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Enclosure Design & Construction
Transmission line: flared?
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<blockquote data-quote="ciaonzo" data-source="post: 6178849" data-attributes="member: 607015"><p>Assuming that you have a traditional line with the appropriate cross section area to suit the Sd and Vas of the driver and the actual physical line length to support a quarter of a 27hz wavelength, you're most likely unloading in the low 20's. What's happening is that the pipe is offering maximum damping to the cone at 27hz but after that, depending on how large the cross section area is in conjunction with the terminus area (the exit of the line), it will offer a varying degree support as it unloads. Going with a shorter line will only make this situation worse, you want to go the other way and make the line longer. A band-aid approach might be to reduce the terminus area by adding a temporary/adjustable board and adding more stuffing to drive Fp downward but that will be at the expense of sensitivity. What you want to do is offer the actual physical line length for the lowest frequency you wish to produce regardless of the driver's Fs. This goes against some ideals but I can tell you from experience this is extremely effective. The offset of the driver's Fs and Fp will actually produce a less volatile phase/impedance plot, and with the minimum amount of stuffing necessary to smooth out impedance, your amplifier will be in heaven. But more importantly, you will not have the problem you described.</p></blockquote><p></p>
[QUOTE="ciaonzo, post: 6178849, member: 607015"] Assuming that you have a traditional line with the appropriate cross section area to suit the Sd and Vas of the driver and the actual physical line length to support a quarter of a 27hz wavelength, you're most likely unloading in the low 20's. What's happening is that the pipe is offering maximum damping to the cone at 27hz but after that, depending on how large the cross section area is in conjunction with the terminus area (the exit of the line), it will offer a varying degree support as it unloads. Going with a shorter line will only make this situation worse, you want to go the other way and make the line longer. A band-aid approach might be to reduce the terminus area by adding a temporary/adjustable board and adding more stuffing to drive Fp downward but that will be at the expense of sensitivity. What you want to do is offer the actual physical line length for the lowest frequency you wish to produce regardless of the driver's Fs. This goes against some ideals but I can tell you from experience this is extremely effective. The offset of the driver's Fs and Fp will actually produce a less volatile phase/impedance plot, and with the minimum amount of stuffing necessary to smooth out impedance, your amplifier will be in heaven. But more importantly, you will not have the problem you described. [/QUOTE]
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Transmission line: flared?
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