Help with box design

[jimmyswan]

I have read tons of posts on this site and AVS about putting together a box for a sub. I'm more confused then ever about how to do this, I dont understand the formulas to use for the design at all. Anyhow someone gave me an Alpine 12" sub SWE-1241, I want to try it for an HT setup. I ordered one of the Dayton 240w plate amps and I have no idea where to start on the box. I would like to do a ported box, would my best bet be to use the Alpine's specs on volume? Sorry for all the new dumb questions but all my experience in this was back in high school years ago when the cool thing was how big of a box you could fit in your car

 

[tomd51]

Hi jimmyswan and welcome to AH!

First off, you'll want to see if you can gather the T/S parameters for the Alpine SWE-1241, I was able to find them here. If the SWE-1241 comes in both single and dual voice coil (SVC/DVC) options, you'll need to determine which one you have.

After you've gathered the parameters and can determine which VC build you have for this driver, you can download WinISD (the non-Pro version is a bit easier to use), create this driver in the database by filling all the T/S parameter info in (you may not have all the params available in WinISD, that's typically fine), then once you've created the driver, you can begin to walk through WinISD, select whether you'd like sealed or vented/ported, then design the size of the enclosure and the amount of ports required as well as length and diameter if you're doing a ported build. You'll want to make sure you don't exceed certain limitations like the 'Vent mach' (usually red text shows an error or problem) or the port(s) length for your enclosure.

WinISD is fairly straightforward, but it does have some built-in help and the WinISD website will have additional info on it's use. I found the more you mess w/it, you'll have questions you should be able to hunt down relatively easily.

Any other questions, let 'er rip... -TD

 

[tomd51]

BTW, the specs look pretty decent for a ported build for this driver.

And all of your questions feel like dumb ones if you're not sure about what you're asking, so do feel bad. I was in the same boat about a year ago... -TD

 

[jimmyswan]

Thank you very much for your help Tom, Ive looked at that program a little before. I will download and explore further this evening. I was hoping this woofer would be fine to try my first DIY.

 

[tomd51]

Not a bad driver at all for something that was given to you as a gift... -TD

 

[sparky77]

Modeled with bassbox pro, it suggests a sealed box of 1.765 cu. ft. if that helps you any.

 

[jimmyswan]

Am i gonna get low with a sealed box or am i better with a ported? If i understand winisd correctly I can go either way. I cant figure out what to enter when it asks for parameter BL, and Pe with a w on the other side? Also looking at the graph do I want a nice sloped curve or a really fast peak right now at 26hz it reads o db then peaks at 41 hz with 3.35 db then tapers to 97 hz at 1 db. Is this good? Sorry for these questions but i might as well be trying to understand Russian here.

 

[annunaki]

That curve is definitely not what you want.

You want it nice, flat, and smooth from say 100hz on down to the tuning frequency, if ported, or to the Fs if sealed. For ported enclosure it will drop off real sharp and sealed it will roll off slowly.

 

[jimmyswan]

I think I understand but I still dont need help with this.I cant figure out what to enter when it asks for parameter BL, and Pe with a w on the other side? Right now what i have entered says I will have to make this thing way too big for my liking.

 

[tomd51]

I'm not going to have time this evening to run this driver through WinISD, but I'll see what I can do tomorrow for you and offer some build suggestions.

The 'BL' parameter isn't always provided by driver manufacturers, so you should be able to enter all the parameters available and work from there. The 'Pe' is similar to the RMS wattage the driver is capable of handling, in your case this would be 200w, but somewhere between the RMS and peak is a typically a good average for a decent driver.

To get a clearer idea as to what most of the T/S parameters mean, take a look at the 'T/S (THIELE/SMALL) PARAMETERS' section on The Subwoofer DIY Page at DIYSubwoofers.org. The ones that aren't covered there, feel free do to some creative Googling... -TD

 

[sparky77]

both are model graphs from bassbox pro 6, first is a sealed ensclosure of 1.764 if I remember correctly and the second is a vented enclosure with a single 4 inch double flared port 6.829 in lenght with a volume of 9.339 cu. ft. sounds way too big even for my tastes. Even though the graph looks good, I would still probably go with the sealed box and go for corner loading and a notch filter. No mater what you do will depend on the room modes and other acoustic variables. Hopefully someone can post graphs from winisd, their graphs have seemed to be more reliable to me but I don't have a copy yet, and then we can compare software.

 

[TLS Guy]

Closed and vented

That driver has a Qts of 0.66 which makes it more suitable for closed box alignment. If you use a vented enclosure it will be large. Here are your alignments.

First closed box.

Name: SWE-1241
Type: Standard one-way driver
Company: Alpine
Comment: Type-E series
No. of Drivers = 1
Fs = 31 Hz
Qms = 9.68
Vas = 61 liters
Cms = 0.178 mm/N
Mms = 147.9 g
Rms = 2.975 kg/s
Xmax = 11.7 mm
Xmech = 20 mm
P-Dia = 250 mm
Sd = 490.9 sq.cm
P-Vd = 0.574 liters
Qes = 0.7
Re = 3.6 ohms
Le = 0.86 mH
Z = 4 ohms
BL = 12.17 Tm
Pe = 200 watts
Qts = 0.66
no = 0.25 %
1-W SPL = 89 dB
2.83-V SPL = 89.6 dB
-----------------------------------------
Box Properties
Name:
Type: Closed Box
Shape: Prism, square (optimum)
Vb = 2.495 cu.ft
Qtc = 0.707
QL = 16.96
F3 = 41.05 Hz
Fill = heavy

Now vented.

