Many designers, architects and owners are these days, choosing glass as their product of choice when it comes to interior acoustic moveable wall space division especially in an office environment. But how “good” is glass acoustically when it is used as the skin component in an operable or moveable wall system?
Glass does not perform acoustically in the same manner as gypsum board (sheetrock, drywall), the most common skin material used in solid moveable walls ( Read link #1 below ). But the way that the acoustical performance of a glass wall is determined and how it is measured, compared and identified, is the same as a solid wall. A laboratory determined (ASTM E-90 test procedure) STC number – the higher the better – is the accepted single number rating system for all interior building partition systems. In order to learn more about what STC is and how it is determined, read link #2 below.
What is the best STC one can expect from a “glass skinned” wall? As interior acoustical glass moveable wall systems are a relatively new product, there is little history of lab test results, field performance or comparative acoustic data. The best forms of comparison available are “fixed acoustical windows that are fixed within acoustical frames” These are basically tests on panels without track, trollies, vertical or acoustical seals etc. In the moveable wall industry these tests are referred to as “panel tests”.
No company has done more testing or has more proven field experience with acoustical windows than Viracon. They have 66 tests on their web-site (https://www.viracon.com/wp-content/uploads/2020/09/acousticperfdatatable.pdf ) on insulating glass acoustical products based on combinations of glass thickness, type of glass and airspace. All units tested were 36” wide X 84” tall, installed in an acoustical frame and sealed around their entire perimeter. The windows were not moveable and did not have any operable seals or flanking paths around the units. Reviewing these results is an indicator as to how well an acoustical glass wall will perform once you add in track, trollies, acoustical seals etc.: when it becomes a “moveable wall”. A generally accepted rule of thumb is that an STC from a “panel test” will decrease by 8 to10 points when tested as a moveable wall panel with seals, astragals, track & trollies. For example a “panel test” that has an STC of 50 would result in a moveable wall panel STC of 40 to 42.
Examples of Viracon window tests on assemblies that resemble an operable wall panel (double glazed insulating glass, minimum 4” airspace) are below. (Note that indicated glass components have a PVB interlayer of plastic resin between two layers that is used to bond the panes together and increase the acoustic results.)
- 4 7/16” overall, 1/8” glass, .030” PVB, 1/8” glass, 4” airspace, 3/16” glass: STC: 48. Estimated STC as an operable wall: 38 to 40.
- 4 11/16” overall, ¼” glass, .030” PVB, ¼” glass, 4” airspace, 3/16” glass: STC: 49. Estimated STC as an operable wall: 39 to 41.
- 4 7/8” overall, ¼” glass, .030” PVB, ¼” glass, 4” airspace, 3/8” glass: STC 49. Estimated STC as an operable wall: 39 to 41.
- 5 1/16” overall, ¼” glass, .060” PVB, ¼” glass, 4” airspace, ¼” glass, .030” PVB, ¼” glass: STC 50. Estimated STC as an operable wall: 40 to 42.
- 4 ¾” overall, ¼” glass, .030” PVB, ¼” glass, 4” airspace, 1/8” glass, .030” PVB, 1/8” glass: STC 51. Estimated STC as an operable wall: 41 to 43.
The Moderco acoustic Crystal Wall, overall 4” thick, ¼” tempered glass, 3 ½” airspace, ¼” tempered glass. Complete with vertical and horizontal acoustic seals.
- Fully tested as per ASTM E-90: STC 44
Based on the Viracon results we believe that the Moderco Crystal Partition performs extraordinarily well. An STC 44 is in theory higher than any of the acoustical results achieved by the tested fixed Viracon window units if they were used as an operable wall. We acknowledge that there is always room for improvement and we are working on increasing the STC of Crystal. But we further believe that, at present, achieving an STC much higher than 46 or 47 if you take into account cost, weight & ease of movement will be extremely difficult if not impossible. And you should be suspicious if any company makes a claim to having an STC higher than 46 or 47 on an acoustic moveable wall system. If you have questions please feel free to call Moderco at 1.800.363.3150
Link #1: https://www.moderco.com/evolution-glass-operable-wall-industry/
Link #2: https://www.moderco.com/acoustics-operable-partitions-operable-walls/
Link #3: https://www.moderco.com/operable-wall-acoustics-101/.
