Vb Calc With/Without Batting?

[robert J]

Hi all,

When calculating Vb I have a couple questions.

1. does adding fill allow for a smaller box? IE: Speaker "A" requires a 34Hz tune, 1.75cf volume empty but only 1.4 with fill.

2. Does that mean I use a 1.75cf enclosure and fill it reducing volume to 1.4cf? or do I use a 1.4cf box and line it with fiberglass sheeting or polyester batting?

3. if a 12" box is tuned to 34Hz will any 12" speaker work in it that require a 34Hz tune, given they are close in displacement volume?

Cheers.

Click to read more...

 

[THATpurpleKUSH 5,000+ posts]

The purpose of adding fill is to absorb standing waves. Standing waves have a wave length equal to twice the distance between two sides. A 40hz note has a wavelength of 28 feet, a 60hz note has a wavelength of 18 feet. Since subwoofers play low frequencies there is no need to use fill with a ported box because the aren't standing waves inside the box.

 

[robert J]

Thanks for the reply. Does that mean that deadening the doors for mid bass is not very effective since a 500Hz wave is over 2ft? Or is that more about redirecting sound energy into the car?

 

[THATpurpleKUSH 5,000+ posts]

Thanks for the reply. Does that mean that deadening the doors for mid bass is not very effective since a 500Hz wave is over 2ft? Or is that more about redirecting sound energy into the car?

Standing waves are different than panel resonance. You still want to deaden the doors

 

[winkychevelle 10+ year member]

Sound absorption material behind almost any speaker will lower rear way distortion though. Since the rear wave will be partly absorbed by the batting it cannot return back and hit the back of the cone with as much energy as it initially started with. Thus lowering cabinet reflection distortion.

Depending on the enclosure, and frequency range depend on how effective the batting will be. Also thicker absorption material will be more effective. 2 inches of fiberglass batting will work much better than 1 inch thick material