Probe Tube Research Articles

Soil probe lubrication and effects on soil chemical composition

Abstract Deep soil‐profile sampling in wet, clayey soils can be difficult. Friction against the probe surface can cause core compression and impedes extraction of intact cores from the probe tube. Lubrication of the probe tube reduces friction and improves core extraction. Two studies were conducted to determine soil‐sample contamination resulting from probe lubrication and possible interactions with probe diameter (surface‐area:volume ratio) and sampling depth. Soils were sampled following probe lubrication and analyzed for organic matter and seven common nutrients. Lubricants tested contained varying amounts of organic matter (24‐>700 g/kg), nitrate‐N (NO3‐N, 3–205 m/kg), phosphate‐P (PO4‐P, 244 mg/kg), potassium (K, 2–1200 mg/kg), and zinc (Zn, <0.1–460 mg/kg) but relatively small amounts of manganese (Mn, <0.1–0.2 mg/kg), iron (Fe, 0.2–2.9 mg/kg), and copper (Cu, <0.1–0.6 mg/kg). Macronutrient content of soil samples was not affected by lubrication beyond variation typical among replicated soil sample...

The use of microdialysis for the study of drug kinetics: some methodological considerations illustrated with antipyrine in rat frontal cortex

1. The neuropharmacokinetics of antipyrine, a readily dialysable drug, in rat frontal cortex were studied and the effect of sampling time and contribution of period sampling and dialysate dead volume investigated in relation to tmax, Cmax, AUC and t1/2 values. 2. After i.p. administration, antipyrine (35 mg kg-1, n = 5) concentrations rose rapidly in rat frontal cortex (tmax, 12 min) and then declined exponentially tmax, Cmax, AUC and t1/2 values were determined after 2 min dialysate sampling and compared to values obtained from simulated sampling times of 4, 6, 8, 10 and 20 min. 3. Antipyrine tmax and Cmax values were directly dependent on sampling frequency. Thus, mean 2 min sampling tmax and Cmax values were 63% lower and 27% higher, respectively, compared to 20 min sampling values. AUC and t1/2 values were unaffected. 4. Adjustment for dialysate dead volume (the volume of dialysate within the dialysis probe and sampling tube) reduced tmax values significantly but did not affect the other neuropharmacokinetic parameters. 5. Contribution of period sampling on neuropharmacokinetic parameters were investigated by comparing plots of antipyrine concentration data at midpoint and at endpoint of sampling time interval. Only tmax values were affected with values decreasing with increasing sampling time interval. 6. In conclusion, although microdialysis is a useful method for monitoring events at the extracellular level and for kinetic studies, it is important to understand its inherent characteristics so that data can be interpreted appropriately. Sampling frequency, particularly during monitoring of periods of rapid change, is very important since Cmax and tmax values will be significantly underestimated and overestimated respectively, if sampling time is longer rather than shorter. These considerations are particularly important in relation to microdialysis studies of pharmacokinetic-pharmacodynamic interrelationships and modelling.

An innovative probe microphone design for use in high‐frequency sound field measurements

There is a need for nonintrusive measurement devices. When the wavelength of the sound wave is physically the same scale as that of the microphone, its sound pressure cannot be measured accurately. Acousticians have worked around this difficulty by using smaller microphones and, when necessary, using probe tubes with even smaller diameters attached to small microphones. This need for very small diameter devices is especially critical at high frequency. The use of probe tubes introduces another level of complexity to acoustic measurements. The resonant dynamics of the tube itself must be taken into account. The tube supports standing waves that cause the microphone frequency response to be very irregular. Typically, damping material, such as foam or steel wool is introduced into the probe tube to attenuate standing waves. However, even when damping is successfully applied, the response remains irregular and the damping material results in a significant reduction of signal‐to‐noise ratio. The new concept is designed to eliminate standing waves without introducing damping in the signal path between the microphone and the end of the tube. Therefore, the signal‐to‐noise ratio will not suffer significant degradation, and behavior will be consistent from probe to probe.

