Loudspeaker interference: Time to be Clear
It’s a buzzkill when loudspeakers suffer interference or distortion. More often than not, we assume the fault lies with the speaker—after all, they’re the ones emitting the sound! But this isn’t usually the case. In this post, we’ll try to help you identify/troubleshoot the source of your speaker disruption to have a pleasant listening experience and be prepared for any future issues.
Hiss hiss; hum hum.
Hissing or humming sounds are a consequence of concurrent sound waves produced with different frequencies and sound levels, the most common being white noise.
Speaker hum and hiss generally come from poor wiring, ground loops or other electromagnetic interferences (AC line hum, RF interference, USB or PC noise).
Poor Wiring:
If there’s a wiring issue, it’s quite likely you’ll experience hissing, humming or popping from the speaker. In turn, this can cause significant issues in performance, possibly even speaker damage.
Audio signals (Alternate Current electrical signals) are passed through conductive wires, amplified and then delivered to the speakers.
When leads or equipment is connected, this electrical signal passes from one component to another.
Wiring issues can be a result of:
– Improperly wired or mismatched equipment/plugs
– Loose or damaged cables
– Loose solder connections
If your speaker is popping or cracking, it’s likely an interrupted current or signal.
Speakers are transducers that convert electrical energy (audio signals) into mechanical wave energy (sound waves) and any interruption to the AC signal will cause this unwanted noise.
Speakers are designed to move linearly according to the applied audio signal. As the AC signal passes through the driver (cone), the driver moves inward and outward to produce smooth sound waves. At the peak of the audio signal (maximum positive voltage in a particular cycle), the driver is pushed as for outward as it will be during that cycle.
At the trough, or negative peak (maximum negative voltage in a cycle), the driver is pulled as far inward
Sine Wave
The diagram above represents a single-frequency audio signal. The dotted line signifies no voltage. The maximum positive voltage (forward current flow) is shown at the peak while the maximum negative voltage (backward current flow) is shown at the trough. It also represents the movement of a speaker tasked with converting the audio signal into sound.
When the signal is at its ‘zero point’ (the dotted line), the speaker will be at its resting position. This is because no voltage is applied to the speaker driver even if only for an instant while the electrical current switches directions.
The sine wave shows smooth movement in the speaker and, therefore, a smooth sound with no crackling or popping.
When there’s a current interruption in the same signal, the resulting waveform can look jagged. In this case, the audio signal and resulting speaker driver movement is affected. For a brief moment, the current will be interrupted, which produces a period of no voltage. We can infer that, then, the speaker will be told to remain at resting position and not produce any sound. The pop is not from the silence of the speaker but a result of how it’s told to get to its resting position. In an example, the audio signal current interruption might happen following the peak. At this point, the audio signal fails instantaneously, plummeting to the zero point, until the signal is once again picked up. The speaker driver is, therefore, tasked with being at two locations at once. In these circumstances, the speaker should be pushed outward and at resting position simultaneously. This is impossible and as a result, the driver attempts to move as fast as it can between the two locations at the current interrupt—this triggers the popping or clicking sound you may have experienced.
In the event that there are multiple audio signal interruptions, and in close succession, “speaker crackle” results.
So how do we resolve these issues? We recommend troubleshooting before steamrolling ahead with any fixes.
First: Check your wiring! See if there are any loose connections in your cables. Play audio at a low level while coaxing the wires to determine where a loose connection may be. In some cases, it could be that re-soldering of the speaker, amplifier or components is required. Don’t be surprised if repairing a wire or replacing a cable is needed too. Do not attempt to work on mains-powered electrical products without professional, technical advice.
Amplifier Gain:
Low-end amplifiers and pre-amplifiers will often add noise to the audio signal.
Minus any audio, turn up the amplifier or speaker volume and it’s likely you’ll notice the speakers produce more hiss. But don’t fret—this sound is the amplifier at work! —when gain is applied to a signal, the inherent noise of that signal is also amplified. Electronic components in audio amplifiers also add their own working noises to the signal. In top-quality amps, this isn’t necessarily a problem.
To mitigate the issue, the gain stages might benefit being set correctly, and the speakers matched to appropriate amplifiers. However, amps are often built into the speakers, and are the only gain stage between the audio device and speaker. Under these circumstances, reducing the amplifier volume is recommended.
When it comes to Public Address systems and other audio devices implementing line/speaker levels and microphones, it’s imperative that the signal strengths and impedances are connected to inputs/outputs intended to manage these voltages to avoid significant noise and distortion.
Ground Loop Noise
A common issue in audio systems is Ground Loop noise. Ground Loop occurs when audio equipment is plugged into different AC outlets. When this equipment is linked together through signal wires and cables, there’s potential for Ground Loop.
All the AC power mains plugs in an audio system should have the same ground potential. If they don’t, a Ground Loop will result.
Imagine two outlets with different ground potentials; a computer is plugged into one, and an amplifier into the other. Both appliances are linked via an audio cable connected to the grounded chassis of both; effectively closing the loop between the power outlets as each has different ground potentials.
The Ground Loop essentially becomes an antenna, gathering the stray magnetic fields that influence a current in the loop via electromagnetic induction. This induction manifests as a 50 or 60 cycle hum in the speaker.
In order to rectify this, the Ground Loop must be broken. The simplest method is to connect all your audio appliances to one outlet. A heavy-duty power strip with surge protection is recommended or an extension lead.
AC Line Hum
This is similar in sound to Ground Loop noise, and sometimes, rectification of Ground Loop can eradicate AC Line Hum. Try this method if you’re unsure—it just might prove worthwhile!
Electrical devices with motors produce electromagnetic interference that can manifest as hum, e.g. a hairdryer. When active, their noise causes listening interference, as well as noise within the audio signal caused by the Electromagnetic Interference they release. You might have noticed this in light dimmer fixtures.
