ACOUSTIC RESULTS OF THE AKUSTIK CHANNEL CLIP IN FIELD TESTS IN SUSPENDED CEILINGS
The versatile Akustik+Sylomer® Channel Clip ceiling hanger and wall support has demonstrated high acoustic performance in real conditions, even with low air gap available between the slab and the suspended ceiling, according to measurements carried out by the French acoustic engineering company Acoustika.
Field tests are a fundamental tool for understanding the acoustic behaviour of construction solutions in real conditions, complementing theoretical calculations and laboratory tests. In this context, the French acoustic engineering company Acoustika has carried out a series of field measurements in an apartment building built around 1970, located in the town of La Garenne-Colombes, with the aim of evaluating the impact of the Akustik+Sylomer®.
Channel Clip hangers in the improvement of acoustic insulation. This test is representative of an acoustic installation in the residential environment in which the saving of vertical space, together with acoustic insulation against noise derived from human activity is a priority.
The test was carried out in the typical configuration in existing residential buildings, where the availability of height for the installation of a false ceiling is limited and the control of noise associated with human activity is a relevant design criterion.
For the test, a laminated plasterboard suspended on Akustik+Sylomer® Channel Clip supports (final configuration with 'Akustik Channel Clip') was added to the original slab (in a 150 mm thick concrete slab, the initial configuration), making measurements before and after the work. Below are the initial and final configurations:
Description of the configurations analyzed | |
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Initial setup | |
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Final Configuration | |
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As this cut shows, the height of the air gap between the slab and the suspended ceiling is reduced, equal to the sum of the heights of the Channel Clip support (30 mm when installed) and the 'Type Omega SPP' profile (25 mm), which is equivalent to 55 mm in height.
In these types of configurations, a low chamber height is often considered to limit the contribution of elastic supports to sound insulation. However, the measurements made allow us to analyse the real behaviour of the system under these specific geometric conditions.
Effect of the height of the air gap
Elastic supports, such as the Akustik+Sylomer® Channel Clip, are used in the suspension of false ceilings, which are characterised by a certain stiffness. In general, a lower stiffness of these elements leads to a lower natural frequency of the mass-spring system and, therefore, to greater acoustic insulation against dynamic excitations above this frequency. However, this behaviour does not depend exclusively on the elastic supports, as the air contained in the chamber between the suspended ceiling and the concrete slab can have a significant influence on the vibroacoustic response of the assembly.
Air is a compressible gas that, when subjected to external work – such as that induced by the movement of the slab excited by a noise source – can compress and expand. This process causes the confined air to behave like an equivalent elastic spring. The stiffness associated with this "air spring" depends both on the thermodynamic properties of the gas and on the geometric variables of the chamber, mainly its horizontal surface and height, as well as its airtightness.
From a mechanical point of view, the effective stiffness of the air adds to that of the elastic hangers of the suspended ceiling, both acting in parallel. This additional stiffness increases the natural frequency of the suspended system and can consequently reduce sound insulation in the low-frequency range.
The stiffness of the confined air is directly proportional to the horizontal surface of the chamber and inversely proportional to its height. Therefore, small air chambers have high stiffness and a potentially unfavourable effect on sound insulation.
The incorporation to the air chamber of mineral wool, inside which the air’s stiffness is lower than outside, makes the global stiffness of the air chamber lower than without it, which decreases the overall rigidity of the system, reducing vibroacoustic transmission [1](A. Buen, 2020). In the same way, the lack of airtightness of the chamber allows air to be exchanged with the environment, avoiding the generation of significant overpressures and cancelling, in practice, the transmission of forces associated with the elastic behaviour of the air. That is why in ventilated ceilings the rigidity of the air becomes negligible.
Considering the most unfavourable case —that is, considering a perfectly airtight air chamber and without absorbent material—, the resulting system would present a natural frequency of the order of 58.4 Hz, with the frequency from which no dynamic amplification occurs being approximately 85.6 Hz. However, the calculation model used predicts a natural frequency of 10.2 Hz and an isolation frequency of 14.4 Hz.
Experimental results show significant reductions of 9 dBA in the airborne noise reduction level in the 63 Hz octave band, which covers approximately the frequency range between 44 Hz and 88 Hz. This behaviour is incompatible with the pessimistic hypothesis, since according to it this band would cover the entire resonance range of the system, in which neither impact noise nor airborne noise attenuation could be expected.
Consequently, these results indicate that the commonly adopted approach tends to overestimate the stiffening effect of the air chamber, which unnecessarily associates the effectiveness in sound insulation with a high demand for space.
