Dummy Head Research Articles

A digital frequency-domain implementation of a very high gain hearing aid with compensation for recruitment of loudness and acoustic echo cancellation

People with loudness recruitment have a compressed dynamic range between the sound-pressure levels corresponding to threshold and discomfort. This highly frequency-dependent phenomenon requires a nonlinear filter for compensation. To achieve the high levels of gain required for profound hearing impairment, the hearing aid must also be capable of canceling the ever present acoustic feedback. This paper describes a digital hearing aid, realized in the frequency domain, that compensates for recruitment of loudness and cancels echos. The DFT-based approach permits the use of fast and computationally efficient algorithms for the nonlinear compensation and adaptive FIR filtering. The echo canceler is adapted using only the available (e.g. speech) input signal. An analysis is presented of the closed-loop hearing aid system and the adaptive adjustment law. The problems resulting from the use of a nonlinear hearing-loss compensator and stability problems caused by a rapidly changing echo path are discussed. The proposed solutions have been implemented and tested on a dummy head using a behind-the-ear hearing-aid device. The result is a device that runs more than 20 dB above the critical gain without any audible artifacts.

Multimicrophone arrangement as a substitute for dummy-head recording technique

Natural sound is usually recorded in head-related stereophony by ear microphones of a dummy head in order to ensure a virtual reality, e.g., for subjective sound-evaluation procedures. However, in many applications the use of a dummy head is disturbing. Additionally, it is difficult to change the geometry or shape of a dummy head in order to adjust a recording individually. The spatial information of the sound field, which is perceived in appropriate stereophonic reproduction, is encoded in the two signals of the ear microphones by recording the modifications of the wave field from the near-field diffraction of the obstacle ‘‘dummy head.’’ A diffraction pattern can be approximated by a sufficient number of monopole sources at appropriate locations, and adjusted in amplitudes and phases. This method of source substitution is used for an arrangement of pressure microphones. Each microphone signal is processed twice and added in the stereophonic channels. If locations and transfer functions are optimized, the two channels represent an approximation of the ear-microphone signals of the dummy-head’s (or real head’s) diffraction information. The preliminary results of the optimization and listening experiments are reported. [Work supported by the German Graduate School on Psychoacoustics.]

Wear mechanisms of sandwich-type video heads

Differential wear between the various material components of composite magnetic recording heads is observed upon running against the magnetic medium. A developing level difference between the magnetic material and the medium bearing surface leads to signal degradation, exponential with the difference and the signal frequency. Experimental evidence is presented for a three-body erosion mechanism in the case of sandwich heads employed in commercial helical scan, Hi-8 video tape recorders. Two sintered ceramic substrates, CaTiO3 and composite Zr-doped CaTiO3, in combination with three soft magnetic materials, amorphous CoNbZr and the nanocrystalline iron alloys FeNbSiN and FeTaN, have been studied. They have been studied in conjunction with commercial metal evaporated (ME) and metal particulate (MP) tapes. Level difference has been measured by interferometry and AFM (atomic force microscopy), the latter also observing level differences between the various components of the sandwich: soft magnetic metal, ceramic laminations and the metallic bonding layer. AFM shows a pull-out of particles from the ceramic substrate with similar sized particles observed on the track. Scanning Auger micrographs have shown the transfer of ceramic particles on to the track and of metal on to the substrate. Wear rates and wear mechanisms have been identified for the materials in isolation by studying single-material dummy heads. This has been identified as plastic deformation controlled microabrasion, transforming to grain pull-out in the crystalline materials in some instances. It is speculated that these pull-outs are responsible for the wear of the soft metallic track when this is out of contact with the tape. The evidence for chemical wear is inconclusive. The involvement of transfer material from the tape to the head is speculated upon.

The development of a dummy head for 3-D audiovisual recording for transmitting telepresence

Manufacturing systems that employ modern technology often deprive workers of their humanity. One such example is seen in teleconferencing between remote plants. Here, it is difficult for participants to make eye-to-eye contact, a major obstacle in the communication of the participants; intentions and emotions. Indeed participants often complain that the facial expressions or emotions of the other side are difficult to perceive, that it is difficult to carry on a friendly, warm conversation, or that it is difficult to convey one's intentions to the other. They thus tend to become irritated during these conferences, and at times make erroneous judgements. In such situations, it can be said that the system users are being deprived of their humanity. This occurs because a machine or computer, when placed between two people communicating, interferes with a natural communication. What measures are there then to achieve a natural communication in such a setting, with a machine or computer between those communicating? These methods are classified here. In this study, a system for communicating 'presence' was employed to achieve a natural communication. The prototype system is call a 'dummy head for 3-D audiovisual recording'. Using this dummy head, dialogue between operators, remote control, as well as the recording of a skilled worker's use of his hands were carried out, and the results were evaluated. From these results, the authors report on how the prototype system, when placed between humans, helps to achieve a natural communication. Finally, some examples are given to show the human need for achieving a natural communication in such interface situations.

