As Rick mentioned bi-amping will enable you to match sensitivities. I've built 7 sets
of arrays, although none with high quality drivers like yours. As you probably know
already, your XO point should guide your woofer spacing. The higher you cross the
woofers, the closer they should be to each other with 1/2 wavelength or less ctc
spacing being recommended, but Dr. Griffin has success with up to 1 wavelength.
Other factors that should guide your design decisions are the ceiling height, listening
distance, how you use your speakers, and your goals in terms of bass extension.
If possible you want nearfield line behavior for any listening position in the room, so
the tonal balance doesn't change with position. Lower frequencies require longer line
lengths, and below 100hz means you they need to couple with the floor and ceiling
boundaries. Also, the further your listening position, the longer the line needs to be.
How you plan to use the arrays isn't often discussed, but it should be a primary factor
in your design decisions. Properly dimensioned arrays are far superior to point source
speakers for group listening, because they fill a room more evenly with sound. For parties,
or if you are up moving around while listening (I use a pair in my workshop area), then
the array height, including HF units, should extend above ear level, because sound is
quite attenuated beyond the ends of the line. This means that while you may get away
with 1 ribbon per speaker for seated listening, you'll probably want a full size array using
2 of the 30" ribbons per side.
My recommendation would be to go for the gusto, if your budget permits, and use 2 ribbons
per side. I'd also go quite a bit taller than 60", so your ear level when seated is fully within
the plane of the bottom ribbon (knees and feet don't need to hear your ribbon, and I wouldn't
have typical ear level right at the transition between the 2 ribbons). Ensure that the upper
ribbon extends above ear height when standing up. Whether 6 or 8 woofers are necessary
will depend upon your XO point, but that line should be as long as you can live with and
definitely extend past ear level when standing.
I promise you that as long as budget isn't a problem, in the long run you'll be happier with
the taller array. Plus it will guarantee that guests will be impressed with their sound.
I suggest you do a little experiment first, so you can really appreciate how powerful array
behavior is. Mount 4 of the woofers on a scrap piece of wood very close together. Wire
them series/parallel for a good impedance load and play some music through them. While
listening nearfield within the array plane, stand up to get your ears beyond the end of the
line and notice the extreme attenuation as your ears go past the end of the line. Then
try the same thing, but with only one driver connected. It's a real eye opener that will
sell you on arrays forever.
