In Loudspeaker Design Cookbook Vance Dickason gives the following formula for calculating box losses - total losses for a vented box:
1/QB = 1/QL + 1/QA + 1/QP
Where:
QL = leakage
QA = absorption (from damping material)
QP = vent losses
In practice he says that QA and QP are insignificantly low so they are generally ignored. This leaves QL. He then makes the rather startling
statement that QL is rather unpredictable and must be measured with a working enclosure. He then proceeds with explaining how to obtain a target Q by trial and error.
Why is modelling QL so difficult? Where do the losses come from? Assuming one can build an air tight box (except for the port - but that is not a leak) and the driver does not have a leaky dust cap, what other losses could there be?
Does this mean that modeling a vented enclosure with WinISD, SoundEasy etc. is like throwing stones into a bush and hoping you hit the dog, with the modelling merely helping you to pick the right bush?
1/QB = 1/QL + 1/QA + 1/QP
Where:
QL = leakage
QA = absorption (from damping material)
QP = vent losses
In practice he says that QA and QP are insignificantly low so they are generally ignored. This leaves QL. He then makes the rather startling
statement that QL is rather unpredictable and must be measured with a working enclosure. He then proceeds with explaining how to obtain a target Q by trial and error.Why is modelling QL so difficult? Where do the losses come from? Assuming one can build an air tight box (except for the port - but that is not a leak) and the driver does not have a leaky dust cap, what other losses could there be?
Does this mean that modeling a vented enclosure with WinISD, SoundEasy etc. is like throwing stones into a bush and hoping you hit the dog, with the modelling merely helping you to pick the right bush?
