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Discussion Starter · #1 · (Edited)
EDIT: Final design is 11.6 ft^3 tuned to 14Hz (see post #8)

I'm about to start building two Tempest-X2 subs to fit behind my screenwall. Depth and width are limited, but height isn't, so they need to be towers to have any large volume.

After running a few WinISD sims, I've settled on the following for reasonably flat FR above 20Hz and decent SPL from 16-20Hz: 12.6ft^3 external, 11.2ft^3 net internal tuned to 18Hz (8" port roughly 32" long). Both will be powered by one Crown K1, 550W into each sub. The WinISD sim below models 11.2ft^3, 18Hz tuning, 550w, 13.5Hz 4th-order high-pass filter and the Crown's 8Hz 3rd-order high-pass filter.

The CAD drawing below shows my rough draft design. External dimensions are 67.75 x 23.75 x 16.25 inches.

I have the drivers, and hope to start building boxes in a week as soon as I can get materials. A recent blizzard might delay my schedule, depends on how soon the ice & snow melts.

Any obvious problems? Is the ring in the port brace good enough for a flared end? There's not much room for a bigger ring.

Dan

tempx2-winisd.gif
tempx2-cad.png
 

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My impression is it looks good:T I'd probably drop the tuning closer to 16-17hz using that hpf setting: it will allow the driver to dig a bit deeper and move the excursion occurring below tuning a bit lower in amplitude, that is, if the 1st port resonance is acceptable. Otherwise, I'd raise the hpf a hz or two.
 

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If you are happy with that size, go for it. Those are large cabinets though and you won't give up much to build them significantly smaller.

Kevin Haskins
Exodus Audio
 

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Discussion Starter · #4 · (Edited)
Yeah, after a certain size, big changes in the box design seems to have relatively small effect on the output. Below are 3 very different size/tuning designs: purple is 7cf/19Hz, white is 11.2cf/17.5Hz, yellow is 15cf/15.5Hz. Any lower tuning at those sizes will give a larger dropoff from 20-50Hz than I want. Wish I could model room gain (3000cf sealed room), maybe the in-room dropoff won't be as bad.

This excursion plot is without any hp filter except the amp's builtin 8Hz hp. What about the excursion blowing up below 15Hz independent of box tuning? Does that really need a hp filter?

Dan

tempx2-sweep.gif
 

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If you are going to tune in the 18hz+ range, you will want to go with a highpass filter for safety. If you drop the tune below 15hz, you should be fairly safe without one.

How far will you be sitting from these subwoofers?
 

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Discussion Starter · #6 ·
If you are going to tune in the 18hz+ range, you will want to go with a highpass filter for safety. If you drop the tune below 15hz, you should be fairly safe without one.

How far will you be sitting from these subwoofers?
Thanks. Distance will be 10 feet.


Dan
 

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Discussion Starter · #7 ·
Just remembered I haven't included any fill in the simulations. That's modeled by Qa (100=none, 50=min, 10=norm, 5=heavy), right?

Dan
 

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Discussion Starter · #8 · (Edited)
Good news: finally had a few days of nice weather so I was able to finish all the cutting and routing

Bad news: another big storm coming today that may turn into an ice storm--if I don't post for a few weeks, it means I've got no power :sad:

After a lot of reading and simulations, I decided to make these an LLT. Final design is 11.6 ft^3 net internal tuned to 14Hz (6" x 29" effective length port), no subsonic filter.

I ran flare-it using the rms velocity numbers from WinISD, and it showed no flare needed for 20Hz and up. Since I have a 1/2" roundover bit, I gave both ends of each port a 1/2" flare, and adjusted the length to give 29" effective length.

Pictures below show test-fitting the pieces, and one assembled enclosure. I need to wait for nice weather before I can assemble the second enclosure and clean up the edges with a trim router and sander.

The last picture shows my free circle cutting jig I like to use for circles less than 10" diameter. I attached a piece of 3/4" plywood to my router base and then screwed it to 2 workbenches. I measure for the circle radius and drill a hole in the plywood, then pivot the work piece while the router stays fixed.

I can't imagine building an enclosure 2-3 times the volume of these. They're nearly refrigerator size and weight!

Dan
 

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Looking good. You seem to have a solid plan. You're modeling seems to imply that you'll be safe with no dedicated HPF. Just play it safe when you first fire them up and if you think you may need one after using them for awhile, add it.

One thing. Since your enclosures are very tall you can get a large resonance in the top of the subwoofer range. I'd recommend stuffing a cheap poly pillow or 4 into the top of the enclosure around the port. It should help to cut down on that resonance.
 

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Discussion Starter · #12 ·
Whoo, we got .4 inch ice coating but didn't lose power! :clap: But there's several inches of snow on my driveway (on top of ice) that will delay any outdoor work by at least a week...

I'm hoping these tall towers behave similar to a tall sonosub. The 90-120Hz 1/2-wave top/bottom resonance predicted for sonosubs doesn't show up in reality with the top stuffed and some think the small area of the top cap reduces the resonance magnitude to below audible.

Boxnotes shows a 102Hz top/bottom resonance for my towers, and a slightly higher resonance between the driver/top. I've got a giant full roll of polyester batting (16oz per yard) left over from my theater build, and I did pack a bunch into the top of the first tower during assembly.

I plan to test the first tower before assembling the second and will try to measure tune/impedance vs sim plus check for resonance.

