Let's build a custom Subwoofer for Carlman's basement theater

[richidoo]

Carl got a nice 15" quad voice coil sub driver from hometheaterdoc, and matching 1000W plate amp. Since I have the table saw and clamps, we're gonna make the box ourselves, to fit his special application. This is a single sub to fit under the upper platform at the rear of the room. There is ~11" space under the platform. This is just for theater use, to get those nuclear blasts and dino footprints just right. Not high end audio, which will have their own custom subs built in a separate thread.

Any help, advice, suggestions are most welcome!!
Thanks
Rich

[richidoo]

I asked Shane Sangster, The Home Theater Doc, for some advice on building the box and received this response. Thanks Shane!!

"I prefer sealed and this driver will work either way.... obviously more output via ported, but it can still shake the walls with it sealed. 

This driver moves a LOT of air.  So you need to build a tough box.  I used double and triple MDF for my sub cabinets.  Front panel was 2.5" thick on my designs, but a lot of that was due to wanting to recess the driver a bit.  box within a box with sand is a bit overboard.  If the walls are thick enough and you use enough braces, that should be fine.  not to say it wouldn't be better to go to the extremes.  I'm just not sure it will help enough to offset the effort involved.

You'll likely want a bit bigger than 3.6 cubic feet... when you do the T/S parameter measurements on the actual drivers, the Vas is much higher than spec.... and Qts is higher as well which allows you to go bigger to get leaner less boomy bottom end.  The plate amp does have a boost circuit for 25Hz which comes in handy. 

You're going to wire it so it's a 5.6 ohm hookup (i.e. all voice coils in series with one another).  That will work best with his plate amp.


--------------------------
Shane Sangster
The Home Theater Doctor "


We should characterize the driver with the Woofer Tester to make sure the Thiele Small specs are correct. But in the end, if we go with a sealed box, they are less critical, as long as the minimum volume of 34 liters is met.

I did some simple simulations with the published driver specs and WinISD speaker software. 60liters is near the point of diminishing returns on bass extension. Carl likes optimizing to the point of diminishing returns, so that will be the target area for volume. Driver specs are not likely to vary too much from the specs, and Volume is the only variable with a sealed box, so hopefully that part will be fairly straightforward. But that's why I'm seeking advice and corrections for my assumptions...  and just to have some fun sharing...

[richidoo]

I'm thinking of making a flattish box under the platform, big enough footprint to give the 60liters we need while staying low enough to fit under there. The driver points out to atmosphere at the rear of the platform, tilted back 45 degrees to fit it in the 11" space under the platform. The sub box will not contact the platform above, unless someone thinks it doesn't matter. I am going on audio dogma here thinking we wanna isolate the vibrating box from the seating platform, but maybe some mechanical linkage would be even scarier.        Mounting the plate amp on the vertical surface of the platform next to the sub hole. Cover the hole with some acoustic fabric.

[richidoo]

Here's the spec sheet for the driver:

TC Sounds 3000 QVC

My webhost is uploading slow today. If it's still slow later, we can host it on AN.
Thanks

[Scott F.]

Hiya Rich,

I agree with your choice in using a sealed enclosure since you've got the boost at 25hz. Not knowing what that amp is, it might not take kindly to the huge impedance bump at the speakers F and tuning point in a vented enclosure. You'll likely get better quality bass with the sealed enclosure. If you've got access to Woofer Tester or some other driver measuring program, you will be surprised at how much the published TS parameters differ from how the driver actually measures. If you do have access to measurement software, be sure to break the driver in with a 20hz signal for a few hours first before you measure it.

[preistube]

If I understand this right, Shane is recommending a little bigger than 100L and you are thinking 60L for a 15" sealed?
Usually it is easier to reduce the volume of a box, if it is too small you end up doing this  .

Lin 

[Black Sand Cable]

Sealed enclosure is a must.

After that.....the sky is the limit. When I built my two sealed Rythmik subs I followed Brian's plan which (thankfully) don't call for anything too crazy and the end result speaks for itself. Everybody to this day who hears them, offers me money for them.

I should mention that I did not go nuts with the box's. Good old 3/4in MDF all the way around with the same being used for all the internal bracing. I get zero box vibration.

I would however not go overly big with the box as bigger doesn't always mean better.

[Carlman]

Thanks to everyone for the help with this, especially Rich.  I've been a bit overwhelmed with work and finishing the basement.  As of today I have full electricity.. including all lights... pix to come on the basement thread...

Seems like sealed is the way to go.  I'm now living nearby to the Hometheaterdoc so hopefully I can swing by and nab the measurement stuff soon.  Carpet comes in a couple of weeks so, I'd like to have the platforms built prior to that... In order to build the platforms, I need the final outside dimensions of the sub.  (Everything in this project requires multiple steps ahead thinking.) 

Thanks again and looking forward to getting the max out of this sub setup.  It's not cheap gear and I don't expect it to be adequate just for boom-boom stuff.  I'll be watching live concerts on DVD as well... so it has to do some music right as well.

-Carl

[preistube]

Carl/Rich,

Would it be possible to build a test box (or two) first?
If you make one large box with an adjustable inside wall you should be able to get an idea how the different sizes will sound.

Lin

[Carlman]

That's not a bad idea, Lin.. but that would make the project a little longer.  To me, it's worth making this sub the best we can on the first try.. and not so much on perfecting it over time.  Basically, I'm way too impatient for your thoughtful suggestion.

[bpape]

Actually, if you know what you have to work with, you can cut a few additional 'ends' that will fit inside the cabinet so you can gradually decrease the cabinet volume.  That's easy enough to do with a test box.  Not sure if you have time though with your schedule and carpet coming in 2 weeks.

