Sundown SA-12 enclosure

[Golitan11]

I have designed an enclosure (using Torres and WinISD) for my Sundown SA-12 (not built yet), which is 2 cubic feet tuned @ 35 hz:

http://imageshack.us/a/img34/3185/2cubes35hz375sqin23dd.png

P.S. I know the 6.25" measurement is bad it's a mistake in the picture I found (which is almost the same as the one I designed).

But then, I found another box design (I don't know what type of box is that) which seems pretty nice:

http://supersteve.me/2013/01/30/codys-sundown-sa-12-enclosure-engineered-by-pwk/

So I have a few questions:

1. Is my box perfect for my system or I should consider another design (just like this one)?

2. Should I put 45 degrees corners (for bracing and sound)? If yes which width?

3. Will DAP ALEX PLUS Acrylic Latex Cault Plus Silicone be ok for sealing this enclosure (I will be running it summer like winter)?

4. Where should I put bracing and what kind (I know nothing about bracing)?

5. Where can I learn box design (like transmission line or bandpass) other than simple ported ones (like bass reflex)?

P.S. I am running this subwoofer with an Hifonics BRX1100.1D amplifier @ 1 ohm and I don't want to buy a design from anybody! I want to learn first!

Thanks.

[bbeljefe]

I'm not bagging on the other box, because the build quality seemed outstanding, but I prefer a larger port like what you've got. Not that his is too small but when you have a driver with a lot of xmax like the SAs and you go with a small port, you risk port noise, which will kill the SQ of any loudspeaker system.

As for what you've drawn, it looks good but I would definitely laminate the baffle with two sheets of material. That's the most important place to strengthen on the cabinet and it will dampen a lot of unwanted resonance. In addition to that, I'd install corners on the wall opposite the port wall and one in the port turn. I use 2" wide corner braces but in the port you"ll need to measure the width of the port corner and make sure the 45 doesn't cause the corner to be narrower than the rest of the port. Other than that, with only a thousand watts there isn't a lot of need for internal bracing in that size box. You could run a brace from the baffle to the back wall but to get any real strength from it, you'd need to move the driver to the left toward the port so you could get the brace as close to center as possible. And that's another thing I would do... move the driver closer to the port, as I've had better luck when the back wave of the driver doesn't fire directly at the port entry.

As for designing other cabinets, you have some pretty good tools already. I've used WinISD beta for years and I also use WinISD... not sure which you're using. Win ISD beta is good for bandpass boxes but you have to do a lot of tweaking and you cannot rely on its calculations for sixth orders... unless you have a 53' semi trailer sized space to put one if it's 6th order recommendations, lol.

The thing to keep in mind with sixth orders, as has been my experience, is to make the passband as wide as possible, unless you're building a burp box. You can get +10-18db low freq peaks from a 6th order but you'll always have an annoying peak at the upper passband. I always try to keep that peak as high as possible so I can cut it with the crossover. Some people will say 1:2 or 1:3 ratio and/or keep the tuning at 1 or 2 octaves apart. Sundown recommends a 1:3 ratio and one octave separation but I haven't found this to always be the best case. I've had better luck with multiples of X.5 octaves, I think because that tuning helps reduce odd order harmonics.

As for transmission lines, there is a thread by Forevrbumpn on this site that was enormously helpful to me. Personally, the quarter wave t-line he talks about is far more simple to design from a mathematical standpoint than a standard bass reflex box. The trade off though is that they're not too easy to design from a size standpoint.

For instance, I built a t-line for a ten with an Fs of 30 hz. The line is a little over nine feet long and about 5" X 14" (70 sq"). Basically, it's a nine foot long port attached to a speaker at one end. The simple part is that you only have to know a driver's Fs and usable piston diameter to calculate the length of the line and the surface area of the line. Squishing that into a car is the hard part. A t-line for that SA 12 would only have to be about 8.5 feet long but, the line itself would need to be ~85 sq".

[Golitan11]

Yeah that's why I told that it was almost the same. I already took the two sheets in consideration. Here is a picture of the actual design (mine) without the top panel:

1. Just to be sure, where did you say to place corners (just tell me the color, sorry I forgot one)?

2. Do you think a T-Line would be a better choice? Why?

3. And for the caulk/sealant?

4. For the subwoofer position, any specific ratio or position?

5. Any other recommandation?

Thanks for your nice help.

[bbeljefe]

1: Green, yellow and red.

2: Louder, yes. Wider bandwidth, yes. Better... Don't know how much space you can afford to lose. My guess is that it would be ~4-4.5 cubes.

3: The painter's caulk you mentioned is fine. I use that or polyseamseal but never pure silicone. It isn't an adhesive and doesn't stick well to MDF or plywood. It also stinks and is messy.

4: In your last picture, to the left. No ratio to follow that I'm aware of, just as far as possible from the port entry.

5: Get to cutting. ;-)

[Golitan11]

I am a bit confused now. A guy on another forum told me the green, the yellow and the missing arrow (for placing corner). May I have other opinions on that and if it is really worth it? Thanks.

[bbeljefe]

There's a thread on this site that discusses small changes that make a difference in SPL and the guy who started it did some testing with corners. When all the corners have 45s, he lost sound pressure.

The function of the corners from a sound pressure standpoint is to guide the sound waves to the port and out of it as smoothly as possible. When you have them in corners that don't do that, they create unwanted turbulence that slows the movement of the air.

But keep in mind, we're talking about tenths of a decibel so it's really not going to make an audible difference for daily listening systems.