Custom Industrial Mufflers
An industrial silencer allows fluid to pass through while dampening the noise from an engine exhaust, a steam discharge, or a ventilation flow. Since 1875, the Groupe Boët has been designing and manufacturing this equipment in its own workshop, based on two key parameters: octave-band attenuation and the pressure drop your system can tolerate. Twelve product lines, one for each noise source—and an ANSYS/CFD aeroacoustic R&D team to determine which one is right for you.
150 years
Expertise since 1875
up to 60 dB(A)
attenuation classes
12 scales
one per noise source
ANSYS CFD
Acoustics and Airflow
Building codes
Quality Certifications
French Code
CODAP
CODETI
U.S. Code
ASME Section VIII
ASME B31.1
ASME B31.3
European standards
EN 13445
; EN 13480
Nuclear sector
RCC-M (AFCEN)
Designed for aeroacoustic performance
This is the contradiction that a silencer resolves: the duct must remain open—the exhaust must escape, the steam must expand, the air must circulate—and yet the noise traveling through that same duct must be attenuated. It is also called a sound trap in ventilation systems, or an acoustic silencer. The principle remains the same; what changes completely is the source: an engine does not produce noise like a steam valve, which in turn does not produce noise like a fan.
Two figures describe a silencer, and you must specify both. Transmission Loss (TL) measures the actual attenuation, per octave band. Pressure drop, in pascals, measures the cost of the silencer to your system: back pressure on an engine, lost airflow on a fan.
A silencer that provides high attenuation but has excessive resistance can damage the machine it is designed to protect. That is why we must optimize both parameters together using ANSYS simulation—this is the core of aeroacoustics.
For an operator, this is equipment designed for a specific site, machine, and regulatory requirement. For a generator set manufacturer, engine manufacturer, or systems integrator, it is a specification developed in collaboration with your teams —balancing noise attenuation, pressure drop, footprint, and weight right from the design phase—then finalized in a manufacturing specification and produced on a made-to-order basis. Same engineering department, same workshop, same quality control. Sizing does not come at the expense of repeatability.
Two mechanisms, often used in combination
Every muffler relies on one, the other, or a combination of both. Knowing which one dominates in your product line means knowing which frequencies it handles.
An engine emits sound primarily at low frequencies —this is the domain of the reactive system. A steam expansion valve or a fan emits sound across a broad frequency range —this is the domain of the dissipative system. Our engine exhaust systems combine both devices in a single unit: the chambers handle the low frequencies, while the absorber handles the rest.
What is the source of the noise?
That’s the only factor that matters when choosing from the product line. The rest—dimensions, materials, attenuation class—can be determined based on the specific requirements.
| Votre source | Ce qui fait le bruit | Famille de silencieux |
|---|---|---|
| Moteur à combustion — groupe électrogène, cogénération, motopompe | Ouvertures de soupapes : bruit impulsionnel, dominante basses fréquences, gaz chauds | Silencieux d'échappement moteur ↓ |
| Vapeur ou gaz sous pression — chaudière, soupape, turbine | Détente brutale à la mise à l'atmosphère : très haut niveau, large bande | Silencieux vapeur & process ↓ |
| Air en mouvement — ventilation, CTA, air comprimé | Bruit de ventilateur et d'écoulement : raies + large bande, débit à préserver | Silencieux de ventilation & d'air ↓ |
A range for each source, not one product for everything
Engine Exhaust
Generators, cogeneration, stationary engines — hot gas, low frequency
Engine noise level: 15 to 25 dB(A)
SMP exhaust muffler designed to address noise reduction challenges through dissipative effects.
Quiet Motor, 30 to 50 dB(A)
The SM EVO 2 next-generation exhaust silencer: a combination of reactive and dissipative devices, DN 50 to 800.
Compact Engine Muffler
SMC compact exhaust muffler, designed for tight spaces.
Steam & Processes
Boilers, safety valves, turbines — very high levels, high temperatures
Release into the atmosphere
Covers the release of pressurized gaseous fluids into the atmosphere: venting, discharge, safety valves, and steam vents.
Industrial Boilers
Cylindrical absorption body for boiler circuits: attenuation tailored to the generator’s spectrum.
