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Old 21st February 2013, 02:30 AM   #31
jbell is offline jbell  United States
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4 sided manifold for the IB. 2 magnets in and 2 magnets out. push pull.
You have the perfect place to put the manifold, it's the 'tried and true' approach others have used for organ.

As much as I'm a fan of TH's, etc... after seeing your pictures, I would have a very hard time not going IB.
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Old 21st February 2013, 06:05 AM   #32
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Quote:
Originally Posted by just a guy View Post
Still not counting on any room gain at all? That response might sound boomy in-room if you don't eq the low end down. If I were you I'd measure the room's response before going too much farther.
To be honest I wouldn't expect much room gain in a room that is about 50,000 cubic feet that has an entire wall open to another room that is probably another 10,000 or 15,000 cubic feet which is open to the stairway down to the entry way... I am no expert though so I could be all wet.

As we get closer to cutting wood (in other words as funding becomes available) I will see about nailing down the room response. If I can't get good measurements I can always knock up a big box with a couple of drivers in it and see what I get. I presume that one of those Behringer measurement mics with some freeware would be all I would need to get a close enough idea of the room response.
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Old 21st February 2013, 06:30 AM   #33
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Quote:
Originally Posted by jbell View Post
4 sided manifold for the IB. 2 magnets in and 2 magnets out. push pull.
You have the perfect place to put the manifold, it's the 'tried and true' approach others have used for organ.

As much as I'm a fan of TH's, etc... after seeing your pictures, I would have a very hard time not going IB.
I like the idea of IB for its elegance and potential for low distortion. What scares me is all of the reading I have done which indicates that guys end up needing four or more such drivers just for their little living room. It makes me wonder about filling a room literally and order of magnitude larger.

Interestingly my recollection of the original Dayton IB was that it had a higher Qts than the current one which seems a bit on the low side for the application. One possible approach would be IB using the FI 18IBs which have slightly higher Q and twice the x-max. They are about $100 more per driver last time I checked but four drivers should reach 123dB at 16Hz at 1 meter.

If I got the Datons and they proved inadequate they could always be used as very capable woofers for the 16' and 8' ranks on the manual divisions so getting some to try would be low risk.
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Old 21st February 2013, 01:17 PM   #34
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Originally Posted by mashaffer View Post
To be honest I wouldn't expect much room gain in a room that is about 50,000 cubic feet that has an entire wall open to another room that is probably another 10,000 or 15,000 cubic feet which is open to the stairway down to the entry way... I am no expert though so I could be all wet.
I've got no experience with very large rooms either so I ran the numbers. Pressure gain is not as strong as I expected.

This simulation accounts for pressure gain and estimated power response of the 3 nearest boundaries, and suggests a bit more gain than a 1 pi simulation in Hornresp.
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File Type: gif Room1.gif (11.4 KB, 90 views)

Last edited by just a guy; 21st February 2013 at 01:19 PM.
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Old 22nd February 2013, 01:29 AM   #35
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So, regarding the manifold IB, I was wondering what effect the manifold would have on the parameters/alignment of the woofers. It seems that just like the rear chamber has an effect the manifold ought to as well. I would like to hear from anyone who has investigated that.

I thought that maybe I would try to model it so I set up Hornresp with a large sealed rear chamber in a short straight horn with offset drivers as my best first try at modeling it. Of course it doesn't model the two drivers firing into each other but it was the best thing I could think of off of the cuff. Is there a better way to model this.

Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

Would you place the manifold on the floor of the chamber close to the outside wall at the front of the chamber or would it be better to place it in the back outside corner of the chamber. The ambiance of the rear of chamber location would not be a bad thing in the case of an organ but I am wondering if the increased output would be negated by the increased distance (about 10 feet) and absorption in the chamber. Although the chamber walls are bare plaster and brick...

