Some time ago, when I was looking for long microphone cables, I came across the idea of using network cables with appropriate adapters. This is a neat idea since you can run four audio signals over one network cable with 8 pins + shield. However, soon questions about the audio quality and other drawbacks came up. Therefore, I did some simple measurements on microphone and network cables of different lengths, which are described in the following.
Measurement Setup
The frequency response is one of the most important characteristics of a cable and so it is for microphone cables. I chose a simple setup to measure the frequency response of the test cables. For this, an audio interface of type Behringer UMC204HD played a linear chirp from 1 Hz to 96 kHz on its output. The signal was fed back to the microphone input of the interface using two short XLR cables, where the different test cables were connected in between. The setup with and without a connected test cable (network cable) is depicted in Fig. 1 and 2.
The impedances of the input and output of the interface are not matched, neither is the cable impedance. However, this is not a problem as it represents an almost realistic situation of a microphone being recorded by an audio interface. The microphone input of the UMC204HD has an impedance of 3 kΩ, while the output has about 100 Ω. Condenser microphones have usually an impedance of about 50-200 Ω. The combination of 100 Ω output and 3 kΩ input impedance leads to a loss of 0.28 dB due to impedance mismatch. This is described in detail here where also the formula is given. The whole topic of impedances of audio equipment is discussed here and here.
Cables
Since the investigation should reveal differences between XLR microphone cables and the direct use of network cables, those two cable types were included in the test. The investigated microphone cables are of type Cordial CCM FM with a length of 5 m and 10 m. This microphone cables use AWG 24 wires, while the impedance of the cable is less than 85 Ω/km and its capacitance 190 pF/m. Using the online calculator of sengpielaudio.com, this leads to a cutoff frequency of about 838 kHz for a cable length of 10 m.
To use network cables for the connection of microphones, an adaptor is needed that translates RJ45 to XLR. In the test, two commercial boxes were used with male (the sssnake Cat Snake 3MB) and female connectors (the sssnake Cat Snake 3FB). The employed network cables are of type CAT 6A S/FTP with a length of 10 m and 30m. The network cables consist of AWG 26 wires and claim to have a bandwidth of 500 MHz. Since no further electrical specification is given for these cables, some characteristics of CAT 5 cables are used instead which are assumed to be similar. The impedance of a CAT 5 cable is given as 188 Ω/km and the capacitance is 52 pF/m. The online calculator reveals a cutoff frequency of 3.06 GHz for a length of 10 m.
Measurements
All four cables have been measured with the described setup. For this a linear sine chirp from 1 Hz to 96 kHz was played back, while the received audio signal was recorded simultaneously. Fig. 3 shows the Fourier transformed frequency response of the cables. Since the cables are of different length only the microphone and network cables which are 10 m long can be directly compared. It is clear that the attenuation at low frequencies is higher for the network cable than for the microphone cable. However, it becomes also clear that the attenuation at higher frequencies is higher for the microphone cable. This is expected regarding the calculation of the cutoff frequency in the Section before. Fig. 4 shows the faster increasing attenuation with higher frequencies of the microphone cable. It is the same as Fig. 3 but with an offset such that all curves start at 0 dB at the lower end.
Conclusions
From an electrical point of view there is not a big difference between microphone and network cables to establish XLR connections. I could also not detect any difference in example recordings. Instead, the big difference may be the durability and flexibility of the two cable types since microphone cables are usually more flexible than network cables. Also the higher effort and additional connector boxes may be a drawback for some applications. Taking everything into account, it is worth having a look at this analog XLR-over-network cable connection.