Originally Posted by pgaiduk
So then does it follow that a speaker with only one driver and one tweeter would be immune to any problems?
Is it solely the introduction of multiple drivers that kills off-axis response and causes these combing effects?
It all depends on the implementation.
For example, the primary source of loss of on-axis response is the diameter of the speaker's radiating surface, presuming that it acts like a piston with a flat top.
It is possible to implement a speaker with multiple drivers active in the same frequency range that is essentially free of any additional comb filtering effects. This can even be done with relatively large numbers of drivers and passive crossovers.
In the realm of implementation details, the speaker drivers can beat simple geometry limits by the following means:
(1) Point the multiple drivers in different directions.
(2) Do some very specific things with the phase of the electrical signals applied to each driver via the crossover, etc.
(3) Use drivers such as dome tweeters or midranges whose radiating surface is not flat.
(4) Place the drivers in wave guides.
(5) Intentionally construct the speaker's diaphragm so that it breaks up with vibrational modes and starts acting like a collection of small more-or-less independent drivers.
All of these things are done in different modern speakers so none of this is science fiction.