The investigation project is carried out in wooden structures and several different solutions are tested.

RECENT TESTS CARRIED OUT IN IFT ROSENHEIM PROVE THE SUPERIOR IMPACT NOISE ISOLATION OF AKUSTIK+SYLOMER® ACOUSTIC HANGERS AT LOW FREQUENCIES.

3/20/2018

The test (test X37) is carried out in a ceiling composed of the following elements:

50mm mortar with a weight of 120kg/m².
30mm elastic thermal isolator with a stiffness of 30MN/m³ and a weight of 5,2kg/m².
2x 30mm fibre cement layers with a weight of 89,3kg/m².
22mm chipboard of 13,3kg/m².
Timber joists of dimensions 80mm x 220mm.
Plenum space of 140mm.
Acoustic hangers.
Crossed CD profiles.
2x 12,5mm plasterboards of a total weight of 20,6kg/m².

The following curve shows the impact noise curve of Akustik Super T-60 + Sylomer® 30 Type A acoustic hangers according to DIN EN ISO 10140-3.

Different acoustic hangers have also been studied under same conditions, changing only the hangers and in some cases the number and the thickness of plasterboards. The results are summarized below:

Tested solutions	Plasterboards	Plenum space	Acoustic Hangers	Ln,w (100Hz - 3150Hz)	CI,50-2500	Real impact noise level including low frequencies
1	1x 12,5mm	27mm	-	36 dB	18 dB	54 dB
2	2x 12,5mm	65mm	Competitor’s acoustic hangers	32 dB	14 dB	46 dB
3	2x 18mm	65mm	Competitor’s acoustic hangers	29 dB	15 dB	44 dB
4	2x 12,5mm	40mm	-	32 dB	19 dB	51 dB
AMC Akustik + Sylomer®	2x 12,5mm	140mm	Akustik + Sylomer® acoustic hangers	30 dB	10 dB	40 dB

Let’s compare the values of Ln,w, it can be seen that the 3rd solution is getting 29dB, the lowest value of all of them. The influence of low frequencies and the correction coefficients that must be considered for a correct evaluation of impact noise will be discussed later.

Another consideration that should be done is that the hanging mass is 44% higher for the solution 3 against the others that have lower plasterboard thickness and therefore lower mass.

The results are also shown in the graph below:

The solution 3 seems to be the best comparing the Ln,w values for the frequencies from 100Hz to 3150 Hz, but the corrective coefficient for low frequencies CI,50-2500 is showing important differences between the solutions.

Akustik + Sylomer® acoustic products have especially good performance at low frequencies.

Considering the real impact noise level including low frequencies, the best solution is by far the one with Akustik + Sylomer® hangers with 40dB, which is 4dB below the 3rd solution, which was the best without having considered the low frequencies.

Is it important to consider the low frequencies impact noise level from 50 Hz?

Andreas Rabold from IFT Rosenheim carried out an study called “Trittschalldämmung richtig bewerten” to evaluate the correlation between the value of Ln,w according to DIN EN ISO 717-2 and the subjective perception of impact noise on wooden ceilings.

To do this, a measurement carried out with the use of standard impact noise generator (tapping machine) according to DIN EN ISO 140-6 and a measurement of impact noise transmission when walking over the ceiling are compared, as shown in the schematics below:


Ln,w measurement of excitation generated with standard impact noise generator.	LAF max,n measurement of excitation generated by walking over the ceiling.

The excitation to measure LAF max,n is generated by walkers with determined attributes and walking in a certain way. The value of LAF max,n is the maximum level measured with A-weighted frequency response and Fast time constant.

The next chart shows the values of each type of test (Ln,w in horizontal axis and LAF max,n in vertical axis) in each type of ceiling. Each point represents the results with a certain ceiling structure.

As it can be seen, the correlation between both test types is weak, as ideally all the points should be laying over a line that represents a good correlation between both tests. Moreover, the subjective perception of noise is in most of the cases lower than the value of Ln,w obtained according to DIN EN ISO 717-2.

The impact noise transmission spectrum of the excitation generated by walking on the ceiling is shown right
This chart explains the reason of the weak correlation between both tests in wooden ceilings. It can clearly be seen that almost all the transmission takes place below 100Hz, while a frequency range between 100Hz and 3150Hz is used to determine the value of Ln,w.
Due to this, it can be concluded that the value Ln,w is not useful to represent cases where frequencies below 100Hz are predominant and that a different evaluation should be used to better represent this case

In order to solve this problem, the correction coefficient CI,50-2500 was established in DIN EN ISO 717-2.

The use of this coefficient shows a much better correlation of the same ceiling structures between the subjective perception LAF max,n and Ln,w + CI,50-2500:

This correction factor allows the use of subjective perception level to determine the target values for good impact noise isolation, having a difference between both values of around 16 dB (A). It also shows the importance of taking the low frequencies into account to measure the impact noise isolation level in wooden ceilings.

Concerning airborne noise isolation, Akustik + Sylomer® hangers have also been tested in two different ceiling structures, one of them (test X38) in the same ceiling structure described above, while in the other (test X40) the mortar is replaced with a fibreboard with a weight of 30,4kg/m2 and only 1x 30mm fibre cement layer is used instead of two. The curves obtained in these tests are shown below: