Elevating subwoofer about two feet off the floor

I think you’ll find that "good" subwoofers are voice by the designers/manufacturers to take into account the floor (even wall) re-enforcement to get the FR as flat as possible in their operational range.

By raising them, they my very well roll off too early and maybe not give the low bass the were designed to do.

Cheers George

Subwoofers "voiced"? There is no voicing possible at subwoofer frequencies. Danny Richie of GR Research addressed this issue recently on his website, in regards to the x/o mod he designed for the new Elac speakers. Voicing involves frequency ranges of larger swathes than a mere 90Hz (10-100Hz). Not even any tailoring, really, as woofers are crossed-over from at too low a frequency to allow or require that. The floor and wall reinforcement you mention effects all subwoofer frequencies relatively equally (in comparison with midrange and tweeter drivers) as far as the subs themselves go, though the dimensions of any given space have an enormous effect on the sound of all subs in that space. With subs it is pure output and room dimensions that are involved, plus non-voicing issues such as distortion at Hz at SPL, time domain behavior (as revealed in waterfall plots), mechanical issues such as motor power versus driver mass, enclosure resonances, etc.

If you remember the work Roy Allison did after he left Acoustic Research, he addressed the issue of floor reinforcement or cancellation from woofers located at certain distances from the floor in his Allison Acoustic speakers by putting the woofer at the bottom of the cabinet, and crossing over to them at a lower than common frequency, with the midrange and tweeter drivers put at ear level. He didn’t voice the woofer, unless you consider floor-loading voicing!

"Voiced" can be an expression of getting it right in the surroundings it’s in. whether it be bass mids or treble or combinations of all.

Moving a sub back and forward in a room to get it phased right to the mains is also call "voicing".

It can measure flat in an anechoic chamber, but then has to be "voiced" for domestic situations (eg: next to a floor).

So I stand by what I said above, that a good sub that’s designed to sit on the floor will be "voiced" to sound right (flat if you wish). By raising said sub high off the floor may be counter productive to it’s designers "voicing."

BTW if you put Roys’ designed corner speaker out into the middle of the room they had no bass, they were "voiced" to get reinforcement from the room and or floor boundaries. And others like Bose with their shocking 901 had no bass if they weren’t near and facing the wall, and their are many others as well, Linn Isobarics etc, all "voice" to be next to a boundary whether wall or floor.

So a good designed subwoofer will sound it's best where it was designed to be, not 10' off the floor.  

Cheers George