Adjusting tuning frequency of square ported box |
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outkast
Registered User Joined: 23 September 2010 Status: Offline Points: 66 |
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Posted: 14 July 2016 at 3:59am |
I have a 18inch reflex bass bin with a square port, dimensions shown in image below. Internal box dimensions are 565mm wide, 615mm high, and 624mm deep, giving a net internal volume of 195 litres (excluding volume of driver and port).
From my calculations the box has a tuning frequency of 42Hz. I am wondering if anyone can tell me how I might go about changing the frequency - I would like to bring it down to 36-38Hz. Everything I found online had solutions for round ports only. TIA. |
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fatfreddiescat
Young Croc Joined: 15 October 2010 Location: N.E.Wales Status: Offline Points: 1081 |
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Make the port longer or decrease the area of the port - ie line the sidewalls with extra ply.
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Meat
Old Croc Joined: 05 June 2009 Location: Manc Status: Offline Points: 1514 |
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Don't trust the calculations. We're talking about fine adjustment so you need to be doing impedance measurements. Measure it. Add a bit of length to the port (or close the port up a bit). Measure again.
Calculations can get you where you want to be within about 5Hz but for the last bit you really need to be measuring. |
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Don't test the champignon sound
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odc04r
Old Croc Joined: 12 July 2006 Location: Sarfampton Status: Offline Points: 5483 |
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WinISD is pretty easy to use and will calculate a square or round port as required.
But what matters is the port area and length. So in theory a round port of equal area to a rectangular one of the same length will perform identically. However in real life, it is never that simple. Different shapes have different drag effects on air movement, and distance from enclosure walls plays a factor. Rectangular ports often share a wall with the cabinet making that effect even more pronounced. |
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