Dimension: To the micro speaker, size has decisive influence on its volume. 5mm difference of diameter might result in double or half area of diaphragm, therefore the SPL is quite different. Besides, the thicker speaker has more space to vibrate the air, and usually has bigger magnet, so it will be more powerful to push the air and emit louder sound.

Power: Mainly refer to how much power can a speaker bear, there is no direct relation to the SPL. The speaker with larger power needs to use thicker diaphragm and sound coil to bear larger power, which will lead to lower efficiency (SPL). Therefore, according to the mechanical design, try to select a larger speaker which matches the outputting power from the amplified circuit, then the best SPL would be emitted.

Impedance: Higher impedance can save more electricity, however, the SPL and the loaded power will go down. The reason is that we have to use thinner wire or to coil more, the front makes the power lower, and the after leads to heaviness and low efficiency.

The material of diaphragm: Most speakers (diameter less than 50mm) use mylar diaphragms, which are easily finished, cheaper and waterproof. However, mylar diaphragm is not good at heatproof and the sound is stiff.

The patterns of diaphragm: The speaker with concentric circles diaphragm is good for the speech sounds. Generally, the SPL is good at the frequency before 5-6 KHz, but will dramatically decrease after 6 KHz. On the other hand, the speaker with radiate diaphragm has average frequency response. Supposing other conditions are all the same, the SPL of radiate diaphragm will lower than the concentric circles one at the frequency before 6 KHz.

AATC Part No. : ADK-1808EA-5W, AK-420808BC-3C
A / AD = AATC
K = Speaker
18 / 4028 = two-figure number means the diameter of the round speaker; four-figure number means the side lengths of the rectangular/ oval speaker.
08 = the impedance of a speaker
EA /BC = The first letter stands for the size of magnet; the second one means the material of diaphragm.
5W/3C = The number means the serial number, W stands for adding wires; C stands for adding wires and connectors.