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

[CleanSierra]

I didn't choose bandpass option when calculating your area. You've got a sub with 10MM of Xmax, you don't need a monster port, bandpass or no bandpass. I didn't see the need to select bandpass for the subs you have in question. Designing a bandpass for those subs is going to lose out on a LOT of output due to the design constraints.

You're not getting hairtricks from 8 subs with 10MM of Xmax. You may get a decently loud setup after a box or two, but you're not getting a hairtrick machine. I know budget, blah blah blah, but those subs are not going to impress in the way that you want.

[CleanSierra]

Stick with a regular posted box and be done with it. Simpler is better in your situation.

[Triticum Agricolam]

Again proof that bandpasses almost have no use in car audio.

Yeah, I agree with you and this was kinda what I was getting at with that graph. Unless there is a reason that you NEED to push all the sound through a port (firewalled trunk, blow through, etc) a regular ported box is going to be a better use of the space if performance is your primary objective. Now with that being said, sometimes the "best" way to do something isn't the most fun or interesting. So if Jeff4661 WANTS to build a bandpass box, I say go for it!

Question for Jeff4661: how much power are you going to be running? All those port area calculators that give you port area based on cone area, xmax, and tuning operate under the assumption that you are going to be pushing those subs to Xmax. If you aren't going to be using enough power to do that, you may not need as much port area. You can model port velocity in WinISD as well if you enter in how much power you are going to run.

Since all your sound comes out the port, you are going to want it to be an efficient as possible. If you can design your port so its a straight shot w/o any bends in it that would be good. With ported boxes I try to keep port velocities under 30 m/sec, less velocity certainly doesn't hurt either. I don't have as much experience with bandpass boxes so I don't really have a good number for you, but if I was going to pull one out of my ass I'd say keep it under 20 m/sec. I've read other folks say 17 m/sec, which sound reasonable too, though no matter what you do you may run into the issue of fitting the port into your space if it gets too big.

[Joe X]

OP pulling hairtricks on 250W, 10mm xmax subs? Why don' you go for 6 15" but better drivers, say 19-20 mm drivers, you would have much higher displacement capability for not too much more money. Obsidians are 20mm Xmax and relatively inexpensive.

[Jeff4661]

I already have the subs. Otherwise I would look into other subs.. I got a hella good deal on these ones. As for power wise I plan on running 2 sound stream rubicon 2500s.

And yes I have plenty of electrical to support it.. 2 280amp alternators, 6 deka AGM Batteries.

So if I understand everything correctly.. u guys are saying that in my application a ported box will be better?

Based on the graphs I will agree it will get louder with a ported box.

So 4th orders are more for a home audio use?

[Jeff4661]

I literally paid like 398.69 for all 8. To me this was a cheap build. After I smoke these I will probably do little more research before buying my next set of subs.. kinda rushed into this the wrong way

[Triticum Agricolam]

I literally paid like 398.69 for all 8. To me this was a cheap build. After I smoke these I will probably do little more research before buying my next set of subs.. kinda rushed into this the wrong way

Sounds like you got a decent deal, so I don't blame you for wanting to use those subs.

In regards to whether a regular ported box would be better, yes it would be, though not by a large margin. If performance is your primary goal, I'd go with the ported box. You may want to consider using some kind of removable or adjustable port system so you can tailor its performance to the task at hand (demos, competition, etc). With that being said, if the 4th order bandpass interests you more and you want something more challenging to design and build I say go for it.

My suggestions for ports would be if you do something like the 1:1 design I graphed I'd use two 12" round ports ~20.5" long, for your 2:1 design I'd up it to three 12" ports ~16.25" long. In either case I'd make the ports long, measure the tuning, and cut them down till the tuning is right where you want to be. Bandpass boxes tend to be more sensitive to the tuning being off than ported boxes are.

[Raptorman]

Ok so I once again am changing box design instead of a ported I am going to go with a 4th order. I have been using winISD to help me plan this. Please keep in mind this is my first 4th order. Just wondering about a few things prior to desinging it all out

A few myths/questions I would like some answers on.

1) port tuning needs to be around 44-47hz for lows? WinISD shows my box would be -3db at 30-31hz truth? Opinions?

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)

3) higher ratio with less power is as loud as lower ratio more power?

4) how much port velocity is to much for a 4th order? My winISD box currently has around 65.5 ft/s or around 21m/s is that to much?

What is a good ratio for a loud daily/spl box? 1:2?

Thease are just a few I have been seeing lately if you guys could help clear the air of these myths?

Also here is a place I found some more information to maybe help some people on 4th orders

http://mobileaudioforum.com/forum/showthread.php?1619-Thought-I-d-share-some-4th-order-design-info

Thanks guys,

1) Tuning should be at your resonant frequency. Port tuning does not determine how low you are able to play. Prime example is my own 4th order. Tuned to 50hz and crush all the way down to 17hz

2) Hard to tell. 2:1 isn't considered "small", it's about normal. Bigger the ratio, the more efficient. Too many factors to answer your initial question.

3) Seems to make sense. Again, too many factors. But I would venture to agree.

4) I don't go by the port velocity like you have. I look at the "vent mach" in winisd. Usually go for .02. I wouldn't worry too much about it personally. Get your port area right. (which, is NOT tied to your ported volume, it is tied to your cone area/volumetric displacement)

A good ratio is 3:1 I find. Still very musical, and more efficient. The higher the ratio the more of a peak you may have, generally.

[Raptorman]

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.

Again proof that bandpasses almost have no use in car audio.

Yeah, don't mind me while I demolish 17-60hz and stay within 1.0db from 25-60hz and tear shit up.

[alaskanzx5]

^^^

I bet your not uu using cheap subs and your running a lot of power.

Then you have more exp then op and I guarantee a lot of time into the build.