What does the size of the tweeter affect?

[The Camry]

is it just more cone area so they can get louder? is a bigger tweeter more of PA kind of thing?

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[LosIsATool 5,000+ posts]

Bigger tweeter gets you a few things. Going from a 25 to a 28mm example will give you more output, wider range, wider sound stage, better in every way.

 

[Jeffdachef 5,000+ posts]

by that logic i'll make a wtb thread for 18" tweeters.

 

[Jepalan]

In general, larger drivers can play lower (very gross generalization here). And, there is an advantage when trying to achieve optimal imaging to having a broader range of frequencies coming from a single source. Ideally you want to cover the entire vocal range from one location (big tweet, fullrange, or tweet+mid) if you can.

On the other hand, the point at which a driver "beams" is directly related to effective cone diameter. The beaming point is the frequency limit above which the driver becomes more directional and off-axis response starts to roll-off. (Again, in general) larger drivers will start to beam at lower frequency, so positioning of a larger tweeter can be more critical. That said, sometimes off-axis mounting can help 'tame' harsh highs by leverage the natural roll-off above the beaming point.

In addition, by lowering the cross-over point between midbass and a larger tweeter you are avoiding more of the beaming frequencies in the midbass driver - which tends to be problematic when they are mounted lower in the doors. To me this is the biggest advantage of tweeters that can play low when using a typical two-way component setup. You can keep the midbass in their omni-directional range and bring more frequencies up to ear level and create better imaging.

Of course, things are a little different for cone-based, dome-based and planar drivers.

(EDITs were made for clarity)