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Bassick
08-27-2013, 03:48 PM
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.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.

Buck
08-27-2013, 03:51 PM
Have you ever seen an ABC box?

chefzane
08-27-2013, 04:25 PM
Have you ever seen an ABC box?

I haven't do explain

Buck
08-27-2013, 05:09 PM
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
08-27-2013, 05:11 PM
t-line if you want to get tricky with it lol

Bassick
08-28-2013, 10:14 AM
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.26544544

Buck
08-28-2013, 11:29 AM
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.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
08-28-2013, 12:06 PM
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. 26544550

Bassick
08-28-2013, 12:13 PM
and oh yeah, Buck, thanks for the reply.

Buck
08-28-2013, 12:29 PM
It's a cool idea. I don't think I would tune that close together.

Bassick
08-28-2013, 12:33 PM
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
08-28-2013, 12:35 PM
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 (http://www.diysubwoofers.org/prt/dual_chamber.htm)

Bassick
08-28-2013, 12:35 PM
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
08-28-2013, 12:40 PM
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
08-28-2013, 12:43 PM
Like dude said, I don't know if it would work with the extra chamber ported out as well.

Bassick
08-28-2013, 01:32 PM
This if for bbeljefe, what you are describing is a ABC band box. I've did my research on that type of enclosure. What I'm purposing is something different, this has never been done (if it has I havn't seen it). This concept works for sealed and ported or any kind of enclosure. At the core the concept is simple: "Increasing the cubic feet as the frequency lowers". And as everybody knows, "increasing the enclosure size decreases the port tuning for a giving port diameter and length".

Bassick
08-28-2013, 01:37 PM
The extra chamber is not ported out its closed off, click on this attachment. 26544551

bbeljefe
08-28-2013, 01:51 PM
Yeah I get what you're saying, which is why I said that I don't think it will make any noticeable difference in Fb, save the obvious difference making the box bigger would accomplish.

I just don't see how porting into a sealed box is going to help anything but I could be wrong. In my way of thinking, you can't expect the sound waves to travel into an empty chamber at one frequency and then back out through the same hole as another frequency. In fact, what it looks like to me is a whole bunch of standing waves inside a ported box... and standing waves are one of the things we spend countless hours trying to eliminate when designing enclosures.

But hey, I'm not Amar Bose so by all means, build it and test it. ;-)

cfox10
08-28-2013, 01:55 PM
Like above... It would seem you would get cancelation across frequencies and standing waves. Just don't see how this would work.

Buck
08-28-2013, 04:09 PM
We are all on the same page at least, lol.

gumby688
08-28-2013, 04:15 PM
If the inside port is ported into a sealed chamber wouldn't it still just act like a sealed too me that looks like it would just be a singled ported box but I am not a audiowiz or anything.

Bassick
08-28-2013, 04:29 PM
Thanks guys for all the input, I understand the problem with the standing waves. I kind of sort of disagree about it tho. I still plan to experiment with this, who knows maybe some other idea may come from it. Thanks guys.

Bassick
08-28-2013, 04:42 PM
oh yes, I forgot to post my system
Head Unit: Alpine CDE 147-BT
X-Over: Kicker Front Row ZXDSP1
Sub Amp: Brutus BRX1100.1 D
Subwoofer: 2 Brutus BRZ15D4
Mid Bass & Mid Range Amp: Brutus BRX320.4
Mid Range Drivers: Door: 2 ATL5768CX (5x7)
Rear Deck: 2 HF8SQ-i4(8" square)
Highs Amp: Brutus BRX160.2
Tweeters: Pyramid TW47

bbeljefe
08-28-2013, 05:13 PM
Definitely do some experimentation and post up pics and video of the results.

ahardy17
09-03-2013, 04:34 PM
seems like each port on those inner chambers would have to get progressively smaller with respect to the chamber size too, to provide a higher tuning frequency for each of them. I can't see it working the other way around. I'm interested in the idea but calculating the reactions between all the ports is extraordinarily involved; you would probably have the best luck starting with just one additional chamber to see how it behaves so you can figure how to effectively tune it in the hopes of stretching a more even response, then add the third chamber in later. You could do an MIT thesis on such on a project. I'm sure there is a way to determine the behavior of 2 ports in such a setup, it's just a matter of whether or not the second (and third) port and chamber combination would behave predictably with the only resistance being the sealed volume of the smallest chamber. I say you must become the pioneer of this concept and enlighten the rest of us!

psych0ticnemes1
09-03-2013, 05:47 PM
I don't understand a lick of how this could work, but major kudos to you for trying something different. I'm a huge fan of trying different things and being somewhat unique. I stayed away from SPL competitions for so long thinking, why build a fart cannon? But what if you stumble across a design that allows you to quadruple output or something? It intrigues me more than just grabbing massive subwoofers and throwing gobs of power at them.

Good luck.

Bassick
09-06-2013, 12:40 PM
ahardy17, You seem to grasp the fundamental of this theory of mine. I appreciate your reply (highly motivational). I don't know your background but could you give me some expert advise as for as the predictability of the ports, if not do you know anybody that can, again thanks

bbeljefe
09-11-2013, 03:26 AM
The ports and additional chambers are going to behave like braces in any other cabinet. They'll have little to no measurable affect and will have even less audible affect.

In a sealed box all you have is the front of the cone to make noise. In a ported enclosure, most people can't hear an audible tonal difference between, say, 35 Hz tuning and 38 Hz tuning.

I predict that adding chambers and ports to a sealed box will yield less than .5 Hz difference in the Fb of the box, relative to the change that simply making the box larger would cause.

In simple terms, you're trying to see if three interconnected 2' boxes will hold more than one 6' box. And the answer is, it won't.

What you will accomplish though is only two of three things a DCBR accomplishes and that's lower driver excursion as a result of the added port resistance and consequently, slightly higher power handling capability. But, less excursion is only desirable if you have a driver with low xmax and with the technologies we have today in the audio world, a driver with low xmax that needs help with power handling isn't worth the time and trouble of making a complicated enclosure for. Especially when you know for a fact that that complicated enclosure won't provide any acoustical gain. Not to mention, the increase in power handling would be negligible because you're not really moving much more air at all across the coil, since no fresh air can enter a closed system.

And please don't get me wrong... I applaud your thinking into it. I just don't see any appreciable benefit from what you're proposing.

Side Show
09-11-2013, 04:50 AM
i'd say you'll get a lot of port noise