As mentioned earlier, most small earphones in in-ear systems don't handle really low frequencies well. This becomes a big issue for drummers using moderate in-ear monitoring, as they can't hear their bass drum properly anymore.
The solution to this problem is a Bass Shaker. Instead of converting low frequencies into sound like a regular speaker, this device converts them into vibrations that can be transmitted through solid materials. Plus, the frequency range, typically 5-200Hz, goes much deeper compared to a speaker, with significantly higher energy. With this Bass Shaker attached to the drummer's stool, they can feel the beat impressively - without damaging their hearing. Larger Bass Shakers can also be used to stimulate stage elements and dance floors. However, one downside is that these devices require a lot of power - operating them requires an appropriate amplifier with a low-pass filter, depending on the model used and the desired intensity.