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Discussion Starter · #1 ·
So I've been working on building my first subwoofer box using WinISD. I'm looking at the Ultimax 15 or 18, in a ported box, with a volume of ~15 cubic ft. I plan to have two of these in a dedicated home theater that is 19' x 14.5' x 8.5' and will be used solely for movies. The kicker is, I'm trying to build this with two dimensions being rather shallow. The box is about 80" wide, 21" tall and 15" deep.

I've attached my two WinISD files (renamed as .txt as I couldn't upload .wpr). I'm looking to see if what I'm thinking makes sense.

1) Looking at cone excursion, both are well under the threshold
2) Air velocity of the port is around 17. (I read that you wanted that to be 17 or lower.)
3) f3 is about 24Hz.

It looks like these subs can do a lot more but adjusting anything much more makes my port too long (currently its at 19x3.5x12.3...so the back of the port is about 3" from the back of the box). I was trying to keep the port a simple rectangle and not an "L" shape since this is my first build.

So, given this configuration, it seems that there isn't much point of me going with the 18's because the graphs (except cone excursion) are almost identical. I suspect this is because I'm not utilizing the full capacity of either driver. Or do I have something mis-configured in WinISD?

Do you have any suggestions for improving the low end response while fitting within the stated parameters?

Lastly, does the port location matter? I usually seem them along the bottom edge but you could place in anywhere on the box....say, 5" up from the bottom or 15" from the left or right?
 

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The port should be within 1/4 wavelength of the tuning frequency of the cone middle.

and since most people tune to 15-25hz, then anywhere in the room should work. hehe! 馃槄

For the box shape, it doesn't really matter. As long as the port isn't restricted, it's mostly the box-volume not any given dimension that matters. The sound wave travels at 1100ft per second, so it "sees" the total volume of the box "almost" instantly.
If one dimension is really long, then you might want to line the walls or start/end with fluff just to reduce any ringing or resonances.

Bracing every 6-12inches as per normal / ideally.

I haven't looked at your files but as long as the box-volume is legit and the applied-power is set, and the HPF is added. Then the SPL chart should be accurate-ish. (Or the Max SPL chart if you haven't set those.)

The default is 1 watt, so maybe that's why they don't differ much. (Or maybe/likely, the box is preventing optimal loading on the beefier driver...)

Usually bigger drivers need more box, and higher SPL needs more port area to reduce wind speed/chuffing noises.
You can only get so-loud before hitting the physical limits of the system\physics involved. i.e. iron's law
Small, Cheap, Loud.
Pick any 2, but not all 3.
 

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Discussion Starter · #3 ·
The port should be within 1/4 wavelength of the tuning frequency of the cone middle.

and since most people tune to 15-25hz, then anywhere in the room should work. hehe! 馃槄

For the box shape, it doesn't really matter. As long as the port isn't restricted, it's mostly the box-volume not any given dimension that matters. The sound wave travels at 1100ft per second, so it "sees" the total volume of the box "almost" instantly.
If one dimension is really long, then you might want to line the walls or start/end with fluff just to reduce any ringing or resonances.

Bracing every 6-12inches as per normal / ideally.

I haven't looked at your files but as long as the box-volume is legit and the applied-power is set, and the HPF is added. Then the SPL chart should be accurate-ish. (Or the Max SPL chart if you haven't set those.)

The default is 1 watt, so maybe that's why they don't differ much. (Or maybe/likely, the box is preventing optimal loading on the beefier driver...)

Usually bigger drivers need more box, and higher SPL needs more port area to reduce wind speed/chuffing noises.
You can only get so-loud before hitting the physical limits of the system\physics involved. i.e. iron's law
Small, Cheap, Loud.
Pick any 2, but not all 3.
This is good information, thanks! Speaking of bracing, is it for more than just structural strength or is that the primary reason? I admittedly haven't look very deep into that subject yet.

And yeah, I did change the input signal strength so I'm guessing you're right that it is the box that is causing what I'm seeing.

The only outstanding question is the port location itself. I have a situation where placing the port at the perimeter of the box will result in it being partically covered when it is set in place. I was hoping I could offset it from the left or right edge by 5-6". Something like this:

3119960

Will this be an issue?
 

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The bracing is to control vibrations in the panels that can cause undesirable sounds emanating from the boxes. Your port location should not be a problem.
 
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