... system TA-502 is a multifunctional 2.4G wireless digital audio intercom which is produced by our own R&D ... ,such as audio amplifier, microphone,speakers, etc.. , and used industrial-grade design standards, to build a multifunctional wireless digital intercom product. ... Frequency: 300Hz ~ 3000Hz 8. Earphone : with diameter 2.5 audio plug, microphone and volume adjust 9. Full duplex voice intercom ...