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Accurately simulating Fb (15" B&C Bass Reflex)
Accurately simulating Fb (15" B&C Bass Reflex)
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Old 3rd February 2017, 08:58 PM   #1
chips and palsa is offline chips and palsa  United States
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Default Accurately simulating Fb (15" B&C Bass Reflex)

Hey Everyone, its been a while since posting but yet again, its time to fire up the saw and bust out the Loctite PL!

I was able to quickly sim a small box for a 15TBX100 in hornresp based on my desired performance goals:

- Relatively small (18x20x22/130L external)

- Relatively loud (if HR is to be believed, just over 125db in half space through most of desired passband at Xmax and 800W)

- Relatively low (F3 Just below 40Hz)

I have used Solidworks to get a 90% model but would like to verify once bracing and handles are added. Volume of the driver is provided on the data page so once I have a further completed version, I will post the results. The port is tapered on both ends (nearly double the CSA of center section) to achieve particle velocity at port exit of 20 m/s maximum before a 4th order Butterworth HP filter is applied.

MY QUESTION IS: How can I do a basic test to check that the box matches the sim once I build it? Or rather, how can I get the sim more accurate.
I had designed a box for my LAB12 subwoofer, approx. 60L net and a linear 2 port that when tested for Fb (changed frequency on a tone generator in 1Hz increments until excursion minima was found) measured 4Hz less than the design Fb of 35Hz.

It would seem that the cabinet can be completely glued except for the last port section which can be held in by screws along with the side panel of the enclosure so that the box could be measured, disassembled, and adjusted as needed.

I am just looking for something I can do to make sure the simulation (mainly just Fb) is spot on when verified the first time. Is there any way to tell the effects of adding expanded foam lining to the cabinet walls?? I plan to get the volume measurements simulated very accurately so it seems that other factors (slot port aspect ratio, damping material) will be the main culprit for mismatched Fb values.

Thanks everyone!
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Old 3rd February 2017, 09:26 PM   #2
snappyturtle is offline snappyturtle  United States
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an impedance sweep will tell you where you are re: tuning. dampening is more of a guess and check sort of thing outside of basic lining.
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