Gas Turbines
Turbine intake and exhaust silencers—flow, temperature, and pressure drop are the key design factors.
Ventilation & Air
Air distribution systems, air handling units, boosters—airflow is the function, pressure drop is the constraint
Ventilation silencer
Rectangular (with baffles) or cylindrical, installed in ducts: sized based on airflow rate, velocity, and allowable pressure drop.
Compressed air silencer
Reduces intake and discharge noise from Roots blowers, vacuum pumps, and rotary compressors.
In-line silencer
A tubular silencer designed to be inserted directly into an existing pipe or duct, without requiring any modifications to the system.
The information needed to size your muffler
Please send them to us: our acoustic engineers will analyze your system and provide you with the selected attenuation curve.
The engine
Make, model, overall dimensions, weight.
Gas flow rate
The temperature of the gases
At the silencer inlet. Determines the steel grade and heat treatment.
Permissible back pressure
The Specter at the Exhaust Pipe
By octave band, if available; otherwise, the overall level in dB(A) and the measurement distance.
The Goal to Achieve
The Location
Line diameter, horizontal or vertical orientation, overall dimensions, lifting equipment, and site documentation requirements.
Are you replacing an existing muffler?
Contact us for a personalized assessment.
What You’re Buying, Beyond the Silencer Body
Manufacturer
In-house sheet metal fabrication in Tourcoing; nuclear-certified welding; painted, galvanized, or stainless steel. Strictly controlled lead times; full traceability.
Aeroacoustics, not just acoustics
TL by octave band AND pressure drop, simulated using the same ANSYS/CFD model. A muffler that silences the machine is not a solution.
Performance guarantee
Noise reduction is specified in the contract from the initial quote onward and verified through measurements. You’re not buying a cylinder; you’re buying a result.
Where We Operate
Frequently Asked Questions
Reactive or dissipative muffler: Which one should I choose?
It depends on the frequency spectrum of your source. An engine emits primarily at low frequencies: this is the realm of reactive damping (expansion chambers). A steam expansion or a fan emits across a broad frequency band: this is the realm of dissipative damping (absorption). Many of our product lines—including the SM EVO 2—combine both types of devices in a single unit. The choice is based on the specific spectrum, not on intuition.How is the noise reduction of a muffler measured?
Through transmission loss (TL): the intrinsic attenuation between the incident and transmitted acoustic power.A general attenuation in dB(A) without frequency-specific details does not allow you to verify that it is achieved at the frequencies where your machine actually emits noise.Does a muffler cause my bike to lose power?
That’s the risk if the pressure drop isn’t properly sized. In a motor, excessive back pressure reduces efficiency and reliability; in a fan, it reduces airflow. We simulate the flow using CFD to keep the pressure drop within the manufacturer’s tolerance—this is just as important as noise attenuation, and the two factors influence each other.Do you manufacture silencers in series for a manufacturer or an integrator?
Yes, and the sizing doesn’t change—it’s the process that changes. We design the reference model with your teams, balancing trade-offs early on between attenuation, pressure drop, footprint, and weight, then we finalize it in a manufacturing specification and produce it on a made-to-order basis. Prototypes, pre-production runs, and production runs all come from the same facility in Tourcoing, with the same quality control and traceability.What temperatures and materials?
Depending on the product line and application: painted, galvanized, or stainless steel; high-temperature absorbents for exhaust and steam; protection of the absorbent with a mesh screen and perforated sheet metal in high-flow applications. Temperature resistance is a design parameter, not an option.Should the silencer be used in combination with other treatments?
Often. On an enclosed generator set, the exhaust silencer is essential —without it, the exhaust bypasses the enclosure. For ventilation, it is combined with acoustic grilles on the front panel. And to ensure compliance with emissions standards, our catalytic mufflers and SCR systems treat both noise and exhaust gases in a single unit.
I'm using an SM30, SM40, or SM50 muffler: what should I replace it with?
In the historical BOËT Stopson nomenclature, SM40 refers to a 40 dB(A) attenuation class —the number represents dB(A)—and not to a specific model. Its direct successor is the SM40 EVO 2, available in sizes from DN 50 to DN 800 (DN 150 to 800 for Class 50). Please provide the nameplate information for the existing unit: we will confirm compatibility and connection dimensions before you place your order.
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