This page details the maths used in the downloadable calculator
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Conventions ID_tube1 is inside dia. of smallest tube OD_tube1 is outside dia. of smallest tube ID_tube2 is inside dia. of middle tube OD_tube2 is outside dia. Of middle tube ID_tube3 is inside dia. Of biggest tube OD_tube3 is outside dia. Of biggest tube L is the physical length of the port T is the thickness of the endcaps |
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Breaking the path into segments for ease of computation ... Acoustic length = A + B + C + D + E A = L - end_gap_tube1 / 2 B = ( ID_tube2 - OD_tube1 ) / 4 + ( OD_tube1 ) / 2 C = L - end_gap_tube1 / 2- end_gap_tube2 / 2 - T D = ( ID_tube3 - OD_tube1 ) / 4 E = T + L - end_gap_tube2 / 2 - T The effective acoustic length is the sum of these figures
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It gets even more complicated if we go to a 5 tube port
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Acoustic length = A + B + C + D + E + F + G + H + I the same as before for A to D A = L - end_gap_tube1 / 2 B = ( ID_tube2 - OD_tube1 ) / 4 + ( OD_tube1 ) / 2 C = L - end_gap_tube1 / 2- end_gap_tube2 / 2 - T D = ( ID_tube3 - OD_tube1 ) / 4 Segment E is different this time E = L - end_gap_tube3 / 2- end_gap_tube2 / 2 - T now add F through to I F = ( ID_tube4 - OD_tube2 ) / 4 G = L - end_gap_tube4 / 2- end_gap_tube3 / 2 - T H = ( ID_tube5 - OD_tube3 ) / 4 I = L - end_gap_tube4 / 2- T The effective acoustic length is the sum of these figures |
The next page details how to make composite tubes with PVC pipe
