Speaker buzzes - but only on three notes

[Johnne]

I was interested in this buzzing issue as I bought an older 12" alnico guitar speaker and it should arrive soon. The owner said the lower three guitar strings made the speaker buzz with no noticable cone issues, so I figured it was a resonance thing, and or connection. Per this discussion I noticed someone pointed out that tube testers did not in fact check for microphonics. To correct this assumption I wanted to point out that my TV-7U does in fact have a way to insert a connection into the circuit and test for microphonics using headphones. Being this is a tester designed for field use I am sure they needed to make sure only the best tubes were put into their equipment like radios of that era. FYI. I will check back when I know what is causing this issue, but wanted to say that some of the older paper cone speakers make killer blues amp speakers or harp speakers. Johnne in Seattle

 

[BogeyBass]

most just tap the tubes with a pencil or tap the chassis nearby to check for microphonic tubes.

technically all tubes will be slightly microphonic. its when the guts or plates really start to rattle youll hear a very pronounced ping or rattle or crackle when you tap the tube.
its more a ping for microphonics, and a rattle or crackle is plates that are rattled loose in the bottle