Pioneer PDP-V402 Technical Manual page 56

Special installation (Installation under the floor)
Securing method: Basically, the unit is secured as indicated below. Keep open all areas other than the shaded parts.
The fixing method marked
When the unit is fixed on a structure, select a structure of the proper thickness and height. Care
must also be taken regarding the number of fixing bolts to be used (see "3.4.1 Fixing on a structure").
<Correct>
Bad example of blocking exhaust
<Incorrect>
56
Beams
cannot be used for the unit.
Beams
Beams
Do not install the horizontal beam at
the same time as the vertical beam.
<Correct>
Beams