Open baffle speakers can work exceptionally well (I own a pair of Orions, and the latest versions are better than everything else I've heard provided you can live with the SPL limitations. Earl Geddess' waveguides crossed to large (10, 12, 15") mid-bass drivers where the dispersion matches are the only thing more than one or two Orion owners have preferred, but I've yet to hear those) but I wouldn't bother with any open-baffle design that didn't use multiple driver sizes and baffle widths scaled to fit the wavelengths involved and active cross-overs at least for the lowest frequency drivers.
The issue is that below some frequency a dipole requires an additional doubling of displacement per octave. For a foot wide flat baffle this happens around 400Hz, 2 feet get you 200Hz, etc.
People who throw too few drivers on a single baffle make it wide to compensate, which in turn produces a multi-lobed polar response that doesn't sound much like music (I say that after having heard the $42,000 a pair field-coil Feastrex drivers in such a configuration both with and with out sub-woofers).
You need multiple drivers and baffle widths which get bigger at low frequencies.
The same issue limits sensitivity at low frequencies. Put a 90dB bass driver in a 15" deep H-frame and it'll match a box speaker's output at 153Hz, 84.4dB at 80Hz, 78.4dB at 40Hz, and 72.4dB by 20Hz. You can use a pair of drivers and load them into half space to boost efficiency numbers to 99/93.4/87.4/81.4dB.
If you don't want to limit low frequency extension, you need to either use an active cross-over (where the low sensitivity in the last octave doesn't matter, because there isn't much musical energy and you'd bottom the drivers anyways) or pad the rest of the speaker down to match which doesn't work. You can also rely on a high-Q resonance to get some low frequency output, but stored energy is never a good idea.
Hotmailjbc writes:
>the costs are minimal evidently but would like to hear from someone with experience about the sound quality of this design using quality drivers etc.
Don't bother with a full range on a baffle even if you add a sub-woofer and/or super-tweeter.
Done right the costs aren't minimal. Current Orion construction costs should be somewhere north of $2500 plus an extra 4-6 amplifier channels. The NaO Note is less expensive but is still a bi-amplified 4-way with 5 drivers a side ($1200 for just the drivers).
