:44 PM
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Quote:
Originally Posted by kcazretsof View Post
I measured again and I think I can squeeze in a 21"-22" depth and not affect the door too much.

So 40"L x 21"H x 21"D or 40"L x 21"H x 22"D.

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My original port would work fine, 2"x19.5" and 41" length. I'd do a sketchup for you but I haven't used it in a bit over a year and man I can't get it to work... The marty calc should do the job in getting you a cutlist.

Heres a WinISD of its projected SPL
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Last edited by Trimlock; 01-14-2020 at 08:49 PM.
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post #15 of 18 Old 01-14-2020, 08:50 PM
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For comparison sake I added the extra inch to the width, which gives you almost an extra cu/f and makes your port 6" shorter (2"x19.5"x35"L).
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post #16 of 18 Old 01-15-2020, 07:29 AM - Thread Starter
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Quote:
Originally Posted by Trimlock View Post
My original port would work fine, 2"x19.5" and 41" length. I'd do a sketchup for you but I haven't used it in a bit over a year and man I can't get it to work... The marty calc should do the job in getting you a cutlist.

Heres a WinISD of its projected SPL
Thank you for your help.

I have attached the updated Marty sheet. Does this look correct? Thanks.
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post #17 of 18 Old 01-15-2020, 11:54 AM
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Quote:
Originally Posted by kcazretsof View Post
I measured again and I think I can squeeze in a 21"-22" depth and not affect the door too much.

So 40"L x 21"H x 21"D or 40"L x 21"H x 22"D.

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Don't forget about the speakON connector. I'd recommend mounting it in the top panel of the box (which will be the side when placed in room), since you have depth constraints.
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post #18 of 18 Old 01-15-2020, 08:22 PM
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Quote:
Originally Posted by kcazretsof View Post
Thank you for your help.



I have attached the updated Marty sheet. Does this look correct? Thanks.


Looks good!


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