[Mike0206]

It's taken maybe 6 months to make a final decision but a few weeks ago I pulled the trigger on 2 FTW-21's and an iNuke NU6000DSP. I received the first FTW-21 yesterday and WOW!! I knew it would be big and I know how to read 21" on a tape measure but I don't think I had any idea how massive a 21" sub really looks. As I stated the first driver came in yesterday and the second one will be here next week. The amp won't be in stock for a few more weeks but I already purchased it and by the time it comes in the subs should be mounted and ready to roll. Here are some pics...

This is basically where the sub will go. The enclosure will be either a snug fit inside the cubby or I will remove the drywall and screw 3/4" MDF to the studs and doing that will give me an internal volume of 9.5 cu ft not including driver. If I make them just fit inside the cubbies then the box will be 7.5 cu ft not including bracing or driver.

Here are some pics of the driver

 

[chrapladm]

Brace brace brace.....brace. Are you doing double walls or baffle?

 

[Mike0206]

Brace brace brace.....brace. Are you doing double walls or baffle?

The front baffle will be 1 1/2" so yes it will be doubled. The idea I have is if I remove the drywall in the cubby I'll be able to screw all the MDF to the studs. That should minimize the need to double wall everything and also minimize bracing. It will also give me a bigger enclosure. Am I wrong in assuming that? If I double wall it would bring my volume way down. I would like to stay around 7 cu ft at the small side.

 

[BD55]

I would still double wall. If your studs are on 16" centers, you will still have large panel areas that will be unsupported. I guess you could stuff some more 2x4s in there and call it good though.

 

[fusseli]

Are you worried about vibration or rattling in the cubbies? It might be tricky to get the completed cabinet in and out of there, they are going to be heavy!

 

[wasser]

I would still double wall. If your studs are on 16" centers, you will still have large panel areas that will be unsupported. I guess you could stuff some more 2x4s in there and call it good though.

But he's removing the drywall and attaching the MDF directly to the studs. He's basically building a box with external bracing.

 

[Mike0206]

Are you worried about vibration or rattling in the cubbies? It might be tricky to get the completed cabinet in and out of there, they are going to be heavy!

Yeah after lifting the 70lb driver I don't think I'd want to pull a box in and out of the cubby. I figured if I screwed the MDF to the studs it would reduce vibrations by making the enclosure extremely rigid. Energy would be absorbed by the framing to a degree. If I just put a box in there and have air space in between the enclosure and drywall then I think there would be more of a chance of nasty vibrations. Does that sound right?

 

[BD55]

But he's removing the drywall and attaching the MDF directly to the studs. He's basically building a box with external bracing.

Yeah, derp moment for me. I've edited my comment to reflect what the post actually was talking about....

Add some 2x4s, slide the box in, and screw it all into every stud.

 

[Mike0206]

Then again it could shake the entire wall.....that might be a problem, sort of, lol!

 

[tcarcio]

I have my subwoofer mounted to the back of the wall and I have no problem with vibrations so if you tie yours into the studs you should be ok unless you listen at very high spl's. I was lucky to have the back side of the wall open so I just extended the mouth of the sub and it worked out great. If you look at post #25 in my CHT setup thread you can see what I did. http://www.hometheatershack.com/forums/home-audio-subwoofers/55959-my-cht-setup.html

 

[chrapladm]

It will definitely shake the wall. I had a pair of 21's and they were in 5.5cuft each and they cause my drywall to crack. I dont listen at insane levels either. And most of the time the destruction was with one 21 on because I was using the other amp for something else.

SO just be aware that your going to probably develop cracks in your drywall and have lots of vibrations because your attaching it to the studs. I would just build a box that has room on all sides. Then add some foam around all sides of the cabinet. As long as it is well braced it wont move alot.

BUT if not attached to the wall will sound horrible vibrating against a wall or side. BUT not being attached to the wall will help in minimizing everything else from rattling.

Just a thought.

 

[tcarcio]

It will definitely shake the wall. I had a pair of 21's and they were in 5.5cuft each and they cause my drywall to crack. I dont listen at insane levels either. And most of the time the destruction was with one 21 on because I was using the other amp for something else.

SO just be aware that your going to probably develop cracks in your drywall and have lots of vibrations because your attaching it to the studs. I would just build a box that has room on all sides. Then add some foam around all sides of the cabinet. As long as it is well braced it wont move alot.

