This 16mm x 9mm speaker could be classified as a "sugar cube" speaker. This style of speaker is often feature in cell phones and tablets and performs slightly differently from standard speakers. This style of speaker REQUIRES mounting with a baffle to produce much sound at all, but once they are mounted they produce significantly more sound than you might expect. Try them out in your space restricted installations.
0.63" x 0.35" x 0.12" or 16mm x 9mm x 3.1mm
Sound Pressure Level
91 dB ± 3.0 dB at 0.7 W, 10 cm, avg 0.8, 1.0, 1.5, 2.0 kHz