Alni 406 Speaker Cabinet
This cabinet is made out of solid pine glued in place with a tight mitred edge. The pine board was repurposed from a leftover remodel trim piece. It was painted white at the factory; paint/primer was somewhat difficult to remove. Turned out that the ¾” thick board had several short pieces of pine glued together to get the 8’ length. These add a distinctive look at the joints.
The cabinet corners are mitered and glued for a very tight clean and strong joint. The speaker baffle and rear panel, made from ½” baltic birch ply, are screwed into cleats made from the same cab pine and are glued glued in place. Inside corners are also cleated for additional strength. The cabinet is to be finished with boiled linseed and furniture wax.
The cabinet houses four vintage 6” alnico speakers that originally were part of a reel to reel recorder/player. Two of the speakers are made by Oxford smooth code with speaker codes 465-539 and two of the speakers are made by Oaktron ribbed cone with speaker codes 918-521. The combination of these two speaker styles will provide complementary sound and tone.
After speakers installed and played it turned out that the lower left Oaktron had an unacceptable vibration buzz on certain low notes. The cone and spider are perfect and the glue attachment seems tight, when the cone is damped in certain areas the buzz is reduced, But rather than continuing to troubleshoot this buzz and try different fixes, it was decided to use a different 6” 4 ohm speaker that was available.
Another interesting finding is that the Oaktron speakers are marked by the manufacturer for reverse polarity for some reason. Maybe because the application called for it. A simple 9v battery test showed that the speaker moved out when the battery neg was attached to the red dot terminal on the speaker. Lesson is to always test your speakers. Even after the buzzy speaker was correctly polarized, it still had a buzz on some low notes.
New replacement speaker appears to be a Jensen (according to Google Lens), it has a large alnico magnet (honoring the “Alni” name), is 6” so fits cab perfectly and is 4ohm matching the other three speakers. As well the new speaker is ribbed cone matching the buzzy Oaktron it is replacing.
Some good buzzy vibration repair advice at ARF. https://antiqueradios.com/forums/viewtopic.php?p=3856416#p3856416
Some additional pictures of the build
