An acoustic test for wood doors takes place in a two-room laboratory setting where the walls, floors and ceiling are all acoustically isolated from outside sound as well as from each other. The test assembly provides the only means of transmission between the rooms.
Both rooms are tested for acoustics with the sample installed per the requirements of ASTM E-90. The data is used to calculate the STC rating per ASTM E-413 and the resulting number or Sound Transmission Class (STC) rating indicates the assemblies ability to prevent the passage of sound. The higher the STC number the greater the acoustic insulation.
The Acoustic Test Report includes details of the tested assembly and the laboratory test conditions per E-90 requirements. It also includes a graph showing the class contour and test sample transmission loss curves.
- Contour Curve – A reference used in the calculation of the STC performance. It is deemed the target curve for acoustic performance.
- Test Sample Transmission Loss Curve – This shows the performance of the test opening at the various measured frequencies.
As we discussed briefly in the first post of this series, doors are sometimes tested inoperable. This is to determine the capability of the door construction by artificially making the transmission through the gasketing equal to zero. Inoperable ratings cannot be used in place of gasketed and operable rating.
Closely related to the issue of operability is the question of what is actually being tested. In an operable test, the door and gasketing system are being tested together. This is why acoustic door offerings typically list the gasketing system required to guaranty the STC rating. The frame may or may not be included in the assembly depending on the performance of the test.
In the absence of valid data and engineering, substitution of one type of gasket for another cannot be assumed to provide equal performance.
The key to the performance of an acoustic door is installation include:
- Use of the door construction, gasket seals and, if applicable, frame used in the tested assmbly
- Proper installation and maintenance of the seals and hardware
Installation is the single biggest variable in the acoustic opening. A series of doors, all made the same, should provide reproducible performance within one STC. Substitution of tested components and improper installation on the other hand will easily swing the performance by several points or more.