The screech
Speaker–mic feedback: what the squeal is and how to stop it
Echo is polite by comparison. Feedback doesn't repeat your voice — it eats the call alive: a hum that becomes a whine that becomes a full-blast shriek in about a second, and it doesn't stop until someone breaks the loop. If your meeting has produced that sound, this page explains what just happened, why it escalates so violently, and the seconds-fast ways to kill it — plus how to stop it happening again.
Echo vs feedback, one line each: echo is your voice coming back once, late — a copy per loop trip, fading or steady. Feedback is sound going around the loop gaining energy each trip, so it snowballs into a howl. Same circuit — speaker feeds mic — different arithmetic. Delayed copy? Go to the echo guide. Rising squeal? Stay here.
Why it howls: the loop with a raise
Picture the circuit: a mic hears a sound, the system amplifies it, a speaker plays it, the mic hears the speaker's version, the system amplifies that, and around it goes. Everything depends on one number — how loud each lap is compared to the lap before. If each pass comes back even slightly quieter, the loop dies out and nobody notices. If each pass comes back even slightly louder, the sound multiplies every few milliseconds. That's why feedback goes from inaudible to unbearable near-instantly, and why it locks onto a single frequency: whichever pitch the loop amplifies best wins the race and takes over. Musicians have known this phenomenon for a century as the Larsen effect; your conference call rediscovers it every time two audio devices get too friendly.
This is also why feedback is binary in a way echo isn't. Echo can be "a little annoying." Feedback either can't sustain itself — or it howls. The fix is therefore simple in principle: push the loop's gain below the tipping point, anywhere in the circuit.
Kill it now (in order of speed)
- Drop the speaker volume — hard. Volume is the loop's fuel. Halving it usually snaps the loop below the sustain threshold instantly. This is the fastest universal move.
- Mute one mic. Any mic in the loop. On a group call where you can't tell whose device is howling, the host muting the two loudest suspects beats a democratic discussion nobody can hear anyway.
- Separate the devices. If two people joined the same call in the same room, that's almost certainly your loop — a mic on desk A picking up speakers on desk B and vice versa. One device leaves, or mutes both its mic and its speakers. Distance and doors also work.
- Turn down mic gain/boost. A hot mic keeps the loop fed even at modest speaker volume. If a device howls repeatedly, its input gain is part of the problem.
Why calls usually don't howl — and what disables the protection
Calling apps have two things working against feedback: the echo canceller, which subtracts each device's own speaker output from its mic before it can circulate, and the network delay, which slows the loop's laps. That's why a single laptop on a call very rarely feeds back even at high volume — its own loop is being actively subtracted.
The classic failure is the loop the canceller can't see: two separate devices in one room, each on the same call. Device A's canceller knows what A is playing — but the sound arriving at A's mic came out of B's speakers, and no canceller models another machine's output. Result: an unprotected loop, and with two amplification stages in it, often an audible one. The same blind spot produces the milder version — the mystery group-call echo — when the loop's gain stays just below howling point.
Other protection-killers: mic boost stacked on driver "enhancements," PA-style setups where a mic feeds room speakers directly (presentation rooms, karaoke apps, "listen to this device" enabled on Windows — a monitoring feature that pipes your mic straight to your speakers with no canceller in the path), and routing tools that bypass app processing. If your setup recently changed and howling started, the change is the suspect — same logic as sudden echo.
Prevention that sticks
- One device per room per call. The two-device loop causes both the worst feedback and the most stubborn echo. Make it a house rule; it costs nothing.
- Volume discipline beats heroics. Speakers loud enough to fill the room are loud enough to feed a loop. Set them for you, not for the hallway. The speakers-only playbook covers living like this comfortably.
- Keep mic and speakers off-axis and apart. A mic aimed away from speakers needs several dB more volume to sustain a loop — that margin is your safety buffer.
- Don't monitor your mic through your speakers. Mic-to-speaker monitoring is a hardwired feedback circuit waiting for volume. If you want to hear yourself, that's a headset feature — see sidetone, explained.
- Cancellation software helps the echo, not the howl. Honest scoping: tools like the ones in our software guide subtract their own device's output and will stop that device's echo loop; a two-device airborne loop needs physical separation. Software is reinforcement here, not absolution.