All in all, it can be concluded that, under real installation conditions, the use of low rigidity ceiling supports such as the Akustik+Sylomer® Channel Clip is feasible even with reduced air chamber heights, without compromising the acoustic insulation obtained.
On the other hand, this improvement in the same band in impact noise is not observed, possibly as a result of an excitation of the slab as a whole that has not been able to be evaluated experimentally.
Measurement Methodology
The measurements were carried out in October 2025 by acoustic engineer Simon Guitton, following ISO 140-4 (airborne noise) and ISO 140-7 (impact noise) standards. Vertical noise transmissions between two overlapping rooms were evaluated:
Airborne noise: Generated in the upper emitting room by a dodecahedron of speakers that emits pink noise. The reduction is determined by comparing the sound pressure levels between the emitting room and the lower receiving room obtained using a calibrated 01dB FUSION sound level meter. The aim is for the acoustic construction to minimise sound transmission.
Impact noise: Produced by a standardized Brüel & Kjær 3207 heel cup that drops weights on the upper floor to excite it with impacts. The measurement is carried out only in the receiving room, seeking to ensure that the sound level is as low as possible.
Results obtained
The installation must comply with the French regulations for residential buildings (Nouvelle Réglementation Acoustique, Juin 1999), which specifies the following parameters:
Requirements in terms of acoustic insulation | ||
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Settings | Airborne noise insulation | Impact noise insulation |
Impact noise insulation | L'nT,w = 58 dB | |
Insulation to aerial noise | DnT,A ≥ 53 dB | |
The data obtained before and after show the effectiveness of the Akustik Channel Clip system: | ||
Initial Setup | DnT,A = 50 dB | L'nT,w = 46 dB |
Final Configuration | DnT,A = 59 dB | L'nT,w = 38 dB |
Summary table of results for airborne and impact noise, before and after the work.
This means that:
Airborne noise reduction (DnT,A): +9 dB. This result indicates that the normalised difference in airborne noise level between the sending and receiving rooms, as a result of the nature of the separating element, goes from 50 dB before the acoustic adaptation to 59 dB after it. According to the spectra obtained expressed in octave bands, the most notable improvement is in the 8th band of 500 Hz, which indicates that the system is especially effective against airborne noise generated by the human voice and music, which is especially relevant in a residential environment such as this where the owners reported being able to hear the sound of their neighbour's television, which has been addressed.
However, throughout the frequency range analysed, a uniform reduction in the airborne noise level of around 8 dBA is observed.
Insulation spectra to aerial noise | Airborne noise insulation levels |
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Natural frequency: 10.2 Hz | |
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Spectrum of the weighted normalized airborne noise level difference (DnT,A) before (red) and after (left) the installation of the Akustik Channel Clip ceiling brackets.
Impact Noise Reduction (L'nT,w): -8 dB This result indicates that the impact noise level measured in the receiving room, as a result of the nature of the separating element, goes from 46 dB before the acoustic adaptation, to 38 dB after it.
If the initial value is in accordance with regulations (thanks to the effect of the carpeting on the floor of the emitting room which reduces the high-frequency components of the impacts produced by the heel pad), the final value represents a very low impact noise level with respect to the limit of 58 dB for the L'nT, w. that the French standard stipulates for residential buildings (Nouvelle Réglementation Acoustique, Juin 1999).
According to the noise level spectra obtained, the most notable improvement is found in the 8th band of 500 Hz, which attenuates average frequency components of the spectrum of impacts also associated with human activity. On the other hand, although a reduction in impact noise is observed in the 63 Hz band, this may be affected by acoustic structural responses of the slab unrelated to the effect of the ceiling supports, although the level recorded is also below the 58 dB required by the standard.
Impact Noise Level Spectra | Impact Noise Levels |
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Natural frequency: 10.2 Hz | |
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Spectrum of the normalized pressure level of impact noise (L'nT,W) before (red) and after (blue) the installation of the Akustik Channel Clip ceiling brackets.
Conclusion and access to the report
The results show that with the help of the flexible ceiling brackets Akustik+Sylomer® Channel Clip, it is possible to meet and exceed the limits of acoustic regulations and optimize sound insulation without compromising the usable height or aesthetics of the interiors.
To facilitate access to the full breakdown of the report, we have added a new entry in our Akustik dB Finder database, where the full technical document with all the details of the measurement is attached.
REFERENCES
[1] A. Buen, "Impulse forces and noise from dropped weights on concrete floors". June 2020.
