How do you decide on your enclosure sizes?

[evilskillit]

I'm trying to model a pair of these for a box for my car's trunk.

http://www.tb-speaker.com/detail/1208_03/w8-670q.htm

If I want the thing to go as far back as possible in my trunk the max width is 18" and height is 14.5. Depth can be anything.

I'm fiddling with WinISD and Unibox and basically I need a box between 1.75 and 2 cu ft. Obviously the box size affects the port size and length and vice versa, especially if you're doing a slot port.

In trying to figure out how to make this thing fit I basically multiply my height by my width then divide the total number of cubic inches I need by that number to get my depth in inches. But then if I work a slot port in there it needs to get deeper, which makes the port wider, which then makes it longer, which makes the box need to be deeper.

Is there a program out there I can use to do this work for me or do any of you have any nifty tricks I could use?

At this point I'm about ready to just build a 2 cu ft box and put the darn port on the outside using PVC tube.

Oh, btw if any of you would like to play along I'm shooting for about a 25hz tune in that ~2 cu ft box for a decently rolling off response that should give me a flat-ish frequency curve inside the car.

I also looked into PRs but the cost is too high considering the cost of the woofers plus lumber and everything else that is going into this is going to be under $40. I don't want to pay like $60 plus shipping for a PR to slap into a box with a total worth of $30.

[Wolf]

You have cabin-gain also to consider. Use Jeff's WBCD spreadsheet along with the Diff&Boundary simulator to get the best results.

I usually shoot for an F3 between 40-60 Hz, and a sealed box with a slightly overdamped Qtc of 0.6.

Later,
Wolf

[evilskillit]

You have cabin-gain also to consider. Use Jeff's WBCD spreadsheet along with the Diff&Boundary simulator to get the best results.

I usually shoot for an F3 between 40-60 Hz, and a sealed box with a slightly overdamped Qtc of 0.6.

Later,
Wolf

Thats what I have right now, figured with cabin gain it would sound pretty flat but in my opinion it doesnt. I'm not terribly impressed with it, thats why I'm wanting to try a ported design, which seems to make those woofers happy anyways.

[mzisserson]

Thats what I have right now, figured with cabin gain it would sound pretty flat but in my opinion it doesnt. I'm not terribly impressed with it, thats why I'm wanting to try a ported design, which seems to make those woofers happy anyways.

Since porting drops the F3 quite a bit you can use a higher Q to achieve a smaller box and a slight "car-box-punch" around 50-60Hz. I would run a 30Hz 12dB/octave HP filter with them The F-mod in-line ones for $20 work pretty good.

[evilskillit]

Since porting drops the F3 quite a bit you can use a higher Q to achieve a smaller box and a slight "car-box-punch" around 50-60Hz. I would run a 30Hz 12dB/octave HP filter with them The F-mod in-line ones for $20 work pretty good.

I'm afraid I don't quite follow you. You mean just as a "rumble filter" to keep the sub from flying apart below its tuning?

Also, to the original question, does anyone know of a program that makes fiddling with box volume a simple sort of point and click drag and drop process rather than just having to try running the numbers until you finally find a size that works for your desired volume?

[mzisserson]

I'm afraid I don't quite follow you. You mean just as a "rumble filter" to keep the sub from flying apart below its tuning?

Also, to the original question, does anyone know of a program that makes fiddling with box volume a simple sort of point and click drag and drop process rather than just having to try running the numbers until you finally find a size that works for your desired volume?

Yes, a rumble filter. It is a necessity when using reflex enclosured in an auto environment.

Bass Box pro is very good as it allows you to add the 12dB rise in a car and fiddle with the reponce. But you have to pay for it

[evilskillit]

Yes, a rumble filter. It is a necessity when using reflex enclosured in an auto environment.

Bass Box pro is very good as it allows you to add the 12dB rise in a car and fiddle with the reponce. But you have to pay for it

As opposed to using a reflex enclosure in a different environment?

Ah, thats too bad as spare cash is something I just don't have a lot of laying around. Maybe some nice bored person with Bass Box Pro could model it for me, or not. Either way I'll be ok.

