Intro
Have you ever experienced a persistent hiss emanating from your speakers, even when no sound is playing? Or been taken out of your favorite movie every time a truck passes your house? This irritating background noise is often a result of a high noise floor, which significantly degrades the audio quality of your system.
In this blog post, we will delve into the concept of noise floor and its implications on your sound quality, and explore effective strategies to mitigate its adverse effects.
Understanding Noise Floor
The noise floor represents the minimum level of background noise in an audio environment when no audio content is being played. It is a combination of unwanted noise introduced by various factors. This noise floor can manifest in different forms such as a faint hiss, a subtle hum, buzzing sounds, crackling noises, or even environmental noise like an HVAC system. The goal of any home theater is to minimize the noise floor as much as possible to prevent these consistent noises from degrading the audio experience.
Implications for Home Theater
An excessively high noise floor compromises sound quality, resulting in a muddy, dull, or noisy listening experience. It reduces the dynamic range by raising the overall noise level, obscuring softer sounds and reducing audio clarity and fidelity.
In the context of movie watching, a high noise floor becomes evident when subtle audio details are hard to discern at normal listening levels. Take, for instance, the movie “A Quiet Place,” where the rustling of leaves under the actors’ feet are subtle but important audio details in the movie.
With an elevated noise floor, you might miss these details or be tempted to increase the volume to hear the footsteps. However, increasing the volume could lead to speaker compression during louder scenes, resulting in a loss of detail within those louder segments. Therefore, the system’s overall audio dynamic range, the difference between the loudest and quietest sound, is reduced. This has the overall effect of reducing the immersion and emotional impact of the content you are watching/listening to.
Common Sources of an Elevated Noise Floor
There are two main sources of an elevated noise floor:
Electrical Noise
Electrical interference is one of the main sources contributing to the noise floor in an audio system. It often occurs due to electronic devices, power supplies, or improperly grounded equipment near or in the audio signal path. When electrical interference enters the audio circuit, it introduces random electrical signals that result in a slight buzzing or hum from the speakers.
To identify whether you have an elevated electrical noise floor, simply set your audio system to your normal listening level and ensure that no audio is playing. If you detect the presence of buzzing or hissing sounds coming from your speakers while in your seat, it is an indication that your system has an elevated electrical noise floor.
Environmental Noise
Ambient noise is another significant contributor to the noise floor. It refers to the sounds present in the listening environment that are not coming from the audio equipment, which can include background noise from air conditioners, fans, traffic, or any other sources of sound in the vicinity. When ambient noise exists, it becomes part of the noise floor and can impact the clarity and fidelity of the audio reproduction.
To assess whether your environment is impacting your audio experience, take a moment of silence with all of your audio equipment turned off and carefully listen to your surroundings. Pay attention to any audible presence of an HVAC system, conversational noise, low rumbling, traffic sounds, or fans. If you consistently hear such noises with clarity, it may indicate that your room lacks sufficient isolation from the external environment.
Measuring Noise Floor
The methods mentioned above are good subjective ways of determining if you could have a noise floor problem, but how do you measure it?
To evaluate the noise floor in your home theater, you can utilize tools like the UMIK-1 microphone along with a computer running REW (Room EQ Wizard). Start by measuring the sound pressure level in your room while simulating a realistic scenario, as if you were about to sit down to watch or listen to content but nothing is playing yet. In a dedicated listening room, you may achieve a range of 20-30dB, but usually, it will be higher. As a general guideline, a measurement below 35dB is considered acceptable for home theater purposes.
For more precise targets, it is advisable to aim for a Noise Criteria (NCB) rating of 30 or below. The NCB rating accounts for the sensitivity of human hearing at different frequencies. For this reason sound criteria are assessed using curves that span various frequency ranges. A NCB 30 rating is recommended specifically for movie theaters and would be a good target to aim for.
Using the RTA feature in REW, measure your room and if your measurements fall under the selected NC curve, your system should have a low enough noise floor to not detract from your experience.
Isolating the Noise
If you discover that your system’s noise floor exceeds acceptable levels, the next step is to determine the source of the noise and isolate it.
