Size and cavity volume act on the result through different mechanisms. Why diameter alone predicts resonance poorly, and how to derive the minimum cavity first. ......
Impedance is an amplifier decision, not a loudness decision. Why equal power ratings need voltages 1.414 times apart at 4 Ω and 8 Ω. ......
Rated power describes coil survival, not loudness. How power follows V²/R, why equal ratings need different voltages at 4 Ω and 8 Ω, and what to confirm first. ......
What a voice-enabled product needs from its speaker: the speech band and local noise floor decide intelligibility, not low-frequency output. ......
Diameter sets the mounting envelope, not the acoustic result. Compare 20 mm, 23 mm and 28 mm round micro speakers by height, construction, cavity and impedance. ......
Choose between 20 × 30 mm and 20 × 40 mm rectangular micro speakers by acoustic role: cavity-mounted driver, front-face module, or narrow low-profile option. ......
What wearable and compact devices ask for: outlet strategies, front-cavity height trade-offs, output variation with wear position, and the driver classes. ......
What handheld gaming audio asks for: grip-dependent output, voice and music in one small volume, dual-driver sharing a cavity, and the driver classes used. ......
What portability changes for a micro speaker: back volume, grip-dependent loading, ambient noise and battery budget, plus the driver classes that fit. ......
How security and access control audio differs: worst-case listening position, a long acoustic path, and the driver classes that fit each role ......