PA subs using Omega Pro 18's - diyAudio
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Old 25th July 2007, 01:34 AM   #1
diyAudio Member
Join Date: Jul 2007
Default PA subs using Omega Pro 18's

My band uses subs that were built by our drummer, who's a decent carpenter. Unfortunately, he's not an engineer! They are single Omega Pro 18's in a 11.1 cu. ft boxes. The "porting" is simply two 4" holes cut into the baffles. Not suprisingly, they sound like crap. I'm trying to come up with the best option to improve the situation.

Here are my options as I see it:

1) Try to tune the boxes with port tubes. Obviously, this would be the easiest from a construction point of view, but using WinISD, it's looking like it's going to be very hard to do--the boxes are simply too big. The pseudo-ports cut in the baffles now are too close to the edges of the cab.

2) Cut down the boxes into smaller boxes and tune with WinISD

3) Build one of the ported designs Eminence suggests---this would be a well-researched design, though they don't really seem to take advantage of the Omega Pro's 800 watt handling. I'd kind of rather build a tried-and-true design than have to work it all out myself---I'm not trying to reinvent the wheel here.

4) Build a vega-type folded horn enclosure---these seems to be popular for the Omega Pro, but will be difficult from a design and construction perspective. While our drummer makes his living as a carpenter, I don't seem him having the patience to precisily follow a plan for a complicated box, though you never know.

5) Buy some empty cabs---might be easiest, though I haven't found anyone selling something designed specifically for this driver (kinda surprised at that).

Which option sounds best? Any input would be much appreciated.
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Old 25th July 2007, 02:29 AM   #2
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Join Date: Jun 2004
Location: Indiana
If you want to make it cheap you could just fill up the extra space. In fact if you put both of those drivers in just one of the boxes and put a divider in between you be getting close to what you need for a nice EBS alignment. If you made the divider out of two pieces of plywood with some Styrofoam sandwiched in between you could take up as much space as needed. Plug and redesign ports as needed.

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Old 27th July 2007, 12:10 AM   #3
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Join Date: Jul 2007
For live sound, is in EBS alignment really what I want? I don't think I really need extra-deep bass response. I'd settle for just "loud".

I'm kinda waffling between a standard ported box and a 6th order bandpass.
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Old 27th July 2007, 02:15 AM   #4
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Join Date: Jun 2004
Location: Indiana
Is it an Omega18 or an 18C? If a C the "maximally flat" alignment appears to be about 5ft^3 (assuming that I have the right TS params) which would be perfect for your splitting up and would give a -5dB point at about 40Hz.

The plain jane 18 however would require you to eat up a lot more space and you would only get -5 point of about 50Hz for maximally flat. However even with that driver it appears that going up to 4 ft^3 and tuning only slightly lower than the MF tuning would get you close to 40Hz and a shelf only down about 1 dB or so it doesn't look like a major problem. YMMV of course.

Now I also noticed that only a slight improvement in Q is required to make the omega 18 behave well in a 5 ft^3 cabinet. Adding 1.5 to 2 ohms in series (coil?) is an immense help. Of course in pro audio you don't like to throw away power but on the other hand you get an extra 10Hz of output. Pick your poison I suppose.

For completeness I looked at sealed enclosures. You might get away with it in a C but the regular 18 doesn't look good.

Or you could take a completely different approach and sell the drivers to someone who wants to build bass horns. Then you could leave the boxes as is except for blocking off the ports and then install these...

Only down 5 dB at 35 Hz and each box capable of 115 dB at that frequency (much more above 50 Hz).

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Old 28th July 2007, 02:03 AM   #5
dangus is offline dangus  Canada
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Join Date: May 2004
Location: Vancouver Island
If the cabinets are too big, why not just cut them down to size? Just saw carefully to avoid the nails or screws. You can get smaller chunks of plywood from Home Depot if you don't have any lying around. Cut it a little oversized, screw/glue it to the rest of the box, then trim flush with a router, then round the edges over if you have one of those bits.

I think that's the same driver I've used house brand versions of (109 oz magnet, 4" voice coil, single spider, cast frame?). I built a couple of 1x18 in roughly 8 cubic foot cabinets, with a pair of 6" round tube ports. I built a couple of other boxes with 2x18, about 14 cubic feet since that made for a good packing size. One version used a shelf port, the other just needed a couple of round ports. With the round ports I could reach in and feel the magnets to see how hot the drivers were getting.

I think the single-driver cabinets went lower, but the lure of more efficiency and power handling won over.
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