Company: Alpine
Comment: Type-E series
No. of Drivers = 1
Fs = 31 Hz
Qms = 9.68
Vas = 61 liters
Cms = 0.178 mm/N
Mms = 147.9 g
Rms = 2.975 kg/s
Xmax = 11.7 mm
Xmech = 20 mm
P-Dia = 250 mm
Sd = 490.9 sq.cm
P-Vd = 0.574 liters
Qes = 0.7
Re = 3.6 ohms
Le = 0.86 mH
Z = 4 ohms
BL = 12.17 Tm
Pe = 200 watts
Qts = 0.66
no = 0.25 %
1-W SPL = 89 dB
2.83-V SPL = 89.6 dB
-----------------------------------------
Box Properties
Name:
Type: Vented Box
Shape: Prism, square (optimum)
Vb = 5.938 cu.ft
Fb = 23.04 Hz
QL = 5.927
F3 = 19.83 Hz
Fill = minimal
No. of Vents = 2
Vent shape = round
Vent ends = two flared
Dv = 4 in
Lv = 18.59 in

Vent velocity with those two vents is 15 m/sec. Xmax is not exceeded in the closed box, but obviously is below cut off in the vented. It takes a 6 cu. ft enclosure though. The vented box gives 112 db to just above F3. If you have the room and want a vented box for that driver, I guess it will work.

 

[sparky77]

Sorry. TLS Guy kinda reminded me of the graph I should've included for the ported box for vent velocity.....

although the vented graph is quite impressive, it sounds like a sonotube project to me......

 

[jimmyswan]

Thanks for all the input, I guess I was using winisd right then. I definitely dont have room for a vented enclosure that size so I guess I will go sealed. This stuff is very interesting, I never realized how much had to go into the design to acheive the best sound. 1 more question then though, everyone talks about bracing, could someone explain that? Does that mean running some pieces across the box are just reinforcong the corners? Thanks again to everyone for all their help.

 

[annunaki]

Bracing the walls of the enclosure help to prevent any resonance. The bracing does not have to be extravagant but the more there is the better, to a degree.

Here is an example of more extreme bracing I did for a JL Audio 12W7 in a sealed enclosure:

http://img.photobucket.com/albums/v157/annunaki_6/000_0310.jpg
http://img.photobucket.com/albums/v157/annunaki_6/000_0313.jpg

http://img.photobucket.com/albums/v157/annunaki_6/000_0316.jpg

 

[jimmyswan]

That looks nice, I better polish up on my carpentry skills. Next question is how do you figure bracing into your total required volume equation. Do you just add say 10%?

 

[annunaki]

I already have the measurments from cutting out the pieces so I figure each piece's individual volume. Then I gauge how much of it has been cut away or measure the pieces cut out of the bracing. In the bracing I did above, There is roughly 40% of each piece left over.

Say all of your bracing pieces total .24 cu.ft. before you cut the 'windows" in them. Multiply the .24 cu. ft. by .40 and that will give you a fairly accurate number. In this example it would be .096 cu.ft. for bracing displacement.

It looks like it displaces a lot, but in reality with all of the "windows" cut in it is not much at all. It sure strengthens the enclosure though. It sounds like rapping on a tree trunk when you give it the "knuckle test".

The biggest downside: It weighs a ton. With the sub it is about 105 lbs. of bulky low end madness. Externally it is about 2.75 cu.ft. or so.

 

[tomd51]

The folks over at Creative Sound have a good example of some solid bracing for their SubDuction drivers.

Here's a link to their cabinet design plans for the 12"... -TD

 

[jimmyswan]

I give up on winisd, even using the parameters listed by TLS Guy I still get like 9 /ft3 even for a sealed enclosure. I obvisouly am missing something and Ive recalculated it a few times now. If 2.5/ft3 for a sealed enclosure sounds right to you guys thats what Im gonna do. Thanks for the pics Annunaki, I think im headed in the right direction now. Dont be surprised if Im back with more ?'s. Thanks again everyone

 

[TLS Guy]

I give up on winisd, even using the parameters listed by TLS Guy I still get like 9 /ft3 even for a sealed enclosure. I obvisouly am missing something and Ive recalculated it a few times now. If 2.5/ft3 for a sealed enclosure sounds right to you guys thats what Im gonna do. Thanks for the pics Annunaki, I think im headed in the right direction now. Dont be surprised if Im back with more ?'s. Thanks again everyone

That will be your best bet. An F3 around 30 Hz is fine especially with second order roll off. That alignment has a Qtc of around 0.7 which is spot on. I think you will be very pleased with the sub. Good luck with the project and let us know how you get on.