|
Resonac
for Rain Noise Reduction of Metal Roof Panels
|
| |
| 1. Why metal roof panels generate so much noise when it rains? |
Typical metal roof panels are either colour-bond
steel or aluminium panels. The thickness of the panels varies from
0.46mm to 1.5mm.
When it rains, the raindrops excite the thin metal panels through
random impacting. The internal loss factor of these metal panels is
very low, the typical value is 0.001. As a result, the thin metal
panels will resonate and therefore generate a high level of rain noise,
especially during heavy rain. |
| |
| 2. How to reduce the noise? |
| One solution is to apply vibration-damping materials
onto the metal panels. These materials absorb the vibration energy
and therefore reduce the resonant noise of the thin metal panels.
|
| |
| Resonac is
specially designed for rain noise reduction on metal panels. It is
a water-based damping compound, which can be sprayed on. It is especially
suitable for panels with complicated shapes. When dry, Resonac
forms a hard visco-elastic film which is insoluble in
water. |
| |
| 3. How to determine the rain noise reduction in thin metal roof
panel? |
| The noise generated from rainfall in lightweight
roof structure can be estimated by (See attached paper Noise From
Rainfall by K.O. Ballagh): |
(1)
|
| where |
 is
the A-weighted sound intensity, |
is the surface density, |
 is
the damping coefficient of the structure, |
is the coincidence frequency and |
| R is the rainfall rate in mm/hour. |
Suppose the damping coefficient is 
before damping treatment and increases to
after the application of the damping materials. If the effect of the
surface density is negated, the estimated noise reduction (NR) due
to the damping of any damping materials is then equal to: |
(2)
|
| |
| 4. What is the estimated noise reduction by using Resonac? |
|
Ø Roof panel: 0.75mm Thick Steel Panel;
Ø Coating thickness: 1mm Thick (wet) of Resonac;
Ø The typical value of
untreated metal panels is 0.01.
Ø With the application of Resonac,
the loss factor can be increased to 0.1, ie
= 0.1. Please refer to the test results on the attached data sheet
of Resonac.
Ø The equivalent noise reduction is the NR = 20dB based on
equation (2) for a large freely suspended panel.
|