Bryan

[richidoo]

Thanks for the great ideas everyone.

60 liters is only a guess, based on simulation with Qtc of .707. With boost at 25Hz I think 34L would be good enough and as tight and controlled as theoretically possible. Of course 100L goes lower with smaller Qtc, but it also requires much more bracing to stop wall flex and flubbies. 60L seemed to be at the sweet spot of added low freq extension for minimum volume. 100L is less than 1dB louder at 30Hz.

The cabinet must be a big square pancake, fitting around the framework for the seating platform above, so there is a limit to the cabinet size. With Two layers of MDF top and bottom, and fitting inside a 11" height space, that leaves 8" box interior height. Which requires 5.3 square feet of floorspace for 100L box, not including internal braces.  We have the space for that, so we could do 100l if necessary.

Either way the volume is a variable to achieve desired system Q, so we have to measure Vas of the driver to know what we really have. We could do a movable wall but coming from engineering background I rather know before hammertime what is correct. To adjust volume I think it would be even easier to put some bricks in there to increase Q if we overshoot the volume.

What about stuffing for internal resonance control? Deflex would be a few hundred bucks, as would blackhole. There are some cheaper versions of blackhole type covering, I gotta lookup the link I got from from JoshK. Or we could go old school, and stuff it with cotton absorbent for reasonable price and we already have that in the plan for treatments so there will be extra lying around. Loudspeaker cookbook only comments on stuffing, usually 1/2 full of stuffing is best in his measurements. Maybe line the interior walls with the 5" thick recycled cotton bat? 

Carl, what is the brand/model of the amp? I am confident that it is more than up to the task. Shane says it is a freaking brute and we will be at 5.6ohm on the driver, coils in series.

Carl when does the MDF show up? I have this Thursday-Friday off.

[Carlman]

MDF will be at my house Thursday... If I have all my work done, I should be able to get it to you then or Friday.  I'll bring the sub and amp as well... It's all boxed up at the moment.
This is the amp: http://www.madisound.com/catalog/product_info.php\?manufacturers_id=137&products_id=372
-C

[hometheaterdoc]

plate amp is a 1000 watt Keiga ICE Power based unit from madisound. 

forget about blackhole or things of that nature.  For the range of frequency this is being used, it really isn't worth the investment.  I'm not saying it won't have an effect, just not enough of an effect to offset the cost involved.  Build a sturdier box.  I like using different thicknesses of MDF and HDF glued together to help with vibration and tuning.  You can get 1, 1.25, 1.5, and 2 inch thick MDF in addition to the standard .75 inch stuff you find everywhere.  The stuff at Home Depot is not really that great.  I get mine at Raleigh Hardwoods over on the east side of town.  They stock a couple thicknesses.  This stuff is heavy, Rich... so make sure Carl is helping you.  A circular saw to trim pieces down before final cuts on the table saw is your friend

I've built at least 150+ boxes over the years.  The best ones used good bracing and different thickness materials moreso than what was stuffed in them.  Depending on the cavity sizes, some acousta-stuff or insulation does tone things down a bit as far as cavity echo...... you don't have to spend a fortune.  An overbuilt box is cheaper to do because the relative cost of MDF is a lot lower than the alternatives that are for sale out there to fix resonances, etc..  Full range speaker boxes are a completely different ballgame than a subwoofer.  For subs, a good design, a good driver, and adequate clean power (I hate ice amps for full range, but do like what they do for subwoofer duty.  The BASH based units are also pretty good for the money) put in a well built box and it's not rocket science to get good sound.  The thing that usually limits commercial subwoofers is that the costs of packaging and shipping don't permit them to build an adequate box for their stuff and keep the price affordable.  I even had to keep my box sizes down to do more than meet WAF factors (which were the major contributing factor to why I kept the box size to ~3.25 cubic feet with this driver in the 15 others I've built and installed here in the area).... a 40 pound plate amp, 50 pound driver, and 150 pound box made it a bit difficult to carry by myself to an install   I finished installing plate amp and driver in the box onsite more times than I can count   I couldn't go much bigger or I couldn't carry the darn thing by myself. 

I personally like bass from a sealed box that has a Q ~0.50-0.55.  It's a bit lean for a lot of folks... but the speed, attack, and quick decay are appealing to me.  I'm not sure you want that for full time home theater, but you'll notice it on concert DVDs.  I'd stick closer to .7 for more universal appeal...

I found the software CD for the woofer tester 2 unit I have.  I'm pretty sure I know what group of boxes the actual measurement unit is hiding in.  I'll try to dig it out tonight or tomorrow.  I still have a sea of boxes to get through.  This past weekend was a bit of a write off as we're still trying to find all the new furniture we're sticking in the place to fill it up..... had a bit of a blow-up over changing plans as to which rooms will house audio gear....  the acoustics are so terrible in most rooms, I'm claiming different rooms just because they will be a bit easier to try and tame things down a bit... which did *not* go over well.... tell me again why I need to live with someone else????  I have a feeling I'll be visiting Carl a lot when I want to hear what a real room should sound like

[mgalusha]

I found the software CD for the woofer tester 2 unit I have.  I'm pretty sure I know what group of boxes the actual measurement unit is hiding in.  I'll try to dig it out tonight or tomorrow. 

Slightly off topic... You might want to contact Smith & Larson who are the folks who make the Woofer Tester 2. They have new software which is a free upgrade and it's much improved over the original versions. They ask that you contact them to get a login to download the software but it's worth the effort.

Their site is www.woofertester.com