Why do You need driver off set?

[Jakob]

I'm just curious about why many speakers have an off set between drivers. Why is this, and is it useful in 2-way monitors? I've been experimenting a bit with my 2441's and E145's, and so far I can tell there is a difference in soundstage but I'm not sure if it sounds better or not.
I've searched the forum about this but couldn't find a good enough answer.

Regards: Jakob

[Zilch]

Offset front to rear? That's time alignment. Generally speaking, the objective is to align the acoustic centers of the drivers vertically. That creates a horizontal plane where the distance between them is constant, and, other factors being equal, sound waves emitted concurrently by the two drivers arrive concurrently at a listener in that plane.

The plane can be angled up or down as desired by adjusting the front to rear offset, as in Project Array, or with differential delay between the drivers.

By offsetting the acoustic centers left to right, the plane may also be tilted horizontally, thereby creating a line of time alignment where the two planes intersect between two speaker systems. "Toe-in" may then be adjusted to set a single point of absolute time alignment precisely in the center of the listener's cranium.... :p

[Jakob]

Thanks Zilch!
I'm aware of the time alignment thing, it was left and right offset i was thinking about. If You don't have an offset between the drivers, could this result in cancellation or amplification of certain frequencies?

-jr

[Zilch]

Asymmetric offset with respect to baffle centerline serves to minimize diffraction effects. They're still there, but them coming from the two vertical baffle edges don't reinforce each other so much that way, at least, as I understand it.

Offsetting one driver from the centerline more than the other generates the horizontally tilted plane of time alignment described above.

Yup, it's multi-source lobing -- cancellations and reinforcements, tho the diffraction effects themselves are a whole 'nother discipline....

[whizzer]

Many so-called authorities claim that offsetting the tweeter 3/4-1-inch from the vertical centerline reduces the "destructive" baffle-edge diffraction effects significantly. Given the rapidly falling magnitude of HF output of direct radiators even 30 degrees off-axis, it might appear absurd to claim that effects generated 90 degrees off axis could be that harmful, yet, if the distance from, say, three baffle edges is identical, these effects do add up to being significant. That's still not the be-all and end-all of the whole thing, however, for other equally authoritative authorities claim that off-axis response suffers greatly by reason of this "mis-alignment" and that since most listening is done, perforce, off-axis, a strict vertical alignment ought to be followed and that the "destructive" baffle-edge diffractions may be ameliorated by "rounding off" the baffle edges. In short, until we can teach a dimensionless point in space to radiate sound, then we're just going to have to choose for ourselves how to rank these priorities and go with the results. I've always preferred the vertical alignment, as much for cosmetic as sonic reasons, and perhaps my ears aren't golden, but I'll be damned if I can hear all that destruction. Of course, this is all moot for horn-loaded drivers.

[Jakob]

Thank You guys! Now I know!