Thinking inside the box

[Bassick]

Thinking inside the box

To anyone with knowledge, be it professional or novice, but only serious answers. Just as the title implies I'm thinking inside the box. I am a huge advocate of car audio, I'm 40 years old, matured in the mid 90's. Been into car audio for a long time as a hobbyist, and for the last 3 years all the technical stuff from T/S parameters to 8th order bandpass enclosures are now making a lot of sense to me. So with that said, here is my question. How would a ported enclosure or sealed for that matter, behave if there where smaller chambers inside the enclosure (we will say 2 more). So picture this inside your head, take a enclosure sealed or ported, and on the back side of the enclosure you cut out a port to what ever size is relevant to the enclosure, now you build another enclosure perpendicular to that side of the original enclosure, and then repeat that process one more time. Each additional chamber would be somewhat smaller than the next.View attachment 26544536 This is my first time posting, I hope this attachment illustrates it better. My goal is to produce a enclosure that would tune itself according the lowest frequencies present. The open port would be tuned to a given freq, as the second port unloads because of its tuning, that would make the first port tuning freq change. Its very hard to contemplate what happens after that. Someone with really good knowledge please reply to what is really going on in such a setup.

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[Buck 5,000+ posts]

Have you ever seen an ABC box?

 

[chefzane]

Have you ever seen an ABC box?

I haven't do explain

 

[Buck 5,000+ posts]

Err I'm not sure if I could explain it 100% accurately, only seen like 1 build ever for it.

It's like you are saying, 1 port directly ported outside from loading chamber. Then another port to another chamber which is then ported outside again.

My question to you is, why? What do you really think you are going to achieve that's better over say just a ported box? I just don't see putting in the work for this and being as happy. More work than happiness at end result maybe is what I'm saying.

 

[des343 10+ year member]

t-line if you want to get tricky with it lol

 

[Bassick]

No, only one port is exposed to the outside. the other two ports are internal. the purpose of this type of enclosure is to have more bass extension with better cone control. Think about this, at port resonance the subwoofer barely moves but below port resonance the port unloads, what if instead of unloading the port could adjust to a lower resonance and thus better controlling the subwoofer. But, it is physically impossible for the port itself to adjust, but if you have another chamber inside the enclosure thats ported and closed off and tuned to such that it will unload along with the port that exposed to the outside. When the inside port unloads the exposed port will see a bigger box (more cubic feet) thus changing the resonance. You have to understand this is just theory. Please, if you do not completely understand this concept, do not reply with the "why not just go with ......" or "have you ever heard of ....." answers. I'm actually looking for expert opinions only.View attachment 26544544

 

[Buck 5,000+ posts]

No, only one port is exposed to the outside. the other two ports are internal. the purpose of this type of enclosure is to have more bass extension with better cone control. Think about this, at port resonance the subwoofer barely moves but below port resonance the port unloads, what if instead of unloading the port could adjust to a lower resonance and thus better controlling the subwoofer. But, it is physically impossible for the port itself to adjust, but if you have another chamber inside the enclosure thats ported and closed off and tuned to such that it will unload along with the port that exposed to the outside. When the inside port unloads the exposed port will see a bigger box (more cubic feet) thus changing the resonance. You have to understand this is just theory. Please, if you do not completely understand this concept, do not reply with the "why not just go with ......" or "have you ever heard of ....." answers. I'm actually looking for expert opinions only.View attachment 26544544

The reason I said abc is because that's like right there looking very close to it. I understand exactly what you are saying, and I think that's interesting and as far as generic specs, I don't think it would be too hard to figure out either.

So by building this box, you would be hoping for a wider bandwidth over ported? Like, where would you want the outer port to unload at, 30 hz? 40 hz? Then the box becomes bigger due to the unloading, and play down to what, 20 hz or something?

 

[Bassick]

Yes, I know there is a lot of calculations to do as for as tuning the ports, cause actually the main enclosure calculations would be for two ports. And after the resonate frequency of those ports are reached, the exposed port will transition back to loaded, so I'm thinking that the internal port should be tuned slightly higher, how higher?, I don't know, but at some point it should unload just before the exposed port. As the exposed port is on the verge of unloading the second port unloads allowing the exposed port to see more air. (As enclosure increases port tuning decreases for given port). So to answer your question about where I would like for the outer port to unload: I would tune the outer port to 30 Hz, and tune the inner port to somewhere less than 32 Hz. The purpose is not to get really low but to have better cone control down to the lowest possible hertz that the subwoofer can handle. The more you think about this concept, the more problems you encounter and unpredictabilty sets in. View attachment 26544550

 

[Bassick]

and oh yeah, Buck, thanks for the reply.

 

[Buck 5,000+ posts]

It's a cool idea. I don't think I would tune that close together.

 

[Bassick]

Not saying that this concept would even work, but I would like to hear your ideas or comments about it and what would you do different?

 

[bbeljefe]

I don't know that you're going to benefit from porting into a closed chamber. It would change the Fb of a sealed box but so will making the sealed box larger. Correct me if I'm wrong but, to realize any benefit from a ported chamber, you need to have that chamber ported into the listening environment at some point.

But basically, what you're describing (save porting into an unused chamber) is a dual chamber bass reflex box. And those are relatively simple to build in one alignment. You simply take the Vb of a ported enclosure for a given driver, and then split that air space into two separate boxes with one of them being 2/3 of the original total and the other being 1/3. You use three ports, all of which are the same size and length as modeled in the original box. The 2/3 box houses the driver and two ports. One vents into the listening environment and the other into the 1/3 box. The third vents from the 1/3 box into the listening environment.

Here's a bit more detailed explanation of them:

The Subwoofer DIY Page - Dual-chamber ported systems

 

[Bassick]

Even tho, I'm just looking at this concept for better cone control, the application (if it works) could be used for other purposes.

 

[Buck 5,000+ posts]

Not saying that this concept would even work, but I would like to hear your ideas or comments about it and what would you do different?

I think you would tune further apart to get a wider range. You might want to have say a 35 box tune until the rear port gives out at, idk, 40 hz, then takes it down to maybe 28 or so. Or however low you want to play. Just have to adjust chamber sizes with port sizes to get tuning you want when it "switches". I just don't know how it would play or transition between notes.

 

[Buck 5,000+ posts]

Like dude said, I don't know if it would work with the extra chamber ported out as well.