Why?

[quarinteen]

I’ve been looking at speaker designs and I found someone who built a base box and put a small bass speaker behind a larger base speaker and I’m wondering what is the purpose of this if somebody wouldn’t mind explaining it I would really appreciate it thank you

 

[shadyJ]

This is a bandpass enclosure. The outer cone is a passive radiator which means it has no motor. The internal air pressure created by the active driver moves the passive radiator. The active driver is also resonating air in the internal port which creates more pressure which further movies the passive radiator. A design like this will have a lot of output over a narrow frequency band.

 

[TLS Guy]

You are correct it is a band pass coupled cavity enclosure. To be precise it is a quasi sixth order band pass enclosure.

It is like this.

The one in the photograph has a passive radiator in place of the port that is open to the outside. The physics is virtually identical. So it will roll off steeply above and below the band.

The higher the system Q then the wider the band, but the more ponky and boomey it will be. The lower the Q the narrower and tighter the operating band will be.