speaker box design physics question

[priscared]

Hey all,
i was just building my speaker box, (See attached image) i stumbled a across a problem, see the ports where the wrong diameter. so heres the question
If the port was meant to be 7.5cm diameter and 27.5cm long, and i have 8.5cm diameter pipe, how long should the pipe be to be equivalent?
as in the relationshipt between diameter, wavelength and length of the pipe.
i thought i should make it shorter, so i tried that, works OK. But id like it to be better.
thanks all again
daniel

 

[sreten]

Hi,

as the port is bigger in crossectional area it needs to be longer.

Its a square relationship, doubling the diameter of a port means
its length needs to be four times as long for the same frequency.

Which gives an answer of 35cm long.

🙂 /Sreten.

 

[priscared]

thanks

thanks man , cheers, now i have to put a right angle in the pipe so it'll fit!
daniel

 

[sreten]

Hi,

don't go the right angle route - it won't work well.

Line the current shortened port with say a stiffish foam to reduce
the effective diameter to nearer say 6.5cm, length then = 21cm.

🙂 /sreten.

 

[priscared]

thanks

yeah i was originally goin to use smaller pipe, 6.5cm, dam it lol. But yeah i think ill have to go the right angle way cause i can use foam without it looking shocking