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Discussion Starter · #1 ·
I currently have a ~88.5 liter sealed Shiva. I was considering porting the enclosure to add a few db, and in modeling I found that a 4" x 15" tube would tune to 25hz and basically bump my response curve 3db all the way across. The old "adire alignment" is a 3" port tuned to 20hz, but winISD shows a lot of port speed at this tuning. ( > .3 mach) Sadly I ordered the 4" port before I found the old white papers with the suggested shapes. Am I making a mistake using the 25hz tuning? I use it almost 100% for HT, and i believe my PE plate amp has a rumble filter (built this thing years ago).
 

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I have 2 170lt shiva sonotubes tuned to 17hz. I have a 4 inch port, Winisd shows vent mach of 0.22 (I think the target is <0.16) I read in the help section that too much port air speed causes the sub to 'whistle'. I've never heard anything like that from mine.

I think the port air speed is also related to how much power you're throwing at the driver, when I change the nominal power to 230w (from 650w) the port air speed graph looks a lot better.

Where did you find the shiva white papers? I looked for them for about an hour yesterday with no luck. I found a set of t/s parameters for the Shiva but I don't know what voice coil wiring they relate to.

Hakka.
 
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Discussion Starter · #3 ·
I received my 4" port yesterday. I think I will take my son camping in it this weekend, or maybe use it to launch ballistic missiles.

I am trying to think of a way to put a 3" pipe inside the 4" to test the differences between 20 and 25hz tuning.
 

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Stephen,

Use your router to cut a donut, make the outside a little small, then some speaker gasket around the outside of the donut, and force it into the 4" port. Speaking of ballistic, don't crank up the bass or you may impale someone with the 3" tube.

Paul
 
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Discussion Starter · #5 ·
So it's finished. On the way, I realized that you cannot put a 15.75" port inside an 18" (O.D.) box, there was only .5" clearance. I had to adjust the tuning to almost 26hz. I also discovered using unibox (awsome program btw) that my PE plate amp doesn't respond much below 20hz anyway, so this made he decision easy. The cone never gets to full extension even vented, and I get 8-10 db more output from 25-40hz or so. This has caused an unforseen problem though, now I am having trouble matching my levels! I had run my sub at -3db and it measured about 5db hotter than the rest (I like that). Now I am down to -12 db and it is still >10db hot. I guess I will have to lower my gain on the amp to about 25% and see if I can get it more in line....
 

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So it's finished. On the way, I realized that you cannot put a 15.75" port inside an 18" (O.D.) box, there was only .5" clearance. I had to adjust the tuning to almost 26hz. I also discovered using unibox (awsome program btw) that my PE plate amp doesn't respond much below 20hz anyway, so this made he decision easy. The cone never gets to full extension even vented, and I get 8-10 db more output from 25-40hz or so. This has caused an unforseen problem though, now I am having trouble matching my levels! I had run my sub at -3db and it measured about 5db hotter than the rest (I like that). Now I am down to -12 db and it is still >10db hot. I guess I will have to lower my gain on the amp to about 25% and see if I can get it more in line....
Yeah 25% on the gain sounds alright. My plate amp is usually set to around 20-25% gain because it seems to blend in best with the rest of the HT.
 

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Greets!

FYI: Keeping vent mach < ~0.5% is sufficient to keep vent noise inaudible. Very low numbers typically cause peaking at Fb and excessive pipe harmonics due to its length that will comb filter with the mains output. This distortion can sound euphonic to some if in very close proximity to the mains, like a '50s Jensen Ultraflex/Onken vented alignment, but distracting if the sub is fairly far away, especially if tucked away in a corner.

GM
 
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