BASSBOSS Questions

Hey BASSBOSS, do you have any advice on subwoofer stacking or placement when using two ZV28s? Should they be vertical side by side or stacked horizontal? Or another config?

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David Lee

There’s not a single best way to position subs because different setups yield different results.

It helps to think of the ground as a sound mirror. The larger the surface you put against the mirror, the more sound gets reflected. If you put a cabinet horizontally on the ground, less sound escapes around the box and more is reflected. Due to the relationship between cabinet dimensions and wavelengths, the longer the surface adjacent to the ground, the lower the frequencies are that get reflected. Two boxes horizontally side-by-side will deliver more of the lower frequencies forward than if the boxes were stacked or standing up. The sound will also be focused forward up the center between the boxes with less energy available to the left and right. If you stack two boxes, the surface adjacent to the ground is half as long, so the lowest frequency the reflection supports is higher, (going from about 40Hz to about 80Hz at 1/4 wavelength directivity.) Since the radiating area is about square at that point, 80Hz is similarly supported both vertically and horizontally. This results in a more “punchy” sound.

Standing the boxes side-by-side has the same 80Hz directivity but the difference is in how the drivers are loaded. When the boxes are stacked, both drivers in each box are equally loaded. The bottom box is loaded differently from the top box because the bottom box is radiating into less space. The ground below doesn’t yield to pressure and the box above provides pressure against which the bottom box must also push. The top box has pressure coming from the bottom box, but that’s not as unyielding as the ground, and above it there is no additional resistance to pressure. The differences are slight but the effect is that each box behaves in a relatively stable fashion, with both drivers presenting the same resistance to the amplifier’s output voltage. When the boxes are standing, the lower driver is in the higher pressure environment and the upper driver is in the lower pressure environment. Each driver presents a slightly different load to the amplifier. This can allow the upper and lower drivers to behave differently, resulting in a different frequency response from when the drivers are equally loaded, and the observed result is that the sound is perceived as being even more “punchy” although this is a trade-off for reduced output at the very lowest range of the boxes' response.

The short answer: Punchiest is side-by-side standing up. Deepest is side-by-side lying down. Stacked is splitting the difference.

And, if the ground is not the only reflecting surface, you may need to change your priorities and adjust placement to compensate for those reflections.The reflections from walls and the ceiling can do a lot more harm to the system response in the listening area than which way the boxes are stacked.


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