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Discussion Starter #1
I've been contemplating building a new sub. I'm happy with my current ported MJ-18M, but I want more on the bottom end. My current sub is tuned to 24Hz and it falls off pretty quickly below that with the high pass set at 20Hz or thereabouts to keep cone excursion in check.

I'm thinking about a IXL-18.2.2 with 2 PR from DIY cable in an 8^3 enclosure. 8^3 is about as big as I can possibly go with cabinet size. To get the low bass I'm looking for dual PR's are the only way I'm going to be able to do it. I could build another ported sub but the port length, box size, and first resonant frequency start becoming issues when I model it out. Couple things I'm not real sure on is how much mass can you get away with adding to each PR? Also in Win ISD does the mass number on the PR tab apply to each PR or both combined?

The IXL-18.2.2 is in stock at Mach 5 but their PR's are not. DIY Cable has their 18 inch PR in stock that's why I'm looking at them. I've already got the amp and EQ so I'm all set there. All told it will cost about $600 to make it happen.

I've attached some screens comparing my current ported MJ-18M compared to the IXL-18.2.2 with dual PR. Should I build it or are the gains down low not worth the bother?




 

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Discussion Starter #3
I can't answer your questions about the PR's but I do think the gains will be worth it. Any chance of tuning a bit lower?
Absolutely, as long as I stick with the 8^3 box size. That's exactly why I posted this thread.

I'm very open to suggestions and I'm not thinned skinned so fire away. :bigsmile:
 

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Discussion Starter #5
MJ-18M is in a 6^3 box. The PR shows in stock until you add it to your cart then it shows out of stock.
 

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The IXL-18 would provide an 8 db gain at 20 hz over the MJ-18M, definitely a big improvement. That's with the IXL-18 in 7 cu.ft tuned to 18 hz using a slot port 4 inches high, 8 inches wide and 33 inches long. Port air speed is good with 1000 watts input and first port resonance is a non issue. The port, sub and bracing would take up about one cu.ft. so this setup would work in the 8 cu.ft. limit that you set. This would cut your build price in half. In 8 cu.ft. with 2 PR's you gain one db at 20 hz. Something you should consider.

Jailer.JPG
 

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Discussion Starter #7
That looks real good Mike.

I've been modeling it with a slot port similar to my current one (wide narrow port) and that's where I was running into trouble with the port resonance.

So what is an acceptable port speed? Everything I've found so far when searching says to keep it under 16 m/s. The model above is upwards of 26 m/s with a 4x8 port.

I'm liking the looks of that 7^3 ported box.
 

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With a high pass filter at 14 hz to protect the sub from over excursion, the air speed is maximum 28 m/s at 17 hz, not anything you'll notice if all the corners are rounded over in the slot port. For subs port compression starts at 26 m/s, with 28 m/s you will be fine.

If you cross your sub over at 80 hz with a 4th order crossover, first port resonance can be as low as 125 hz with no effect on the frequency response. This was shown in a test Andrew did. This allows the use of ports longer than 36 inches, which is commonly believed to be the maximum length a port should be.
There was a discussion on port length recommendations at the link below that addressed these issues:

http://www.hometheatershack.com/for...ported/12042-port-length-recommendations.html
 

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Discussion Starter #9
I read through the entire thread. Good info there!

I'm kind of leaning towards doing another ported now. I just can't pass up the idea of free performance by building a slot port. The money isn't really the issue, but why spend it if you don't have to?

So a question about ports. My current sub has a single 90 deg bend in the port. It was built along the bottom and back wall. Is there any advantage to having two 45 deg bends instead of one 90 deg? I've already got an idea of how I would do the two 45's, but a single 90 would be a lot easier to build.

Decisions, decisions. :dumbcrazy:
 

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Discussion Starter #13
The port in my last build took up almost exactly .6^3 feet. Driver displacement .2 and bracing worked out to .1 IIRC. So 8^3 feet external would be real close to 7 internal once it's built.

Still trying to decide whether or not to pull the trigger. My woodworking guy on the other hand is dying to get started. I told him he could have my current one when the new one was built so he's plenty motivated to do it. :bigsmile:
 

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Discussion Starter #14
Well the project has been put on hold. Interest rates bottomed out the end of last week so we are taking advantage of the situation and re mortgaging our home. So all my extra cash is going into that and I'll have to work some more overtime to rebuild my stash of play money.

At least my house will be paid for about the same time I retire now. :T

Hopefully later this summer I can revisit this.
 
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