Pelliott321 wrote:
Thanks Tom
How does it cancel 2nd order harmonics and nothing else
I understand that you have to wire opposing drivers out of phase
Actually I should have been clearer when I said it reduced the distortion. Since the second order distortion can be different in the two directions, when they are mounted facing the same direction the distortion from both drivers stays the same in one direction. Since distortion measurements do not take into account direction the distortion is the same. When they are mounted in opposite directions you get the higher distortion on any half cycle only from one driver.
Just for grins I'll put some numbers to it. If each driver creates 10% distortion in one direction and 0% in the other direction (it actually won't happen that way) the total distortion in one direction will be 10% and 0% in the other. the reason the distortion numbers as a percent do not add is that each driver is not only adding more distortion, but more fundamental sound as well. therefore the distortion percentage remains constant. If the two drivers are reversed, the distortion will now be 5% in each direction, 10% from one and 0% for the other in each direction. Remember it is a percent not absolute pressure. Since both the "good" and "bad" driver are creating the same amount of the fundamental but only one is now creating the distortion, the fundamental doubles but the distortion remains the same, therefore the % halves.
I have only heard this effect mentioned as far as second order but perhaps it works for other orders as well but that may depend on the driver construction and geometry to a greater degree for higher orders. I have no clue. However, although this may reduce some distortion, the 800 pound gorilla in the room is always insufficient linear displacement from the drivers. Once you exceed XMax, the distortion rises dramatically which is far more noticeable than whether or not the drivers are mounted the same way or not. The opposite direction mounting is just the frosting on the cake. If the drivers are mounted in such a way that the view of the back side of the driver is hidden it will not hurt to mount them in opposite directions. I did not do that with the eggs because with low distortion drivers to start with the acoustical gain was not enough to have to look at the back side of one of the drivers. It would have totally destroyed the visual effect of these speakers for very little advantage.