Identifying unsound resonances of smartphone loudspeakers

Problem

Miniaturized smartphone loudspeakers must balance compactness with audio quality. While microphones can detect sound pressure distortions, they cannot identify the mechanical origins of resonances, which are often influenced by materials, design choices, and manufacturing tolerances.

Solution

The PICOSCALE Vibrometer was used to directly measure vibrations of two smartphone loudspeakers. By imaging both diaphragm and housing at different focal planes, SmarAct’s system made it possible to correlate spectral irregularities with mechanical resonances.

Implementation

• Two loudspeakers (with transparent and metallic diaphragms) were mounted and excited across 0.5–16 kHz.

• The amplitude spectrum was recorded at selected points using the integrated lock-in amplifier.

• At specific resonance frequencies, 1 Megapixel scans of both the diaphragm and housing were taken to reconstruct vibration modes.

Results

• In Loudspeaker 1, resonance peaks at 7.5 and 12 kHz corresponded to distinct bending modes of the diaphragm.

• In Loudspeaker 2, the 6 kHz resonance originated from the metal cover, while 11.5 kHz activated the diaphragm’s second mode.

• These findings show that not all resonance peaks originate from the diaphragm, highlighting the importance of full structural vibration analysis.

Conclusion

PICOSCALE Vibrometry offers precise insight into the vibrational origins of unwanted resonances. This helps engineers refine loudspeaker designs by addressing not only the diaphragm but also structural elements like the housing and protective covers.