Balanced vs Unbalanced Cables for Hum

If you can only swap one cable, swap the longest unbalanced one — the numbers below explain why.

Balanced and unbalanced lines differ in how they treat noise. An unbalanced -10 dBV (0.32 V) jack carries signal against ground, so any hum on the ground arrives with the music. A balanced XLR carries the signal between two wires and ignores whatever arrives equally on both, which is exactly what induced mains hum does.

The measured gap is large. Over the same run, balanced XLR at +4 dBu (1.23 V) typically rejects common-mode hum 50–80 dB better than unbalanced -10 dBV jacks. That is the difference between a hum you chase for a weekend and one that never reaches the speakers.

Shield construction decides what the cable itself leaks. Braided shields usually cover 60–90% of the cable, while foil shields cover 100% — but a foil shield only works if its drain wire is terminated at one end. A drain floating at both ends, or at neither, turns the foil into a collector rather than a screen.

Length multiplies every weakness. Microphone cable is commonly specified at 30–70 pF per metre, and past 10–15 m an unbalanced run both loses high frequencies and collects more field-induced hum. Keep single-ended runs short; let balanced lines do the distance.

So the swap order writes itself: replace the longest unbalanced run first, re-terminate any foil shield with a floating drain second, and only then consider premium braid. Frequency confirms the target — 50/60 Hz hum suffers most from ground and length issues, while 100/120 Hz buzz points you back to the supply.

• Longest unbalanced run — swap to balanced XLR or TRS first
• Foil-shielded cable — terminate the drain at one end
• Runs over 10–15 m — shorten or balance them
• Fixed-frequency check — confirm 50/60 Hz before blaming the cable

Further reading

• 50 Hz vs 60 Hz Hum: What Your Buzz Frequency Means
• How to Find and Fix a Ground Loop