I've seen a couple of plans that specify for the tweeter to be below the woofer....does it sound different from a more conventional tweeter above woofer?
Typically it's done to compensate for lobing. The main lobe may point downwards so by flipping the drivers it will point upwards. Of course the actual tilt, driver height, and listening height all influence this decision.
Assuming a 2 driver 2 way - there are a few of reasons (and probably more):
1. tilt the primary vertical lobe upward, since the acoustic centre of the tweeter is further forward that the woofer. This would normally place the woofer on the listening axis. The same effect (tilting primary vertical lobe) can be achieved with asymetric crossover slopes
2. Position the woofer to minimise the 5th harmonic pipe resonance in very tall enclosures
3. Place the woofer appropriately in a desired transmission line
Essentially - driver orientation, as well as off centre baffle placement are merely different solutions to the same problems. With speaker building there are often (at least) a couple of solutions to each problem.
David.
1. tilt the primary vertical lobe upward, since the acoustic centre of the tweeter is further forward that the woofer. This would normally place the woofer on the listening axis. The same effect (tilting primary vertical lobe) can be achieved with asymetric crossover slopes
2. Position the woofer to minimise the 5th harmonic pipe resonance in very tall enclosures
3. Place the woofer appropriately in a desired transmission line
Essentially - driver orientation, as well as off centre baffle placement are merely different solutions to the same problems. With speaker building there are often (at least) a couple of solutions to each problem.
David.
Inverted drivers are at times used with odd order crossovers to compensate for the downward polar tilt caused by phase difference between the high and low pass sections.
If the geometry of the drivers are done correctly then you can get a +15° tilt from the drivers which compensates for the -15° tilt from the odd order filter. Result ZDP (zero delay plane) becomes 0°.... sort of a pseudo time alignment.
There's some info on it in the Loudspeaker Design Cookbook (7.23 in 6th edition).
If the geometry of the drivers are done correctly then you can get a +15° tilt from the drivers which compensates for the -15° tilt from the odd order filter. Result ZDP (zero delay plane) becomes 0°.... sort of a pseudo time alignment.
There's some info on it in the Loudspeaker Design Cookbook (7.23 in 6th edition).
I know a skilled and VERY critical designer, who would never do that, but he actually ended up doing just that, so yes I suppose it can be done right ... as rabbitz points out, if you know what you are doing 
I suggest to play with Edge :
http://www.tolvan.com/
to observ the diffraction effects on a tweeter positionned on a more central position than usual.
http://www.tolvan.com/
to observ the diffraction effects on a tweeter positionned on a more central position than usual.
As Dave said, this type of design is often required in folded pipe designs , where the main driver needs to be at a specific position in relation to the pipe. This invariably (because of the way things need to be done) puts the woofer at the top the box, near the fold.
So it is generally the woofer position that forces this type of design.
That being said, so long as you watch the acoustic axis of the x-o, there should not be any problems.
So it is generally the woofer position that forces this type of design.
That being said, so long as you watch the acoustic axis of the x-o, there should not be any problems.
One benefit, I can think of, is to have tweeter at ear level in case of very tall speaker, or in case that you listen from bed.
I don't think there are many other differences.
I don't think there are many other differences.
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