Can you electronically adjust-control sound by putting thin electro-magnets inches above speakers to control sound base and vibration of speakers and will higher power magnets increase the base power?
First, I am not a speaker designer or an electronics engineer, but only a hobbiest of about 45 years. Therefore, until a true expert improves this answer, it will be from a layman's viewpoint. Speakers consist of a fixed permanent magnet located on the axis of travel of the coil and diaphram. On quality speakers, there are a couple of "collars," one fixed, and one mounted on the moving diaphram, to insure that movement is confined to the axes of the coil and magnet. Any magnet(s) NOT located along the axis [i.e., "...above the speakers..."] will result in an excentric [misaligned] force on the diaphram, which probably will result in one collar dragging against the other, further resulting in distorted sound, and accelerated wear-out of the speaker. The speaker diaphram, permanent magnet, and coil are all designed for optimum output at the rated power input, and to "mess with" the physical design, will only serve to reduce the efficiency of the speaker. It is possible that increased magnet power [ i.e., replacing the original magnet with a more powerful magnet of the same size and shape, in the precise location of the original] MIGHT result in increased power output from the speaker. However, I doubt this as I think the "power" output you want is a product of the electrical voltage input to the speaker. Anyway, what you suggest, would be extremely difficult, time consuming, and require precise alignment, all of which suggest that it would be much simpler and more effective to buy an amplifier.