environments (80 dB or more). Types and use cases Simple earplugs Basic foam style earplug protection is often worn by industrial workers who work within hearing distance of loud machinery for long periods of time, and is used by the British Ministry of Defence (MoD) for soldiers to use when firing weapons. Earplugs are rated for their ability to reduce noise; see . Most disposable earplugs are elastic ones made of memory foam, that is typically rolled into a tightly compressed cylinder (without creases) by the user's fingers and then inserted in the ear canal. Once released, the earplug expands until it seals the canal, blocking the sound vibrations that could reach the eardrum. Other disposable plugs simply push into the ear canal without being rolled first. Sometimes earplugs are connected with a cord to keep them together when not in use. Other common material bases for disposable earplugs are viscous wax or silicone. Other devices that provide hearing protection include electronic devices worn around and/or in the ear, and are designed to cancel out the loud noise of a gunshot, while possibly amplifying quieter sounds to normal levels. While rich in features, these electronic devices are more expensive, compared to their foam counterparts. In other activities, hobby motorcyclists and skiers may also choose to use decibel reduction earplugs, to compensate for the ongoing noise of the wind against their head or helmet. Musicians' earplugs Musicians are exposed to potentially harmful levels of sound, which can lead to hearing loss, tinnitus, and other auditory symptoms. Because of this, musicians may choose to use earplugs. Musician's earplugs (also called Hi-Fi or Lossless earplugs) are designed to attenuate sounds evenly across all frequencies (pitches) which helps maintain the ear's natural frequency response and thus minimizes the effect on the user's perception of timbre (frequency spectrum, f.ex. bass and treble levels). These are commonly used by musicians and technicians, both in the studio and in concert, to avoid overexposure to high volume levels. Musician's earplugs generally achieve a more natural frequency response by incorporating a small diaphragm or membrane together with acoustic channels and damping materials. Simpler variants with only a small hole introduce a low frequency leak, and will not achieve a flat frequency response. Examples of manufacturers of membrane-based earplugs are ACS, Etymotic and Minuendo. Preformed earplugs, such as the ER-20 earplug are universal (non-custom) earplugs with a noise reduction rating