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Test procedure for floor toppings
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| Floating wood |
A common technique for improving impact sound insulation is to cover the basic floor surface with a resilient layer, such as a carpet, or a resilient layer covered by a hard walking surface, such as hardwood. The impact insulation class obtained with the standard tapping machine depends on the combination of the topping and basic floor. It is not possible to compare two toppings if they are tested on different base floors.
Fortunately, the improvement provided by a topping on a concrete slab is largely independent of the slab thickness and its other properties. So, the improvements can be compared and the toppings ranked. Work at NRC-IRC has led to the development by ASTM committee E33 of a new standard method for evaluating floor toppings - ASTM E2179. Internal report IR-802 describes the work.
Toppings are usually more effective when placed on concrete slabs than they are on joist floors with wood subfloors. Work is continuing as part of NRC-IRC strategic research supporting ISO and ASTM activities to develop a test method for evaluating toppings on joist floors.
Impact sound transmission tests
Impact sound transmission tests are carried out using a standard tapping machine that incorporates 5 steel-faced hammers. These are driven by a motor so they strike the floor being tested 10 times per second. The tapping machine is placed in several positions on the floor and the impact sound pressure levels are measured in the room below in the frequency range 100 to 3150 Hz.
The single-number ratings calculated areimpact insulation class (IIC) (ASTM E989), and the weighted index Ln,w (ISO 717).
To obtain the single-number ratings, a reference contour is used in a procedure that is analogous to that for Airborne Sound Transmission Loss. In this case the contour extends from 100 to 3150 Hz. The measured 1/3 octave band impact sound pressure levels are fitted to the contour as shown, subject to the following rules:
- Deviations occur when a measured value (red bars) is greater than the contour (blue line).
- The contour is adjusted until sum of deviations
- The IIC value is read from the contour value at 500 Hz using the right hand axis. The Ln,w rating is the value of the contour at 500 Hz.
The IIC rating, like STC and Rw, increases as the impact sound insulation improves. The Ln,w rating decreases as the impact sound insulation improves.