Evaluation of artificial head recording systems

Artificial head (or dummy head) recording and playback systems are increasingly used. The main advantage of these systems is their ability to reproduce three-dimensional spatial aspects of sound. However, the exact reproduction of direction has been questioned from time to time. The study presents an objective and subjective evaluation of eight artificial heads. In the objective test, the head-related transfer functions of the heads were compared to those of humans. Significant deviations were seen for all heads, and none of them can be characterized as a mean, median, or typical head. In the subjective test a panel of listeners indicated direction and distance to sound sources recorded by the head and reproduced by means of carefully equalized headphones. The reproduction of direction was in general poor, especially in the median plane.

Consistent physical measures of auditory source width for various frequency components of reflections

At this writing, there is no physical measure that can evaluate consistently the auditory source width (ASW) perceived for sound fields consisting of a direct sound and reflections with various frequency components. In the experiments, a music motif is used as a source signal. The frequency components of reflections are varied by changing the cutoff frequency of low-pass, high-pass, and band-elimination filters, and simultaneously their directions are varied from ±18 to ±90 deg by steps of 9 deg. ASW and some physical measures are obtained for all sound fields in the experiments. The results on ASW indicate that any frequency component of lateral reflections contributes to create ASW almost equally. The comparisons of ASW with many physical measures show that ICCavg and Lfavg can evaluate ASW for all sound fields consistently with high accuracy. They are the average of the degrees of interaural cross correlation and the lateral energy fractions for 1/1-oct bands for 125 Hz to 8 kHz, respectively. Furthermore, the average of the degrees of cross correlation between two points 30 cm apart without using a dummy head for 1/1-oct bands for 125 Hz to 8 kHz is also adequate, although it is less accurate than ICCavg and Lfavg.

A new configuration of dummy head microphones using neural networks

A binaural recording and reproduction system using a dummy head microphone (DHM) has been used in various applications such as virtual reality systems, transaural reproduction systems for entertainment, and evaluations of many sound fields. However, the size and weight of the DHM have been inconvenient for many practical uses. An alternative to an ordinary DHM was proposed which consisted of a microphone array and a neural network controller. Thanks to the electronic configuration of the new DHM, many advantages are expected. For example, not only will it include a downsized microphone, but also several advantages, including multiple HRTF configurations, could be realized. In this paper, an efficient algorithm is used in the learning process of the neural network. The results of subjective evaluation for perceived directions compared to those of the ordinary DHM will be shown.

Comparison between the 1/10-scale model experiment and the full-scale measurement in a concert hall

In order to examine the accuracy of acoustic scale modeling, the experimental results of a 1/10-scale model study performed for acoustical design of a concert hall and those measured in the full-scale hall after the construction are compared. In the scale model study, the impulse responses were measured by the direct method using a spark discharge source and monaural and binaural microphone systems. For the measurement of the binaural impulse response, a 1/10-scale dummy head system was made on a trial basis. In the real hall, impulse responses were measured by the sweep-pulse method using a dodecahedral omnidirectional loudspeaker and monaural and binaural microphone systems. The monaural impulse responses were measured at the corresponding points in the scale model and the real hall, and such quantities as D50, C80, and Ts were obtained and compared. The binaural impulse responses measured in the model and real hall were convolved with the same sources of a variety of music and presented to the subjects through a transaural reproduction system using two loudspeakers. Through these quantitative and subjected investigations, a fairly good correspondence has been found between the scale model and the real hall.

Passenger Train Crashworthiness—Secondary Collisions

Secondary collisions in passenger train crashes are considered and a companion paper dealing with primary collisions is followed up. The effects of crash pulse magnitude and duration, occupant flail distance, and the nature of the impacted surface are considered. The constitutive relationship for a Hybrid III dummy head satisfying the peak acceleration requirements of FMVSS208 is developed and used with the crash victim simulator MADYMO to investigate the impact response of train passengers seated in a unidirectional layout. It is shown that the design of the coach shell and the interior have to be integrated to obtain train designs that will minimize occupant injuries in the event of train collisions.

