SB Acoustics 2.5" full range speaker with 64mm square polymer chassis, aluminum cone with resonance reducing indentations and low damping surround. This speaker is getting out beyond 20,000Hz with a rising response. That rise is thought to be beneficial to listeners whose hearing is rolling off in the upper frequencies. In a half to one liter sealed box this speaker should get down to about 140Hz. This speaker has many uses in sound bars, electronics, computer speakers, medical equipment, etc.