Micro-speaker

Micro-speaker

The most popular type of micro-speaker is dynamic micro-speaker, which contains coil, magnetic and yoke. Apart from dynamic ones, there're also piezo planar ones and MEMS ones, which are used in special final products. Compared to mono-tone buzzers, micro-speakers are good at playing out multi-tone audio content, such as human voice and music. 

Common shapes of micro-speakers are circle, oval and rectangle or squares. Round ones are the most popular, with diameter ranging from 10 to 70mm. Our customers usually choose between 20mm~ 40mm. To be able to place the micro-speaker into the customer's limited mechanical space, we sometimes recommend oval micro-speakers as those limited spaces are mostly narrow and long. Regarding rectangular and square micro-speakers, they usually consist of a square metal basket with round/ oval micro-speakers in them. This basket lets the customer fix the micro-speaker with ease on their final product's housing, as there're holes on the basket for screws to pass through. Some micro-speakers come with a enclosure box, and they're mostly rectangular. These are well-suited for clients who don't design their own micro-speaker enclosure.

Micro-speaker's input power is described in wattages. Wattages range from 0.5W to as high as 10W. Usually most micro-speakers fall into the category of 0.5W~ 3W. For high-wattage micro-speakers, the coil and diaphram structure has to be carefully designed and manufactured to prevent from burning down. Note that you don't have to choose a high-wattage micro-speaker to deliver large sound. If properly designed, a 1W micro-speaker can deliver enough Sound Pressure Output (SPL). When it comes to power, another critical parameter is impedance. Rated impedance of a micro-speaker is usually the DC impedance of it, being 4ohms or 8ohms. For micro-speakers used in telephones, mobile phones, earphones or headsets, rated impedance are typically 16ohms or 32ohms. As we increase the input frequency from 0hz to resonant frequency, we get ever increasing impedance. The impedance at the resonant frequency may be a few ohms higher than that at DC supply. The appropriate input voltage can be calculated based on rated power and rated impedance.

Advantages of larger sizes are not only higher SPL but also lower resonant frequency. Lower resonant frequency is often associated with better bass performance. Resonant frequency is often coined as "fo" or "f0" in the acoustic industry. If you play out sound of which the frequency is lower than the speaker resonant frequency, then you might get lower sound output and sound quality. Frequency range of human voice can be as low as hundred hz, so micro-speakers for speech use must have resonant frequencies in hundreds. To further lower resonant frequency, it helps to soften the diaphragm material and the suspension system. This is why subwoofers in our daily life is large and soft. On the other hand, tweeters are small and hard. Some tweeters' diaphragms are even made of metal composites.

In general, you want to see a flat frequency response, with bandwidth extending to mid to high frequencies. At the resonant frequency, the response curve would peak a little bit. The level of the peak dependes on the Q-value of the micro-speaker. Advanced designers will choose an appropriate Q-value according to their enclosure design. The Total Harmonic Distortion (THD) of a micro-speaker shall be as low as possible. Low THD means the material and the shape of the diapgram are designed properly. Audio quality of the micro-speaker is not only affected by the bare component itself, but it's also affected by the external resonance chamber and its driving circuit. Our company is delighted to provide advice on such topics.