V-Series Set-up and Calibration
Vertical orientation of stacked V110 units:
The V-series has a large radiator acoustically, in the vertical direction. The driver is located at one end, and this is usually what becomes the bottom. This gives a radiation pattern that is slightly frequency dependent, where the lowest frequencies are distributed equal along this narrow, tall radiating surface, and the higher frequencies are stronger towards the driver end near the bottom.
Now, is it then important how the upper unit is oriented, when stacking 2 units, to form one tall radiator from floor to ceiling.
With the upper unit mirrored so that the driver is towards the ceiling, the radiation from the system will be symmetrical.
If the upper unit is mounted with the driver at the bottom, so that this driver end now is located near the center of the room vertically, it will no longer be symmetrical, but it will be better distributed across the front wall.
So, which is best - driver up or down. We will look into that, and we will see that it may not be that important.
A picture from the 4x V110 system in Room2, so we can see what this is:
The V110 units fill up the corners, and we can not see the orientation of the top V110 units, which, in this case, is with driver facing up towards the ceiling. (Actually, on closer inspection, it is possible to see the drivers!)
Nearfield measurements of the sound radiated from the vertical port reveals that the output changes in the vertical direction, so that there is more output at higher frequencies close to the driver, and low frequencies are more evenly distributed. This is measured inside the port, and it is the raw response before any compensation eq:
Top line is the sum, the 4 lower lines form different vertical positions, where the one line that has a little higher output is the one close to the driver.
The 4x V110 system in Room2 was compared with 1x and 2x V110 in this article (Norwegian language only):
https://www.kvalsvoll.com/blog/2018/03/10/4x-2x-1x-subwoofere-hva-er-forskjellen/
The measurements of sound field velocity reveals how the 4x changes the velocity of the sound field. 4x system creates a more planar wavefront:
This shows the measured velocity at the listening position in the vertical direction. The red line is 4x V110, we see there is a reduction in vertical velocity component.
My recommendation is to place the top V110 units with driver down, so the driver is located closer to the center vertically, between floor - ceiling.
This will create a sound source that is better distributed along the front wall, and that is better than having a symmetrical field vertically, because it will tend to smooth out reflections better.
The difference may not be large enough to even be noticeable. The V110 is already acoustically large in vertical direction, and though adding the 2.nd units on top creates even better vertical sound field by objective measurement, the major benefit from 4x compared to 2x is the increased capacity and reduced distortion.