What causes "cupped hands"?

I've been dealing with this puzzling phenomenon for several months. I can't seem to rid my system of the "cupped hands" or megaphone effect. Acoustic treatments seem to help but haven't diminished it to an acceptable point. I've been told that cables can cause it but haven't been able to confirm this. The system consists of:

Mark Levinson 390S CD Player
Antique Sound Lab KMP-60 Fox DT Amps
Aerial Acoustics 7B Speakers
1.5 Meter ZCable LIVE v4 Interconnects
4' ZCable PASSION v3 Speaker Cables

Any ideas?
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.

Hi sorry guys, what's "cupped hands"?
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:
including the results of the cryo immersion experiment.
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!
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:
If my math is right it seems you have your speakers 2.5' away from the side walls and 10' apart. The first thing I'd do is try moving the speakers closer together and possibly a little further out--maybe try something like a 7' or 8' equilateral triangle setup. In any event, I'd want the speakers a little further from the side walls to let them open up a bit and decouple them more from the room. Best of luck.

If you have the speakers 10' apart and are sitting 9' from them you are too close to the speakers or they are too far apart.....Think in terms of X x 1 wide and X x 1.15 to your ears........Something else that might be causing this is cable break-in as had something like cupped hands here a few days ago but leave everything on and playing as trying to burn in some teflon caps I use to roll off the lows in my main amps......Turn off your amps when not listening, but leave the CD player running on repeat for a few days to see if the problem doesn't go away.....
Could it be a speaker/amp problem? How powerful are the Fox DT amps? The 7B is listed 86db with a 4ohm min. Some speakers require a lot of current and can sound "closed in" or "cupped" with less muscular amps. Have you tryed other electronics?
I like Tim's suggestion re setting up an equi-tri first.
I also found that 5" midranges USUALLY sound "cuppier" than 6-7" midranges, all other things being equal. Something to do with 2-pi/4-pi stuff and resultant non-linearities with cabinet edge-diffraction. Found Aeriels to sound that way, as well that otherwise-nice Linn 3-way 5176 (?).
I found the Revel F30 and especially the Verity Audio Fidelio and Parsifals to NOT exhibit this 5" mid cuppiness, however. Somehow 6.5" 2-ways sound more easily "open", and are thus more forgiving of room setups.
Keep trying, and good luck.
I'll further add that I 've found that the cuppiness relates to a mild peak around 800-1k with 5" drivers. Similar peaks around 600Hz with 6.5- 7" mids CAN sound flatter. It's part of the reason designing (and integrating) a GREAT 3-way with a 5" is so tricky, and why 6.5-7" 2-ways are easier to live with. I tried in vain to voice a 3-way design of mine, but couldn't successfully get rid of that "pinched" peak at 800-1k with a nice Seas 5 that was otherwise super-smooth.
Bur Revel did get it right for $3500 with the F30, and of course the Verity Audio Parsifal is absolutely revelatory at $10k+.
Well, being from the northern clime, I know that the family jewels often tend to get frosty below the freezing mark, Hence the "cupped hands" to warm the jewels syndrome. I've heard that a good cable burner, or torch welder may help this problem too, but one should exercise caution with both methods.
good luck,