How do I clean a sticky speaker

You may want to try Goo Gone. It is available in most hardware stores.

Or M1 remover, also available at most hardware stores.

Try Afta - cleans anything!

With all proper precautions when using this flammable agent, lighter fluid often works when all else fails.
I have used in the open air outside of the house for removing the occasional anonymous sticky material that seems to afflict the used components we all buy.
Test a small area to check if the speaker cabinet finish is preserved.
Happy New Year, minus the incendiary display!