Sound - for the purpose of creating vibrations

Question

What is the best way to distribute noise from more than one source (I'm envisioning a system with many), within a dome, with the ground as its primary target, at optimal frequencies and volumes to create maximum vibrations on the ground?

Think, this picture - http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/imgaco/foc3.gif - but with more than one source.

I'm assuming you would want the dome to be perfectly circular, and have the point at which the dome wall meets the ground at a slight incline (as opposed to vertical) so all the sound stays directed at the ground. Imagine a tennis ball which is cut in half, but was split just before the equator. You take the side that is smaller, and flip it over. Thats what I am imagining. I'm just judging from the above drawing that you would want the sound sources crammed as close as possible in the center of the dome, in as perfect as a circle as you could design it, and maybe directed so that they are all pointed to the center of their own, independent, equally sized areas (the dome being the total area of the surface that the sound is being pointed at). It seems like if you could cram all the sound into a point of singularity and put it at the center of the dome, and then release it somehow - that would be ideal (although that sounds pretty complicated). Not sure about frequencies and volumes.

Answer 1

Well as that diagram you posted shows you'd need a parabolic curve not perfectly circular one to get all the sound to direct to a single point but unless that single point has a high absorbability the sound will then diffuse from that point.

And taking into account you want vibrations <100hz or even <20Hz the wavelengths are going to be huge. Even if you were to design and build a room such as this the only benefit (assuming phases are maintained) is an increase in amplitude.

Take this video

you can achieve enough amplitude with what looks like 18 12" drivers to physically push air in and out of his mouth. Be careful though that you would obviously never play a noisy signal or anything above 100Hz at that kind of amplitude.

But onto the sound design. I have had some success in using additive synthesis to produce what are basically slightly inharmonic sounds. Taking a fundamental of about 40-60Hz and only having the first 3 partials and then detuning them slightly will give a powerful rumble to the perceived vibration of a sound. Either that or take out the middle man (air) and design a stage where the speakers are directly underneath the floor connecting the vibrations to the feet of the participant directly.