Building Ported Box

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boardinbum

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Joined: February 07, 2005

Location: United States

Posted: August 05, 2005 at 12:03 AM / IP Logged

I'm going to build a ported box for a 12" Alpine SWR-1221d.

I've tried modeling up different boxes in WinISD. But to be honest, I'm really not totally sure what I'm looking for. I read through the Getting started thing. But I'm still kind of lost. After reading it, I messed around for a while, and came up with a 1.75ft^3 box tuned to 43hz. Is that anywhere near what I'd want?

I would really appreciate it if someone else tried modeling this up, and helped my with the volume/tuning freq of the box.

Thanks in advance for your help.

stevdart

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Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: August 05, 2005 at 1:01 AM / IP Logged

I took a look at that. Tuning freq should be low, because the Fs is low at 27 Hz. The good thing about this sub is that you can actually come up with a smooth curve. Here is a graph of a good way to do this box:

vb_response_swr1221d.gif (wait a few seconds and click the icon that appears in the lower right corner to enlarge the graph)

The box is just a hair over 2 cubic feet net (after displacements), port diameter is 4.72 inches, port length is 22 inches. Tuning frequency is 30 Hz. Use a small amount of polyfil in the box and one port. You can convert the port to a slotted type if you wish.

This is a DVC 2 ohm woofer, so I figured that the coils would be wired in series for a total 4 ohms.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

boardinbum

Silver - Posts: 358

Joined: February 07, 2005

Location: United States

Posted: August 05, 2005 at 1:11 AM / IP Logged

Thanks for the quick reply. However, I'm still somewhat lost. Why do you want to try to get the curve as smooth as possible? Just so it'll play all frequencies at close to the same volume?

stevdart

Platinum - Posts: 5,816

Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: August 05, 2005 at 1:14 AM / IP Logged

Yes, you want to avoid peaks in the response. The only time peaks are in demand is when you are specifically tuning for SPL (competition). And keep this in mind: the car's cabin gain will peak the response and that is not shown in a computer mockup.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

boardinbum

Silver - Posts: 358

Joined: February 07, 2005

Location: United States

Posted: August 05, 2005 at 1:16 AM / IP Logged

No, what I mean is, what does the smooth curve mean to me? That it'll play all frequencies at close to the same volume?

boardinbum

Silver - Posts: 358

Joined: February 07, 2005

Location: United States

Posted: August 05, 2005 at 1:21 AM / IP Logged

Another question I have is, in a post from Alpine Guy, he said (talking about his Type R) "... Iv had box's made for me with 2 cube's of air space and tuned to about 45hz, it was stupid loud..."

My question is, how did tuning it to 45 hz make "stupid loud"? Are most bass notes in music closer to 45hz than 30hz and that's what makes it play louder?

stevdart

Platinum - Posts: 5,816

Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: August 05, 2005 at 1:34 AM / IP Logged

Yes, the combination of the box tuning and the car's cabin gain. But the majority of well-recorded music sources would benefit greater with a response curve that mimics the response of a sealed enclosure...only the ported box is going to provide a greater response in the low freq range. If you are building for the purpose of enjoying music, build with the idea that you want to extend the freq range as low as you can. On the other hand, if you are building with the idea that you want the most popular mass-recorded beats to hit harder than everything else to the point where they become the primary focus of your sub...tune in the 40s up to 50. That is the primary difference of SQ vs. SPL.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

boardinbum

Silver - Posts: 358

Joined: February 07, 2005

Location: United States

Posted: August 05, 2005 at 2:17 AM / IP Logged

At the risk of sounding like someone that would be just as happy picking up a few Audiobahn Flame Q's, setting them in a bandpass box, and hooking them up to a 10,000 watt Audiobahn amp, that is basically what I'm looking for.

I have it in a ~1.3 ft^3 sealed box right now, and it sounds great. I'm just building this ported box for the fun of it. I'm thinking I'll give both the nice sq ported box and the "stupid loud" ported box a shot.

Thank you very much for the quick responses, and all the help. I really appreciate it.

boardinbum

Silver - Posts: 358

Joined: February 07, 2005

Location: United States

Posted: August 05, 2005 at 2:40 AM / IP Logged

One last question - How do you determine if you need to use 1 or 2 ports?

stevdart

Platinum - Posts: 5,816

Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: August 05, 2005 at 5:59 AM / IP Logged

There's only a few cases where you might need to use multiple ports:

If you work up a box and the port is very short in length, you could go to two so that the length becomes increased.
You could use two if the port opening, at the size it has to be to eliminate port noise, doesn't fit the design of the box. Using two allows for more port opening area, but if the length of one is long you'll have even longer lengths if you use two.
Aesthetics...just the look of the box.
Depending on enclosure size and placement, and the number of subs in the box, using two will sometimes spread out the sound better in the installation. Like, if you had two subs in a box that fit from side to side in the trunk, using two could place a port on each side near the walls. Additional ports, of course, add to the overall size of the box.
If you have certain port diameters available and are trying to figure how to use them instead of customizing an exact size round port. Coverting to a slotted port opening is a good remedy for this.
And most commonly, if using multiple subs in multiple chambers, using a port in each chamber.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

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