What does Q mean in speaker specifications?

Here is simple/nutshell info on such from a speaker manufacturer.

Having used various vintage single driver speakers, mated with various tube/SS amps, for the past 20 years (as well as different enclosures - including open baffle) I do pay attention to the combined QTS measurements (and/or guessed values based upon listening/experimentation) of the drivers I've owned/used/consider'd.

Damping factor (low values) of the amps I've used/use is also a consideration.

DeKay

erik_squires is correct. The original LS3/5a had a Q of 1.2 which produced a bump in the mid bass. This was done to balance the bass to the rest of the sound spectrum since a flat speaker sounds lean if it's bass resonance is high like the LS3/5a. But the price of a high Q to balance the sound is increased overhang in the bass roll off and thus decreased definition in the bass.

Dyna:

Do you have documentation for the 1.2 "Q" measurement?

Having owned Rogers Ls3/5a's for 1979-1986 I find that spec hard to comprehend (considering the cabinet size).

Yes, they did had a mid-bass hump - making them difficult to properly mate with subs (including their non-sub AB1's which I also used).

DeKay

The system Q of driver & cabinet has been used as an essential guide to a speaker's bass quality since the seminal work in modeling bass alignments using filter theory was done in the late 50s-early 70s by several people.  The parameters identified are typically called the Thiele/Small parameters,  Q itself is unitless and represents the damping factor (tendency to return to rest).  There are several Q values (speaker electrical, speaker mechanical, box) in modeling a driver & enclosure, but speaker makers (as opposed to driver makers) will typically only use the Qtc of the bottom end, which includes the speaker and enclosure.

In general, a Q of .5 is critically damped, with no resonance & ideal transient response.  A Q of .707 is considered maximally flat, with a 3 db rise at the system resonance.  Higher Q values result in progressively more boost & poorer transient response.  Note that I'm only talking about closed boxes here.  All I can tell you about bass reflex is that transient response is always worse and the roll-off below resonance is 24 db/octave vs 12 for closed boxes.  And don't get me started on those port plugs!

This is the measured response of the LS3/5A, according to Hi-Fi World.  As speakers go, it doesn't look bad at all.  The bass alignment can be seen in the steady climb to the left below 300 hz & peaking around 100.

This is all great information. You learn something new everyday. @yogiboy are you planning to order the Q7s?