speaker port question

[intojazz]

What is reason for the porting on bass bins. In this case (2) 4" by 10" long ports at the bottom of the bin. Do they function as tuning vents to increase/decrease pressure on the driver cone to achieve a certain response. Also, what about the internal volume, how does it affect tuning?
Approximate size of the bin is 4.7 cu. ft
Thanks,
John

 

[Paul Joppa]

The port and box together make a resonator, which (properly tuned) extend the bass, typically by a half octave. There is no free lunch, so the price you pay is a faster rolloff below the lowest useful frequency.

What happens is, the mass of the air in the port resonates against the stiffness of the air in the box. Much the same as a coke bottle, and different from an organ pipe or clarinet.

Google "ported box speaker design" and you'll find plenty of sites.

 

[intojazz]

Thanks Paul,
Good vacation?
John

 

[earwaxxer]

The port and box together make a resonator, which (properly tuned) extend the bass, typically by a half octave. There is no free lunch, so the price you pay is a faster rolloff below the lowest useful frequency.

What happens is, the mass of the air in the port resonates against the stiffness of the air in the box. Much the same as a coke bottle, and different from an organ pipe or clarinet.

Google "ported box speaker design" and you'll find plenty of sites.

very cool port explanation!

 

[4krow]

It should also be mentioned that the size of the enclosure 'loads' the cone of the driver, allowing the cone to be controlled by the mass of air being compressed. The bigger the box, the less 'load' there is on the cone allowing more cone movement, but also less control. This equates in more distortion if there is too little control, albeit more output from the driver. The cabinet volume is determined by the parameters of the driver so as to get good output with less distortion. The port is icing on the cake if chosen, to extend and tune the bass. I think we have all owned something chosen more for it's boom than it's accuracy.