why are two subs harder to place than full range?

Generally fullrange speakers offer fewer placement options than two subs would, but on the other hand the designer probably has a pretty good idea of where they will be placed in the room. With dual subs, the range of possible placement options expands enormously as compared to a pair of fullrange speakers.

If you can crossover at or below 80 Hz, and with a 4th order lowpass filter on the subwoofers, then you have a great deal of flexibility regarding subwoofer placement. If you have to cross over higher and/or do not have a steep lowpass filter, then keep the subs near the main speakers. The point of this paragraph is, you do not want to be able to hear the subs as separate sound sources due to lower midrange energy coming through them.

Assuming you can place the subs as you see fit, yes there are several different placement strategies. I favor asymmetrical scattering to average out the room-induced peak-and-dip patterns generated by each low frequency source. You want the subs to be spread out in at least two dimensions, relative to the room boundaries. As the number of spread-out low frequency sources goes up, the importance of the exact placement of any one of them goes down. So in practice, multisubs are usually more placement-forgiving than a single subwoofer is.

Duke
dealer/manufacturer

thanks duke, i really respect your postings, both in terms of tone and content.

For more than a dozen years I used a pair of Magnepan MMGs, each sitting atop its own PSB Alpha subsonic. The combination looked beautiful, and sounded wonderful. I positioned them where the MMG's sounded best, and the subsonics always followed gracefully.

I'll bet my 1.6s would scare you sitting on top of my HSU VTF2mkIII. Total of about 7 1/2 feet tall!