Soundproofing an RV Generator
Soundproofing an RV Generator is just one of the types of soundproofing assistance we offer for the dozens of types of generators on the market today.
Recreational vehicles (RVs) contain electrical power generators that are installed within the body of the vehicle (Figure 1).
In some vehicles, the generator enclosure (shown in green) is completely enclosed within a sheet metal compartment, which is part of the body of the RV. In other RVs, the generator compartment is open to the road below, with the generator enclosure supported on a frame. Generators can pose numerous noise problems both inside and outside of the RV. Most generators will produce noise of 48–65 dBA at a distance of 50 feet. This translates into noise levels of 78–95 dBA within the generator compartment. This application note examines some of the sources of noise from RV generators and provides insight into how these noise problems can be addressed.
The key to soundproofing an RV generator is to locate all of the generator noise sources.
Generators produce noise across the audible spectrum from numerous airborne and structureborne sources. A review of some of these noise sources is provided below:
- Fan Noise – Water-cooled generators will have a cooling fan and radiator. The fan will emit pure tones at the fan blade pass frequency and its harmonics. Typical blade pass frequencies will be in the 120 – 160 Hz range. Fan noise can propagate through openings or gaps in the generator compartment or directly through the generator enclosure if there is not adequate sound proofing installed in the panels.
- Exhaust & Inlet Noise – Generators that do not have adequate exhaust mufflers or intake plenums will emit low frequency noise at the engine firing frequency. Exhaust pipes will typically pass through the generator compartment and will be connected to a muffler that is located underneath the RV. If the end of the exhaust pipe does not extend beyond the passenger compartment, pressure pulsations from the exhaust may be heard inside the RV. The inlet air plenum may or may include a muffler and is typically located within the generator enclosure.
- Engine Noise – The combustion impulses during operation of the engine excites resonances of the engine block pistons and valve train that are heard as a high frequency “ringing” or “pinging” noise at the engine firing frequency. This noise radiates in all directions, however, it is more prevalent on the bottom of the engine when it passes through the relatively thin sheet metal of the oil pan. If there is a resilient structure underneath the generator, noise from the oil pan will reflect off of this structure and reverberate within the generator compartment.
- Mount Noise – The generator will have periodic vibrations at the rotational speed of the motor and at the engine firing frequency. These vibrations should be damped by the generator vibration isolation mounts, however, it is not always possible to tune the mounts for vibration control at the motor operational speed. This is due to the fact that the mounts must also isolate the generator for road vibrations, requiring stiffer mounts. Vibrations from the generator can therefore be passed into the structure of the generator compartment, causing panels to vibrate at their natural frequencies and radiate noise like loudspeakers.
- Exhaust and Cable Grounding Noise – The exhaust system and electrical cables are typically held in place using elastomeric mounts or grommets that are supposed to isolate vibrations from the engine from the generator compartment. During transportation, it is possible for these vibration mounts to become misaligned, resulting in the exhaust system or cables contacting the structure of the generator compartment or RV. Noise due to grounded exhaust pipes or cables can pass directly through the body of the RV and into the passenger compartment. This noise typically sounds like a low freqency “moaning”.
Soundproofing an RV Generator
A typical RV generator compartment will consist of sheet metal walls on all sides, with an outside cover with a screen to allow for the flow of cooling and induction air (Figure 2).
The generator is then installed within the compartment and bolted into place. The compartment will typically have minimal or basic soundproofing materials installed from the factory. The hard walls within the compartment can act like a sound box, where noise from the generator is reflected and amplified. This sound and vibration can pass through the walls of the generator compartment directly into the RV and disturb its occupants or it can escape through numerous open airflow paths into the environment and disturb neighbors.
Sonic-Shield can assist RV owners throughout the soundproofing process by identifying the source(s) of the noise problem(s) and the noise transmission path(s). Once these are known, Sonic-Shield can assist RV owners in implementing soundproofing for their generators. Following are some general guidelines:
- Sonic-Shield can help you identify if there is excessive noise transmission from the generator compartment into the passenger compartment. In such cases we might recommend that you line the inside of the generator enclosure with a Class A sound barrier material, such as Sonic-Shield Noise Barrier. This material has a thickness of 1/8” and includes a reinforced foil facing to resist heat and fire. The Sonic-Shield Noise Barrier can also provide damping to the generator compartment walls to prevent them from re-radiating noise into the passenger compartment.
- If there is excessive noise from the exhaust system, Sonic-Shield can assist you with trouble-shooting and implementing a practical solution. The RV owner should examine the exhaust pipe mounts to ensure that they are not “grounded” to the structure of the RV because of worn or displaced mounts. If this is the case, we would recommend that you replace, repair or re-align these mounts to eliminate contact between the exhaust pipe and RV structure. We also recommend that the exhaust pipe be extended beyond the passenger compartment to eliminate noise from the end of the exhaust pipe.
- Sonic-Shield can help you determine if there is excessive noise being passed into the RV through the generator mounts. In such cases, the generator mounts may not be adequate to properly attenuate vibration which can be converted into noise within the RV passenger compartment. The RV owner should avoid bolting the generator enclosure directly to the generator compartment without the use of elastomeric mounts. When mounts are present, we recommend that the RV owner inspect the mounts to ensure that they are not misaligned or damaged. In such cases, we can help recommend more compliant (or higher damping) vibration mounts to further attenuate generator vibrations.
- If there is excessive noise that propagates from the generator compartment to the environment, Sonic-Shield can recommend the optimum type and amount of sound absorbing material, such as Sonic Fiber, which reduces the amount of reverberation within the generator compartment. This material is not flammable and we recommend that it be installed on large flat surfaces within the generator compartment, including the top, back and cover. Special care should be exercised so as not to block airflow to the generator.
- For generator compartments with airflow paths underneath the RV, noise can strike the surface underneath the RV and reflect out to the environment. For such situations, we do not recommend blocking the air path. Sonic-Shield can provide a lightweight, yet effective sound attenuating panel that can be placed in front of the generator compartment after the RV is parked, which will cover the gap between the side of the RV and the ground to effective block and absorb this reflected noise.
Sonic-Shield has an engineering staff with advanced technical capabilities who can assist RV owners in the selection and installation of soundproofing materials and products to reduce noise and vibration problems from their generators. Soundproofing an RV generator used to be difficult. No longer! We look forward to hearing from you to help you with your generator noise.