1. The noise of turning on and off the machine is low, which not have much impact on the speaker. However, it is suggested to add a horn protection circuit, which can not only the impact noise of power amplifier on and off, but also avoid the output DC from burning the horn when the power amplifier is damaged. Unusually high children's shoes have not been tried. Please give us feedback if you have tried any children's shoes with noisy speakers. 2. The background noise is very small, and the noise can hardly be heard when the ear is close to the speaker, which can be ignored. 3. The zero drift of the speaker is small, so there is no need to do any debugging after installation. The output zero drift voltage generally not exceed 50mv, and it is relatively stable, so it is very practical to use. 4.Because the classic circuit is used, the work is stable and reliable, and some misoperation in the production may not damage the components, so it has certain durability and high production success rate. 5. No debugging. As long as you install it correctly and there is no human error, it is basically a success, and beginners have a very high success rate without any debugging. Colour:black Material:ABS+electronic components Package Contents: 2 * monoaudio amplifierboard Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.