Recently I built a custom pair of speakers based on the Planetarium Alpha system. My customer couldn't spare the floor space that the multisub system demands, so I built them as floorstanders with the bottom half of each speaker being a built-in downfiring subwoofer.
The subwoofers are driven by a single external shelf-mount amplifier that puts out about 500 watts into the 8-ohm load that the subs present (they are 4-ohm subs, wired in series because the amp isn't rated for 2-ohm operation; this configuration doubles the effective damping factor). The amp has a single band of parametric EQ and a switchable bass boost feature, so extension into the mid 20's is quite feasible. The sub is a 10" unit with enough excursion to handle the full output of the amp down to 20 Hz, in a Qtc = .5 sealed box. So it's nice and tight, with very solid impact on kickdrum.
The finish is a custom black stain that allows the woodgrain to show through, and then there's a hard clearcoat on top of the stain. I think I'll call this finish Black Oak. This is the first time I've had my woodworker do this type of finish (which was at my customer's request), and it came out really nice. The front is solid 3/4" oak backed by 3/4" MDF, and the other surfaces are veneered MDF. There are solid oak "skis" on the bottom for protection.
Here's a shot of the front:
And, here's a shot of the rear:
The bottom set of binding posts is the input for the subs. The set just above that is the input for the main speaker section. The top set of binding posts is for the external level-setting resistor for the compression driver (which can be seen in the picture). The port is for the midwoofer, and is tuned very low so it actually increases the power handling by reducing cone motion from bottom-octave signals. It also decreases backpressure on the cone in the midrange region.
The 45-degree angled rear/corner panels make it easy to visually line the speakers up at the 45-degree toe-in angle that I recommend. This gives a very wide sweet spot, and very good tonal balance throughout the room.
I haven't decided whether this will become a regular part of my lineup, but at least it's something I can do on a semi-custom basis since the design work has already been done.
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Specifications:
Type: Controlled-pattern monopole with built-in subwoofer
Woofer: 12" prosound type with treated paper cone and high quality motor
Tweeter: 1" compression driver, neodymium magnet, polyester diaphragm
Subwoofers: 10" long-throw, Qtc = .5 sealed box
Subwoofer amp: 500 watts into 8 ohms, 4th order filter (30-200 Hz variable), 1-band parametric EQ, switchable bass boost, continuously-variable phase control
Waveguide: Low-coloration 90 degree constant directivity
Crossover: 1.5 kHz, asymmetrical transfer function
Impedance: Between 8 and 12 ohms, aside from bass impedance peaks
Efficiency: 96 dB/1 watt at 1 meter
Typical System Bandwidth: 25 Hz to 17.5 kHz in-room
Power Compression: Less than 1 dB of compression at up to 112 dB/1 meter SPL
Recommended Amplifier Power: 3-100 watts (unclipped peaks up to 200 watts acceptable)
Dimensions: 44" tall by 14.25" wide by 14" deep
Weight: 110 pounds each + 30 pound subwoofer amplifier
System Price: $6000 in Oak finish; Black Oak (shown) slightly more
