Pioneer PDM-4001 Technical Manual page 43

Special installation (Wall hanging (vertically wall-hanging equipment))
Securing method: Basically, the unit is secured as indicated below. Keep open all areas other than the shaded parts.
The fixing method marked cannot be used for the unit.
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").
Bad example of blocking exhaust
<Correct> <Incorrect>
Beams
Beams
4 3