Buzzy Speaker in New 406 build

[scstill]

I have had four vintage alnico 6" speakers, two ribbed Oaktron and two smooth Oxford for some time
Finally built a cabinet for them this weekend from a remodel left over pine trim board
discussed here https://stillampd.com/alni-406
Came out nice and sounds good,

But one of the speakers has a buzz on several low notes.
I inspected the speaker thinking that maybe the spider cone was loose from dried out glue
I could not see any fault
I can reduce the vibration buzz by applying pressure on certain areas of the cone.
Not sure how to proceed, should I create a damping hack for the cone.
Reglue the spider / cone (which are perfect)
Or some other approach?

[scstill]

I found I had another 6" 4ohm speaker that I tried in this cabinet and it sounded great no buzz
But what is unusual that I discovered is that the two Oaktrons had their marked polarity reversed
That is the "red dot" on the Oaktron is the negative wire (speaker moved out when 9v neg attached to red dot)
very strange that the mfg would mark this way unless they intended the application to be reverse polarity.
I guess the lesson is always test your speaker

Anyway even when trying the buzzy speaker correctly polarized it still buzzed so the new speaker will be used. It is likely a Jensen alnico from the 50's although not marked.

This 406 sounds great with the new speaker (lower left in pic)
Deeper than I would have thought, mids and highs are quite musical, piano like with good sustain
Played through Hami 18 https://stillampd.com/hami18

[scstill]

Here is some great remedial repair advice from ARF
Gonna try it...
https://antiqueradios.com/forums/viewtopic.php?p=3856416#p3856416