Nasty slap echo

Thanks for the picture links. Hard to really hear it when music is playing. My wife is off today so i will have her clap at the speaker locations and see how bad it is in the sweet spot.
When i walk around the front part of the room clapping my hands it is really bad...clap.ping...clap..ping.

"How does the room sound? ...Sometimes a little echo can yield very nice ambiance to the music. "

That's an important point! It's always useful to understand your room's acoustics and how they are working, but a "slap echo" may be a good or bad thing depending. I've heard some very lively rooms at dealers not unlike yours with significant "slap echo" sound uniquely engaging and lifelike, even quite holographic (in a good way) as opposed to the opposite, ie dull and lifeless!

Even if you can reduce or change it temporarily and listen as a test first using whatever means available, that would be useful prior to making any permanent changes.

Josefm, This is why I always caution on using too much room treatment.

Streetdaddy, Instead of clapping at the speaker locations you should be clapping where you listen from. If you want to make this simple put your system on the long wall and you will only need to treat the wall behind your head. Unfortunately you will have to sit beside each other like normal people, but you will have a broader sound stage and you won't have to worry about side walls. You will get a bigger sound stage, better midbass, less room interaction, less room treatment required and you get to sit next to your wife.

BTW legend has it that the original Three Stooges has slap echo down perfectly in their listening room.

Curly: "A whooba whooba"!
Moe: "Shaddap and listen!" Slap!
Larry: "Leave him alone"!
Moe: Slap!
Curly: Nyuck Nyuck Nyuck!

You get the picture...