What does the term "Speed" mean in a speaker?

Mass and inertia guys. Transient response is how fast the driver starts and stops. Lets say you have 6 inch speakers with identical voice coils and magnets. In one the cone weights 1 oz and in the other the cone weights 2 Oz.  When I play a transient sound like a drum stick hitting a steel plate the 1 oz cone will start moving fractionally before the 2 oz cone because it has less inertia. It will also stop faster with fewer oscillations (ringing). Things are really more complicated as the Transient response of a driver is not only determined by the mass of its moving system but also by the power and damping capability of its motor. So an 8 inch woofer does not necessarily have better transient response than a 12" driver. Speakers with better transient response have a crispness to their sound missing in speakers that don't. This becomes quite evident when listening to ESLs, well designed horns, ribbons and to a slightly lesser extent planars. Speakers with better transient response are more revealing and can easily be made to sound crappy with bad or poorly set up equipment which I think is why some people have a jaundiced opinion of them particularly horns which are also not easy to design. 

I think a lot of what you are writing about, mijostyn is actually related to room interactions.

Your writing, while accurately portraying how dynamic drivers work makes a leap I don't feel comfortable following.

A dynamic driver can have a lot more dynamic range, smoother frequency response, better low frequency and lower distortion than a planar speaker attempting the same. What it won’t do is interact with the room the same way. Genesis got around this by making towers of 12" drivers. :)


Snell mounted the woofers as close to the floor as possible.

The final result is always a matter of speaker and room interactions, but the idea that planar speakers are measurably faster is not true.


Best,

Er

mass and inertia matter, but you missed one parameter, driver surface area, which determines the amount of excursion for a particular level of volume, which goes a long way determining the linearity of the response.

mostly in the mid bass you find one driver, maybe two. or two crossed over. my speakers each have -4- 97db, 7ohm, 11" ceramic matrix woofers. covering 40hz--250hz. with all that surface area and a very stiff light ceramic membrane, the need just a tiny bit of excursion so they stay linear. and the amplifier is not stressed by the load with 97db efficiency.

so you get planar or horn type speed, but dynamic cone impact. images have weight and authority. tonality is maintained and not washed out.

Speakers with better transient response are more revealing and can easily be made to sound crappy with bad or poorly set up equipment which I think is why some people have a jaundiced opinion of them particularly horns which are also not easy to design.

I am not quite sure this is entirely true.  A driver that has better transient does not mean it should have more detail or more revealing.  Better transient allows better micro-dynamic or macro-dynamic or both, BUT dynamic is not the same as detail or at least it's not a one to one exact.    

Now on the other hands, if a driver has more "resolution" then it will have more detail, but a more accurate characterization is to say the driver will "reveal" more details.  It shouldn't create more details that was not on the tape in the first place.

Transient and resolution are mutually exclusive that is one driver can have either or both.  Having one does not automatically also having the other.

Aluminum driver is usually perceived to have more "details" but a lot of that comes from it upper frequencies which tend to have a lot of break up and people sometimes interpret excess high frequencies as "detail".  And if the designer does not address the break-up, then aluminum will sound "crappy", but is it the driver fault or the designer fault?  I personally have used some cheap aluminum driver and expensive paper driver, and although the aluminum may appear to sound faster, the more expensive paper driver reveals more details, more natural detail.  So go figure.  

As for speakers that "sound crappy with bad or poorly set up", I think a lot of that comes from final implementation.  I've had the Thiel CS2.4 which is very revealing but it never sounds crappy even on bad recordings.  Speakers that sound crappy on bad recordings tend to have excessive energy on the high frequencies or some weird frequency response.  

I think there's a big gap between a speaker that sounds fast, and a driver that IS fast.

I mean, there's a lot of reasons for speakers having more detail or jump factor. The actual transient response of the drivers used does not really contribute to all of it.
How the speaker mates to the room, and frequency response I think are probably the first two things the casual listener associates with speed.

That's fine, nothing wrong with that since the end result is what matters.