First, let’s ignore the environment that the earplugs is needed, and cover the basic physiology before we go any further. Musicians have to be able to focus on the different layers of instrumentation. That simply is not possible when you destroy the natural resonance of the external ear as happens with other ear plugs. Earasers maintain the shape of your ear canal until just before the ear drum, causing the basic shape and relationships of all the layers of music to be retained right up until the last possible second.
Most of us have heard for years that a flat frequency response is better. Let’s take a step back and revisit that topic. When you were looking for a pair of stereo speakers, this was the golden rule. Maybe you heard microphones should have a flat frequency response? What does “flat” mean anyway? In these examples, we were looking at electro-acoustic devices with the intent of replicating a sound source. “Flat” implied that the source would be replicated as close to the original input signal.
In a passive situation, ie. Earplugs, we are not dealing with the concept of replicating a sound source. We are hoping to preserve the sound source....NOT replicate. Thus, the goal of MUSICIAN's earplugs should be twofold: 1. To protect the hearing of the musician and 2. To preserve the nuances of the music at the levels we intend to appreciate the music.