I assume you mean they disappear. A mid and tweeter effect from reducing any edge diffraction that may localize the sound.
I find that tall narrow speakers (less than 8 inches), and small box designs (like satellites) often disappear most easily, as the edge diffraction in these designs become indistinguishable from the direct sound radiating from the driver.
I find that the big box speakers with large front baffles of a foot or more wide have a greater tendency to suffer from edge diffraction. Designers will usually offset the tweeter and mid range to one side to reduce the audibility of this. Triangular and odd shaped baffles also help in a similar way to offseting the drivers. Placing the tweeter or mid range on top in its own little mounting (like B&W) also helps.
Soffit mounting of big box speakers definitely has an audible improvement in completely "freeing the speaker from the box"; achieveing more solid and precise images between the speakers than freestanding. I have observed this myself.
Furthermore playing speakers without the grill can make matters worse, as the grill is often designed to help reduce edge diffraction artifacts.
Just my two cents... from the above you can usually make a good guess at how well a speaker will sound free of the box.
I find that tall narrow speakers (less than 8 inches), and small box designs (like satellites) often disappear most easily, as the edge diffraction in these designs become indistinguishable from the direct sound radiating from the driver.
I find that the big box speakers with large front baffles of a foot or more wide have a greater tendency to suffer from edge diffraction. Designers will usually offset the tweeter and mid range to one side to reduce the audibility of this. Triangular and odd shaped baffles also help in a similar way to offseting the drivers. Placing the tweeter or mid range on top in its own little mounting (like B&W) also helps.
Soffit mounting of big box speakers definitely has an audible improvement in completely "freeing the speaker from the box"; achieveing more solid and precise images between the speakers than freestanding. I have observed this myself.
Furthermore playing speakers without the grill can make matters worse, as the grill is often designed to help reduce edge diffraction artifacts.
Just my two cents... from the above you can usually make a good guess at how well a speaker will sound free of the box.