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<blockquote data-quote="brad.farmer" data-source="post: 217661" data-attributes="member: 547961"><p>FINAL POST (to the delight of many). My original post was:</p><p></p><p>"A ported box is almost always louder than a sealed box. But a sealed box is able to get lower notes than a ported box, and tends to be cleaner, while loosing SPL, which looses the amount of amplitude.</p><p></p><p>brad.farmer"</p><p></p><p>A port is an acoustic high pass filter (when placed in the rear chamber of an enclosure). That has approximately a 12db per octave rolloff below the ported frequency. Therefore, the 3db gain you get at the ported frequency is overcome by the 12db per octave rolloff around half an octave below the cutoff frequency. My statement addresses the output below the ported frequency (hence a sealed box has more output at these frequencies - TYPICALLY). There is a tremendous amount of variation in both speaker characterisitcs and box design.</p><p></p><p>To illustrate this take a look at two response curves:</p><p></p><p><img src="http://www.mtx.com/caraudio/products/subwoofers/T4512-44.pdf" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p><img src="http://www.imagedynamicsusa.com/website/tech/data_sheet_idq10d2v2.html" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>The MTX has both a ported with less low frequency extension and one with more low frequency extension.</p><p></p><p>The image dyanmics driver has equivalent output at 20 hz for both selaed and ported. The output below 20Hz (below everyone's hearing limits) is higher.</p><p></p><p>So the final defense of my statement - phrase by phrase</p><p></p><p>"A ported box is almost always louder than a sealed box. "</p><p></p><p>I DON'T THINK THAT THERE ARE ANY OBJECTIONS TO THIS... BUT WHO KNOWS.</p><p></p><p>"But a sealed box is able to get lower notes than a ported box, and tends to be cleaner, while loosing SPL, which looses the amount of amplitude."</p><p></p><p>THE SEALED BOX USUALLY HAS MORE RESPONSE BELOW THE PORT FREQUENCY OF THE PORTED BOX. THIS STATEMENT I HAVE BOTH PROVED AND DISPROVED. SORRY I WAS SPEAKING IN GENERAL TERMS (WHICH I STILL BELIEVE TO BE TRUE).</p><p></p><p>SECOND POINT, SEALED BOXES DO TEND TO BE CLEANER THAN PORTED (WHEN YOU CONSIDER THE ENTIRE RESPONSE CURVE - PORTED BOXES TEND TO BE CLEANER AT THE PORT FREQUENCY DUE TO THE REDUCTION IN EXCURSION). THIS IS DUE TO THE PHASE VARIANCE BETWEEN THE PORT AND THE DRIVER AT FREQUENCIES AWAY FROM THE PORT FREQUENCY. THE COST OF THIS INCREASED SQ IS LOWER OUTPUT.</p><p></p><p>As promised, this is my last posting. Guys bash away... I won't be seeing it anyway.</p><p></p><p>brad.farmer</p></blockquote><p></p>
[QUOTE="brad.farmer, post: 217661, member: 547961"] FINAL POST (to the delight of many). My original post was: "A ported box is almost always louder than a sealed box. But a sealed box is able to get lower notes than a ported box, and tends to be cleaner, while loosing SPL, which looses the amount of amplitude. brad.farmer" A port is an acoustic high pass filter (when placed in the rear chamber of an enclosure). That has approximately a 12db per octave rolloff below the ported frequency. Therefore, the 3db gain you get at the ported frequency is overcome by the 12db per octave rolloff around half an octave below the cutoff frequency. My statement addresses the output below the ported frequency (hence a sealed box has more output at these frequencies - TYPICALLY). There is a tremendous amount of variation in both speaker characterisitcs and box design. To illustrate this take a look at two response curves: [IMG]http://www.mtx.com/caraudio/products/subwoofers/T4512-44.pdf[/IMG] [IMG]http://www.imagedynamicsusa.com/website/tech/data_sheet_idq10d2v2.html[/IMG] The MTX has both a ported with less low frequency extension and one with more low frequency extension. The image dyanmics driver has equivalent output at 20 hz for both selaed and ported. The output below 20Hz (below everyone's hearing limits) is higher. So the final defense of my statement - phrase by phrase "A ported box is almost always louder than a sealed box. " I DON'T THINK THAT THERE ARE ANY OBJECTIONS TO THIS... BUT WHO KNOWS. "But a sealed box is able to get lower notes than a ported box, and tends to be cleaner, while loosing SPL, which looses the amount of amplitude." THE SEALED BOX USUALLY HAS MORE RESPONSE BELOW THE PORT FREQUENCY OF THE PORTED BOX. THIS STATEMENT I HAVE BOTH PROVED AND DISPROVED. SORRY I WAS SPEAKING IN GENERAL TERMS (WHICH I STILL BELIEVE TO BE TRUE). SECOND POINT, SEALED BOXES DO TEND TO BE CLEANER THAN PORTED (WHEN YOU CONSIDER THE ENTIRE RESPONSE CURVE - PORTED BOXES TEND TO BE CLEANER AT THE PORT FREQUENCY DUE TO THE REDUCTION IN EXCURSION). THIS IS DUE TO THE PHASE VARIANCE BETWEEN THE PORT AND THE DRIVER AT FREQUENCIES AWAY FROM THE PORT FREQUENCY. THE COST OF THIS INCREASED SQ IS LOWER OUTPUT. As promised, this is my last posting. Guys bash away... I won't be seeing it anyway. brad.farmer [/QUOTE]
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