Long distance audio transmitting with cable

Hi all ;

i have a project about transmitting audio signals to the long distance ( about 1000 meters ) with cable connection inside a building. there is now way to transmit audio with any RF modulation or optic systems. so i have balance or unbalanced options. i am not the expert of audio so i need some help and some ideas to solve this problem.

- how can i simulate and calculate the values for the 1 km lenght cable ? ( ohmic , capacitic and noise etc. )

- do i need balanced audio or isolation transformer ? balanced audio idea looks simple and easly applicable. isnt it ?

- i have one rs485 transmission line near the audio cable. and that will make some
digital noise into audio. the communication speed is about 19200 to - 57600
bauds simply the faster communication makes higher frequency noises and i thin
i can make some low pass filter to reduce this noise. it there any other idea ?

i really need ideas and recommendations.

thanks.

This is a very old technology problem with solutions that have worked for the same time period.

1. Use shielded twisted pair cable.

2. Use transformers at each end with the shielding connected to the center tap of the receiving end transformer.

3. Use the largest possible signal level.

For your calculations of the cable loss, make an equivalent RC network with the R being the wire resistance (For both wires) and C the capacitance between the wires. For these short lengths, a one lumped circuit will work.