New 2x12 cab. home built

[Phendyr_Loon]

Hey folks. I'm new to the TB forums, though I've been lurking on this useful site for quite a while.
So to the main point of this thread, I'm sharing photos of my latest cabinet build. It's a vented two chambered compact 2x12, tuned to 30hz. 17" wide x 34 7/8" tall x 15 1/2" deep. It's my 6th cabinet build, the first build which I used a cab design calculation program.
The case is made of 3/4" MDF, this was cut from a full sheet know in the woodworking trade as a "top sheet". Basically it was on the top of a pile of MDF so it had quite a bit of marks and gouges in it, so to save on finished cab weight (and to make use of a free 4' x 8' sheet of MDF) I sanded it down to a thickness of 11/16".
I've built cabs both larger and smaller. My criteria for this cabinet was to be narrow enough to be able to carry through a doorway (without bashing my knuckles), tall enough to be able to hear when standing from a short distance away (without the need of an amp stand), and compact enough to not be a back-breaker and to be able to fit it my Jetta (trunk or backseat). And had to have a low tuning frequency to accomidate a low B string.
The first photo is during installation of the 3/4" x 3/4" poplar interior bracing, chamfered on the inside edge with a 45 degree router bit so as to limit square interior edges.
The second photo is with the top driver installed. I'm using Eminence S2010's for power handling and to save weight. The head I'm planning to use is my Eden WT300.
More photos to come, tell me what you think!

[billfitzmaurice]

Honestly?
MDF is too heavy, and lacks strength. Well braced 1/2" plywood is much lighter, weighing like half as much, yet is stronger. For a good example of how to build strong but light weight cabs look at the fEarful threads. Your full sized shelf brace contains enough material for a half dozen smaller braces that, if spread about the cab, would be at least four times as effective.
The ports are half the diameter required, and 30Hz tuning is at least 10Hz too low, even for drop tuning.
I assume your drivers are S2012s, as S2010s are tens. S2012s prefer a much larger box, at least 4 cubic feet net each, rather than the roughly 2 cubic feet net each you have. With a box that small you'll get a better result across the full spectrum all the way down to 20Hz with 40Hz tuning.

[Phendyr_Loon]

Thanks for the input. The port size (diameter and depth) was determined by the speaker enclosure calculator which I used. And yes I am using the S2012's I mistakenly typed S2010. The S2012's specs called for a porter cabinet cubic foot range of 1.5 to 3 feet. As far as the build material, I'd have to agree that MDF is quite heavy though the MDF was free and good quality 1/2" such as BB is hard to come by at my job and I honestly was not aware of anyone using something that thin for cabs.

[billfitzmaurice]

Originally Posted by Phendyr_Loon

Thanks for the input. The port size (diameter and depth) was determined by the speaker enclosure calculator which I used. And yes I am using the S2012's I mistakenly typed S2010. The S2012's specs called for a porter cabinet cubic foot range of 1.5 to 3 feet. As far as the build material, I'd have to agree that MDF is quite heavy though the MDF was free and good quality 1/2" such as BB is hard to come by at my job and I honestly was not aware of anyone using something that thin for cabs.

Try a different program. WinISD Alpha Pro is the standard for freeware. It would have told you the optimum net size box for the 2012 is 6.5 cu ft with 39 Hz tuning, though you can usually get away with as much as a 50% volume reduction without seriously compromising the result. It also tells you the velocity of the vent output at any input power, so that you may size the vent large enough to prevent chuffing.

[will33]

Bill's right about the tuning. It could even go as high as 45-50 depending on how you want it to sound. Basslites can perform ok in a box your size even if it's not optimal. 2.5cu.ft. per driver works well too. When you try raising the tuning, double your port area. If that's stuffing in the lower chamber in your pic, pull that stuff out of there and line it with mattress top foam, the eggcrate looking stuff. You can get it cheap at any place that sells pillows, blankets, fabric etc.

[Tusec]

Just curious -- what will be the difference in mattress foam versus the stuffing the OP used?

