Resurrecting an old thread to share some of my thoughts:
A 100-watt amp through A 2x12 should be loud enough.
Speaker efficiency also plays a factor in loudness.
http://www.octasound.com/pdf/bulleti...d_solution.pdf
Now whether a 2x12 sounds as good as a 4x12 is another matter.
I've discovered that bigger cabinets sound better than smaller cabinets. They sound bigger and fuller. I think that's why we are seeing more "oversized" cabinets on the market today. Given a speaker configuration, e.g. a 1x12, an "oversized" cabinet will sound bigger than a typical 1x12 cabinet.
American Viking said a 4x12 spreads the sound better. But another way to spread the sound is to use the "detuned" approach mentioned by PaoloJM where you remove a speaker. If you search the internet, you'll find others that have discovered that removing a speaker doesn't really decrease the volume much (if at all).
Currently I use a cheap $69 2x12 cabinet from Shredz Music in which I installed only one speaker. So technically it is an oversized 1x12. It has way more bass and spreads the sound better than my bandmate's Marshall 1936 2x12 cab. It actually has too much bass. We both run Marshall 6100 amps with similar settings, except I have to run my bass controls at or near zero.
Check out these cabinets that use a "detuned" approach (they have openings in the front of the cab):
- Freda Live
- Port City Wave
Mills Acoustics also makes cabinets that reportedly have the spread of a Freda or Port City Wave cabinet yet have a tight bass response. I'd really like to try one myself.
I was worried about my 100-watt Marshall exceeding the power limits of my speaker (which handles 65 watts). But when I measured the number of watts actually output by the amp at the speaker at gig volumes, I discovered that I was only using about 5 watts max. I'm using a WGS Veteran 30 speaker which has a sensitivity rating of 100dB SPL for 1KHz signal at 1 meter.