A full range speaker?

Just buy a pair of Svs SB 3000 subs or
the Svs 3000 mini subs  they are loaded with DSP technologies 
and agreat app for integrating Bass and adjustments on the fly 
this way you Can concentrate on the much more critical mid range 
on ,and have free shipping and a 45day audition. And refund 
policy Nothing to loose and excellent sounding tuneful Bass.

All full range drivers got poor ability not only 20-60 Hz , but also 60-300 Hz , so adding sub is not solved the problem, we  still have big gap in mid bass. . Sound not full scale ,like traditional 3  Way LS. 
If you like how full range sound , the need  add regular woofer with crosspoint 400-500Hz like  all my line  of speakers 

is a bit looney.

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EDIT
OK I just read your post a  2nd time, just after posying the response below...
Grant it , in  some new age electronic music, there  is a  good representation of the  super low, super high fq.s
Exception to the rule. 



Take a very close look at the classical orch fq chart above,,somewhere,,,
I downloaded the page and use a IP camera to blow up the image so i can see the main fq’s region .
60hz-2khz
I am not sure who started this idea of musical notes within the 20hz-40hz and above 12k hz ~
There is nothing there.
If we go to Mr Carlson’s lab and he sets up a testing of these 20-40hz and above 12khz...you would be in shock at how puny, minisclue is the sound force.
And then ask Carlson to find these notes within a jazz, classical, or rock LP, he would be at a loss. His gadget meters would only faintly register these hits.
Only if we get a bass drum smashed hard by Keith Moon. And a cymbol smash by Billy Cobham. will we see the below 40hz and above 12k fq registered. 
And when Carlson adds up all the fq’ timings hitting below 40 and above 12k,.,,,would result is1%

Its all flufff,
WE;ve been propaganadized, pure snakeoil

All (well 99%) of classical muisc falls in the 60hz-2500hz.
THe purpose of a tweeter is to add sheen and sparkle
Tweeter=tweeter, All good tweeters are equal. What makes a tweeter superior vs the other is sensitivity rating.
Below 91db is weak and lacks voicing force/power.

Also this 60hz-2khz region is mostly carried by the midwoofer,.
making the midwoofer the very heart of the speaker.
Thus the cone material is most critical in how these fq’s will sound.
Which is why I do not like paper in my midwoofers.
Magnesium has superior damping character, giving us a much lower distortion/coloration .
Which equates to a sweeter, cleaner musical image.

for good bass 40 hz and up is good enough

Mozartfan, all you need is a transistor radio and you will be happy as a lark. But, what the heck are you doing here? Why don't you join a bridge club.

There is more to live music than the frequency of any given note especially when it comes to percussion. But, since you insist, the lowest note on a pipe organ is 8.17 Hz. The lowest note on a tuba is 16.35 Hz as is the lowest note on the Bosendorfer Imperial grand piano.

You obviously have not heard a proper system. In the minds of little people if you have not experienced it, it does not exist.