Originally Posted by coctostan
Well, the better extension is a tradeoff and not just with efficiency. If you don't need the extension, then you should use the M version. It is simply better from 200hz and up. If you need the extension, you will take a hit in frequency response. You can correct for that surround resonance so it is not a deal breaker by any stretch. It is just a matter of intended use.
For my purposes, I'll take the extension hit.
We both would (and do) buy the TD12M for the same reason but if most people can not hear the "simply better" then does it really matter?? The added extension is a bonus at a sacrific of sensitivity.
It once again comes down to specific design goals, knowledge and acceptance of any compromises.
Some 2-channel guys don't even use subs and most don't have proper bass management like HT guys. It is the same reason most retail speakers have extension down to 30-50hz. Some people have crappy sounding subs that are better crossed at 50hz. Some people are hanging onto ideas that IMO died 20 years ago like separate subs are bad or any processing is bad, etc.
FWIW, After all my research and experience the idea of a 80Hz XO point to separate bass between main speakers and subwoofers is a compromised solution that limits having the smoothest in room response and best time domain control. Instead I would go with Geddes premise of running mains full range and having "double bass" processing abilities.
The XO point of 80Hz (or whatever the the exact number 70Hz to 120Hz) is more about removing the flaws of the main speakers in the bass department. If we instead design main speakers that have high quality bass then we can use the to help with the big bad bass issues everyoen has.
Instead of thinking about removing main speakers from the bass equation I think in theory we are better off thinking about having main speakers compliment quality sub systems. Hard XO points do not allow for this.
Conclusion, there are in room bass response advantages to having main speakers play down to 30Hz at a high quality level. They allow us to have "extra" bass points and that can compliment very well with a mulitiple sub solution.
I never liked any 2-way waveguide solution with a F3 point at 70 or 80hz in the first place either, I understand the high F3 point is simply a fact of science (higher sensitivity, higher frequency performance = less low frequency extension). I always added bass bins below to extend the response.
It goes like this..
Main speaker with limited bass performance say below 80Hz + subwoofer system is a compromised choice.
Full range main speaker alone is a compromised choice.
Full range high performance main speaker + Subwoofer systems is hypothetical the non-compromised solution choice.