BR 2x12 ports

[SG3525]

Hi,

I'm designing a PA 2-way BR mid-top box with 2x12" drivers + 1,4 comp. My current port layout is similar to the Coda RX40. I have done a few BR designs in the past and always tuned all the ports to the same Fb. Now after some research i see that a lot of PRO audio manufactures use the same port lengths regardless of their area in there "multi port" systems. Why is that? Is it maybe because the secondary smaller ports are in a corner and the air is at a higher pressure than the air at the middle ports so in a way they compensate for that pressure difference?

Thanks.

 

[Inductor]

...a lot of PRO audio manufactures use the same port lengths regardless of their area in there "multi port" systems.

I doubt it.

 

[whgeiger]

One Virtual Port

Hi,

I'm designing a PA 2-way BR mid-top box with 2x12" drivers + 1,4 comp. My current port layout is similar to the Coda RX40. I have done a few BR designs in the past and always tuned all the ports to the same Fb. Now after some research i see that a lot of PRO audio manufactures use the same port lengths regardless of their area in there "multi port" systems. Why is that? Is it maybe because the secondary smaller ports are in a corner and the air is at a higher pressure than the air at the middle ports so in a way they compensate for that pressure difference?

Thanks.

View it as one virtual port where area Sp = 2*Sp1 + 2*Sp2 for the example given. Then port length Lp = Lp1 = Lp2. (maybe)

The only difference is that air flow resistance and turbulence will be higher for the multi-port implementation.

Note that it is only the total acoustic mass of air [Map] in the virtual port that matters; so, Map = 2*Map1 + 2*Map2 for the example given. Here Lp1 and Lp2 do not have to be equal and probably are not.

Complexity arises when applying the required end corrections to calculate component Map
Regards,

WHG