Mathematical 3-D Model For Whiplash Simulation

Several Years Ago, The Author Developed A Mathematical 2-D Model To Quantitatively Describe The Forces, Moments, And Motions Of Vehicles And Dummy Occupants During Collisions. The Equations Of Motion And Applicable Logic Statements Were Programmed In Basic To Use On Pcs (Ibm Compatible Personal Computers). Simulations Of Many Crashes Have Been Successfully Run On Pcs Using The 2-D Model. Clients Are Usually Interested In The Responses Of The Dummy Head And Torso And The Calculated Magnitudes Of Forces And Moments In The Neck Joint. These Data Are Particularly Useful In Litigation Cases Where Medical Findings Are Subjective (E.G. Soft Tissue Injuries) And Opinions Of The Treating And Adverse Health Care Professionals Differ Significantly. When Additional Relevant Information Has Been Received, The Model Has Been Refined. The Model Has Been Modified To Accommodate Crashes In Which The Target And Bullet Vehicles Are Off-Center And Reasonably Close In Axial Alignment. A Description Of The 2-D Model Was Presented At The 1993 Annual Meeting Of The American Academy Of Forensic Sciences At San Antonio, Texas. In A Particular Recent Case, The Nature Of The Collision And The Posture Of The Occupant Driver Are Not Within The Inherent Constraints Of The 2-D Model. In Order To Adequately Study This Case, A Mathematical 3-D Model Would Be Needed.

Passenger Train Crashworthiness—Secondary Collisions

Secondary collisions in passenger train crashes are considered and a companion paper dealing with primary collisions is followed up. The effects of crash pulse magnitude and duration, occupant flail distance, and the nature of the impacted surface are considered. The constitutive relationship for a Hybrid III dummy head satisfying the peak acceleration requirements of FMVSS208 is developed and used with the crash victim simulator MADYMO to investigate the impact response of train passengers seated in a unidirectional layout. It is shown that the design of the coach shell and the interior have to be integrated to obtain train designs that will minimize occupant injuries in the event of train collisions.

Coupling of a finite element human head model with a lumped parameter Hybrid III dummy model: preliminary results.

A skull-brain finite element model of the human head has been coupled with a multilink rigid body model of the Hybrid III dummy. The experimental coupled model is intended to represent anatomically a 50th percentile human to the extent the dummy and the skull-brain model represent a human. It has been verified by simulating several human cadaver head impact tests as well as dummy head 'impacts" during barrier crashes in an automotive environment. Skull-isostress and brain-isostrain response curves were established based on model calibration of experimental human cadaver tolerance data. The skull-isostress response curve agrees with the JARI Human Head Impact Tolerance Curve for skull fracture. The brain-isostrain response curve predicts a higher G level for concussion than does the JARI concussion curve and the Wayne State Tolerance Curve at the longer time duration range. Barrier crash simulations consist of belted dummies impacting an airbag, a hard and soft steering wheel hub, and no head contact with vehicle interior components. Head impact force, intracranial pressures and strains, skull stress, and head center-of-gravity acceleration were investigated as injury parameters. Head injury criterion (HIC) was also calculated along with these parameters. Preliminary results of the model simulations in those impact conditions are discussed.

Finite Element Model Study of Head Impact Based on Hybrid III Head Acceleration: The Effects of Rotational and Translational Acceleration

The translational and rotational components of acceleration measured at the center of gravity of a Hybrid III dummy head were used to investigate their individual and combined effects on a two-dimensional finite element model of the human brain. Each component of acceleration generated distinct patterns of deformation. Although translational acceleration is related to pressure and rotational acceleration has a dominant effect on shear deformations, complete acceleration (combination of translation and rotation) yielded the highest values in all stresses and produced a maximum shear stress at the top of the brain.

Technical matters relating to the measurement of interaural cross‐correlation (IACC) coefficients in concert halls and opera houses

The interaural cross‐correlation coefficient (IACC) has been shown to be an important measure, along with others, of the quality of acoustics in concert halls and opera houses [Schroeder et al., 1199 (1974); Ando, Concert Hall Acoustics (Springer‐Verlag, Berlin, 1985)]. When measured in auditoriums with binaural heads (real or dummy) using an impulse source, means must be adopted to achieve accuracy and precision, and to select the type of impulse and processing methods to make IACC most useful in the prediction of acoustical quality. Subjects covered include: (1) type of impulse, (2) convolution signal, (3) integration limits, (4) directivity and positions of source in the hall, (5) parameters of head, (6) comparisons of measurements made with real and dummy heads, (7) value of torso, (8) measuring positions in hall, (9) comparison of measurements of IACC in halls with upholstered and nonupholstered seats, (10) comparison with IACC measurements made by other laboratories, and (11) some preliminary data on differences among IACCs measured in occupied and unoccupied halls.

