tunning of a ported box will be the same for all sub sizes ?

[Diy_Ambitious]

OK , I was searching around on how to tune ported boxes and came across this site

http://www.clubknowledge.com/Car_Audio_FAQ/?t16

So, for example if I got a ported box for an 8" tuned to 35hz. If I put a 6.5" inch or another sub bigger will it still be at 35hz ? Do I loose or gain any efficientcy by using a smaller or bigger ported box ?

 

[bigmike216]

The short answer: Pretty much.

The box is tuned to a certain frequency because of the volume of air in the box, not because of the size of the driver. I say pretty much, because the vilume displacements of the two woofers would be slightly different.

 

[BassAwdyO]

as bigmike said, the box tuning itself is an effect called resonation due to the system acting as a mass and a spring. the mass is the air inside the port, while the spring is the air inside the enclosure. This is why box volume is calculated without including port volume. A frequency response graph shows the sensitivity/bandwitdth of a speaker/enclosure system. You can find modeling programs like winISD that will do the work for you, all you have to do is enter in driver parameters, box size, and tuning frequency. Frequency response graphs use frequency on the x axis and sound intensity(in dB) on the y axis.

 

[Dave Jones]

The tuning doesn't depend on the driver size per se, but in practice bigger speakers tend to require bigger boxes. You need to read up on Thiel/Small (TS) parameters.