Professional audio

Feedback is a loop: sound leaves the loudspeaker, re-enters the microphone, is amplified again and feeds itself. Breaking it means weakening any point on that path.

Shure’s recommended steps:

• Move the microphone closer to the source — the single most effective move; the closer the mic is, the less gain is needed for the same level
• Use a directional microphone, positioned to reject the direction the loudspeaker is in
• Mute microphones that are not in use — every open mic adds another path into the loop
• Keep the microphone away from the loudspeakers
• Do not cup the capsule — a hand around the grille destroys the polar pattern and turns it into a microphone that hears everything
• Improve the room acoustically
• Ring the system out with EQ

Shure also warns that automatic feedback suppressors do not replace a correct installation. A suppressor is the last margin of safety on a system that is already set up properly; it does not rescue one that is not, it only delays the problem.

Intelligibility has measurable targets. For a typical small conference room or classroom, Biamp gives:

Parameter	Target
Reverberation time (RT60)	~0.4-0.6 seconds
Background noise	no more than 35-40 dBA (NC 25-30)
Talker level above room noise	at least 10 dB, near 25 dB for good intelligibility

Classrooms have a dedicated US standard: ANSI/ASA S12.60 sets 0.6 s RT60 and a 35 dBA background noise limit for small classrooms.

What these numbers mean in practice: changing the microphones and loudspeakers in a reverberant hall does not fix it. A sound system makes the room audible; if the room rings, a more powerful system gives you a louder ring. This is AVIXA’s point too — a good display and a good microphone do not correct bad acoustics.

The right order is measurement, then acoustic treatment, then the sound system. Done the other way round, the money usually goes on both and the result still does not arrive.

The usual cause of a constant 50 Hz hum is a ground loop: cable shields and mains earths form a closed loop across several devices, and that loop couples mains hum into the signal.

The durable fixes:

• Use balanced connections. A balanced input rejects noise common to both legs, which removes most of the problem at source.
• On balanced lines, lifting the cable shield at one end usually kills the hum.
• Use isolation within the rack.
• Separate signal cables from power cables — parallel runs are the easiest place to pick noise up.

One warning matters: both Sound On Sound and Rane caution against disconnecting the mains protective earth. The advice circulating online to “lift the ground and the hum goes” does stop the hum — by removing the device’s protective earth, which trades electrical safety for quiet. Rane asks that factory grounding is left exactly as it is.

This is one of the few subjects where we say plainly: do not try to solve it yourself.

This one has a clear answer from official Turkish sources, and it matters for any organisation operating venues in Turkey.

In BTK’s technical criteria for radio equipment exempt from frequency assignment (Board decision 23.09.2022, 2022/İK-SYD/245), Article 12, Table 10 lists these wireless microphone bands:

Band	Power limit	Standard
29.7-47.0 MHz	10 mW e.r.p.	TS EN 300 422
174-216 MHz	50 mW e.r.p.	TS EN 300 422
470-694 MHz	50 mW e.r.p.	TS EN 300 422
863-865 MHz	10 mW e.r.p.	TS EN 301 357
1785-1795 MHz	20 mW e.i.r.p.	TS EN 300 422
1795-1800 MHz	20 mW e.i.r.p.	TS EN 301 357
1800-1804.8 MHz	20 mW e.i.r.p.	TS EN 300 422

The point to notice: the table goes straight from 470-694 MHz to 863-865 MHz. There is no wireless microphone entry between 694 and 862 MHz.

Nor is that range empty. BTK’s frequency map assigns 700 MHz (703-733 / 758-788 MHz) and 800 MHz (791-821 / 832-862 MHz) to Turkcell, Vodafone and TT Mobil. The 5G tender covering 700 MHz closed on 16 October 2025, and 5G entered service across all 81 provinces from 1 April 2026.

BTK’s notice to wireless microphone users states that the 790-862 MHz band was allocated to mobile broadband and asks users to move to the other permitted bands; it adds that where microphone signals are detected in that band during field measurements, action will be taken under Law 5809.

What to do in practice: read the frequency label on the back of your transmitter and receiver. If the equipment works between 694 and 862 MHz, it falls outside the exempt bands listed above. Some older systems can be retuned in firmware; where they cannot, the equipment has to be replaced.

The above reports what the official documents say. If you need a binding assessment for your own installation, consult BTK’s current text and take legal advice.