[guest42212]

How high off of the floor can one situate an OB before loosing the 'mirror image' effect, or 1/2 space vs. fullspace or ?

[Luigi]

Dick Olsher reckons don't raise them off the floor at all, or you lose bass. see here: tip 55 in www.blachdahlia.com

He writes: "First, the baffle should be designed so that it is flush with the floor, rather than being elevated off the ground plane. This generates a mirror image of the baffle in the floor plane, effectively doubling its area and increasing the effective baffle dimension by the square root of 2 (a factor of 1.414). In this manner, the baffle may be decreased from 168 cm to 119 cm without affecting the bass cutoff."

[Bob in St. Louis]

hitsware, I've had mine 3 feet in the air and had wonderful imaging, I've had them six inches off the carpet and had wonderful imaging. Bass will be dependant on assistance from the floor, walls, baffle size and baffle construction.
But regarding your question this would be room dependant, source dependant, placement dependant etc... I believe height is one of many factors that EFFECT the imaging, but there (to my knowledge) is NO hard and fast rule for max/min height.

Bob

[hurdy_gurdyman]

hitsware,

After several baffles for my SI Coaxials, The low one I'm using now sounds best overall of any of them. Drivers are as close to the floor as I could get them and slanted back about 10-12 degrees, with a narrow baffle.

http://new.photos.yahoo.com/the_hurdy_gurdyman/photo/294928804242079143/2

Dave

[guest42212]

Nice grills ! 
I know on the floor is best but I need to raise mine slightly on some sort of feet or somesuch since my floors are ceramic tile and not quite even in places.
Guess I could get some strips of thick carpet and not worry......

[JohninCR]

Don't worry, a small gap will make little or no difference.  It's not like the pressure of a box trying to leak out, and most of the gain is just the boundary gain, not from blocking the rear wave from getting around that way.

[johnk...]

The transition from 2Pi to 4Pi due with distance off the floor (or ground plane) will be over a frequency range where the wave length is between 10 and 2 times the distance. If the wave length is greater than 10 times the distance you are in the 2Pi region. If the wave length is twice the distance you are pretty much in the 4Pi region.

[guest42212]

Don't worry, a small gap will make little or no difference.  It's not like the pressure of a box trying to leak out, and most of the gain is just the boundary gain, not from blocking the rear wave from getting around that way.

Yea. The interesting thing though is that there is a simularity to a 'box' ...
Seems there is no 'continuum' .....
I've tried before to measure the "sealedness" of a sealed box ......
(lower the driver slowly towards 'sealdness' and observe ...
(both aurally and instrumentally(observe impedance on scope))
It's like a ' jump mode ' ......