All dimensions are the same as shown in the cad drawing in post #1, except for the port. Outside size is 23.75 W x 16.25 D x 67.75 H. They will just barely get past my screenwall framing, but once in position will have 4 inches between the driver and fabric covering the screenwall. Don't forget the clearance in front of the driver, it moves!

Dan
 

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Discussion Starter · #13 · (Edited)
Got the Speakon connector and driver wired and installed today. Had about an hour to play with it. No major problems--tiny bit of cabinet buzz in one spot so I'll add more glue and a strip brace there.

First REW sweeps look pretty good to me. Sub was near (3ft from) it's final location, and the mic was at listening position. The sound card unbalanced output was connected directly to the amp balanced input, and with SPL calibrated to 100dB. Still plenty of headroom there. I use an individually calibrated mic/preamp from ETF Acoustic.

tempest-x2-prelim-rew.gif

Things to note: 11Hz bump is where sim shows excursion takes off. Zero cabinet resonance at 102Hz (predicted top/bottom resonance). I'm not worried by the big dip at 79Hz, as that doesn't show up when I test my mains (12" high-excursion driver) at the final location. I've got serious room gain starting at 25Hz.

I didn't try to push for max spl today, but did push to 105dB. The sweeps that started at 4Hz had crazy amounts of excursion, but never heard any sounds of strain from the driver. It was enough to make lights flicker, rattle the house, etc. Can't wait to get two of these up and running!

Seriously, I'm really interested in how these will actually sound with music and HT LFE.

Dan
 

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Got the Speakon connector and driver wired and installed today. Had about an hour to play with it. No major problems--tiny bit of cabinet buzz in one spot so I'll add more glue and a strip brace there.

First REW sweeps look pretty good to me. Sub was near (3ft from) it's final location, and the mic was at listening position. The sound card unbalanced output was connected directly to the amp balanced input, and with SPL calibrated to 100dB. Still plenty of headroom there. I use an individually calibrated mic/preamp from ETF Acoustic.

Things to note: 11Hz bump is where sim shows excursion takes off. Zero cabinet resonance at 102Hz (predicted top/bottom resonance). I'm not worried by the big dip at 79Hz, as that doesn't show up when I test my mains (12" high-excursion driver) at the final location. I've got serious room gain starting at 25Hz.

I didn't try to push for max spl today, but did push to 105dB. The sweeps that started at 4Hz had crazy amounts of excursion, but never heard any sounds of strain from the driver. It was enough to make lights flicker, rattle the house, etc. Can't wait to get two of these up and running!

Seriously, I'm really interested in how these will actually sound with music and HT LFE.

Dan
Looks good.... nice construction and the measurements look promising.

Kevin Haskins
Exodus Audio
 

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Discussion Starter · #15 · (Edited)
Thanks Kevin, I'm happy with it so far.

Finally had a day with temperature above 40F, so I assembled the second enclosure. This pic shows the strip braces and extra blocks for the mounting screws. The first enclosure had all of these except the two strips on the top panel.

assemble-2nd.jpg

On the first assembly I used lots of clamps & weights but no screws, just brad nails. This time I used screws and it went together faster and tighter (more glue squeezed out).

Just need a couple more days over 40F to prep, prime, and then paint flat black.

Dan
 

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Discussion Starter · #16 · (Edited)
I finished painting these on 2/19 and then they sat outside my theater until I got around to installing this weekend. Good news is they fit behind the screenwall (barely!), no rattles and initial measurements look great down to 8Hz.

Bad news is the 76-78Hz dip at my listening position is a real room problem. I measure full level at the floor, but 3ft up and that frequency disappears. It's such a narrow dip that it might not be noticeable with real material. I haven't done any listening yet since I just finished initial calibration. I hope to go through some familiar material this week.

tempest-x2-all-listen.gif

Dan
 

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I finished painting these on 2/19 and then they sat outside my theater until I got around to installing this weekend. Good news is they fit behind the screenwall (barely!), no rattles and initial measurements look great down to 8Hz.

Bad news is the 76-78Hz dip at my listening position is a real room problem. I measure full level at the floor, but 3ft up and that frequency disappears. It's such a narrow dip that it might not be noticeable with real material. I haven't done any listening yet since I just finished initial calibration. I hope to go through some familiar material this week.

Dan
Is that measurement with the main speakers running a test-tone too? If not.... that may fill in your hole. Also... if you are crossing it over around 60Hz or under it may not make much difference.

Kevin Haskins
Exodus Audio
 

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Discussion Starter · #18 ·
Is that measurement with the main speakers running a test-tone too? If not.... that may fill in your hole. Also... if you are crossing it over around 60Hz or under it may not make much difference.
I need to check tomorrow, but I think it was sub only. The crossovers weren't set consistently (front full w double bass, center/sides 80, rear 100), so I need to clean that up and measure sub+mains. If necessary I can definitely fix the dip by hooking up my old sub on the back wall.

After listening to several music and movie clips, I haven't found any that are less than amazing. The best part was playing LFE heavy scenes from "The Haunting" and "War of the Worlds" for my wife who asked if I had moved the bass shakers from the bottom of the seats to the back. Nope, they were turned off! The subsonics were hitting back, front, legs, feet, everywhere!

I'm gradually inching up the volume (pod race 110dB measured, WotW vol at -12) and haven't heard any hint of strain. I wouldn't want to listen much louder than this by myself, and will usually stay below -15 with others around, so my limit will be reached before the Tempest's.

All the long hours were worth it when you experience something that you never knew was there, like feeling the subsonic PUNCH the first time the energy beams are fired in WotW! Looking forward to feeling all of the soundtrack from now on.

Dan
 
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