STC (Sound Transmission Class) openings have gained popularity in the recent years for many reasons. The healthcare market require STC partitions because poor acoustical conditions may have a negative impact on a patient’s physiological health and increase their chances of being readmitted to the hospital. Acoustics can also impact perceptions of privacy, comfort, safety, and security for patients and their families. Military, education and office environments require acoustical performance for security, privacy and improved conditions.
Keep in mind that STC ratings are intended to dampen speech. The frequencies test range from 125Hz to 4000 Hz. Amplified music, mechanical equipment noise, transportation noise or any sound with low frequency energy below 125 Hz in not part of the STC test criteria. Alternatively, Outdoor-Indoor Transmission Class (OITC) is a standard used for indicating the rate of transmission of sound between outdoor and indoor spaces in a structure that considers frequencies down to 80 Hz (Aircraft/Rail/Truck traffic) and is weighted more to lower frequencies. Do not be surprised if the high STC partition has a much lower OITC rating as the lower frequencies are more difficult to suppress.
Make sure the STC test information you receive is listed as an operable test. This ensures that the product has been test as a working opening. An inoperable test is just rating the panel and not how it works with the frame and wall. In most cases the difference between an operable and inoperable test is about 2-4 STC points with the inoperable being higher.
The first and most important consideration is the sound partition as a whole. The wall, frame and door should work together to block sound from one side of the partition to the other. The STC rating of all the components of the partition should be the same. If the STC rating of the wall is lower than the rating of the door or windows, the rating of the partition will be equal to the lowest STC rated product. Sound waves will travel the path of least resistance.
When a door manufacturer goes to an independent test lab to run a STC test, the test lab requires them to run the test with a high STC rated block wall and the frames to be grouted into the wall. This ensures that the sound waves do not flank (go around) the door and frame and negatively impact the acoustical test. Non concrete block walls have a maximum STC 46 rating. Anything above this requires some sort of concrete block or Concrete Masonry Unit (CMU). If this is the case the frame should be grouted into the wall to ensure the maximum resistance to sound. If the wall sheet rock, then carry the wall construction and wall insulating material into the throat of the frame.
The door should be installed as a normal door with the addition of the sound seals. The door and frame manufacturer should be able to supply you with installation instructions for the seals, thresholds or door bottoms to properly seal the door to the frame. Improper installation or changing the location of the seals will result in poor acoustic performance or poorly operating doors. Make sure the seals are in the right location on the frame and are orientated the correct way. Thresholds need to be level to make sure the bottom of the door properly seals.
After you have installed the door, seals and hardware, do a quick and easy check of how the seals and door work together. Take a credit card and try to slide between the door and frame. The seals should make this difficult to do. This ensures a tight seal between the door and frame. Take a flashlight and with a person on the other side of the closed door run the light around the perimeter of the door, including the bottom edge to see if any light is reaching the other side of the opening. If you can see light, then the performance of the opening is lessened. Adjust the door (shim) or adjust seals to close off any gaps.
These ASSA ABLOY Door Group brands offer a wide variety of acoustical solutions.
Ceco Door STC Product Information
Curries STC Product Information
Frameworks STC Product Information
Graham STC Product Information
Maiman STC Product Information
I hope this helps answer question you have on STC openings. If you have other questions please leave them in the comments section and I will get back to you.