Humming current acoustic radical solution: how to deal with ground loop interference? Don't just rely on isolators.

Masters who do sound engineering, conference system and stage leasing should have encountered this kind of "metaphysical failure":

All the equipment is normal, the microphone has no noise, and the line is not connected wrong, but as long as the computer, projector and player are connected to the system, the speaker will continue to emit buzzing low-frequency current sound.

Turn up the volume and the noise will increase, and the noise will still exist when the volume decreases. It is useless to adjust the balance and reduce the gain.

90% people's first reaction: add an audio isolator.

It can really solve some problems, but it can cure the symptoms rather than the root cause.

The real root of the disease, the vast majority come from-ground loop interference.

Today, I will talk about the underlying principle+a complete set of radical treatment methods that the industry master does not want to elaborate.

01. What is a ground loop? Why is there a current sound?
To put it simply: if the grounding potentials of two devices are different, a voltage difference will occur.

The most common combination of meeting rooms and event sites:

Computer/projector/player+professional sound system

-The computer is connected to an ordinary household socket.

-The power amplifier, processor and mixer are connected with special engineering ground wire.

When the potentials of two ground wires are not equal, a "circular loop" will be formed between the lines.

The weak current keeps flowing in the coil, picked up by the audio wire, and finally amplified into a continuous 50Hz/100Hz buzzing noise.

This is the legendary: ground loop noise.

It is not a problem of broken equipment, poor wires or debugging, but a problem of power supply environment in the construction site.

02. Why do many people still have noise after installing isolators?
Many masters habitually go to the isolator when they encounter noise.

But it often appears in real projects:

Slight interference: isolator can solve perfectly.

Severe ground ring pressure difference and multi-channel equipment mixed connection: isolators can only be weakened, but cannot be eradicated.

The reason is simple:

The audio isolator is a "noise reduction mask"

Dealing with the potential difference of the earth ring is the "radical cure"

Only relying on isolators to carry it hard, there will still be low-frequency noise in the scene where large venues, multiple devices and old and new circuits are mixed.

03, the ground loop interference four most common scene.
By contrast, you must have met:

1. The computer screen in the conference room will buzz as soon as the audio is plugged in, and it will improve immediately when the computer ground wire is unplugged.

2, outdoor performance generator power supply, sound source equipment and sound system have different circuits, and the noise floor is huge.

3. The old and new circuits in the site are mixed, with some grounded and some ungrounded.

4. The LED large screen, the lighting console and the sound system share a set of power supply, which leads to mutual crosstalk.

All these are not equipment problems, but typical ground crosstalk.

04, from simple to professional, a complete set of radical solutions (in order of priority)
Scheme 1: Unified power supply circuit (most effective and zero cost)
All audio equipment and sound source equipment:

All plugged into the same group of plugs and the same power supply.

Avoid all the power on the computer, the mixer and the big screen.

Unified loop = eliminating potential difference = directly eliminating ground loop.

80% of the scene noise, this step can be directly done.

Option 2: Correct use of audio isolator (quick emergency)
Suitable for: conference projection, fixed venue, temporary external audio source.

Function: isolate the ground loop and block the transmission of clutter.

note:

-Try to use balanced input-output isolators.

-Do not connect multiple isolators in series, which will compress the sound quality and make it boring.

Option 3: Single point grounding method (engineering standard practice)
Professional audio and video room standard:

All equipment ground wires eventually converge to the same grounding point.

Put an end to multi-point grounding and different potentials.

Many old conference room noises are permanently cured by re-grounding.

Option 4: DI box isolation (first choice for stage performance)
Unbalanced signal input system for mobile phones, computers, players and musical instruments;

Priority on passive DI box

With isolation and variable balance signal, the anti-interference ability far exceeds that of ordinary isolators, which is necessary for stage and outdoor performances.

Option 5: Power purification and independent transformer (high-end venue)
High-end lecture hall, banquet hall and live broadcast room:

The power supply is cluttered, and the large screen of lights has strong interference.

Need to be matched with audio dedicated purification power supply/isolation transformer.

Completely cut off the mains clutter and the earth ring.

05. The details of pit avoidance that the master only understands.
1. Don't unplug the equipment ground wire casually.

Temporary mute is ok, but long-term use is risky to get an electric shock and burn the equipment, which is illegal operation.

2, the balance line ≠ 100% anti-interference

No matter how good the wire is, the potential difference of the earth ring is too large, and there will still be floor noise.

3, lighting, big screen, audio shunt power supply as far as possible.

High-power equipment is the biggest interference source.

4, the scene noise first check power supply, and then change the line, and then change the equipment.

Most of the sound current is not caused by poor equipment or rotten wires, but by the ground loop.

Ordinary masters can only add isolators to make do with it;

Professional engineers unify the circuit and standardize the grounding, and directly and permanently cure it.

Only by understanding the underlying principle can the system be stable and clean.