I have been modeling for days. I purchased one of Erich's 3.5 subwoofer flatpacks. (Awesomely constructed by the way.) The problem I am running into is location and length/width of the aeroports I want to use from partsexpress.
From the front of the chamber to the interior bracing there is only about 10 1/2 inches of clearance. For a 24hz tune, I would need 15 inches in port length, which is too long. Winisd says that 2 two inch (0.047 meters in Winisd) Precision port flared ports will generate a vent mach of 15, which is acceptable to winisd, but higher than the more standard 10 that I read about. The precision port website calculates that I will need 8.5 inches of length for this tuning.
I know that these ports sizes are considered small, but they seem to model ok. Any thoughts or recommendations?
For that sub, I would use nothing less than one four inch port, or two 3 inch ports. There is no way that you will be happy with the two inch ports.
(Bill I have bought your plans the THTs. Love em', just couldn't the get the wife to love them as much yet so the Lab-12 is going to this smaller project. I'd love to fit two ports, but the lengths are pretty long at about two feet each.)
I found a way to fit a 4 inch port around through the bracing. I can fit a one 4 inch port 13 inches (about 27 hz) or 15-16 inches (about 25 hz).
25 vs 27 hz.docx 94k .docx file
I think I favor the 27hz tuning due to increasing the sensitivity and output about 27hz or so compared to the lower 25hz tuning. There is, however, a steeper roll-off so less deep bass output. I have read the precision ports tend to increase output by about 3 decibles at the tuning frequency compared normal ports, but that could be marketing.
The 27hz tuned port will fire out the left side of the cabinet. I actually like that because my daughter is less likely to try to stick things inside and it fires about 18 inches away from the corner in a very large open layout house. The 25hz tuning would fire out the front baffle directly below the driver.
This have been a great experience and motivates me to build my own cabinets now that I see tradeoffs are always involved any other way.
Am I on the right track here? Thanks for anyone's responses!