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JTR Noesis 3TX Port Geometry
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<blockquote data-quote="David Morison" data-source="post: 209131" data-attributes="member: 2076"><p>Plus one to everything Art said of course.</p><p>Remember also that a shelf vent can behave as if it's larger than the physical shelf, due to 3 out of the 4 walls continuing on beyond that.</p><p>So if you were comparing the predicted vent length from a modelling program like WinISD etc, you'd need to adjust that expected length downwards.</p><p>Using the alternate End Correction factors <em><a href="http://www.avsforum.com/forum/155-diy-speakers-subs/1490258-calculating-subwoofer-port-length-not-so-simple.html" target="_blank">in the first post here</a></em>, a rough estimate of something like the 3TX (30l net internal tuned to 73Hz) the actual shelf length required might be as low as 3cm; ie only a double thickness of the timber. Even if the net internal volume of the cab is smaller, or the tuning lower, the required length is still short - 25l to 70Hz would need 15cm of shelf, compared to the 39.2 predicted by WinISD.</p><p></p><p>HTH,</p><p>David.</p></blockquote><p></p>
[QUOTE="David Morison, post: 209131, member: 2076"] Plus one to everything Art said of course. Remember also that a shelf vent can behave as if it's larger than the physical shelf, due to 3 out of the 4 walls continuing on beyond that. So if you were comparing the predicted vent length from a modelling program like WinISD etc, you'd need to adjust that expected length downwards. Using the alternate End Correction factors [i][url=http://www.avsforum.com/forum/155-diy-speakers-subs/1490258-calculating-subwoofer-port-length-not-so-simple.html]in the first post here[/url][/i], a rough estimate of something like the 3TX (30l net internal tuned to 73Hz) the actual shelf length required might be as low as 3cm; ie only a double thickness of the timber. Even if the net internal volume of the cab is smaller, or the tuning lower, the required length is still short - 25l to 70Hz would need 15cm of shelf, compared to the 39.2 predicted by WinISD. HTH, David. [/QUOTE]
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