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I was looking at a Leslie 760 today, and I found radial cut-outs in the horn shelf around the normal hole for the horn driver. I've never seen anything like it and was wondering if anyone else has. I can't imagine what their purpose is.
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I'm David. 'Dave' is someone else's name. -
Maybe to allow bass frequencies to leak through from the woofer cavity to be picked up by the horn rotor mics?Current:
1971 T-202 with Carsten Meyer mods: Remove key click filters, single-trigger percussion, UM 16' drawbar volume correction. Lower Manual bass foldback.
Korg CX3 (original 1980's analogue model).
1967 Leslie 122 with custom inbuilt preamp on back panel for 1/4" line-level inputs, bass & treble controls. Horn diffusers intact.
2009 Marshall 2061x HW Plexi head into Marshall 4x12 cabinet.
Former:
1964 C3
196x M-102
197x X5
197x Leslie 825 -
I've never read an authoritative source on it, but know what my guess would be: fatigue.
In layman's terms, the same reason they put score marks on concrete walks and drives and the same reason the dashboards on old minivans crack.
The 760 was a 'black and chrome' Leslie that was part of a series made in response to various rock-n-roll hotrod attempts. One idea being that instead of running 2 or more wood boxes to get the volume, maybe just one of suitable design would suffice. (you know this, i'm just filling backstory) They worked and especially along with the 900 series could get crazy loud.
Prolonged exposure to those kind of vibrations, plus motor switching and rotational vibrations would definitely be considered 'hostile environment' for most equipment. I would suspect they had seen troubles of this sort - which would look like termites had gotten in -- and were exploring cures. Radial cuts would be such a cure. It would certainly work in theory, thus giving the vibrations "somewhere to go" (yes, I know that durability tolerance is far more involved than that, just keeping it simple.)
By cutting it like a pizza around the penetration, the paths of propagation are broken. This allows anything suspended to move out-of-plane, however microscopically, and to resonate (everything has a resonant freq) at a much lower value.
Further guessing you haven't seen this before because it either 1) didn't work or 2) wasn't needed fleet-wide. That is either 1), it wasn't efficacious. Looked good on paper, but didn't. This is unlikely. Or 2) maybe not worth the cost of manufacture as they found out that failures due to sonic/mech damage were rare and only extant among the most hardcore of noisemakers.
Or 3) it was a theoretical preventative measure to a problem that never manifest itself. If it's a very early serial, this is also possible.Comment
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Sounds like a similar idea with holes in an Rv cabinet for the 6x9 reverb speaker box.
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