Modes of smaller rooms lead to a sound decay and uneven frequency responses. In some critical listening spaces , this result in defragmentation of the quality of sound. The problems come in when there is low frequency due to the resultant low modal density. Many designers have tried to overcome these problems but most of them have ended up choosing the wrong methods. This paper is interested in the choice of room dimension that will end or minimize coloration effects. It starts by a discussion of previous studies and a new method is outlined. The old and new methods are put on the weighing scale and compared philosophically. Results are then given in the ending part of the paper to demonstrate the weight of the new method.
Acoustic inventions relate to the improvement and developments of anything to do with sound production particularly the earpiece of sound producing objects. In this note, we emphasize on the improvement of sound quality in the mobile phones and other sound producing gadgets. This has been one of the most challenging of acoustic works since most of the gadgets are very small contrary to the goal the professional wish to accomplish. Some of the problems experienced in the attempt to achieve these goals is the challenge of moving the principle from big to a smaller speaker which in the end result in lowering of frequencies. This forced the inventors of these small gadgets to improve on their sensitivity in the different underlying acoustic conditions. The high intensity of variation between users has also to be put into consideration. The most important of all acoustic parameters is associated low and poor frequency of audio quality and is commonly known as acoustic leakage (Cremer & Mu%u0308ller, 1982). The leakage formed in this manner causes the speech from the ear piece of the sender to sound too weak and feeble due to low content in frequency.
Standardisation of earpiece designs have been developed which are less torelant to accoustic loads that keeps on fluctuating due to large variations that the user impose. poor and low frequency audio performance are the results which causes speech output to sound and thin. Stable audio quality over a wide range of consumers provided for by low torelant designs and operating conditions. One of the most advanced leak conditions and designs are less sensitive to external loading conditions which are provided for by introducing an acoustic leak designed in the front cover of the gadget. Practically, the speaker is held some millimeters away from from the gadgets (phone) front cover then, the sound energy is leaked internally into the phone. This internal leak causes the speakers output to be at low frequenciesand less dependent on the external load variations. However, it is difficult to practically provide for this leak torelance design.
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With regards to the current inventions, a resonator is always provided to a radiotelephone which has a housing that has an earpiece and the loudspeakers ports. The resonator is comprised of a housing ( a first channel that channels sound between the earpiece and the loudspeaker ports) and an internal cavity and of the earpiece port. Self contained accoustic solutions have been found to be more favourable due to a number of reasons.
First, it is reported to have the ability to leak torelance characteristics which are independet of the internal characteristics of the telephone itself. Therefore, these leak torelance qualities do not vary with age and internal accoustics of that radiotelephone and this self contained accoustic solution has been found to be more reliable than the already existing leak torelance solutions. This leak torelance solution is more phone enabled to allow for the earpiece solution to be applied in most of the available ranges of phones.
Second, the design inhibits the ingresssion of water and dust into the system. Contrary to the current leak torrelant which require very large earpiece port, the designs of the new invention works better with smaller speakers and consequently improves its protection. And because of this separation of the acoustic system with the internal phone electronics,water or dirt that did not manage to enter the system via the earpiece cannot reach the internal system and therefore not in a position to damage the elecronic components.
Third, there is no additional leakage of sound to the phone as compared to non leak torelant phones. Accoustic coupling between the microphone and the speaker is similar with the non-leak torelant phones. According to the current innovation, the design avoids as much as possible any uwanted acoustic coupling between the two ends of the appliance (earpiece and microphone ).
This may occur in in present leak tolerant system whenever the sound energy from the loudspeaker is leaked to the phone. According to the new system, the internal cavity of the resonator can only be exposed through an open face in the housing of the resonator. The open face can be alternatively be enclosed by part of the housing to reduce the radio telephone. The resonator may be comprised of internal cavities and the choice to have or not to have may be determined by the acoustic characteristics that is required in any given specification. In addition, there may be provision of low frequency response to the loudspeaker which is a compliment of the specified resonance performance. Consequently, this would in turn provide for a combined flat response that brings the high quality and stable audio performance. Various modifications may also have the resonator and the speaker being part of the acoustic system.
Four, the radiotelephone system comprise preferably of a compensation filter that compensate the specified resonance performance. Such compensation filters can only be realized by the loudspeaker having the required frequency response that complements the specified resonance performance. However, all this issue of resonance performance can be realized by the use of a digital signal processor. With time, this last option has been the most preferred as it enables the user to apply convectional speakers with an enhanced low frequency response. For instance, the housing of the radiotelephone may form the at least part of the resonators housing. But it may not exclusively be used to cover the open face of the resonators housing to enclose the resonator’s internal housing. Any shape can be used to form the design of the internal cavity which may form a ring, rectangle, square or even a circle.
