... the search function on the << left margin comes up with a few previous threads. 

[Says a guy that wouldn't recognize an overtone if he tripped on one.   ]

Thanks, Owen,

I did this on my phone and did not see the search function due to terminal stupidity. There are some decent replies but no one seems to have a definitive answer other than "stuff a towel in it." I suspect that it is too subjective an issue for some objective study.

I have found that small bubble wrap rolled up loosely, like a burrito, and placed on the inside along the rim works very well.

I think some people recommend the banjo bolster for that sort of thing. I’ve never tried it myself.

I use a piece of foam plastic which fits and pressed up between the head and the co-ord rods (Wildwood Troubadour) and the dowel stick (Enoch Tradesman). It works great.

The Burns Mechanical Sock ....

John Balch supplied me with some bits of sheep's skin/wool when I bought some pre-mounted goat skins.

I place one of them between the head and dowel at the end near the neck. Works great.

A "shoe shine rag" provided in a hotel room ....

I have used the drum dampener.
I was given several by a real drummer.
I like the moveable nature.
I like the simplicity and durability.

I’ve seen many personal innovations, from laundry to rolled up this and that.

I am finally using a drum dial to give consistency, so the dampener gives a lot of variability. Ok?

I’ve used a lot of things behind the head of my open back banjos to decrease annoying harmonics and currently like the banjo bolsters which take up a lot of the space behind the head (without touching it, I might add) and seem to help with my perceived sound.

I was struck by the seemingly scientific, or at least precise, use of both the large dampeners and the small gel style stickers on specific parts of the head in order to change or modify the sound of a drum.

After all, a banjo is just a drum on a stick so there must be some value in exploring the concept of precise dampening of parts of the head the way they do with drums. I have found that I can eliminate an annoying high pitched sound that my microphones pick up when I try to record using gels. I have several banjos and placement is different for each. A larger gel just under the bridge seems to kill any interesting sounds while planting smaller gels on the periphery an inch or so in helps with the teeth rattling quality of my Ren head when it is at 92 or so.

There is a lot to it, but I was wondering if there are any studies besides anecdotes that might help. Each banjo is different, so are there guidelines on how to use these dampeners in a logical (if that is the word) fashion?

I think it’s as subjective as individual hearts and ears.