There are a lot of things to consider when trying to create a desired sound on a keyboard instrument.
I usually follow a few basic considerations when making these choices:
Based on the music passage, you will want to consider the area of the keyboard in which a good majority of the notes will be played. This is more of a consideration for marimba since there are often many more keys compared to a vibraphone or a xylophone.
Often a larger, heavier mallet will make very little sound on the top part of the board while a smaller, lighter mallet with a harder core will make a very glassy sound on the bottom part of the board (and often lead to cracked keys).
I generally try to pick the mallet that will create the most TONE on that particular part of the board. Some passages require a lot of motion up and down the board and there are certain mallets that can work best for that. Usually a mallet that has a pure rubber core has a little more flexibility on different parts of the board.
When you have a plastic core wrapped in latex, there usually becomes a breaking point in stroke velocity where the sound changes from warm to bright. The pure rubber core has a more consistent timbre through all dynamic ranges.
The biggest question I ask when considering tone color is whether I’m looking for the individual’s sound to blend with other sounds, or rather be a soloistic color within the ensemble.
Of course if you are playing solo literature, it is more a matter of taste. It is important to think holistically in this situation, because the listener takes in everything at once. What may sound good up close on an individual instrument may not sound ideal from the back of a concert hall or the press box of a stadium.
I find that xylophone mallet choice is the most polarizing in terms of it’s role in the ensemble. You can pick a mallet that blends well with other keyboard textures, or something a little more punctuated as a solo color.
This choice is often up to the artists, instructors, and conductors of depending on the context. The wrap material (or lack thereof) plays a small part in this choice, but a lot of it has to do with the core of the mallet. Warmer sounds have a lower density core or a thicker latex wrap (and vise versa for the brighter sounds).
The amount of total sound production mostly comes down to the weight of a mallet. That doesn’t mean the sound will always cut through the texture the way you want, but a heavier mallet will give the opportunity for more vibration from the keys.
This allows a more sustained, fuller sound. The weight of a mallet is often considered in a player’s comfort on a particular passage, but you must be careful that you are also getting the projection you want.
The ideal mallet will have just enough weight to get a full sound, and be light enough that there is a good balance in the player’s hands.
Birch vs. Rattan
Mallets with rattan shafts can help produce a little more velocity in the stroke. The natural “give” in the mallet while moving towards the board produces a little more “slap” in the sound. This is practical on vibraphone where the music is often less dense due to the nature of the length of sound.
Mallets with birch shafts are easier to control and are more desirable for faster music. Players generally prefer birch mallets on marimba since the parts are often busier and they are easier to manage with the Stevens grip. I like to use a rattan mallet on the low end of a marimba since those parts are often more open, and the cores are a little less dense to help those keys vibrate.
A lot of times it is assumed that harder mallets equal more volume, and softer mallets equal less volume. Although there is some truth to this when considering the front of the sound, it doesn’t always provide more total sound.
Conductors often question mallet choice when they want to hear a phrase a little more or less. More often than not, the right answer is to simply play louder or softer rather than change the color of the sound.
There were several times while playing in a wind ensemble where the conductor asked me to try a louder mallet. I would pretend to switch mallets while keeping the same ones and play louder on the next rep and every time they were happy with the result!
There is no right or wrong answer when picking the right tool for the job, but there are factors that go into helping you find the right sound for YOU. If you are asking the right questions then you will be much closer into getting that desired sound.
Hopefully these ideas will help you along that journey!