How loud is loud, What DB is actually loud?

The 3 db gain is correct for free space ( anechoic) go ahead and measure your hi-fi system, with speakers l/r and with room gain it is more than 3 db, when you turn off one side from the listen position.

regards,

"Play your system in mono, turn of one channel , guarantee you will have more than a 3db loss"

Yes, but not because of the smaller radiating area but because you cut off half of the power.

yes, there is room gain, but since it applies to both speakers it disappears when you'll take the difference - the gain is still 3dB.

I must be missing something - I would thing that if one speaker is creating certain SPL at my sitting position (including room reverberation) second exactly same speaker will double this SPL. Doubling SPL means 3dB increase

Very good write up of all this sort of stuff at www.phys.unsw.edu.au/jw/musFAQ.html (FAQ in music acoustics). In particular, "Does adding two equal sounds give an increase of 3 or 6 dB? Why?" is explained very clearly.

Frank

Frank, Thanks, great link.

Interesting thread.
Mainly of the "who knew?" variety, re: SPLs in a car.

As to the substance of the OP's original question:

I'd propose that he might want to find subwoofer(s) that will produce single digit THD at 95 db (quasi)anechoic - the conditions used for most subwoofer tests - at 30-35 hz. That will allow a safety margin for music, particularly when room gain is considered. There aren't all that many single subs out there that will satisfy this condition - JL, SVS, Rythmik are a few that will do so. A pair (or more) of subs buys more headroom and a wider variety of choices. Once you've found a suitable subwoofer (or subwoofers), your choice of main speakers will be much broader.

If max clean SPL is the main goal, it is the unusual circumstance where you should probably choose a subwoofer first and work backwards to the rest of the system.

Just MHO.

Marty