Bandpass

[ThatChevyGuy 5,000+ posts]

Im am seeing this design in my head i know its some kinda band pass and i want to build it but i dont want it to sound like shit. Its for 4 12's, facing each other about 16-20" apart sealed on both sides with a top and bottom and back kind of creating a port, but without port length, its just open. Any help with this? It is not drawn to scale. I think it would be loud if its done right.

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[Immacomputer 10+ year member]

It would be more of a transmission line with a compression chamber, not a bandpass enclosure. You would be dealing with 1/4 wave theory but it does have potential.

 

[ThatChevyGuy 5,000+ posts]

I just drew up an image for a basic idea

 

[Immacomputer 10+ year member]

I knew what you meant.

 

[ThatChevyGuy 5,000+ posts]

Ok cool.

 

[iDesignBoxes 10+ year member]

For a box that would be built this way, and the subs being mounted in the directions that they are in, I would worry about cancellation. Maybe I am not seeing it the way you guys are.

 

[audioholic 5,000+ posts]

That is not a bandpass, nor do I see how it would be a transmission line. It just looks like a sealed box with the subs facing each other. That's a very common layout for blo-thru's for example. Ive seen it done many times, shouldn't pose any unusual problems.

 

[ThatChevyGuy 5,000+ posts]

Yes there would be some cancellation issue, but i think it would still be loud. And deeper than firing them up in a trunk //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

 

[ThatChevyGuy 5,000+ posts]

Should the open end be towards the trunk or firing into the backseat?

 

[Immacomputer 10+ year member]

That is not a bandpass, nor do I see how it would be a transmission line. It just looks like a sealed box with the subs facing each other. That's a very common layout for blo-thru's for example. Ive seen it done many times, shouldn't pose any unusual problems.

Oh it most certainly will act like a transmission line, just like the cabin of a vehicle acts like a transmission line with a closed end at the trunk or rear and the open end at the windows.

The tunnel would act like a transmission line and resonate at the 1/4 wavelength frequency of the tunnel that you create. This would cause a resonance and boost output around and above those frequencies. It would also help control the cone similar to how ported enclosures control the cone around tuning. Below the transmission line 1/4wave frequency, the sealed enclosures would help keep the subs controlled and the low end would be boosted slightly by the transmission line but also by cabin gain. The low frequency extension will probably be pretty nice but I would bet it to peak kind of high due to how long you would need the transmission line. A 45hz transmission line will need a length of about 6.2ft and a 60hz line would need about 4.65ft.

Another thing that would help that is to wire the rear subs to one amp and wire the front subs to the other amp (make sure to give them all separate chambers) and from there, if they have variable phase, set the front two slightly out of phase from the others (depending on how close they are to each other). That would help bring the subs closer to the open back more in phase with the enclosure.

 

[audioholic 5,000+ posts]

The tunnel would act like a transmission line and resonate at the 1/4 wavelength frequency of the tunnel that you create. This would cause a resonance and boost output around and above those frequencies. It would also help control the cone similar to how ported enclosures control the cone around tuning. Below the transmission line 1/4wave frequency, the sealed enclosures would help keep the subs controlled and the low end would be boosted slightly by the transmission line but also by cabin gain. The low frequency extension will probably be pretty nice but I would bet it to peak kind of high due to how long you would need the transmission line. A 45hz transmission line will need a length of about 6.2ft and a 60hz line would need about 4.65ft.
Another thing that would help that is to wire the rear subs to one amp and wire the front subs to the other amp (make sure to give them all separate chambers) and from there, if they have variable phase, set the front two slightly out of phase from the others (depending on how close they are to each other). That would help bring the subs closer to the open back more in phase with the enclosure.

That's only if the 'tunnel' were designed as such. More often than not, if that wasn't considered, the 'tunnel' would end up being built so large (as indicated by his illustration) as to pose to real restriction on air flow, and thus create no 'tuning' nor work as a t-line.
Again, Ive seen many setups like this, helped build one back in the early 90's. It acted like a simple sealed environment. Lets not over-complicate this. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[ThatChevyGuy 5,000+ posts]

God dammit why do all these threads go to shit.

lol, I get what you are saying tho, I planned on running each side off an amp. Its not gonna be v'd so it shouldnt matter. Any idea's on dimensions and doing the math?

 

[BrianChia 10+ year member]

I agree with audioholic. Anything can exhibit 1/4 wave behavior but this would not be a 1/4 wave design.

 

[Immacomputer 10+ year member]

That's only if the 'tunnel' were designed as such. More often than not, if that wasn't considered, the 'tunnel' would end up being built so large (as indicated by his illustration) as to pose to real restriction on air flow, and thus create no 'tuning' nor work as a t-line.
Again, Ive seen many setups like this, helped build one back in the early 90's. It acted like a simple sealed environment. Lets not over-complicate this. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

I'm not worried about what you have seen or built, I'm telling you how it would react. Any restricted tunnel, hallway pipe cave or even an MDF square will have 1/4 wave resonance. As long as we're not in a vacuum, air will resonate. Period.

If the line is long enough, the gain from the transmission line could very well be beneficial. It would definitely need to be longer than 5ft to get much bass gain though. Maybe the stuff you have worked on has had minimal gain due to a high 1/4 wave frequency. The line will only boost frequencies at and above the fundamental frequency, just like a car's cabin gain is only so good below the 1/4 wave frequency of the car. I have measured that in my car, gain below 28hz drops off pretty dramatically. It did that in my 240sx below 25hz.

Everything affects everything, it's just a matter of how much. If he makes it long enough, he could have some decent potential there. Think about all those "bass tunnel" trucks back in the early 90s. Notice how low they could drop? Now think about how deep some of those tunnels were (8-9ft which is around a 30hz line). Some of the setups I saw like that could not drop anywhere near that low in a sealed enclosure (I'm talking power irrelevant frequency response here).

 

[ThatChevyGuy 5,000+ posts]

I dont think i could make it any longer than 4 foot deep, and 38"wide.