Built-in subwoofer project

[Wayne A. Pflughaupt]

Background
I’m contemplating a built-in DIY subwoofer in our living room. I’ve been using couple of “throw-down” subs for the past several years, a couple of 12” Shiva drivers dropped into some old ’70s tower speakers I had taking up space in the closet.

Even though the boxes are pretty big, they’re only about 2.0 cu ft. each, which is on the small side for the Shivas. Response peaks out at about 40 Hz, and some serious EQ boost is required to get them down to 25 Hz. They’re powered by an Adcom GFA-555II amp, which delivers 325 watts per channel into the 4-ohm load.

Here are both unequalized and equalized graphs with the subs in their current location.

Baseline Response


Equalized Response

Believe it or not, even with the modest power and huge EQ, these subs have been adequate for the 9200 sq. ft. family room in the house we moved into a few years ago (that includes all other areas of the house open to the room). At the maximum volume I listen to, the Adcom’s clip lights will flicker at about the time the drivers reach their limits in the depth charge scene of U-571.

Here are the subs in their present location. Normally they are hidden behind a chair.

The Proposal
Basically, I want to get these things off our living room floor. This family room is smaller than our last one, not to mention much more “classy,” so these big boxes on the floor behind the chair are just out of place.

I had my eye on a built-in cabinet/book case (right behind where the subs are sitting) for a “stealth” sub installation soon after we moved in, but figured it would be too problematic and dismissed it as an option. Here’s a picture of the built-in with the subs moved out of the way.

I’ve also toyed with the idea of an IB, as there is attic space available above the built-in (where you see the AC vent in the picture). However, it would cost a minimum of several hundred to a thousand dollars, money we just don’t have right now. (Okay, I do have the money, but I’m lusting after a fretless bass at the moment, and some new equalizers for the HT system. It’s my perennial problem, too few dollars chasing too many hobbies and interests! ) Not to mention, the work may involve moving the AC duct and other stuff I’m not sure I want to deal with.

That brings me back to the built-in. I originally dismissed it for a number of reasons. Primarily, I feared vibration would be horrendous, both from the cabinet itself and everything on the shelving above it. Then there was the problem of outfitting two 12” speakers in a long, “low boy” um, “enclosure.” Mounting the drivers side by side, the only apparent viable option (each door opening is 17"x17"), would create a time alignment issue at the listening position, not to mention the prospect of drilling holes everywhere to properly secure a baffle board over or behind the cabinet openings was unappealing. Properly sealing off the other door openings, while leaving the doors themselves intact (for obvious aesthetic reasons) looked daunting as well. On top of all this, there is a gas jet valve for the fireplace inside the cabinet.

I think I’ve come up with solutions for most of these issues. For the first three, I think I can address them all in one fell swoop by utilizing an IB-type manifold, mounting the two drivers opposing each other. That should take care of the vibration issue, and fit nicely into the hole where the last door (nearest the corner) would be removed. Unlike a baffle board, it shouldn’t be hard to secure a manifold inside the cabinet without drilling holes in the front of it. I though I would try to utilize the removed door’s original hinges for a fold-out grille frame. Naturally, this will all be hidden from view by the chair that normally sits catty-cornered in front of the built-in.

About the only thing I haven’t figured out yet is what to do about the gas jet. Anyone have any ideas? It’s a square shaft that a handle fits onto. If not, there’s a fireplace store in the neighborhood; I might drop by and see if they have some kind of extension.

Potential performance
Okay now for the good stuff, crunching the numbers. The built-in cabinet has 17 cu. ft. internal volume. Giving up maybe 1.5 cu. ft. for the manifold, we have about 15.5 cu. ft. total to work with, which means each speaker will see a little less than 8 cubic feet (or 225 liters). That’s nearly 2 cu. ft. (or 48 liters) more than the largest size Adire recommended for the Shiva in their white paper.

I’m no subwoofer-building expert, but I figure I’ll have no problem hitting 20 Hz or lower with this thing with no help from the equalizer. That should mean I'll be able to get output comparable to the small-box set-up without maxing out the amp and drivers like I am now – right? (Based on the fact that EQ boost will no longer be needed to get the added extension.)

