I have a 30lb speaker that came with a built in keyhole mount and a few 2.5 inch wood screws. I have 2 Lally columns surrounded by 1.5 inches thick of wood on each side. I would like to mount it on a Lally column. Obviously the 2.5 inch wood screw won't work. Is there anything else I can use for this to hang the 30lb speaker while keeping it secure and using the built in keyhole mounts?
It would kind of depend on how your column is framed and where the keyhole is on the speaker. Is the column wrapped with drywall? If so, you're probably have a horizontal piece of lumber at the top, bottom, and roughly midway. For that kind of weight you're going to want to make sure you're hitting solid wood. I'd use a #12 sheet metal screw (they have a flat head) about 2" long (the drywall is 1/2" thick).
There are also super heavy duty hollow wall anchors but you may not have enough clearance between the drywall and the column to use one.
If I'm missing something, maybe you could post a couple of pictures?
I have a couple of thoughts but need to ask you a couple of questions. Is this a square box around the column and if so, how big is the box? Do you know how it was constructed? Or is this one of those "wrap" type coverings where narrow strips of wood are attached to a flexible backing?
This hanger will secure into the 1/2-inch wood, is padded to prevent damage to the column, and provides more than enough weight support to handle your 30-pound speaker.
As mentioned above, I recommend using two for stability ... and to help by sharing the load.