Sorry guys, bit of a newbie here but why would you want to put anything under the sub?
I have a floor facing sub, would I notice an improvement if I placed something under my sub?
Thanks
It depends on what you are trying to achieve, the subwoofer itself and the type of floor and possibly the floor covering.
Isolation with foam and other compliant materials is intended to stop vibration from the subwoofer enclosure from physically shaking the floor. This helps to limit sound travelling beyond the room. Though the low frequency sound waves also travel well.
I noticed no difference (at all) when I tried a massive, round, concrete slab under my SVS cylinder on a very flexible, carpet covered, suspended, wooden floor. I can't think of any advantage in using hard materials except appearance and offering a flat supporting surface on thick carpet.
It pays to keep an open mind and experiment. Safety is a serious consideration as vibration may cause a subwoofer to topple if it is placed on something unsteady or tall.
If a subwoofer "walks" in use then it probably helps to put something under it. Foam is helpful because it has very high friction to sideways movement when loaded. If the foam is completely flattened by the heavy object then it offers no "suspension" because it effectively becomes hard and thin. This may not be a problem if you simply want to stop the subwoofer from moving about.