Yes, I know it would probably be better for each driver to have its own enclosure, but that’s just not practical here. Or even possible…

So – whatd’ya think? I’m open to any suggestions or tips on possible “gotchas.”

Keep in mind that this is a low-budget proposition, using the drivers and amps I already have on hand. I also have most of the lumber on hand, primarily a good-sized sheet of 3/4” furniture-grade plywood that I’ll build the manifold out of. A primary consideration is that I have to be able to restore the cabinet back the way it was in the event that we ever move again. So any permanent, visible damage to the front of the cabinet is out of the question.

Aside from better extension, what I can I expect from this set up, compared to what I’ve had before with the smallish boxes? What effect will the larger enclosures have on detail, dynamics, etc.? My expectations are pretty low-key; if it performs at least as good as the “throw-down” subs, I’ll be happy.

Regards,
Wayne

[Mike P.]

Is this going to be a sealed or ported application?

[Wayne A. Pflughaupt]

I expect that sealed is the only option. The cabinet depth is only 19-20" from the doors to the back. I expect that rules out any chance of integrating a port in the back of the manifold, as it could be only a few inches in length. I suppose removing the second door from the corner and putting in a port there might be an option, if you guys think it would be worthwhile and time alignment wouldn't be an issue.

Regards,
Wayne

[Mike P.]

The manifold depth only needs to be 12 inches as that's the diameter of the subs. That would leave 7 - 8 inches of room from the end of the manifold to the back of the cabinet. That's plenty of room to install a 4 inch elbow on the end of the manifold to run the ports. Would that be an something you would consider? Is this for Ht and music?

[ModMark]

The gas value issue.

If the current location of the gas value would be inside the cabinet, remove the value and attach flex pipe. Run the flex pipe to the front of the baffle and install a new value. However, I not sure the gas company would approve a gas line runing inside a sub woofer cabinet. It could become a real "boom" box one day.

Another solution which would be permanent, install a new value on the exterior front face of the cabinets. The value would still be mounted inside the cabinet with just the handle or knob on the outside. You should be able to buy a nice brass knob for the value which would look nice.

If the bottom shelve of the cabinet could be removed, the pipes could be run along the brick floor inside the cabinets.

[ModMark]

Sorry, I am still a rookie in building sub woofer but I do have a few DIY home projects under my belt..

For appearances, I am having a hard time imaging just one cabinet door being removed and replaced with a speaker grill. It may look unbalance and like a DIY job.

Since it is your money and I love spending other peoples money http://www.hometheatershack.com/foru...s/bigsmile.gif, a long term solution for me would be to remove all the doors and replace them with custom made grills ie: match matching wood doors with speaker cloth in the middle.

Question, can the bottom shelve be remove gracefully or you may get lucky and the whole front face of the cabinet could be temporary removed. If the cabinet maker just used 'L' brackets to attach the front face, this may be easy.

The goal here, build a speaker box which can be attached to the brick floor. I share the same concerns, vibration of the shelving unit. Mechanically isolating the woofer box from the cabinet would be ideal.

[ModMark]

One more thought..

Remove the two center doors and replace it with a grill cover. Now the cabinet will have a balance look, two doors on the outside of the cabinet with the grill in the middle.

This may require the installation of a vertical brace next to the cabinet door but it will be a small piece of wood ie: matching it to the existing cabinet.

[Wayne A. Pflughaupt]

Mike P. wrote:

The manifold depth only needs to be 12 inches as that's the diameter of the subs. That would leave 7 - 8 inches of room from the end of the manifold to the back of the cabinet. That's plenty of room to install a 4 inch elbow on the end of the manifold to run the ports. Would that be an something you would consider? Is this for Ht and music?

Music and HT.

Wow, a 90˚ port? Can’t say I’ve ever seen that done…

That said, I’d certainly consider it, if you guys think it would offer a sonic benefit over a sealed system.

Here’s a graph from the Shiva sealed applications paper, and one from the ported applications paper.