P.S. I also noted that by opening up the manifold into a Vee like shape (opening larger than the back of the manifold) it tames the huge spike in the output above 100Hz.
Attached Images
File Type: png ManifoldParameters.png (8.0 KB, 176 views)
File Type: png ManifoldSchematic.png (11.2 KB, 98 views)
File Type: png ManifoldResponse.png (10.4 KB, 102 views)
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Last edited by mashaffer; 22nd February 2013 at 01:37 AM. Reason: P.S.
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Old 22nd February 2013, 06:26 AM   #36
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Hmmm... Traditional MLTL seems to give one a lot of control over the slope. In playing with this alignment I discovered that the enclosure is very tunable so that the slope can easily be matched to the actual room acoustics. That is an attractive feature and two enclosures with Dayton IB15 may be sufficient.

Click the image to open in full size.
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File Type: png IB15MLTL.png (28.4 KB, 104 views)
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Old 22nd February 2013, 04:22 PM   #37
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Originally Posted by mashaffer View Post

I thought that maybe I would try to model it so I set up Hornresp with a large sealed rear chamber in a short straight horn with offset drivers as my best first try at modeling it. Of course it doesn't model the two drivers firing into each other but it was the best thing I could think of off of the cuff. Is there a better way to model this.

Would you place the manifold on the floor of the chamber close to the outside wall at the front of the chamber or would it be better to place it in the back outside corner of the chamber.

P.S. I also noted that by opening up the manifold into a Vee like shape (opening larger than the back of the manifold) it tames the huge spike in the output above 100Hz.
The way you model seems correct.
"V" shapes do seem to be less peaky than parallel wall plenums.

If you do decide on IB, I'd suggest flush mounting at the front of the chamber for a smoother frequency response.

Seems that the chamber itself could be used for the outer walls of a horn, you would only need to build a small portion of a rather giant horn.
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Old 24th February 2013, 12:32 AM   #38
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Hmmm... Believe it or not I never thought of doing a corner horn in the chamber... (need a :scratchchin: emoticon here). The walls are about 8 or 10 feet I suppose. I would have to cover the windows I suspect. Will have to cogitate on that a little bit and see how one might model and build such a beast.

Click the image to open in full size.

When I first considered IB I thought of running a floor to ceiling manifold exhausting into this attic opening in the ceiling of the left hand chamber.

Click the image to open in full size.

In any case I am concerned about the cracking plaster. My fear is that a large amount of bass energy could bring the house down - so to speak. For this reason I am inclined to stick with sub-woofers at the front of the chamber firing directly into the sanctuary space to avoid damage.
Attached Images
File Type: png SmAttic.png (399.8 KB, 68 views)
File Type: png SmLeftChamber2.png (963.6 KB, 67 views)
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Old 24th February 2013, 01:12 AM   #39
jbell is offline jbell  United States
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yea -- respect the glass... it tends to rattle when exposed to 16hz.....
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Old 24th February 2013, 10:28 PM   #40
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Would be rather an expensive mistake to take one of those out. What I will probably end up doing as soon as I get a VPO computer back on line is to build a 30Hz sub using a 15" that I have on hand and move it around to different locations to do some experimentation (limiting myself to 16' pedal stops).

The only place I see where there is enough contiguous wall space on both sides of a corner for a corner horn is in the choir loft and that might be a bit painful for the choir members. Similarly firing through the side openings of the chambers into the loft for resonance purposes would be problematic. So at the front of a chamber or on the floor in the corner at the front of the sanctuary are probably the only real options.

As to taking room modes into account my current thinking is to design the subs for flat into 1-pi space and use eq to reduce the low bass output if needed rather than design compensation in and possibly have to boost. My thinking is that a simple 1st order filter at the input of the power amp should be adequate to handle any boominess if it shows up and cutting the low bass frequencies will conserve power amp headroom as well as reduce any low frequency noise as opposed to running amps flat or boosted. This also increases max SPL as I get a bit more output for the same x-max.
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