The Grotto

Welcome to Joe’s Bar and Theater

Subwoofers

Big Joe

Because my theater is small, I’ve got to be creative in hiding all the gear. The electronics are all outside the room, but that doesn’t work for speakers. For the seven surround speakers, I’m using identical MTM in-wall speakers that will all be hidden by either the screen, or fabric panels that will cover the walls. For the four overhead Atmos speakers, I’m using four identical in-ceiling speakers that’ll also be covered by fabric. You won’t see any of them. However, it’s a little more difficult when it comes to subwoofers.

Like my last house, I could’ve put a store-bought subwoofer in a front corner of the room and been happy with the sound. But I didn’t want a typical black box that stood out in an otherwise clean room. I also wanted bass that was loud, low and clean—which isn’t cheap when it comes to subwoofers. And I’m cheap thrifty.

 

Many people who build dedicated home theater rooms in their houses who have larger rooms, are able to build false walls for their screens, and are able to hide large ported subwoofers behind these walls, keeping the decor of the room clean. As my space is only 12′ 2″ x 16′ 6″, I don’t have that luxury.

So I decided to build my own subwoofers that I can build into my front stage. Parts Express had 15″ Community subwoofer drivers on sale, which would be perfect for a pair of sealed subwoofers in my room. These drivers are normally used for pro-audio subwoofers that cost well above what I’m willing to spend, but because I’m building these myself, I’ll be enjoying quite a cost savings.

The math said that with these drivers, a box size between five and seven cubic feet of volume would give me the best performance. So I designed a box two feet high, one and a half feet deep, three feet wide in the back, and two feet wide in the front. Taking into account insetting the back and front, driver volume, and bracing volume, final interior box volume is just under six cubic feet.

 

While I previously build a bass amp out of baltic birch plywood, for this project I decided on using MDF due to its higer density and weight. It also mills and cuts very easily. Unfortunately, It does not hold screws or nails well. Because of this, I decided to assemble the boxes with traditional joinery via dados and rabbets with wood cleats to hold screws. Adding glue, caulk, and bracing, these will be very strong boxes. I filled them with five pounds of poly-fill each.

The math also says that with taking room gain into account, I’ll be able to hit 110db from 23hz to 120hz ±3db at the front row. We’ll find out how well practice hits theory later.

To fit the design of the room, the tops of the subwoofers will be covered in the same bamboo flooring that I used in the rest of this project, and the front and angled side will be covered in the same navy fabric that’ll cover the walls. The stage piece between them will also be finished the same, after being stuffed with insulation to keep from becoming a resonant cavity.

 

Once assembled, I tested by powering ’em with an old Pioneer VSX-D850S whose preamp stage had been fried by lightning. I wasn’t sure if the amp section would work at all, and I also wasn’t sure if the rated 110 watts to each sub would be powerful enough, but to my happiness, it did, and it is. And holy moly do these subs deliver. I still need to buy a measurement microphone to see if I’ve hit my mathematical goals, but in several weeks of music and movies so far, my ears (and body) say success.

 


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