Ported



Sealed
88.54 liters 101.5 liters 178 liters

Pretty strange that doubling the size of a ported enclosure gets virtually no added extension. Despite Adire's marketing pitch, it looks like this driver gets the best performance in a ported enclosure. So ported appears to be worth serious consideration.

How would you determine port size/length/number for this?

Regards,
Wayne

[Wayne A. Pflughaupt]

ModMark wrote:

The gas value issue…

Hi Mark,

The gas pipe is inside the wall behind the cabinet. Just a small hole where the square shaft sticks a few inches to the inside the cabinet. Obviously I don’t want to be ripping out walls to re-route the thing!

One more thought..

Remove the two center doors and replace it with a grill cover. Now the cabinet will have a balance look, two doors on the outside of the cabinet with the grill in the middle.

When I was originally considered building in a sub system there, I was thinking four drivers, in place where each of the doors are. I took REW measurements and response was best at the corner location. From there, response progressively deteriorated at each further-from-corner location.

For appearances, I am having a hard time imaging just one cabinet door being removed and replaced with a speaker grill. It may look unbalance and like a DIY job.

There will be a large overstuffed chair that’s part of our living room suit sitting catty-cornered (angled towards the fireplace, not the window!). It mostly hides all of the doors, and the corner door will be behind it. We’ll go with a brown-colored grill cloth to minimize attention being drawn to it. Probably not the optimal approach, but overall things should look much better than having the boxes on the floor!

The goal here, build a speaker box which can be attached to the brick floor. I share the same concerns, vibration of the shelving unit. Mechanically isolating the woofer box from the cabinet would be ideal.

Well, I waded through a lot of information when I was contemplating an infinite baffle sub, and found that a manifold arrangement, where the drivers are mounted opposed to each other (as opposed to a line array) would greatly reduce vibration, due to mechanical cancellation (that might not be the technically correct terminology). That’s where I got the idea of going with something like that for my application. In addition to significantly reducing cabinet vibration (I have no illusions that it will be entirely eliminated), it also allows me to “vent” the output of two drivers in the same front-panel area as one, and effectively eliminates any potential time delay problems.

Regards,
Wayne

[Mike P.]

I've used 90 degree elbows in one of my builds. Very easy to use and cheap. I paid under $3 a piece for 4 inch schedule 40 PVC elbows at a hardware store. There's a couple of pics in my build thread.

http://www.hometheatershack.com/foru...8-4-build.html

As for the Shiva ported applications, it's your choice. Go with the EBS if you want the most low end extension.

[ModMark]

Wayne A. Pflughaupt wrote:

The gas pipe is inside the wall behind the cabinet. Just a small hole where the square shaft sticks a few inches to the inside the cabinet. Obviously I don’t want to be ripping out walls to re-route the thing!

Wayne,

So what is behind the cabinet wall? Can you make a small open there and turn the gas value 180 degree ie: turn the gas on/off fro the other room?

By the way, that is a beautiful looking cabinet. My wife wouldn't even consider it, off to the attic!

[ModMark]

Good luck with your project.

I having a hard time figuring out how you can assemble a large woofer box inside the cabinet ie: can you build it in the basement and slip it in.

I am struggling now, I getting a 12" Shivia from Mike P and I know my wife will not approval of a standard 4.6 cu ft black box in our family room.

I would like to build something like this, only in white, with a built in subwoofer.




or this



Of course, now my wife just want to buy an entertainment system which we do NOT have the funds for.

I may just build a 14"x14x48" tall "post" and trim it using Craftsman style molding. A risky design I must say, it will be unique!

I am hoping, if I build the sub woofer first in this style, she will approval of a matching entertainment center :-)Attachment 11379

[Bent]

Wayne, where did the Sketchup images of the drivers come from?
(Or did you draft them?)

Either way, cool!

[Wayne A. Pflughaupt]

ModMark wrote:

Good luck with your project.

I would like to build something like this, only in white, with a built in subwoofer.

