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Old 10-10-2008, 03:03 PM - Thread Starter
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My friend and I have another thread started attempting to use sulfurhexafluoride gas in sealed subwoofer enclosures.

http://www.avsforum.com/avs-vb/showthread.php?t=1072502

The idea is to place multiple drivers in very small boxes using the gas to increase the effective box volume. This is a fun project and very educational. However, results thus far have been less than promising. We will continue down that path until it either proves out or falls on its face. After that we will put the "use of gas in speaker enclosures" question to rest so everyone can benefit from what we learn....good or bad.

Anyway, one always has to have a plan "B". My current sub, while being quite effective is HUGE and is incapable of the SPL's I desire at subsonic frequencies. My friend and I bought a ton of drivers on the ED 16ov2 blowout deal. My plan "B" is to use 8 of these in an IB configuration.

Most of the IB installs I have seen are large permanent installs. I have this idea I would like to bounce off the group to get some feedback. The concept still involves cutting holes in the floor, in my case to vent into the garage under my living room. The twist from most install photos I have seen is to build two 18-20 inch cubes with 4 drivers each. Basically the smallest cube that will fit one driver on each of the four sides of the cube. The bottom of the boxes would be completely open and just sit on top of holes cut into the floor. The holes would be located directly under my L and R front speakers and the cubes would become the L and R speaker stands.

The big advantage I see to this idea is a minimal amout of "permanent" house modification to achieve the desired goal. The house could be put back to original with much less work than some of the permanent installs I have seen. Plus the cubes should make relatively good speaker stands. I get to loose my giant sub, and the IB "subs" sit nicely under my L+R speakers which is real estate already occupied.

I think the cabinets would be heavy enough that I could just place them on the carpet over the holes and that would be it. Instant IB. Hopefully All the benefits and few of the drawbacks.

What do you think?
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Old 10-10-2008, 04:22 PM
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I think this may be the answer your question:

15) How big an opening should there be for my manifold ?

Regardless of it's Vd, any surface mounted speaker has an opening only as large as it's overall diameter. So in theory the best choice for a manifold would be an opening equal to the summed area of the diameters of the drivers. In the real-world an opening as large as the sum of the Vd's usually isn't necessary nor is it practical. The recommendation is make the opening as large as practical given the limits of stud/joist spacing or other physical considerations of the install. As a rule the recommendation is not to use an opening smaller than 50% of the summed Vd of the drivers.


Taken from the "Cult of the Infinately Baffled" FAQ:
http://home.comcast.net/~infinitelybaffled/
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Old 10-10-2008, 04:22 PM
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What you're talking about is called an 'outie' IB.

Here are examples....





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Old 10-10-2008, 06:22 PM - Thread Starter
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Wow! Thanks guys! That's a HUGE help. To think, it already has a name!

The hole I had in mind would be smaller than the ones shown in the photos. I was hoping to get away with a square cut between two joists. I wouldn't worry too much about a loss of efficiency, but I am able to imagine the cabinet acting like a tuned vented enclosure.

If the tuning of the enclosure turns out to be in my desired passband for the sub, I think that would not be so so good.

I can imagine modeling the box with vent the size of the hole I have in mind for the floor in WinISD. (Actually having my friend do it, he's the computer whiz and I am the electronics guy of the two of us) However, the port would share different airspace than the cone in actual application. Would that screw up the model? The goal is just to see if the box would have undesirable characteristics.

Thanks again for the quick and helpful feedback.
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