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The Halcyon


By: Curt Campbell

Main / Design Goals
Halcyon (pronounced HAL C en) Denotes a period of time in the past that was idyllically happy and
For me I remember the days as a young pup when the main entertainment item in the living was the
big floor standing radio. This furniture quality wood beauty got several bands, including shortwave
and aircraft bands. -It even got AM! If memory serves, the speaker in this behemoth was 12 inches
for certain, and it had such wonderful tone, and brought much music, radio programs, and enjoyment
into our home. That full range coherent sound was my goal for this design, although with the
refinements of a half century of speaker design I'm sure this design sounds much better than the
Of course there are many examples of full range drivers, and some provide excellent bass, or great
high end performance, but rarely does one excel at both. I found the Alpair 10P to have a nice paper
sound, and great top end performance, but likely wouldn't provide the bass frequencies at the SPL
levels I was looking for. I also felt the Alpair would perform better if those lower, excursion
demanding frequencies were removed from its duties. In addition, I wanted the enclosure to have a
more modern look.
To maintain that coherent sound I decided a first order crossover to the woofers would be essential. I
felt utilizing a series crossover would just add icing to the cake.
Major specifications
A 2 way vented design featuring the SB17RNX2C35-8 uncoated paper cone woofer
and the Mark Audio Alpair 10P full range driver. The Alpair is housed in a semi open back cylindrical enclosure, while the SB17's perform in individual transmission lines that are merged at the port in a mass
loaded configuration Nominal Impedance: This one is definitely a 4 ohm design. As a consequence of the first order crossover the impedance curve flirts with 3 ohms at some frequencies below 500 Hz, but spends it time above that point at 8 to 12 ohms. The worst amplifier load is 3.8 ohms and -40 degrees at 80 Hz. This suggests the partnering amplifier should be capable of driving 4 ohm loads with good current
Dimensions: external: 9" wide, 38.25" tall (including the 4" base) and 22.5" deep
Basic Sensitivity: Approximately 88 dB / 2.83v / 1 meter
Max SPL: (Modeled at woofer published Xmax) 104 dB / 1 meter

The Halcyon kit is available here.

See full design below.

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