I hear ya, Mark. Personally, my woodworking skills are pretty minimal. I can throw a box together, no problem, but making it look nice, with veneers and such - beyond my talents. I'm really lucky to have this nice looking built-cabinet in what's also the best subwoofer location in the room.

I having a hard time figuring out how you can assemble a large woofer box inside the cabinet ie: can you build it in the basement and slip it in.

I have it all figured out; I'll post pictures as the project progresses.

Bent wrote:

Wayne, where did the Sketchup images of the drivers come from?
(Or did you draft them?)

Ha, I wish I could say I drafted it! It came from an IB FAQ article our moderator thxgoon is drafting for us (hopefully to be posted soon). I “borrowed” it from him.

Regards,
Wayne

[Wayne A. Pflughaupt]

Mike P. wrote:

I've used 90 degree elbows in one of my builds. Very easy to use and cheap. I paid under $3 a piece for 4 inch schedule 40 PVC elbows at a hardware store. There's a couple of pics in my build thread.

http://www.hometheatershack.com/foru...8-4-build.html

As for the Shiva ported applications, it's your choice. Go with the EBS if you want the most low end extension.

Wow, nice sub there, Mike! I’m one of the lucky guys with a easy-going wife, too. She loves the surround sound thing as much as I do. In fact, it was my idea to do the built-in and get the boxes of the floor – she was fine with them!

I really have no idea how to figure out what would be needed for the ports, and I doubt anyone else can either, since TS parameters for the Shivas are hard to come by since Adire folded up shop. So I guess sealed is what it’s going to be.

The project is on hold for now. The cabinet is full of what-nots and knick-knacks that my wife stored away to make way for Christmas decorating, so I have to wait until she gets all that stuff out. In the mean time, I’ll get the speaker wiring run through the attic from the equipment rack.

Regards,
Wayne

[Mike P.]

When you do decide to build, I have all the parameters for the Shiva. Going ported is not a problem should you decide that's what you want to do.

[Aaron Gilbert]

Wayne A. Pflughaupt wrote:

Wow, nice sub there, Mike! I’m one of the lucky guys with a easy-going wife, too. She loves the surround sound thing as much as I do. In fact, it was my idea to do the built-in and get the boxes of the floor – she was fine with them!

I really have no idea how to figure out what would be needed for the ports, and I doubt anyone else can either, since TS parameters for the Shivas are hard to come by since Adire folded up shop. So I guess sealed is what it’s going to be.

The project is on hold for now. The cabinet is full of what-nots and knick-knacks that my wife stored away to make way for Christmas decorating, so I have to wait until she gets all that stuff out. In the mean time, I’ll get the speaker wiring run through the attic from the equipment rack.

Wayne,

First off, cool project! You've received a lot of good suggestions so far, and I don't have a whole lot to add. I'm in the same situation as you and Mike regarding my wife, which I can't complain about! I've got six rather large speakers in our living room, plus the giant subwoofer, and not only does she have no problems with them, she compliments me on how good they all look and sound (though she admits she doesn't hear quite all the details which I do). She's almost too easy-going sometimes - wants me to make all the decisions, if she could get away with that. Anyhow....

Regarding the Shiva specifications, are these Shiva Mark I, ie the first Shivas? If so, I can probably help you out. I just happen to have a Shiva Mark I on hand, as well as a woofer tester, and it would be no problem to take measurements. Of course, it'd be better to use your own woofers, but that should get you close enough. Sealed should still work well, though. As I recall, the original Shiva modeled with a bit lower F3 than later versions.

You know, if you work together to clear out knick-knacks, it goes twice as fast. My wife and I just reorganized and cleaned out our spare bedroom, only took a few hours including moving about 300 books.

Edit: Shoot, Mike beat me to it with the Shiva parameters. Oh well.

[Sonnie]

Hmmm... a couple of these pics in this thread look familiar.

Wayne... I remember us discussing this when I was there. Seems I remember you were considering using that room on the other side and doing an IB, but I agree that could end up being costly, especially since you got the Shiva's already.

This should be cool indeed... and I am looking forward to those pics...