Chin strap forces in bicycle helmets

Abstract The objective of this experimental investigation was to find out what dynamic forces a bicycle helmet' retention system is subjected to when head impact accidents take place. Different helmet models were subjected to simulated accidents, of the type with the head first (with vertical and horizontal velocity) against a rigid asphalt surface. The chin strap forces developed in the accident simulations of the present study were low compared to the requirements of most of the existing standards for bicycle helmets. The arithmetic mean of the chin strap peak forces of all impacts was 42 N. Three types of helmets were investigated, one hard-shell helmet, one non-shell helmet and one ribbed helmet (large ventilation holes) with hard shell. A six-year-old child test dummy and a car-crash test facility with a piece of inclined asphalt road on the carriage were the main attributes of the study. The test dummy was suspended from the ceiling and was hit by the piece of asphalt road mounted on the stiff car-crash track carriage. Several different single-type accidents were simulated. All impacts were carried out with the helmeted dummy's head impacting the asphalt layer first. The types of accidents simulated were all meant to simulate the case in which the bicycle is blocked in one way or another and the rider continues with a certain horizontal and vertical velocity. As a subsidiary result it was discovered that the rotational effects of the tested helmets differed appreciably. The shell helmets did not grip the asphalt layer at all and did not rotate, which implies that the headform did not rotate either. The non-shell helmets gripped the asphalt layer in each impact, rotated and transferred this rotation to the headform. The stability of children's helmets should be considered more important for the helmet's ability to stay on the wearer's head than buckles that withstand high force levels. The helmet design in itself could result in different chin strap forces in accidents. One of the key factors is probably the helmet's area of coverage and its fit to the head. This study of the chin strap forces developed in bicycle retention systems in single-type accidents indicates that chin strap buckles with a self-release function are applicable to children.

A practical evaluation method of auditory source width in concert halls.

This paper investigates how to measure the degree of interaural cross correlation (ICC) as a physical measure of auditory source width (ASW), the just noticeable difference (jnd) of ASW and the estimation equation of ASW in degree for a music motif as a practical evaluation method of ASW in concert halls. Some physical measurements and psychological experiments show the following results.(1) ICC measured without Aweighting using a dummy head without ear simulators agree with spatial impression measured by Barron and Marshall which corresponds to ASW. It is termed DICC, in distinction from IACC measured with A-weighting.(2) Weber's law is applicable to the perception of ASW. The measured jnd becomes smaller as DICC becomes higher, and the Weber's ratio, ΔDICC/(1-DICC) is almost constant in the range from 0.2 to 0.3.(3) The equation and the chart to estimate ASW in degree are obtained as functions of DICC and the binaural summation of sound pressure level (BSPL). An increase of DICC by 0.1 causes a decrease of ASW by about 4° and an increase of BSPL by 1 dB causes an increase of ASW by about 1.6°. A decrease of DICC by 0.1 is equivalent to an increase of BSPL by 2.6 dB in ASW.

Development of hard carbon coatings for thin-film tape heads

Major problems in thin-film recording heads are pole tip/gap recession in the inductive head and scratching/smearing, electrical short, electrostatic charge build up, and corrosion of the MR stripe in the MR heads. Wear of head structure can be minimized by depositing a hard carbon coating over the entire ABS including the head structure. In this study, we have deposited carbon coatings on Ni-Zn ferrite and Al/sub 2/O/sub 3/-TiC substrates and dummy heads by various deposition techniques and characterized for mechanical and tribological properties. Ion beam carbon coatings on Ni-Zn ferrite and cathodic arc carbon coatings on Al/sub 2/O/sub 3/-TiC heads exhibit most wear resistance compared to other coatings in a tape drive test.

映像機器のメカトロニクス ヘッド窓なしドラムにおけるヘッド・テープインタフェースの検討

To design a low-tape-tension mechanism, the differences in the head-tape interface between a window-type drum and a non-window-type drum (without the head windows) in a rotating head system were investigated. The head-tape spacing was observed using a transparent dummy head instead of the actual magnetic one, and tape deformation was measured using a non-contact displacement meter. In addition, tape deformation near the head was simulated numerically. We found that tape was deformed at the drum gap, and tape tension at the head-tape contact was lower in the non-window-type drum than in the window type. We concluded that a low-tape-tension mechanism useful for thin tapes can be constructed using a non-window-type drum.

Measuring simultaneously linear and angular acceleration during a crash

AbstractThe new translational/angular accelerometer presented in this paper consists of a pair of identical preloaded quartz shear elements inside a metal housing. Integrated impedance converters transform the piezoelectric signals to low impedance voltages. The rugged sensor is mounted on the surface of the structure under test by fixing it with four screws. It allows the simultaneous measurement of translational and angular acceleration. Due to its construction, the small and light weight sensor is suited for shock application, e.g. during crashes. An example of linear and angular acceleration acting on a dummy head during a crash is presented.

Radiopacity of elastomeric impression materials.

The purpose of this study was to measure and classify the radiopacity of various elastomeric impression materials available on the open market and to compare their appearance in radiographs of the oral tissues. In order to measure and classify their radiopacity, twenty-eight specimens of various materials were placed and exposed on film together with an aluminium stepwedge. A dummy head was used to investigate the radiographic density of the above specimens in comparison with that of simulated oral tissues.