OB bass augmentation w/ PA drivers

[scottw]

There have been several examples of people using fairly inexpensive PA drivers to augment the lower frequencies in OB speakers. An example is Martin J. King's Project 7(with Alpha 15A):

http://www.quarter-wave.com/Project07/Project07.html

Even these large PA drivers(15 inch) are designed to go up to a few kHz, although in this application they are only used up to a hundred or so Hz. These drivers also tend to have fairly stiff treated cloth surrounds.

What kind of changes would you expect if you replaced the stiff surround with a more complient foam surround? Increased VAS and Qms? Would the Fs change?

Is the low frequency roll off usually seen on SPL plots of PA drivers (on infinite baffles) related to the stiff surround?

I'm just wondering if a more complient surround could help a PA driver operate from Fs to around 150 Hz.


Scott

[phase_accurate]

Is the low frequency roll off usually seen on SPL plots of PA drivers (on infinite baffles) related to the stiff surround?

I'd say it is a little bit because of the stiff surround which increases fs.
But to a larger part it is due to the low Qes which is good for efficiency but bad for LF reproduction in infinite baffles and OBs.

Regards

Charles