[Wayne A. Pflughaupt]

Thanks for the Shiva specs, guys. Aaron, I'm pretty sure mine are the original Shivas, not the Mark I's. I'm pretty sure they date back to '97 or '98.

I might try it both sealed and ported. It would be easy enough to change out the back panel of the manifold.

Anyone know how to do the modeling for sealed vs. ported with this cabinet size?

Regards,
Wayne

[Aaron Gilbert]

Wayne A. Pflughaupt wrote:

Thanks for the Shiva specs, guys. Aaron, I'm pretty sure mine are the original Shivas, not the Mark I's. I'm pretty sure they date back to '97 or '98.
...

Wait, I thought the Mark I were the original Shivas? The Shiva I have is from the very first batch, like driver #10, from 1997, so I guess that makes it an 'original' Shiva.

[ModMark]

Wayne,

Concerning my woodworking skills, chalk is a wonderful thing :-)

For your considerations, if the cabinet starts to rattle once you fire up the woofer, check out the thread concerning fiberglass and resin. You could glass in all the inside seams to secure the cabinet piece while preserving the looks of the cabinet.

[fredk]

You could glass in all the inside seams to secure the cabinet piece while preserving the looks of the cabinet

That will be a challenge without inhaling serious amounts of toxic fumes.

[Mike P.]

Aaron is correct. The original Shiva was the Mark I, then came the Mark II and III.

[Wayne A. Pflughaupt]

Sonnie wrote:

Hmmm... a couple of these pics in this thread look familiar.

LOL, we sure enjoyed it when you guys were here!

Okay, here's my plan of attack. For the two doors on the right side, I'll cut a solid panel, probably out of decent quality 3/4" plywood, that's larger than the opening. As you can see, with both doors open, its one large opening in the cabinet with no separation piece centered between them. Naturally, that horizontal shelf is going to have to come out first. (Sorry for the mess, my wife pulled out all the knick knacks, but can't put them out because of this and other HT related work I'd also doing in the room, re-routing our front speaker wiring and video cabling.)

I’ll remove both doors and all hinges, and the panel will fit up to the backside of the opening, fully covering it. I’ll secure it by drilling and screwing through the front of the cabinet, right between the screw holes for the hinges. This way, when the doors go back on, the hinges will fully cover the screw heads. Nice, huh?

So, only 4 screws total to secure the cover panel. Might not seem like much, but the way I see it, any internal air pressure will be pushing it tighter against the cabinet, right?

To give the panel bit of central reinforcement, I’ll replace the current #8-32 screws holding on the door pull-knobs with longer ones that will go all the way through both the cover panel and door. The knobs will screw back on, and when I tighten it doen, it'll pull in the center section of the panel to the cabinet. So, the doors will no longer open. Actually, I’ll be doing this with only one of the doors; the other will have to be able to open to access the extension for the gas valve.

For the left side of the cabinet, it’ll be the same way, except that the left side of that cover panel (i.e., closest to the corner) will have a large square hole cut that’s the same size as the opening for the manifold. The manifold will go in first, temporarily pushed to the back of the cabinet. The panel will then be installed and secured to the cabinet; then the manifold will be pulled into position and secured. I’ll probably shoot a few screws through the bottom of the manifold into the cabinet floor (those holes could easily be sealed with wood putty in the event that I ever remove it), then more screws through the face of the cover panel into the front of the manifold. I’ll be ready to rock then, except for the grille frame.

Here's a shot that shows the gas valve, which is the only thing still up in the air. In the event that I can’t find a suitable extension of some kind over the counter somewhere, my son’s father-in-law is a metal fabricator by trade; he can make me anything I might need.

Regards,
Wayne

[Wayne A. Pflughaupt]

Aaron Gilbert wrote:

Wait, I thought the Mark I were the original Shivas? The Shiva I have is from the very first batch, like driver #10, from 1997, so I guess that makes it an 'original' Shiva.

Mike P. wrote:

Aaron is correct. The original Shiva was the Mark I, then came the Mark II and III.

I misread Aaron's post - sorry! Mine are probably the Mark I version, unless Mark II was out in '97 or '98...

Regards,
Wayne