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Elite Shackster
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Discussion Starter · #1 ·
Its a seemingly contradictory title but bare with me. I have recently moved house and sold my old DIY sub so I can build another 2 for my new home. I was looking at the house and pondering on if an IB is possible, if I would want to and if I should.

The only probable way would be to have the manifold built into a brick wall, and this makes construction of a true IB sized square hole an issue. I was having a think about this and was trying to think how could reduce the hole, so I got to wandering if I could go with some small port sized holes. Obviously this is a ported sub, something I dont want, so that made me consider an IB, but that discharged into a cabinet that ported into my room to keep hole size as small as possible. Its basically a 4th order bandpass design, but using an IB section instead of the usual sealed.

Has this been done before, would it work, does anyone have any thoughts on the idea, and has anyone actually tried this?
 

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I was having a think about this and was trying to think how could reduce the hole, so I got to wandering if I could go with some small port sized holes.

I don't understand what some small port sized holes has to do with a IB manifold. Can you post a drawing of what your ideas is?

 

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Elite Shackster
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Discussion Starter · #4 ·
Ive uploaded a google sketchup model Mike, its much better than a picture and no more difficult to produce. Ive run a couple theoretical models and one thing I realised is that this isnt an IB in any shape or form, and apart from the Manifold resemblance and 10 times vas or more the cabinet volume is, thats about it. You loose all the efficiency of the IB, so you still need the more expensive high excursion and high power handling drivers. The response is still a pseudo twin tuned bandpass type and this looks like it would be fairly expensive to build in comparison to an IB, basically the same a building normal subs but with more drivers.

The advantages would be that you have a huge cabinet if you want, and if applying it to how I was thinking, theres no putting huge 400mm dia holes though a brick wall, plus the listening room looks sub-less. The disadvantages are no cost savings that IB's enjoy, and no IB type performance. The application of something like this would really be dependant on individuals needs I think, but it would work. How it would sound is anyones guess, could be awesome or could be very unruly. What do you think Mike?
 

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Not trying to be a dud, but I think it would be very difficult to model and thus be doing more hoping than planning on your desired performance, though I really like the idea of it and hope you can get it done successfully.
 

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Elite Shackster
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Discussion Starter · #7 ·
No sweat Mike. Something else that might interest you mic, is I think Ive come up with a way to make dual concentric ports work in a sonotube cylinder sub. I also ave access to tubes that dont need bracing to maximise volume. Might take an experiment though. I'll add a screen shot of the model for you in a minute.

Edit: pics added. Ignore the coloured lines, they are just guides that I forgot to remove before I took the shot. Hopefully you can see the IB style manifold, the wall which would separate the rooms and the ports. The pic isnt an accurate model, just something to give you a visual on what I am thinking about.
 

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Elite Shackster
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Discussion Starter · #8 ·
Not trying to be a dud, but I think it would be very difficult to model and thus be doing more hoping than planning on your desired performance, though I really like the idea of it and hope you can get it done successfully.
Modelling isnt hard, as long as you know the volume of the room acting as a cab, but then an IB cab can be huge if you want. The difficult part might be getting the bandpass where you want it so I can see how that might be what you talking about. I guess a build and test might be the only way to know for sure if a model will translate in an accurate result.

FYI, I'm not going to be building this, as Ive decided it isnt practical, its just some general discussion on the theory.
 

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Elite Shackster
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Discussion Starter · #10 ·
Interesting idea. For proper modeling the volume behind the subs would need to be known.
Thats the easy bit, but accounting for stuff in the room isnt. Volume accuracy isnt essential for an IB, but I reckon it would be for this.
 

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Basically it is a 4th order bandpass but with a massive rear chamber.

Main considerations are:

Vent compression, the vents will need to be fairly large if you do not want to "choke" the output of the design.

The vents will like any bandpass act as a high pass filter so above the vent tune it will roll off on the upper bass.

You won't be able to hear the drivers distress and make bad sounds should you push them too hard.
 

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This IMO would be a research-oriented engineering project. I've not seen anything like it and would caution anyone else from undertaking this. However you are a pretty sharp guy and my learn a lot from this. I'd just build the subs into the wall with a backer box and the ports. Though I understand you are trying to hide the subs from view. You could build a box on the back.
 

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Elite Shackster
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Discussion Starter · #14 ·
As you say mic, the ports need to be quite large, but the good thing about this is that you wouldnt be trying to get the ports inside your enclosure, they could run outside of it if you wished. I ran a model with 3 ports at 200mm dia and IIRC they were about a meter long. You cab could be fixed in one spot, and ports run from it and into the listening room. Another advantage it the holes into the listening room could be smaller, and another is that your ports could cross a corridor if you so desired or required. It looks on paper to be very customisable and adaptive, but something that would be quite rare. Ive no idea how it might sound, and that open baffle is a big variable. The porting can be changed a lot though, so there is plenty of room for adaptation.

The main thing that I thought about with this is how to get through a solid wall, and how to remove the subs cab from the listening room. Also, a single sub could have 4 ports, with 2 being located close to your front pair if possible. Its a definite custom job, but could be interesting. My main line of thinking was derived from an IB, but the brick wall is a supporting one and the brick is tough as .
 

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As the ports would be tuned fairly high I would tend to ensure they are not too far apart as you will start to encounter phase shift issues as you pass the 1/4 wavelenth between them, just like you get with speakers.

Yes you are correct it would give you massive scope for adjustments.
 

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Elite Shackster
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Discussion Starter · #16 ·
I think though that this would actually be the biggest obstacle to getting a working design to turn out exactly as you intend.
 

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Dan,

In short...Don't do it.

This will be a 4th order bandpass and those have limited range. Also what happens when you have a huge back chamber in a 4th order BP? You lose power handling on the low end just like a an IB. However with a 4th order BP you usually want to cover a fairly narrow range in order to get some extra efficiency out of it. If you wanted this to be a device with a broad flat frequency range, you would want a very small front chamber which will limit efficiency and cause issue with the ports actually fitting in. You would need very large ports to handle multiple 15's without serious compression effects, at which point you migt be getting to a size where it's not that much bigger of an opening to do a manifold for a true IB. I think it's much more trouble than it's worth especially if it's a huge 4th order using very small vents.
 

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Elite Shackster
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Discussion Starter · #18 ·
I think the unknown elements of the design make it an undesirable project for anyone other than an experimenter with time and money on his hands. Its probably a workable idea but a considerable effort I'm not willing to go to.

As t happens, Ive discovered that I have a suspended wooden floor, with the perfect volume for a true IB in the floor and using 2 Fi IB318's with 500 watts of power, so guess what is on the drawing board now :devil:
 
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