Changing to a 4th order? Truth vs myths? Help

[CleanSierra]

I'm at 250" of port for 4 12s.

Port area is based on Xmax, tuning frequency and cone area. 250" of port works for MY 12s. Half of cone area is not necessarily correct for all subs.

[Jeff4661]

Ok we my subs have 10mm Xmax I have 8 of them. I was thinking around 300-400" of port

[CleanSierra]

I come up with 200" @ 46 Hz for a tune.

[TaylorFade]

2) less subs,higher ratio is better than more subs in a smaller ratio box?

2 12s in a 1:3 ratio box will yield more output then 4 12s 1:2 ratio.. ( just examples)

My last statement was addressing this.

[Tarball]

I know only the basics about building these types of boxes but i wanted to chime in about my own personal pet peeve.

You are talking about a band pass box which is a type of 4th order. A ported box is also a 4th order enclosure. A box with 2 chambers- one being sealed firing into a second chamber that is ported is a 4th order bandpass enclosure.

analretentive.exe /off

[Jeff4661]

I know only the basics about building these types of boxes but i wanted to chime in about my own personal pet peeve.

You are talking about a band pass box which is a type of 4th order. A ported box is also a 4th order enclosure. A box with 2 chambers- one being sealed firing into a second chamber that is ported is a 4th order bandpass enclosure.

analretentive.exe /off

To be correct in defining the type of box yes you are correct.. I am building a 4th order bandpass box in which it is one part sealed one part ported..

[Jeff4661]

I come up with 200" @ 46 Hz for a tune.

For my setup?

Could you kindly explain how you determined this? I'm trying to understand the math behind all of these boxes as well.

[CleanSierra]

I come up with 200" @ 46 Hz for a tune.

For my setup?

Could you kindly explain how you determined this? I'm trying to understand the math behind all of these boxes as well.

Yes, for your quantity of subs, Xmax and tuning. You don't necessarily need that exact amount of port area. Sometimes a little less or a little more is needed, but that formula is a decent way to take into account the proper parameters.

I acquired the number through magic

Or through here:

http://www.carstereo.com/help/Articles.cfm?id=31

[Triticum Agricolam]

I got a chance to play around with your box specs a bit. A lot of the stuff I was going to say about bandpass boxes was already covered by TaylorFade, but maybe I can expand on a few things.

The first thing to keep in mind is bandpass boxes offer a lot of flexibility to the designer, they have the ability to trade efficiency for bandwidth and vice-versa. This means there are more than one "right" way to design them, it just depends on what your goals are. If you want a very musical box with a smooth and broad bandwidth you can do that, or if you want a one-note-wonder that gets you max deebeez for you watts you can do that too, you just can't do both at the same time.

Like TaylorFade said, the sealed section largely dictates how low you can play, the ported side determines your efficiency/bandwidth. As you make it larger you will get more efficient, but over a smaller range of frequencies. While a box with less subs, but higher ratio may get equally loud at a certain frequency as a box with more subs and a lower ratio, it will do so over a smaller range. So if I had to pick between the two I'd go for more subs and a smaller ratio.

Anyway, here is some stuff I played with in WinISD.

The red line is the box you gave the specs for above. The yellow line is a box for 8 subs, with 9 cubes rear volume, 9 cubes front volume, and tuned to 48 Hz. The red box will get approximately 3 db louder in the low 40 Hz region, but is more peaky. The yellow box has a smoother response and slightly lower F3, but gives up a little efficiency. Its up to you to decide how much ability to play music well you are wiling to give up to get the extra output.

If you aren't totally comitted to those SWA-12 subs you might consider using Infinity 1260W subs. They come in single and dual voice coil flavors, have a 13 mm xmax, and are rated to take more power. They also should give pretty much equal performance to the Alpines, but in a little smaller box (7.5 cubes sealed, 16 cubes ported).

Here is one last thing to think about:

The red line is the same red box from above, the green line is eight Alpine subs in a 24 cube box tuned to 36 Hz. With the plain ported box you get at least 1 db more output, smoother response, and a lower F3 all from a much simpler box that takes up the same space.

[alaskanzx5]

Tons of info here. Looking this thread.