[will33]

Stuffing like that is good to use in sealed cabinets. The foam lining takes care of mid cancellations just fine in ported cabs and leaves space for the ports/speaker combination to work together. I'm sure there are more technical descriptions of why and why not, I'll leave that to the degreed engineers. I can tell you having the end of the port running into a bunch of stuffing is going to restrict airflow working against what a port is supposed to do.

[billfitzmaurice]

Originally Posted by Tusec

Just curious -- what will be the difference in mattress foam versus the stuffing the OP used?

Stuffing has it's benefits in sealed cabs, especially in those that are too small, which is most of them.
Vented cabs should be lined with an inch to inch and a half of foam, polyester batting or felt carpet padding. More than that does more harm than good.

[Stick_Player]

Vented cabs should be lined with an inch to inch and a half of foam, polyester batting or felt carpet padding.

Do you mean that ALL surfaces (6) inside should be lined, including the baffle board (around the speakers) and inside back?

[will33]

The baffle doesn't have to be but line the other five sides. I cutout around where there's a jack, brace, maybe handle or whatever but make sure the vast majority of the 5 sides are lined. Staples or glue, doesn't much matter, staple gun's easy unless it's a tiny space.

[praisegig]

Originally Posted by Stick_Player

Do you mean that ALL surfaces (6) inside should be lined, including the baffle board (around the speakers) and inside back?

This is the back view of my fEarful 12/6, before the back was installed. The back also had the 1" foam installed, bought at Walmart.

[Stick_Player]

Lon, will33, billfitzmaurice, thanks for the foam lining information!

[pin_head_47]

Something I've always wondered about lining - when you add it, do you have to figure the amount of volume that it takes up when you determine the overall internal volume, the same way that you have to subtract the amount that the internal bracing takes up?

[billfitzmaurice]

Originally Posted by pin_head_47

Something I've always wondered about lining - when you add it, do you have to figure the amount of volume that it takes up when you determine the overall internal volume, the same way that you have to subtract the amount that the internal bracing takes up?

No.

[pin_head_47]

Alright, good to know. Is there any reason to this, perhaps because the lining is so porous, or am I just thinking about it too much?

[billfitzmaurice]

Originally Posted by pin_head_47

perhaps because the lining is so porous

That.

[Phendyr_Loon]

Just a quick question to clarify on box tuning frequency. Through my research I came to the understanding that in building a box to specific dimensions and setting port length and diameter you are determining the actually box tuning frequency correct? So in setting the box tuning frequency of say 35hz you are in effect saying 35hz is the lowest frequency the speakers in that enclosure will produce, right?

[will33]

Not really, you're tuning the box to work together with the speaker. Look at the excursion graph on your box program. The speakers starts moving farther and farther the lower you go in frequency until you approach the tuning frequency of the box, then the speaker calms down and the ports are putting out most of the sound at that particular frequency. As you move below the tuning frequency of the box, excursion goes way up quickly. That's what they mean when the say the speaker is unloading when playing stuff that's below the tuning of the box. Tuning the box lower or higher also affects the response in the bottom end. Lower tuning, more shallow rolloff that starts a little higher in frequency, higher tuning makes the response hump up towards the lower end.

[will33]

Originally Posted by Phendyr_Loon

So in setting the box tuning frequency of say 35hz you are in effect saying 35hz is the lowest frequency the speakers in that enclosure will produce, right?

The speaker has to be designed to play at 35hz if it's going to at all regardless of the box. If it's designed to play that frequency it will if it's in a big enough box. 35hz is pretty much useless for bass guitar, even a 5string. Most of what you're hearing is a the 1st harmonic, 62hz or so. Around 80 for a 4 string. 30-40hz stuff is what's coming from the big subs in a PA system. Some bass cabs can produce down there but not many, at least not at a volume comparative to the rest of the sound. From experience, a bass cab that's -3db somewhere in the lower to mid 50's will make a deep, full sounding cab. No need for 30-40hz stuff at volume, that's usually -10-20db or lower.

[billfitzmaurice]

Originally Posted by Phendyr_Loon

So in setting the box tuning frequency of say 35hz you are in effect saying 35hz is the lowest frequency the speakers in that enclosure will produce, right?

Not at all. The Fb is just one of a dozen odd variables that all contribute to the end result.