What causes "cupped hands"?

Speaker placement can be a major cause. Are your speakers well away from walls and not back in corners? Also could happen if you inadvertently have a backward LE-DE room. I.e. the speaker end of the room is live and the listener end is dead.

will

Hi sorry guys, what's "cupped hands"?

Cupped hands effect produces sound like when you cup your hands around your mouth to focus your voice....like a megaphone used by a cheerleader. The room I'm listening in is 15' x 35' with the speakers placed 5' out from the 15' wall and 30" in from the side walls. The listening position is 9' from the speakers. The room has a sloping ceiling that rises from 8' at the speaker end to 16' at the opposite end. My cables are pretty short with the ICs being 1.5 meters and the speaker cables only 4 feet long. Acoustic treatment has yielded only marginal improvements, but with a room that big, it could take considerably more than I have. Thanks for your comments so far!

May be non-linear phase response or cable reflections/electrical resonance. This can be caused by cables, particularly long ones. Lossy cables can cause general musical soup as well, particularly in the high-frequencies. This effect was obvious in my system when I immersed some IC's in LNO2 as an experiment. It damaged the surface finish of the wire, I believe. Sounded like the music was coming through a tunnel. The correct way to do this is to lower the temp and raise the temp slowly. It was just an experiment, but yielded useful information.

You can learn more about electrical resonance at he Audio FAQ page of:
http://www.empiricalaudio.com
including the results of the cryo immersion experiment.

Your placement sounds unusual. Usually in a rectangular room, the (box) speakers are about 2 feet from the back wall, with the listening position around mid-room, which would be around 10 feet away from the speakers. In order to get the optimum image from most speakers, an equilateral triangle is usually used. This would make the triangle 12 feet on each side. I would measure this. Then play with aiming the speakers in and out fo rhte best dispersion, sweetspot and image. Now the ceiling, being shorter at the front, will cause a horn-effect, which should not impact the image, but may cause some boominess in the bass.

The other thing to do is treat the sidewalls and backwall. Sit in the listening position and have another person put a hand-mirror against the side wall and move it until you can see the tweeter from the listening position. This is where you will need absorbing materials on the side walls. I use 4" thick Sonex myself. It can be wrapped in cloth to address the spouse factor. Wall hangings can work reasonably well too. As for the back wall, this is often better treated with a dispersive reflector. If you have vertical blinds, these can be half-opened. Heavy curtains work well too. There are several examples of different room treatments on the Audio FAQ of my website:
http://www.empiricalaudio.com