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Original Message
RE: Lowther PM6C in Karlson 12
Posted by freddyi on December 6, 2016 at 01:28:38:
I think I would use a single vent rather than the six slit distributed vent. May depend upon your music. "If" the slit vent were presented with a true sin wave in the region of tuning, then it would produce overtones. K12 changed a bit from 1954 as the "Karlsonette" (before K8 was introduced) with a horizontal slot vent to a distributed 6-slit vent around 1956. One later model had a hole array and was apparently sold sometimes with a blank port panel. That model re-introduced a full width rear shelf. In the 1954 K12, there was a sliding 3 position bar to tweak the rear lowpass gap.
if you build a version with full width lowpass gap, then it might be useful to tweak that gap using music with clean transients on things like drums, and plucked/slapped upright bass viola
below are approximate dimensions - material thickness was 3/4" - not 5/8" but GregB was working from Karlson's drawing in the kit's manual
a single vent of about 12 sq. inches would be ballpark for a K12
all K12 seem to have the same size from 1954 to Karlson's death in 1973 - ~24.5" H x 16.75" W x 13.75" deep.