Krieger Specialty Products
Acoustical Questions
STC stands for Sound Transmission Class. STC is a single number rating system derived from measured values of sound transmission loss in accordance with ASTM Classification E 90 and E 413. The higher the rating, the more sound is blocked. An STC rating provides a standard industry-accepted method for evaluating and comparing the sound reduction effectiveness of various acoustical doors and windows.

Some people refer to a sound control door as a “soundproof” door because of the high level of noise reduction it provides. But technically speaking, there is no such thing as a soundproof door because no door can stop 100% of the noise. However, you can control the amount of noise leakage by using special designs and materials. Krieger’s acoustical doors employ these elements to create custom doors that come with an STC rating.

To receive a Sound Transmission Loss test report, which certifies an STC rating, a manufacturer must arrange for a product to be tested in an acoustical laboratory. The laboratory must be accredited by the United States Department of Commerce, National Institute of Standards and Technology (NIST) under the National Voluntary Laboratory Accreditation Program (NVLAP) for the testing procedure. This laboratory testing ensures that the manufacturer’s door or window performs to its specified STC rating.

The laboratory test report should be issued on the laboratory’s own letterhead and be clearly dated. It should name the company requesting the test and assign a report number. There should be an introduction indicating which test method is being utilized and whether the laboratory is accredited.

There should be a description of the item being tested, which indicates the essential details of the product and the result of the test measurement. The report must be signed by the certifying technician and a laboratory official. Finally, the report should be accompanied by a graph indicating the STC contour.

Field Sound Transmission Class (FSTC) evaluates the sound isolation between two rooms and the performance of the partitions installed in the interior of a building, whereas Sound Transmission Class (STC) represents optimum conditions of a laboratory that is rarely achieved in actual construction.

The difference between the FSTC and STC results is based on the receiving space, which may not be calibrated for sound absorption or from sound leaks and “flanking” paths. Flanking is sound that travels between two rooms along paths other than through the partition being tested. Because of this, partitions composed of multiple elements such as doors, windows, and walls will usually need an overall FSTC close to the lowest FSTC value of any component.

The results of the FSTC tested per ASTM E 336 are usually lower than in E 90 laboratory tests for the same specimen. The normal rule is to specify an STC rating of five points higher than the field result required.

Laboratory STC certification is intended to test a specified construction and design, not every conceivable configuration. Once a design is certified at a specific STC rating, the size of the requested door retains that certification.

Based upon previous testing experience and laboratory reports, calculations can be made to accurately estimate the STC value of a door with various vision lite sizes. For example, a laboratory tested STC 46 door can have up to 900 sq. in. of glass. Similar glass sizes can then be furnished based on calculations extrapolated from the tested door.

Currently there are no louver designs that provide optimum sound reduction quality, therefore Krieger does not recommend them.

Pairs of sound doors require acoustical astragals at the meeting stile. This astragal should match the perimeter seals in design. Depending on the STC rating required, either a single or double astragal will apply.

ASTM E 90 is the Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements. The sound transmission loss is calculated from a basic relationship involving the sound levels, absorption levels, and the test specimen size. The transmission loss data is used in E 413 (Classification for Rating of Sound Insulation) to determine the STC. Both specifications are important when specifying an acoustical door or window assembly.

As the leader of the acoustical door industry since 1936, Krieger was the first door manufacturer to achieve an STC 51 and then STC 53 in a 1 3/4" thick door without a raised sill. Krieger was also the first to achieve an STC 47 on a 1 3/4" thick wood door. Requesting the KriegerSonic (Krieger acoustical) brand will assure you receive the highest quality product and STC rating. We are proud to provide Krieger’s 10 Year Manufacturer’s Guarantee on our products.

Investigate whether it comes from a manufacturer that specializes in acoustical doors and windows. Find out if the manufacturer’s available literature shows current testing data from an accredited laboratory. Consider if the finished product is developed in-house from start to finish, or if it is a collection of components from various manufacturers. Also ask if the field performance is guaranteed and backed up by accepted ratings in the industry.

KriegerSonic acoustical doors are available with fire labels for up to 3 hours for metal doors and “S” (smoke)-labels up to 3 hours for metal doors. Wood doors come with fire labels up to 60 minutes, and S-labels of 20 minutes, 45 minutes, or 60 minutes.

Krieger offers acoustical doors with ratings up to STC 55 and acoustical windows up to STC 56. Please note that the highest STC may not be the right solution for you. Our knowledgeable and experienced sales staff is available to discuss your requirements and help you identify the optimal STC rating for your project.

The complete tested acoustical assembly comes supplied with the door, frame, perimeter sound seal, and door bottom. Cam Lift Hinges and an aluminum threshold are included on doors rated STC 45 or higher.

Materials with similar Sound Transmission Class (STC) ratings can provide similar performance in many applications. However, the resonant frequency of different materials may change the STC ratings required. Whenever possible, use a consultant to advise you on the proper STC ratings to use when designing your project.

Yes, an appropriately fitted threshold is critical for achieving a good seal and an optimal acoustical barrier.

Krieger’s Cam Lift Hinge lifts the door during its travel and seats the door bottom for a positive seal in the closed position. It is available in standard and electrified options.

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Acoustical doors are typically heavy doors. KriegerSonic doors range from 7 lb/sq. ft. to 22.9 lb/sq.ft. depending on size and type. Despite this additional weight, Krieger doors are designed to be easy to operate and to comply with the ADA standards if needed.

Yes, Krieger’s acoustical products come with a performance guarantee.

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