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<blockquote data-quote="Rashaddd" data-source="post: 5247085" data-attributes="member: 592162">This only works if you have the exact same proportion of box size to port area regardless of the particular box. For example...if you always use exactly 12sq in of port area per cube, then yes, you will always have the exact same change by lengthening or decreasing port length by a specific amount. DD recommends what I believe 16sq in per cube and that&#039;s what all their recommended boxes are calculated at, so all of their boxes have the same ratio of port area to air space, which means all of their boxes will be affected by a 1&quot; decrease or increase in port length in the exact same way.Certainly not a good idea to use this as a rule of thumb, and it will never be 1&quot; = 1hz for any number times you do it, because the rate of change in frequency will also change over the range of port lengths due to the fact that the port is inside the box and by changing it&#039;s length you also change the boxes air space and therefore tuning is affected twice. The &#039;L&#039;s in a slot ported box will also make variations in the rate of change of tuning frequency based on change in port length because of the extra wood that is being used and the wood length to actual port length being inconsistent.</blockquote>

[QUOTE="Rashaddd, post: 5247085, member: 592162"] This only works if you have the exact same proportion of box size to port area regardless of the particular box. For example...if you always use exactly 12sq in of port area per cube, then yes, you will always have the exact same change by lengthening or decreasing port length by a specific amount. DD recommends what I believe 16sq in per cube and that's what all their recommended boxes are calculated at, so all of their boxes have the same ratio of port area to air space, which means all of their boxes will be affected by a 1" decrease or increase in port length in the exact same way. Certainly not a good idea to use this as a rule of thumb, and it will never be 1" = 1hz for any number times you do it, because the rate of change in frequency will also change over the range of port lengths due to the fact that the port is inside the box and by changing it's length you also change the boxes air space and therefore tuning is affected twice. The 'L's in a slot ported box will also make variations in the rate of change of tuning frequency based on change in port length because of the extra wood that is being used and the wood length to actual port length being inconsistent. [/QUOTE]

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