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Discussion Starter #1
I'm looking into changing my box from a ported box to a 4th order isobaric compound box. I input the data into WinISD and it came up with a solution of .46 cf for the rear sealed chamber and .825 for the front/ported chamber. On another forum site I was told that I need to halve both of those sizes given. If that's true, then that's pushing it for me to even try to fit the motor assembly in the box. But I know you tune the box and halving that would change the port dimensions, correct?

I'm also wondering, are the volumes given even correct? The title for the box in WinISD states 4th order bandpass.

So I ask, What do I do?

If I knew how to copy/paste the screen, I would post the WinISD results. I love the looks of the freq curve for this setup, it's exactly what I'm after. Higher low end output w/the SQ of a sealed box.

The subs I am using are two TREO SSi12.22's.

What I'm after (which is what I got from the WinISD plot) is a flat as possible response from 30Hz to 60Hz.

Anyone know of a box calculator for making 4th order isobaric compound boxes?

Thanks in advance.
 

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Discussion Starter #3
Correction, the 2nd one down IN the box outlined/titled "Single Reflex - Band Pass Enclosures"
 

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I've got a program called Low Frequency Designer, v3.02.
Made by a company called SpeakEasy.
It allows user-defined enclosure configurations.
Sealed, ported, BP4, BP6, serial and parallel ported configurations.
Also allows you to choose the driver config. Single driver, dual standard,
dual isobarik.
It's great for the quick & dirty approach. Otherwise, I use LEAP, which
allows for a much higher level of enclosure/driver/environment analysis.
Strictly command-line interface (v4.51) and very much GIGO.
If you've got TS for your drivers, I could run them through LFDES, just to give you
a bit more info to work with, rather than relying on a single analysis/modelling program's
results.
 

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go back to WinISD again and recheck. Are you running the pro alpha .50a7 version? I just checked mine and you choose isobaric then click next then 4th order. So, you should be able to stick with WinISD.
 

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go back to WinISD again and recheck. Are you running the pro alpha .50a7 version? I just checked mine and you choose isobaric then click next then 4th order. So, you should be able to stick with WinISD.
 

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Discussion Starter #8
No, I'm using beta.

I have issues loading driver T/S as they don't have the TREO SSi12.22's in their list. Then when I try closing the program, I get some error message stating that it can't close.
 

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not to derail what you are trying to do, but if you are already at about 1.5 cuft total for a 4th order, why not use a single driver and call it a day? (that is really small, what size sub are you using?) an isobaric may require less space, but it is alot less efficient too, ussualy about 3dB less than a single driver.
 

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Discussion Starter #11
Two 12" TREO SSi12.22's. Same as the TREO SSp's. Use the T/S from the SSp12.22.
http://treoonline.com/infosheets/ssp_subwoofers.pdf

Currently I have 2 of them in a ported box, 1.5 cf each. So I'm already "there" as per the thought of just one in a ported box. What I'm after is a "natural" low end response. The curve of the setup I'm after is +/- 0dB from 31Hz to 53Hz and -3dB from 26Hz to 66Hz.
 

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Two 12" TREO SSi12.22's. Same as the TREO SSp's. Use the T/S from the SSp12.22.
http://treoonline.com/infosheets/ssp_subwoofers.pdf

Currently I have 2 of them in a ported box, 1.5 cf each. So I'm already "there" as per the thought of just one in a ported box. What I'm after is a "natural" low end response. The curve of the setup I'm after is +/- 0dB from 31Hz to 53Hz and -3dB from 26Hz to 66Hz.
Whether we can design a box with that response in bbpro or similar is moot as soon as you put it in your car. With that in mind what are your other considerations? Size? Efficiency? etc.
 

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I thought on a isobaric 4th order, you are only cutting the sealed section in half. Your ported side size (port /lengh tuning) remain roughly the same, sometimes bigger. I had some old credence clearance woofers and had a 4th order iso design done. I by no means am a guru on this stuff, so I tried to match the design to some other resources so I could learn how he came up with it. Nothing every came exactly, but I can say that all the ported sides were very close whether it was the standard bandpass or the iso bandpass. The difference in size was the sealed section which was close to half the size.
 

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I've modeled some enclosures, for flatest response go for a vented isobaric 1.475cf tuned to 22.12Hz. Will dig deeper than the rest, this is the dark blue trace.

Light blue trace is the subs in their optimum vented enclosure, but huge at 5.9cf

Yellow trace is a single tuned BP, total volume is 0.93cf front chamber is 0.384cf and vented, rear chamber is sealed and 0.546cf-also has lowest group delay

A parallel tuned enclosure, purple line, will give the widest BP response, 0.738cf front chamber and 1.745cf rear chamber 2.483cf total volume.
 

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Discussion Starter #15 (Edited)
Thanks for graphing those for me Baron Groog. The yellow plot is the same as what I was getting with WinISD and that's the one I want, but in a 4th order Isobaric compound box.

What would I need to do to make it a 4th order Isobaric compound? Can you give me the port length for a 3" port and for a 4" port (both round). What I want is both subs facing each other, one wired out of phase as to be in phase with the other sub, one sub in the sealed box and the other in the ported box, is that something you can plot?
 

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That is a 4th order bandpass, with isobaric mounting and that's the good news.

Now the bad news-for a 3" vent you'd need 25.76" length, and get chuffing between 26 and 38Hz. If you go for a 4" vent you can expect to have a length of 46.35" but get no chuffing-in other words this is going to be the mother of all fockers to build.

I don't really play with BP designs-never had the need/want to but will have a mess for you. If I make the box bigger (that actual box wouldn't fit your drivers in it) the response becomes more peaked, but you could EQ out the peak to get the flat response you're after-again, please remember this will be nothing like flat in your car.

What are the gross dimensions the box must fit in?
 

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Discussion Starter #17
I have 3 cubes total to deal with. A 46" port is nothing, I have just the spot for it.
I have an audio control dqs I can use to flatten the response out. I under stand cabin gain will change things.

Again, thanks for your help.
 
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