A: Studio monitors tend to be designed to function best when placed either vertically or horizontally. A big factor in this is the dispersion of the high-frequency driver. In most cases, the HF driver is designed to spread sound wider left/right (in the horizontal plane) than up/down (in the vertical plane); this is to create a wider sweet spot. When you turn a vertical monitor on its side, for example, the width of the sweet spot narrows and the tweeter throws more sound up toward the ceiling and down toward the floor. This may or may not cause acoustical anomalies. If the monitors are active, with cooling heat sinks on the back, you may also impact proper airflow for adequate cooling.
For these reasons, it’s best to follow the manufacturer’s recommendation regarding placement. However, if the monitor placement in your studio is already compromised, changing the monitor orientation may result in fewer problems. You might also try placing the speakers vertically, but upside down (so the tweeter is on the bottom and the woofer is on the top). In some cases this can work very well.
Our advice is to try the monitors oriented several ways, then use your ears to decide which gives you the best results.