Begin by turning off your audio system completely, thereby eliminating the possibility of electrical noise. If you observe a significant drop in the noise floor, it indicates the presence of an electrical noise problem within your system. Next, start turning off and unplugging devices until you can isolate which piece or pieces of equipment are contributing to the noise.
However, if the noise persists even after turning off the audio system, proceed to inspect your surroundings. Go through your house and systematically switch off any devices or equipment that generate noise or vibrations. This includes appliances, fans, air conditioning units, or any other potential noise sources you can identify.
By methodically eliminating sources of noise and vibration in your environment, you can narrow down and pinpoint the root cause of the elevated noise floor in your system. Once the problem has been found you can take steps to reduce the impact of the source.
Improving Noise Floor
If you are looking to decrease the noise floor in your audio system, here are common methods to assist you:
Electrical Noise
Ground Loops
Ground loops are a common cause of audio noise and video distortion. Symptoms include a buzzing or humming sound from the speakers. Ground loops happen when different components of your entertainment system are plugged into separate AC outlets and connected by signal cables (e.g., RCA, HDMI) with grounding. This creates a loop antenna that attracts electromagnetic noise.
To eliminate the noise, break the loop by powering all equipment from a single AC socket. Connect everything to a power strip or surge protector, then plug it into the wall. If some equipment cannot reach the same outlet, consider using a hum eliminator to interrupt the loop in the signal cables. Beware of scam devices as not all devices work as advertised.
If the HDMI cable is causing the ground loop, you can try optical HDMI cables that lack a copper control line. It can sometimes be trial and error before you find one that will work.
AC Line Noise
Devices with motors (e.g., hair dryers, blenders) and dimmer switches can cause interference in audio signals. Avoid using such devices while watching TV or listening to music. Alternatively, use a line interactive UPS or switch the circuits the devices are plugged into (a solution that has worked for a friend of mine). A line interactive UPS converts AC to DC and back to AC, effectively eliminating electrical interference.
Wires
To minimize noise, try to minimize power cables that run across or near audio/video signal cables. Three-wire balanced signal cables (e.g., XLR) are less susceptible to power cable hum and could be a solution. Keep speaker cables isolated from AC cords, especially over longer runs. Avoid looping cables as this leads to turning the cable into an antenna, therefore increasing noise.
RF Interference
Conductive materials like metal block RF signals. To reduce RF interference, keep RF-emitting devices (e.g., portable phones, cell phones, Wi-Fi equipment, computers) away from your audio setup. Ensure proper shielding for devices near your setup. Focus on minimizing the strength of incoming radio signals.
Environmental Noise
Room Treatment
Acoustically treating a room is a highly effective method for reducing environmental and stray noises that can disrupt your space. By implementing proper acoustic treatments, such as the installation of acoustic panels, thick curtains, and rugs, it can help reduce the impact of background noise. To help reduce outside noise even farther, make sure that all windows and doors are sealed, as little cracks can let in sound from outside places.
If you would like to know about how to acoustically treat your room, we have created a room treatment guide to walk you step by step through treating your space to improve your sound quality, check it out here or by clicking below:
HVAC
Air conditioning units and ventilation systems often produce background noise, which can contribute to the overall noise level in a room. This constant humming or airflow noise can have a negative impact on audio clarity. To address this issue, there are several steps you can take.
If the noise originates from an air vent, you can minimize it by adjusting the airflow. Increasing the number of vents or enlarging their size can help reduce the velocity of the air passing through, thereby diminishing the associated noise. Additionally, ensuring that the air ducts running through the room are well-insulated can help prevent vibrations in the ductwork, further reducing noise transmission.
In cases where the HVAC unit itself is the source of the noise, there is another approach to consider. Placing rubber isolators beneath the mounts of the unit can effectively absorb vibrations generated by the machine and minimize the amount of noise transmitted into the house.
Additional Help
If you would like additional help with locating or eliminating the source of your high noise floor or any other home theater related topic, feel free to leave a comment or book some time with us. See more about it here, or by clicking below.
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