Port tuning advice

[Jaam]

Hi,

So I've been able to make two loudspeakers so far and in both I have noticed the port length is considerably shorter than the equation I have spots out. Can anyone explain why the actual length of a port to achieve the correct box tuning is shorter than the maths suggests?

Thank you

P.S. sorry if this is in the wrong section, I wasn't sure where to ask the question.

 

[Mario Pankov]

Can you provide some basic drawing of the enclosure and port? What drivers are used and have you measured their parameters?

 

[Mark Tillotson]

What equation were you using?


There are many sources of error, but a notable one is end-corrections for the port, which will depend on the flare, if any, the distance from any obstructions that affect the airflow.


It may also be that the equation used overestimates the length to be on the safe side (shortening a port is easier than lengthening it).

 

[Galu]

Can anyone explain why the actual length of a port to achieve the correct box tuning is shorter than the maths suggests?

The effective port length is longer than its physical length because the vibrating mass of air within the port actually extends beyond the physical length of the port.

To which maths are you referring? Some equations calculate the effective length and an 'end correction' is necessary to arrive at the physical length.

 

[Jaam]

Unfortunately I can't provide a design at the moment but end correct ion may be the answer, seems like I've not been applying enough correction. Thank you

 

[Galu]

If you have any specific port design questions in future, don't hesitate to ask them in the 'Loudspeakers', 'Multi-Way' forum.