I'm building a BR using Ampslab's recommended 25 liter enclosure with the Silver Flute W20RC38-08. He calls for a
2" diameter port 6 1/2" in length. My cabinet will be 9" deep or 7.5" internal. To leave plenty of clearance from the back wall can I use two 3 1/4" ports and accomplish what I need to? Thanks for any suggestions.
2" diameter port 6 1/2" in length. My cabinet will be 9" deep or 7.5" internal. To leave plenty of clearance from the back wall can I use two 3 1/4" ports and accomplish what I need to? Thanks for any suggestions.
That's terrible tuning for a BR IMHO. The default tuning on Madisound's page for this driver is way better.
jeff
Hmm, in dia., (2) 3.25" dia. = 3.25*(2)^0.5 = 4.6" eff. dia., ~2.3x greater, so their length will be way longer. You need to go enough smaller that the summed area is significantly < a 2" dia. area to shorten the vent, which in turn may cause vent compression at high SPL.
Regardless, the vent starts on the face of the baffle, so 9" - 0.75" rear plate thickness = 8.25" - 6.5" vent = adequate gap to rear wall IME, but if still paranoid for whatever reason you can cut the vent at a > ~30 - 45 deg angle to mimic a bit of a flare relative to the cab's walls. Technically, the slant cut will raise tuning a little, but the 'fanning' tends to lower it a bit, so audibly no obvious change IME and in theory tends to allow higher power before chuffing.
edit: seems area is what 'we' are comparing, so 2^2*pi/4 = ~3.14"^2, 4.6^2*pi/4 = 16.62"^2 or ~5.29x larger.
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Your port appears to be tuned to around 38Hz. To achieve the same frequency using two ports you need to reduce the diameter to 32mm (1 1/4") and the length to 5".
Net 42 liters provides a cleaner and less resonant bass quality for this driver.. I've worked with SF models for about ten years, many acoustic measurements, boxes and test boxes, modeling, etc... I'm converting 2 speakers sets with 45 liter boxes that hold 2X SF20RC38-08 to 1 woofer per box.. Depends what your going for I guess, but I'm seeking the lowest coloration as possible.. The box sim has a little added port and box leakage and some absorption..
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Think of it this way.
With a single port - if you increase the cross sectional area, to maintain the tuning frequency, you must lengthen the port.
So with 2 ports of the same cross sectional area, both must be longer as the cross sectional area has doubled by having 2 ports.
With a single port - if you increase the cross sectional area, to maintain the tuning frequency, you must lengthen the port.
So with 2 ports of the same cross sectional area, both must be longer as the cross sectional area has doubled by having 2 ports.