Backbox help???

[Nans_Micra]

Anybody know what you call these kind of boxes? And should I get one for my k12?

 

[Nans_Micra]

are they rare or something?

 

[frank]

it looks like a 1/4 wave resonator thingy (probably just a gimic tbh)

 

[imp124]

It reminds me of those pulse jets they kept building on scrapheap challenge