Scanning acoustic principles and current development
An acoustic wave is a natural phenomenon that is responsible for the transfer of shear and dilatational strains. They are of three types and can propagate along a specific direction having each spreading on its own velocity while imparting oscillatory motion in particles of that medium that is within its path- a process known as wave polarization. There are only two types of waves that propagate as an isotopic solid; that is traverse and longitudinal ones. Particles are displaced in the direction of the motion of the wave while the total strain transmitted is a combination of shear and dilatation strains. Traverse waves can only transfer shear strains, this is where particles of the medium arbitrarily oscillates on a plane that is normal to the propagating direction.
A distinction between longitudinal and the traverse waves in a crystalline solid can make no sense because the three acoustic waves spread in a given and transfers both the shear and the dilatational strains. However, a wave in which the longitudinal displacement of particles dominates is called a quasi-longitudinal which is normally propagated at the highest velocity. The rest are fast and slow traverse waves but vary in accordance with the value of the propagating velocity (Cremer & Mu%u0308ller, 1982). A crystalline medium, even of that high symmetry, can demonstrate a significant anisotropy of its acoustic characteristics.
Longitudinal waves alone can transmit in liquid where no shear forces exist. Though, many liquids exhibit notable shear stresses that are of hypersonic frequencies and thus approaching solids in their mechanical characteristics. In this connection, also high frequency shear waves can also propagate in them. This phenomenon was revealed when studying the Mandelstam–Brillouin scattering on anisotropy fluctuation in the liquids that are essentially shear waves.
The absorption coefficient and the propagation velocity of acoustic waves are the primary characteristics of the acoustic properties. According to the expected concept of fluid mechanics, the velocity of sound is a parameter of the medium which does not depend on frequency. The rate in which the acoustic waves are absorbed depends on the dissipative properties of the fluid. That is, the heat conduction coefficient and the viscosity which are generally assumed to be persistent regardless of the used material (Basu, Micchelli & Olsen, 1999). Though, the absorption coefficient is proportional to viscosity and increases in proportion with the sound frequencies.
v = α α v2
In this assumption, dispersion of acoustic velocity is demonstrated at very high frequencies where the concept of continuity of material is usually unjustified and the distinct nature of the material apparent itself.
Physical doctrines of scanning audio microscopy
In this concept, the lens system is the basic test for scanning the acoustic microscope. This is a process where an ultra-wave is generated in the acoustic lens system by a transducer that is mounted on both its ends. The waves extents through an acoustic duct that has a very large acoustic impendence and it is then focused with the assistance of spherical lens at the other end in the immersion material filling the space between object examined and the lens. The immersion liquid offers a large refractive index for the lens and a good acoustic contact between the object and the duct. The concentrated beam interacts with the object though partially being reflected and scattered by the object while partially being transmitted through it. If that refracted wave is detected, the microscope operates in the mode of reflection and when the transmitted acoustic flux has been recorded by the second lens, we have completed the acoustic transmission microscope.
However, it is important note that there has been a suggestion of a large number of modifications in the basic principles that extend opportunities in the method. Therefore, detection of acoustic radiations being scattered by the object is arranged by rotating the lens at different given angles with respect to the axis that is emitting lens. This regime provides similar results with the dark field regime of the optical microscope and thus allows for effective and in depth resolutions to be varied.
Additional information can be acquired through the use of various nonlinear regimes where the signals emanating from a focal zone to be recorded in harmonics of the input signal or at a combination of frequencies. In this situation, linear and nonlinear properties contribute to the required measurement of results.
Currently, some promising approaches are and have been in the process of enhancing the contrast and improving the quality of the image. One of the approaches is the use of the appropriate immersion fluid especially those with the lowest speed of sound value and low transmission coefficient.
Lastly, the opportunities of acoustic microscopy can be extended significantly to invoke the contemporary methods of computer audio and visual processing. This will definitely improve the sound quality, enable the resolution and offer the possibilities of processing and documenting the data while at the same time analyzing the dynamic processes. The most important features of this method are that fact that there is instrumental resolution and penetration of deep radiations. With an increase in resolution, the depth of ultrasound penetrating the object reduces. Thus, the ultrasound frequency to be should be selected after accounting for the properties of the object and the problem that require solution. The ultrasound radiations certify one to have new information about the mechanical qualities of a given micro object that cannot be provided for by other microscopic methods (Holm & Lothe, 1979).
Qualitative methods of acoustic microscopy and the principles of acoustic imaging
Acoustic imaging cannot be understood without a strong understanding of the physical formation mechanisms and the characteristics of acoustic contrast. The basic knowledge of these mechanisms allows learners to perform measure and categories quantitatively the material under study. Measuring the output signals, amplitude and phase of the acoustic microscope and comparing them with those of a reference fluid, we obtain information regarding the sound speed, geographic characteristics, attenuation and acoustic impedance.