In order to remove AC line hum, the best way is to remove the appliances creating the interference—though this doesn’t come without its troubles. Uninterruptable power supplies, or again, extension leads can eliminate interference from an AC device.
Radio Frequency Interference (RFI) is a specific type of EMI occurring in the radio frequency band. Many wireless devices, including those with Bluetooth, incorporate RF Carrier Signals to transmit data wirelessly. These signals can cause noise in audio systems which translate to the speaker.
When data is transmitted wirelessly, RFI occurs. If you’re operating a wireless device close to an audio system, keep alert for faint buzzing and hissing.
In the event that the RFI is overly problematic, try keeping unnecessary wireless devices at a distance from all audio systems and speakers. The blocking strategies previously mentioned for Electromagnetic Interference may work in these instances.
Intrinsic Noise in the Audio Signal
In some cases, there might be a hissing or humming noise present in the actual audio signal. Speakers reproduce audio signals, therefore any unpleasant noise in the audio will often come out of the speaker as such.
The resolution, if viable, would be to remove the disruption from the audio. E.g. If you’re recording the mix, remove the interference at the source or find a better quality audio file.
Loudspeaker Interference
Hiss or hum isn’t a symptom of passive sound transducers dependent on an input device, but rather the input devices. It’s recommended that you inspect your A/V (audio/visual) receiver or amplifier.
Amplifiers always emit a basic or inherent sound; best heard when nothing but the speaker is connected with the volume low. When in close proximity with a speaker, you’ll always hear a little noise. This is often referred to as signal-to-noise ratio (S/N). The audibility of this is dependent on the system’s sound quality—the listening experience should not worsen.
Blown Speakers
Is your speaker distorted or noisy even at low gain? This can be indicative of a blown speaker. Dependent on the severity of a blow out, the speaker can be unable to produce sound.
Other ways of noticing a blowout include:
– burning or melting of the voice coil.
– deterioration/damage to the suspension and speaker cone.
To troubleshoot a blown speaker, listen for noise and distortion, and limited frequency response.
More often than not, it’s easier and more cost-effective to replace the whole speaker, as is the case with most inexpensive and passive types.
Subwoofer hum or buzz, a low-level noise, can be present when a passive or powered subwoofer is active, playing or not. Generally, it only takes changing the way the subwoofer connects to power for the issue to be resolved.
You might try some of the fixes already mentioned, e.g. separating cables to sufficient distances, switching AC outlets or using supportive components.
It may be worth changing the polarity of the subwoofer’s connection.
If a subwoofer has stopped delivering heavy bass and has begun to sound rough and raspy, something’s gone wrong. In most cases, it shouldn’t be too hard to fix, but it’s worth noting the subwoofer could be broken and caught in a Ground Loop.
So what causes the humming? There are three possible explanations for it dependent on how the subwoofer sounds. If it’s very quiet and doesn’t get louder when the volume’s increased, it’s likely you’re hearing the power supply as the subwoofer isn’t working as it should.
If it’s dependent on volume and clearly audible, there could be a disturbance in the mains or a poorly placed subwoofer or mains cable.
If the humming’s independent of the volume and still clearly audible, the issue is likely a Ground Loop produced by resistors from the power outlet leading to the source device and then the subwoofer, causing the hum at the end.
Not much can be done in the case of an extremely low hum, but you can see if the humming is amplified or minimised by adjusting the volume to exclude the other two possibilities. To find out, pull the audio cable out of the subwoofer input. If the humming ceases, a Ground Loop is to blame. Alternatively, if the hum is still present, Ground Loop is not the issue and the fault is probably mains interference of inefficiently shielded cables.
If you suspect Ground Loop, check the connection between the subwoofer and its source device, or those devices additionally connected to it. If your source device is a receiver, remove the antenna cable and check again for humming. In the instance that it still exists, you could use a sheath current filter to remove the unwanted noise, or you might instead try disconnecting all the appliances from the source device to determine which interrupts the Ground Loop.
If all else fails, contact the device manufacturer or B L Acoustics for advice.
Helpful information: A sheath current filter is a tool for preventing ripple anomalies which sometimes occur with the operation of a subwoofer. It’s placed between circuits where the device splits the input device to reduce the interference problems.
Transformer Noise
Transformers in the mains and power supplies of an audio system’s components can cause mechanically-induced hum. This hum can also be suffered by speaker amplifiers, prompting noise to the speaker. All transformers have what is known as ‘lamination rattle’. This refers to a direct current voltage on the line. This noise amount can vary due to its dependency on the quality of the AC line voltage. If the experienced noise is not indicative of RFI or Ground Loop, and changes over time, it’s quite possibly a result of transformer noise.
If it’s persistent interference, an AC power regulator can aid in the eradication of direct current on the power, thus transformer noise from the speakers.
Computer Noise
Internal soundcards/motherboards in computers, smartphones and tablets are prone to EMI that, within their structures, can’t be eradicated.
Computer to output audio will likely emit noise. It might be worth upgrading the computer’s soundcard or installing a PCI (Peripheral Component Interconnect) card—the connection interface that connects computer components to the computer—or a PCIe (e = express) card—an interface standard for connecting high-speed components that could assist in reducing or potentially eliminate this unwanted noise.
Conclusion
It’s unlikely the loudspeaker is the issue.
– When soundwaves have different frequencies and levels, unwanted noise occurs.
– Hissing and humming have different causes.
– Unwanted noise is typically a result of an amplifier or input problem.
– Faulty amplifiers could be worsening the loud hissing of your speakers.
– Check your cables!
As always, there is no one-size-fits-all answer. Every method has its advantages and disadvantages, and very much depends on a particular situation.
