What matters most in speaker design?

Up until the analog signal reaches the loudspeakers, it's a two-dimensional signal: Variations in intensity (voltage) over time. The loudspeaker has to deal with six dimensions: Variations in intensity (SPL) over time, across three dimensions of space (including reflections), and finally the signal processing of the ear/brain system.

Now the ear/brain system does not hear waveforms as such; it deconstructs the waveform into a series of excitations along the cochlea in a manner that is non-intuitive. So waveform preservation is relatively non-critical. In many cases audible benefits attributed to waveform preservation may well be due to other factors that matter more, such as minimizing diffraction or avoiding abrupt changes in the power response. I can explain why these things matter to the ear/brain system if anyone is interested.

Duke

The most important part of a speaker design? Listening to it after fabrication. Voicing it.

What is great sounding speaker? Sound depends on many factors and people have different preferences. Do you prefer speaker with underhung motors (less distortion and less dynamic) or overhung motors(more distortion and more dynamics) . Do you listen soft or loud. Do you listen to Jazz or Organ music? Do you crave for pinpoint imaging or heavy metal punch. Do you care how large sweet spot is. How does it perform in small or large room etc. How easy it is to drive.

Frequency response test is pretty much useless. Bad speakers with horrible phase errors might show with excellent flat frequency response.

I would agree with Shadorne on transducers. If pair of speaker costs for instance $1k then manufacturer sells it to stores for about $500. Components cannot cost more than 1/3 of it (to cover labor, expenses etc). Now we are left with $170. Both cabinets will cost $50 both and we're left with 120$ for let say 6 transducers and crossover components. That's why my speaker had originally $25 Vifa tweeter and Mylar + electrolytic caps in crossover. Good tweeter is 10x this and good cap is $100 (I just replaced $15 caps wit $100 caps of the same value and sound + imaging improved a lot).

There is no universal answer but you won't get very far with cheap transducers (especially tweeters). I don't design speakers but after concept design I would start with the best tweeter I can afford and worked down from it.

Uniform polar response with a slow monotonic decrease in total power above a few kilohertz preferably with less output towards nearby objects.

Getting there is a function of driver diameters, driver bandwidths, spacing, baffle shape/dimensions, and the cross-over.

There appears to be a point at which drivers are "good enough" in terms of distortion and stored energy.

Provided output levels are limited, you sit closer to accomodate the reduced directivity, and get farther away from the side walls my Linkwitz Plutos ($140 driver cost) are surprisingly close to my Orions ($1400).

"There appears to be a point at which drivers are "good enough" in terms of distortion and stored energy."

Drew - are you saying that Beryllium tweeters in new Revel Saloon 2 or diamond tweeters in B&W are mistake (unnecessary expense)?