BUT if not attached to the wall will sound horrible vibrating against a wall or side. BUT not being attached to the wall will help in minimizing everything else from rattling.

Just a thought.

Actually my sub isn't physically atached to the wall so you could be right. I also have no drywall in the wall that might crack.

 

[Mike0206]

Hmmm..... So it seems the safer bet is to leave the cubbies alone and just do a free standing sub. That wasn't in the design plans but I could rethink this as I haven't started yet. I'm beginning to wonder of an LLT maybe in the cards? It would probably need to be 25+ cu ft but even if I do a 9 cu ft sealed enclosure I won't be able to move the thing by myself anyways. Any ideas on what would be better? Will the walls crack irregardless of whether they are in the cubbies or not?

 

[chrapladm]

I cant say for sure if your walls will crack or not. Thats a matter of build properties. The pair of 21's has the potential to shake EVERYTHING for sure. SO IF wanting to go ported then yes a very large 20cuft + would be killer. Maximizes the 21's full potential while needing less watts to do it. BUT it is a HUGE cabinet so not for everyone.

What sizes can you accommodate?

 

[Mike0206]

Well originally I was hoping to just go sealed but a slot port wouldn't be too difficult. Also the plan to put it in the cubby holes is what I was aiming for but everyone had me worried about cracking drywall and stuff. I really don't want to deal with that. If I go ported I could make them any size I suppose and put them on rubber casters to move them easily. If I do indeed try that route I could place them nearfield on each side of my sectional and veneer them to make them look like a sofa table. What size would be good for them? 30 cu ft? 5' L X 3' H X 2' D?

 

[Mike0206]

I've decided to stick with sealed but I have made a few adjustments to the plan. The cubbies are elevated about 7" off the ground. I am going to get rid of the bottom of the cubbies completely and that will give me 31.5" of height. With that height I can make the box narrower and shallower in order to not have it be too close to the cubby walls. It will also be sitting on concrete so that I'm sure will help with vibrations through the walls. My net cu ft after driver and bracing will be a hair over 8.6 cu ft. That should work out nicely. I will post pics of my progress over the next few days. Driver two is en route and should be here Tuesday.

 

[chrapladm]

Sounds like a plan.:T

 

[cellarnoise]

Look up my sealed build...
I think I am at 6.2 internal after driver takes up volume. I think u could go a bit larger internal, but not too much.

I started off with a 6 inch layer in the back wall of r-21 fiberglass and then 3 walmart pillows of stuffing. I feel it was over dampened. Not have no stuffing and may add back the pillows just to play around.

These put out huge bass, and now I am chasing room modes and rattles... In the wrong spot I get huge booming and in other locations bad in room vibrations at higher spl.

This is with only one ftw21.....

We love it, but the power is amazing. They can use more than a single channel of inuke 6000 also...

I am going to do cheap bass shakers next and eventually another sealed 21. Though it won't he'll without fixing the room some...

Good luck.

 

[Mike0206]

Look up my sealed build... I think I am at 6.2 internal after driver takes up volume. I think u could go a bit larger internal, but not too much. I started off with a 6 inch layer in the back wall of r-21 fiberglass and then 3 walmart pillows of stuffing. I feel it was over dampened. Not have no stuffing and may add back the pillows just to play around. These put out huge bass, and now I am chasing room modes and rattles... In the wrong spot I get huge booming and in other locations bad in room vibrations at higher spl. This is with only one ftw21..... We love it, but the power is amazing. They can use more than a single channel of inuke 6000 also... I am going to do cheap bass shakers next and eventually another sealed 21. Though it won't he'll without fixing the room some... Good luck.

My room is pretty big at 22 ft wide by 34 ft long and 9 ft ceilings. I sit 1/3 of the length back from the main wall and I get fairly even response at the moment. I'm hoping to not have to deal with too many room problems as the front wall is bass trapped already and I will be adding more after the build. I will also be putting r-19 on all walls of the enclosure but not sure if it'll need any more fill after that. My hope is that 2 FTW-21's will be able to fill the room and I'm sure I'll be dealing with rattles for a while. I modeled in 9 cu ft in WinISD and it had a much gentler roll off down low so that's what I am aiming for in going 8.5 cu ft and fill. Nice job on your build by the way!

 

[Mike0206]

Here are some sketch ups of the box I'm planning on building. Total interior volume will be almost 8 cu ft which will give a Qtc of .707. This includes deducting .5 for driver and .5 for bracing.