LLT Subwoofer -WinISD design help - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 9 Old 06-17-2019, 01:14 AM - Thread Starter
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Question LLT Subwoofer -WinISD design help

This is a first time build using UM18-22 powered with Inuke6k DSP.
Planning to build 2 to go behind the AT Screen

calling the pros & experts, please validate attached Specs and graphs.

Box Dimensions: 20" x 30" x 64" (DxWXH)
Volume at 19 cu.ft tuning at 14 Hz

Ports: 2 @ 3" X 8.875"; Port Length: 34"

1st PR came to ~198 Hz

The Box design with Port and corresponding graphs are attached.

Thank you for the advice..
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Name:	Cone Excursion20-Vents2at 3by8.875 length34-1PR 198hz.jpg
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Last edited by SNcube; 06-18-2019 at 09:50 PM.
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post #2 of 9 Old 06-17-2019, 04:43 AM
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Use only 85% of the value given in WinISD, not the full 34", so 28.9". Then a you will need to subtract 3" more inches from the vent, with it exiting on a 90 degree angle the height is added to the vent length. 26" will be close to the end result, but with the shorter port you just added more volume, so the tune just got lower with the 26" vent.
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post #3 of 9 Old 06-18-2019, 02:05 PM
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If vent length only ends up being 26”, id increase the cross section to get it back up to 34”
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post #4 of 9 Old 06-18-2019, 03:56 PM
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model as a single port, not two.
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post #5 of 9 Old 06-19-2019, 05:34 PM - Thread Starter
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Here's the new layout.

I modified the WinISd numbers with the exact (close enough) interior volume of 16 cuft and port tuning @14Hz. I got a port length of 39.5" with 1PR @ 171Hz.
When I lowered the tuning to 13Hz, the port length increased to 46.6" (which I can accommodate) but the 1PR dropped to 144Hz. ( I read some where that it should be above 160Hz. So, I decided to leave the tuning at 14Hz.

Gentlemen, am I on the right track?

@Red Five , I changed the port orientation (see attached). but what is the theory behind using 85% of prescribed port length?
@SteveCallas , thanks, Can you please check the new layout?
@notnyt , thank you. I changed it to single port 3"x 17.75"
@LTD02 , @eng-399
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post #6 of 9 Old 06-19-2019, 05:46 PM
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post #7 of 9 Old 06-19-2019, 05:54 PM
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I do not have sims handy at this time, but WinISD is off about 15% when calculating slot ports. The other option is model in Hornresp which I would if it were handy

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You can always turn it down, but you can only turn it up so much (before you run out of power, excursion or structural integrity).
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Last edited by Red Five; 06-19-2019 at 05:59 PM.
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post #8 of 9 Old 06-19-2019, 06:04 PM
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One other note, you are over 48"s so standing waves in the box are now a thing to consider. Pickup a pillow stuff if over that middle brace.

Stormbreaker | Wisconsin Home Theater Meet Thread | B.M.D. (in progress)
You can always turn it down, but you can only turn it up so much (before you run out of power, excursion or structural integrity).
7.1.4 | Yamaha A3070 | Crown XLS 1502 | iNuke 3000 DSP | 2x Aphex 124A | 2x Bic EV15 | 7x Bic FH6 LCR | 2x Bic FH65-B | Sub 21" Stormbreaker | Epson 5010e | 120" DIY AT Screen
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post #9 of 9 Old 06-20-2019, 04:40 AM
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I would shrink your FR to 10-100hz when modeling to see more detail. I would never use a 14hz highpass filter on a 14hz tuned subwoofer, drop it much lower.
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