Speaker Placment Rules?

[Operandi]

What exactly makes one speaker better for near wall placement than another?

As I understand it from how folks here talk about it from a design perspective the main consideration its how much baffle step is designed into the crossover, but is that the only factor that determines placement? Is general tonality and voicing also a consideration to how its going to sound when placed near a wall?

When reading some write-ups for designs sometimes its specifically called out but now always so I just assume a 1 - 3' away and not up near a wall. I know you want to avoid room reflections so you generally don't want a speaker right up against a wall if its not designed for that but if someone designed a speaker 3' away from the wall and I build it and place say 1.5 -2' away how much am I compromising the sound?

[billfitzmaurice]

The issue is Allison Effect, the cancellation that takes place where the speaker is 1/4 wavelength from the wall. It happens with all speakers. The only way to prevent it is with flush mounting or by not placing the speaker where it's 1/4 wavelength out from the wall within its pass band. With separate mains/subs that's easy enough, put the subs close to the wall and the mains further away. With a full range speaker it can't be done, but the effect can be minimized with thick acoustical damping on the wall.

[Operandi]

So the Allison Effect is just describing bass response and the effect the room has? I think I get what the theory is stating and what the effect is but as someone that just likes to build and listen (and though I like to think I'm not a complete idiot) acoustic theory is a bit out my depth so you'll have to talk to me like I'm in the 5th grade when it comes to this kinda stuff.

I also read that to get the proper sound stage the speaker should be "X" distance from the walls. Would that be solely bass effects you described ruining the imaging of the speaker or is there more to it than that? If so how is that accounted for in the design since when measuring the response of a speaker its done if free space or anechoic chamber?

[billfitzmaurice]

Allison Effect only describes the cancellation from the wall reflection. Every boundary contributes to in room response. There is no simple formula for speaker placement. Spend a few weeks, if not months, reading these and you'll begin to understand.

http://ethanwiner.com/articles.html

http://realtraps.com/articles.htm

[Steve Lee]

Or just spend a few hours repositioning your speakers in your room while doing some critical listening and come up with your own empirical rules that will stick with you longer - that's what I do . . .