First, we consider how the how the output signals of acoustic lens can form a general case. A piezoelectric transducer is used to detect the signals with a linear response. For a transducer to generate the needed signals, the incidence wave has to be parallel to the surface. In other words, all beams should pass through the focusing lens and all must arrive at the transducer at the same phase. Without this, signals from other beams can interfere and attenuate the resulting signal. The usage of linear lenses that stimulate Raleigh waves from turning in one direction has turned out to be of so much information in reflection microscopy. This method was successfully developed by the Japanese scientists who had also proposed it (Holm & Lothe, 1979).
To measure quantitatively the local mechanical properties of a sample, we have to develop a method A (z) characteristics. The A (z) curve is a dependence of the output signal A which is the receiving lens on the distance Z away from the lenses. The change of the A (z) maximum is proportional to the difference between the immersion fluid and the speed of sound and the object c and the sample thickness can be summarized as;
Limitation of the methods
The methods of acoustic microscopy is generally sensitive to the presence of various non-uniform characteristics in a sample and to break the continuity of the material for reasons of acoustic impendences at the boundary can bring about extreme reflection. Currently, the method allows one to reveal and not only limited to the following defects; exfoliation, alien inclusion, failure of adhesion, micro cracks, deviation from pressure among others. Based on those reasons mentioned, the following points are significant in developing the reflection methods that transcends acoustic microscopy.
The morphology of smooth faces with inhomogeneous dispersal of acoustic properties includes characterization of specific components and laminated structures. The measurement of common values of the transmission velocity and attenuation of Raleigh waves in those materials employing acoustic microscopy techniques where cylindrical and spherical lenses are made use of.
Room resonance is like an organ pipe. It is an unwanted additional instrument playing besides the speaker. To minimize the coloration which is one of the strongest base frequencies, we design a good room. At high frequencies, the room has an effect but resonance is less problematic as it is easier to absorb it at higher rates. This section deals with the room treatment especially the walls that are aimed for high frequencies. The advent of high velocity digital signals has increased the possibilities of revising room acoustics with digital filters. In this section, there has been provided for both measured and calculated results. Most calculations are centered on image analysis. The subwoofer is idealized for the purpose of calculations and is assumed to generate sound at a flat level of 0 to 200Hz to give the researcher the attention of focusing on the room itself. Unavoidably, the collected data involves the effects of a loudspeaker and the CLIO system has been put to practice (Kuttruff, 2002).
Most of the literature provided for in this section is directed towards developing and designing a professional sound studio. It attempts to provide for a situation where fairly acoustic principles are applied. Upon application of the methods provided for in the report, a sweet spot can be literally located at a point where the focal point of the design is, although it can be made larger. The perfect frequency is smooth with no valleys or peaks. It can be obtained from a perfect anechoic chamber. This is a room with walls that absorb sound without any being reflected. However, to most people, this solution is not feasible and would practically sound more weird than workable. In almost any sound system, the room determines the frequency response at lower frequencies.
Any room including those with odd shapes will always resonate at multiple frequencies. The bass response is acutely boosted for a narrow frequency band that’s near resonance and then depressed between them. The sharpness and the height of the resonant peak depend on the rooms sound absorbing properties. For example, a room with a heavy carpet and soft furniture is considered dead as the peaks and valleys of response frequency usually vary by a range of 5-10dB. Another room with open walls and the floor is considered live as it has a variance of 10-20dB. The absorption coefficient of 0.2 is used to produce the figure corresponding with reverberation time of about 0.5 seconds. However, many people are misconceived that curving the walls may eliminate resonance (Basu, Micchelli & Olsen, 1999).
Optimum room dimensions
A room with good acoustics can be designed by a standard modal approach. This is enabled by creating a room with as many different resonances and as spread as possible. One is advised to apply the Bonelo Criterion to calculate the spread of the resonance. The lowest resonance can be determined by the biggest dimension of the room. Generally, the lowest the best for the initial resonance frequencies as this region is the place where frequency response is most variant. The bigger the room the lower the space available between resonances and at this point, the cost is the constraint to consider.
The width and the heights of the room are not in exception, they give rise to another series of resonances. These two dimensions are primarily the axial resonances that involve reflection of two opposing planes. More resonance can also be as a result of reflection that echoes off the four different surfaces. These tangential resonances are usually weaker for the reason that energy is lost in each and every reflection. And finally, there is the oblique resonance that echoes off all, the six walls. In this resonance, each reverberation gives rise to a mode that have a characteristic spatial variation in pressure. To spread all these resonances in the most uniform way, various ratios between the length, width and height have been suggested.
Optimum room dimensions
1.14 x height
1.28 x height
1.60 x height
1.39 x height
1.54 x height
2.33 x height
According to the design, a cube is the worst of all room shape followed by a room with all dimensions being a multiple of the height.
The following has been the standard recommendations of acoustic modal design and specification that can provide the minimum possible resonance. It is required that the floor be smooth, unpainted, covered by concrete and a 9mmtufted pile wall to wall carpet which is felt underlay. The walls and the ceiling should be made of plasterboards on frame of 12mm thickness and an empty cavity of 100mm.
Room dimensions Length 6.25 meters Width 5.4 meters Height 2.6 meters