| Questions about box tuning F3, F10, etc. [message #18953] |
Tue, 03 October 2006 06:01  |
Bill Epstein
Messages: 1088
Registered: May 2009
Location: Smoky Mts. USA
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Illuminati (2nd Degree) |
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Been looking at Win ISD, specifically a 4 cu ft box for the 2226J tuned to 40 Hz. WinISD has this box (32 3/8x20 3/4x13) down 3dB at 56 Hz, down 6dB at 40 Hz and down 10 dB at 33 Hz. Is the tuning frequency always F6? I thought it was F3? Would this larger box be less or more boomy on a suspended floor? Or would the 4Pi Pro 2.5 cu ft box be better? Finally, I know there's a post somewhere about the size of a circular rather than a rectangular port for the 4Pi but I searched and can't find it.
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| Re: Questions about box tuning F3, F10, etc. [message #18954 is a reply to message #18953] |
Tue, 03 October 2006 08:43  |
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Wayne Parham
Messages: 18691
Registered: January 2001
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Illuminati (33rd Degree) |
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A bass-reflex cabinet uses the box as a Helmholtz resonator, which doesn't really care what shape the port is. If it is very long and/or thin in one dimension then standing wave issues can come up, but baring that, the port can be circular or rectangular to the same effect. As for response, the Helmholtz frequency doesn't set the f3, f6 or f10 points but the interaction of the Helmholtz frequency, box size and electro-mechanical parameters sets the curve. It's an interaction between two resonators that sets system response, lower cutoff and Q. Experiment a little bit with WinISD, changing box size and tuning frequency and you'll see what I mean. If the box size is fixed, say your 4.0ft3 example, then box tuning between 35Hz and 40Hz gives the 2226 a nice flat curve. Set the Helmholtz frequency lower and the curve looks more like a sealed box, having a slower rolloff but a higher f3. Set the Helmholtz frequency higher and the response becomes underdamped, having a peak near the box frequency. Also try it with smaller and larger boxes to see what that does to response. You might be interested in the post called "Response curves of closed vs. vented systems", which shows various alignments and the response curves that result.
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| Re: Now a question about all these ports from JBL [message #18955 is a reply to message #18954] |
Tue, 03 October 2006 12:33 |
Bill Epstein
Messages: 1088
Registered: May 2009
Location: Smoky Mts. USA
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Illuminati (2nd Degree) |
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Look at the 'equivalent duct tube and ID' column. Do they really mean the 2226 has to have 2 ducts that size? Look at the double 2226 enclosure. We all know the 4648 cabinet has 2 ducts, not 4. And a 2245 subwoofer needs 6 ducts? Can't figger this one out.
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