Hoover and Strong, a manufacturer of recycled precious metals, had an HVAC noise problem. Their clean air blower installed in the work area was creating an organizational hazard as noise levels were distracting to employees. Acoustical Solutions developed a custom fitted sound enclosure to reduce noise levels by 50%.

Application Introduction:

Hoover & Strong is a manufacturer of precious metals that has been in business since 1914. One hundred percent of all of their precious metals including gold, platinum, palladium, silver are recycled.

Hoover & Strong utilized a recirculating clean air unit which uses a variable speed blower designed to clean the air that is then ducted within their HVAC system.

Typically these units are installed on roof tops or above ceilings because of the noise levels emitting from the blower.
In Hoover and Strong’s case, the unit had to be installed within a mechanical room right next to a smelting work area.
Their intention was to offer a better, cleaner work environment. They did not want to do so by subjecting their employees to the excessive noise levels being created by the clean air unit.

Treatment Provided:

Acoustical Solutions scoped out the job site and saw three initial problems:

  • The unit was suspended from threaded rod, but there was no isolation or vibration hangers separating the unit itself to the ceiling deck above.
  • The blower on the unit was excessively loud and needed to be enclosed or blocked off from the mechanical room.
  • The Isolation Hangers that Acoustical Solutions chose to use were the ISOH3B which use both neoprene for stopping high frequency vibrations and a spring mount that works well with the low frequency problems.

The sound blankets that Acoustical Solutions chose for this application were the ABSC-25 because they are a class 1 fire rated blanket suitable for indoor use, and they not only absorb sound energy, but block transmission as well.

Knowing that the blower on the unit is set within a close proximity to a work area, Acoustical Solutions needed to add as much sound blocking as they could to the unit, and ABSC-25 sound blankets utilize a two pound version of mass loaded vinyl sound barrier, sandwiched in between two one-inch layers of fiberglass quilted into a vinyl covering. This version of the product provided optimal sound blocking power, making it the perfect enclosure material.

Installation of the isolation hangers was very straightforward, Acoustical Solutions simply cut the existing threaded rod, breaking the metal to metal connection between the unit and ceiling deck, and inserted the isolation hanger, tying off the threaded rod to the top and bottom of the hanger.

The ABSC-25 sound blankets were a little more challenging. First, there were a number of cut outs that would be required for the enclosure, and secondly the unit still had to be able to draw in air, but be  acoustically sealed on all sides.

The blankets on all four sides of the enclosure went on first, attaching to a concrete header. The cut-outs for ductwork were field measured, then cut with a utility knife to the appropriate size, taking care to not make too large a cut which would sacrifice the sound attenuation of the enclosure.

Extra edge binding was then wrapped around the cut-outs and stapled into place to assure that no loose fiberglass was open to the mechanical room.

The second issue of allowing proper airflow to the unit was achieved by making the bottom blanket equipped with a large air flow vent baffle which is an acoustically lined convoluted path that will freely allow the air to pass, but will absorb the sound energy as it passes through the ninety-degree turn within the vent baffle.


After the installation was complete and the unit was turned back on, the on-site supervisor from Hoover and Strong commented: “The unit is at least 50% percent quieter than it was before!”

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