Speaker impedance patterns - how to read them?

Most conventional cone speakers have a rising impedance as frequency goes up.

I’m sorry that’s not really true. You are describing the impedance of a coil.

It is true that larger cone drivers have this, and that this effect needs to be dealt with but it is not true for a speaker as a whole. A quick survey of impedance curves at Stereophile would show this.

Here’s a random sample:

https://www.stereophile.com/content/stenheim-alumine-three-loudspeaker-measurements

It is also true that the most challenging areas for a conventional speaker tends to be in the bass, but the impedance curve of a raw woofer is not at all a good indicator of the impedance curve of the speaker as a whole.

You are starting at the wrong link in the chain  start with speakers you like what if you don't like any speakers with your amp and you can crunch all the numbers you want its not going tell you how they sound demoing is the only way if your dealer don't have your amps bring the amps there 

Enjoy the Music
Tom

Actually Eric,  it is absolutely true.  You provided one driver.  I've measured hundreds of impedance curves not a couple.  
Yes,  I used a woofer as an example, but this happens in many mids, tweeters etc and their individual impedance curves do show up on a graph.  Of course, I've stated often on this site, overall, I do prefer and recommend impedance compensation networks. 
Unless you are describing some sort of ribbon/amt's which tend to have a very flat impedance curve. 

Basically the frequency response of an amp with a low damping factor(high output impedance) will be affected by the peaks and dips of the speaker. The amp even if it's flat into a test resistor will not be flat into a reactive speaker load. The amp response will have dips and peaks at the same places as the speaker impedance curve. How big these will be depends on the damping factor(which can vary with frequency by the way). The higher the damping factor the smaller the changes in response until the damping factor is high enough so the amplifier frequency response is flat with the speaker.

I recall a letter years ago to Hi Fi News that said that using very low resistance speaker cables minimized the affect for low damping factor amps. Frequency response was shown for normal resistance cables which exhibited the frequency variation. But with very thick cables(about 4 gauge if I recall correctly) the frequency variation essentially was gone. But this was before modern cable technology and just changing to very low gauge cables will probably also affect other variables in cables which may or may not be good.

Published loudspeaker frequency response is virtually always measured with a solid state amp which puts out increased wattage into an impedance dip, and decreased wattage into an impedance peak. Most speakers are "voiced" for this type of amplifier.

Relative to a solid state amp, a tube amp puts out more wattage into the impedance peaks, and less wattage into the impedance dips. So the speaker’s frequency response will be modified accordingly. In general the lower the speaker’s impedance, the more pronounced this effect.

Ime a relatively high and smooth impedance curve tends to work well with tube amps. The bass impedance peaks can sometimes be manipulated a bit by lowering the port tuning frequency, and/or adding damping material inside the cabinet, if necessary.

Occasionally you find a loudspeaker whose impedance curve zigs where its frequency response curve zags, and that can work well with tube amps. I recall seeing such "complementary" measurements for one or two Silverline Audio models.

I’d suggest asking the loudspeaker manufacturer whether they recommend tube amps for their speakers. Audio show reports can also be a source of information about amp/speaker pairings.

See this paper by amp designer Ralph Karsten:  

http://www.atma-sphere.com/en/resources-paradigms-in-amplifier-design.html  

Duke
tube amp dealer, tube-friendly speaker designer