My dad recently asked me if he could set his right front speaker on top of his subwoofer. I wasn't sure if the magnets would cause interference or not. Can anyone advise?

For the love of all that is holy - don't let him do it. Tell him to put the sub off to the side in an optimal location.

by the way:

What kind of speakers/subwoofer does he have?

What are the dimensions and present set-up of the room?

Well it can be done but I would not for a few reasons.

1- bass has a very large wave lenght so it is difficult to put into a room. Think of a plus wave and a reflected minus wave hitting the same place at teh same time. This is how noise concellation works. So position in the room can cause peaks or nulls. To fix it you need to either move the sub or move the seat.

2- Almost all subwoofer boxes buzz at some freaquency. If you have anything on top of the sub it will amplify this buzz.

If you have to do this put something between the two to minimize the buzz.

He was going to set a piece of marble between them. To answer your question, B.A., the speaker & sub are both JBL Northridge series.

A center channel should be as close to the tv and or/image as possible. I cannot imagine how his system must be set up. A subwoofer will generally sound the best when in a corner anyway.

You want something soft between them. The marble would have the same problem as the speaker cabinet -vibration noise.

Another question - is he wanting to put a bookshelf speaker on top of the sub or is it a floorstanding/tower speaker? If it's the latter it might be placing the tweeter/midrange of the speaker too high and taking it out of optimal listening position and screwing up your front sound field.

It's a floorstanding probably about 34" or so high. I'm with you guys and have strongly encouraged him to seek alternate placement of the subwoofer.