[bmaupin]

For car stereo it is recommended to work with cabin gain than to ignore its effect. Like Wolf said, a sealed 12dB rolloff from a 40Hz f3 is about perfect. Otherwise, shoot for an EBS ported alignment that provide a shallow initial rolloff. With your 2cuft box, a 3" x 10" long port gives the following. I tried modeling the W8 in a smaller box with low tune to provide the EBS alignment, but the port ends up too long. In the 2cuft box, a 15" port provides EBS with a corner around 21Hz - the corner in the plot is about 27Hz.

[DS-21]

I haven't done a vented box in quite a while - sealed subs are smaller, which allows more placement flexibility, which in turn generally results in higher performance than a sub with less placement flexibility - but my "box design" methodology has changed over the years.

I used to design a box to a Qtc of ~.6 and then use stuffing to further lower the Q.

These days, research into bass performance in real rooms has led me to conclude that a more useful approach is to simply take the xmax of the box and the rated power of the amp you plan to use to drive it, and design the box so that the airspring rolls off the driver at or slightly below the driver's excursion limits. Either that, or just build boxes for the locations I want to use, the biggest that will unobrusively fit, and apply EQ to get the response right once the subwoofer system is in place.

[johnnyrichards]

The reason a system which is predicated on the 12db/octave cabin gain might not sound flat is because it probably isn't. 12db/octave is pretty optimistic. 8db is more like it.

[evilskillit]

Yeah right now I'm running one of those 8" subs in a .75 cu ft box stuffed heavily in the rear passenger floor board. I just wanted to see what it would sound like and it sounds pretty wimpy. Its got better bass than my factory speakers but it sounds like the lowest notes are missing quite a bit of emphasis.

I'm using this amp, because I got it for free.
http://www.caraudiomag.com/testrepor...ier/index.html

I know if I go to 2 subs I'll get way more efficiency because I can wire it down to 4 ohms instead of 8 and I'm doubling my SD. But even if I do that and double the box size the response curve would still be the same and I think the lowest notes might still be too quiet. Lumber isn't too expensive so I don't mind trying a ported box. If I don't like it I can always build a sealed box again.

If the port ends up being too long to fit in the box I also have no problems building a folded slot port and/or running the port outside of the box. It doesn't have to look show ready, as long as it sounds great and leaves trunk space for a stroller and groceries.

[mzisserson]

Ah, thats too bad as spare cash is something I just don't have a lot of laying around. Maybe some nice bored person with Bass Box Pro could model it for me, or not. Either way I'll be ok.

Ask, and thou shall recieve!

1ft3, 1.116ft3 including the drivers and port. 3" port, both ends flared(velocity is a little high, but I have had similar results with and the port runs silent using precision ports), .75" material will give you external dimensions of 14.5"x18"x10.5" AT max RMS input of 140W, you will not exceed Xmax down to 25Hz. F3 is 21Hz.

I have made dozens of subs for people with great results (my dual 8" TB setup with the 150W version of your sub fools people into thinking its dual 12's).

Some food for thought anyway.

[evilskillit]

I guess I kind of left this thread hanging huh? Thanks for the model mzisserson. I think I'll try that.

I think I'm going to try going with an external 3" pvc port and use elbows to wrap it around the box. I'm not going to glue it up initially, and I may try varying the length a bit of I'm not 100% satisfied right off the bat. I can make a thread with my progress and post some pics and impressions here if anybody cares or is interested. Eventually when I have some time and figure out how to use my Dayton measurement mic I can even post some measurements.

[mzisserson]

I guess I kind of left this thread hanging huh? Thanks for the model mzisserson. I think I'll try that.

I think I'm going to try going with an external 3" pvc port and use elbows to wrap it around the box. I'm not going to glue it up initially, and I may try varying the length a bit of I'm not 100% satisfied right off the bat. I can make a thread with my progress and post some pics and impressions here if anybody cares or is interested. Eventually when I have some time and figure out how to use my Dayton measurement mic I can even post some measurements.

Glad to help Keep us posted, no project is too small or big! The more info we all gather, the better!