I agree with the rule of thumb about odd fractions of the room dimensions. They should be measured from the centre of the bass drivers.
I believe the rationale is SBIR (Speaker-Boundary Interface Response) interacting with room modes in the bass region. SBIR is wavefronts direct from the speaker being overlayed with reflected wavefronts. Imagine the driver is in the wall i.e. soffit mounted. All the bass energy that would have gone backwards via diffraction around the baffle is immediately reflected forward. So all bass frequencies are boosted 6db. Move the bass driver away from the wall and you'll find some higher frequencies are now cancelled and some are between boosted and cancelled. (Note the lowest frequencies remain more boosted than cancelled because, considering their wavelength, the reflection is more in phase than higher ones.) Move further away and also more of the lower frequencies' reflections start to get more out of phase i.e. even less bassy overall. Now back to room modes. Wavelengths of twice a room dimension will produce standing waves. Placing the bass driver at 1/4 from the boundary means the first reflection will boost optimally a wavelength of 1/2 room dimension, but the reflection's reflection will boost optimally a wavelength of twice the room dimension. This is the same frequency as the natural room mode - which is bad. Also I think harmonics come into it, perhaps someone knows more. I think this is where the odd fractions rule of thumb comes in...I have found it helpful, myself. Darren -- darrenyeats http://www.amazon.co.uk/gp/richpub/listmania/byauthor/A3H57URKQB8AQO/ref=cm_pdp_content_listmania/203-7606506-5721503. SB Touch ------------------------------------------------------------------------ darrenyeats's Profile: http://forums.slimdevices.com/member.php?userid=10799 View this thread: http://forums.slimdevices.com/showthread.php?t=93111 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
