Sound Frequency Response Research Articles

Measurements of low frequency impact sound frequency response functions and vibrational properties of light weight timber floors utilizing the ISO rubber ball

Impact sound performance below 100 Hz forms part of a design criterion that is particularly important for multi-story timber buildings. An ISO tapping machine, which is predominantly used for impact sound measurement, has properties that may result in less measurement accuracy in the low frequency range, down to 20 Hz, than in its traditional measurement range above 100 Hz. The characteristics of the pistons’ impact are dissimilar to the impact of a human foot in this lower range. This may cause low signal-to-noise ratios in field measurements and the test data may also be less representative due to the test objects’ possible structural nonlinearities affecting impact sound transmission. The ISO rubber ball has shown to bear a close resemblance to a human’s excitation in the low frequency range, which makes it a suitable excitation device from this perspective. To support correlations between simulations and measurements, measuring impact forces in order to extract frequency response functions would be beneficial. To enable measurements of impact forces that stem from the ISO rubber ball, equipment for field measurements of forces and potentially point mobilities has been manufactured and evaluated. Furthermore, an investigation has been conducted into the repeatability of the rubber ball’s low frequency force spectrum for floors with different mobilities. Impact force measurements have been made on lightweight timber floors as well as on concrete floors. Within the frequency range up to around 55 Hz, it appears to be possible to use a prescribed force spectrum for the ISO ball, together with impact sound measurements, to create accurate impact force to sound frequency response functions for different floors. Also, instrumenting the impact point with an accelerometer enables estimates to be made of direct point mobilities.

Force to sound pressure frequency response measurements using a modified tapping machine on timber floor structures

In recent years, research has shown that the lower frequency portion of impact sound, down to 20 Hz, is of significant importance to residents’ perception in buildings that have lightweight timber floors. At low frequencies, the finite element method is a useful tool for predictive analysis. Impact sound frequency response functions, which are easily calculated using finite element software, are useful as they offer a common ground for studies of correlations between measurements and analyzes. On the measurement side, the tapping machine is well defined and has become the standard excitation device for building acoustics. When using a tapping machine, the excitation force spectrum generated – necessary to achieving experimental frequency force to sound response functions – is unknown. Different equipment may be used for excitation and force measurements and if a structure behaves linearly, the use of any excitation devices should result in the same frequency response functions. Here, an ISO tapping machine hammer is fitted with an accelerometer, enabling estimates of input force spectra. In combination with measurements of the sound in the receiver room, frequency response functions are then achieved using an ISO tapping machine. Various excitation devices have been used on a floor partition in a timber building and on a cross-laminated timber (CLT) lab. floor in order to compare the resulting frequency response functions. Structural nonlinearities are evident, implying that for accurate frequency response measurements in acoustically low frequencies, excitation magnitudes and characteristics that are similar to these which stem from human excitations, should preferably be used.

A low density, high stiffness flat loudspeaker with combined feedback-feedforward response correction

This paper presents a novel perforated flat loudspeaker with improved sound frequency response by applying velocity feedback control. Flat loudspeakers provide advantages of compact dimensions and high durability. Known flat loudspeaker technology is based on high model density. However, the resonances in the panel are complex and difficult to control, which often leads to complicated computations and insufficient low frequency response. The flat loudspeaker in this paper comprises a novel panel structure, which offers low density, high stiffness, and efficient space utilization. Direct velocity feedback control provides a simple and stable control loop. We apply the multiple direct velocity feedback control method to obtain flat sound frequency response. Furthermore, a Linkwitz filter is applied to our system to increase response at very low frequencies. Experimental results show that a multiple combined feedback-feedforward control method effectively improves the performance of the flat loudspeaker with extended low-frequency response.

Otoferlin, Defective in a Human Deafness Form, Is Essential for Exocytosis at the Auditory Ribbon Synapse

The auditory inner hair cell (IHC) ribbon synapse operates with an exceptional temporal precision and maintains a high level of neurotransmitter release. However, the molecular mechanisms underlying IHC synaptic exocytosis are largely unknown. We studied otoferlin, a predicted C2-domain transmembrane protein, which is defective in a recessive form of human deafness. We show that otoferlin expression in the hair cells correlates with afferent synaptogenesis and find that otoferlin localizes to ribbon-associated synaptic vesicles. Otoferlin binds Ca(2+) and displays Ca(2+)-dependent interactions with the SNARE proteins syntaxin1 and SNAP25. Otoferlin deficient mice (Otof(-/-)) are profoundly deaf. Exocytosis in Otof(-/-) IHCs is almost completely abolished, despite normal ribbon synapse morphogenesis and Ca(2+) current. Thus, otoferlin is essential for a late step of synaptic vesicle exocytosis and may act as the major Ca(2+) sensor triggering membrane fusion at the IHC ribbon synapse.

Using optimized surface modifications to improve low frequency response in a room

A case study of improving sound energy distribution at low frequency in a small orthogonal room is presented in this paper. The effects of the geometric modifications of wall surface on the sound frequency response have been investigated in depth. In order to find the optimal modifications for the wall surface, an optimization procedure, based on finite element analysis, has been developed. The uniqueness of this method is that it takes both modal redistribution and sound diffusion into account during optimization process. As a result, the promising improvements of sound frequency response have been obtained at the frequencies around 100 Hz in all rooms tested, particularly in those where the serious modal concentrations are met. The maximum reduction of sound fluctuation in such a room could reach a mount of 4.6 dB. The work opens up the possibility of improving low frequency sound quality by a means that considers both modal changing and surface scattering at same time.