Sound calibration and distortion product otoacoustic emissions at high frequencies

Distortion product otoacoustic emissions offer the potential for assessing inner ear function at high frequencies. However, commonly employed methods for calibrating the acoustic system used in these studies can lead to errors of ± 20 dB or more in the estimate of eardrum sound pressure levels above 2–3 kHz [Siegel, J. Acoust. Soc. Am. 95, 2589–2597 (1994)]. We assessed the magnitude of these errors by measuring the distortion product emission 2 f 1– f 2 ( f 1 < f 2) in human subjects using either of two microphone locations to calibrate the stimulus. Either the emission probe microphone itself or a probe tube positioned near the eardrum were used in calibrations. The emissions collected with f 1 in the vicinity of 5–7 kHz showed a pronounced peak in level relative to other stimulus frequencies when the emission probe was used for calibration. The peak at 5–7 kHz disappeared when the probe tube near the eardrum was used for calibration. The discrepancy in emission levels between the two calibration procedures was as large as 20 dB. The difference is attributed to the presence of standing waves in the ear canal. The systematic errors in estimating eardrum sound pressure level using the emission probe microphone undoubtedly contribute to the variability of emission measurements for high-frequency stimuli.

Measuring the human head-related transfer functions: A novel method for the construction and calibration of a miniature ‘‘in-ear’’ recording system

A method for the construction of a small "in-ear" system for recording the human-free field-to-eardrum and headphone-to-eardrum transfer functions is described. Customized in-ear inserts were obtained by a simple ear printing and electroplating method, resulting in a thin (< 0.25 mm) outer shell that minimized obstruction of the entrance at the ear canal. The insert can be used to position a microphone probe tube deep within the auditory canal. The effects of this recording system on the sound field in the ear canal were calibrated using a model head equipped with a second internal microphone close to the eardrum. Transfer functions were recorded for 343 different stimulus locations in free space and for a headphone sound source. For the free-field stimuli the presence of the recording system resulted in a small attenuation with maximum effects around 3.5 and 12.5 kHz (-1.5 and -2.0 dB, respectively). Passing the data through an auditory filter model reduced the averaged attenuation to less than -1.4 dB. Phase was undistorted up to 2.5 kHz. These results suggests that the perturbations produced by the insert are unlikely to be perceptually relevant.

Method for fitting binaural hearing aids

For a hearing aid wearer to perform binaural sound localization and to utilize directional hearing in noisy environments, it may be important to maintain at audible levels the binaural cues (i.e., interaural time and level differences) present without the hearing aid(s) in place. A method of achieving this hearing aid fitting goal for use with a prototype digital signal processing hearing aid has been developed. The method includes two major steps: hearing aid equalization (HAE) and hearing loss compensation (HLC). HAE is achieved with an FIR filter, which equalizes the amplitude and phase insertion effects of the hearing aids and maintains the binaural cues with the hearing aid(s) in place. The HAE filter coefficients are obtained from insitu probe tube measures of aided and unaided test signals using optimal filter calculations. HLC is also achieved with an FIR filter and associated gain. The HLC filter coefficients are obtained by using a weighted least-squares filter design technique. The target response for the HLC filter is determined from measures of electrical signal levels in the hearing aid circuit during threshold tests and during reference signal presentations in the sound field. The HAE and HLC filters are convolved to produce a single filter. A description of the fitting procedure will be provided, as well as examples of its use with hearing impaired individuals.

Adaptive plasticity of the auditory space map in the optic tectum of adult and baby barn owls in response to external ear modification

1. This study demonstrates the influence of experience on the establishment and maintenance of the auditory map of space in the optic tectum of the barn owl. Auditory experience was altered either by preventing the structures of the external ears (the facial ruff and preaural flaps) from appearing in baby barn owls (baby ruff-cut owls) or by removing these structures in adults (adult ruff-cut owls). These structures shape the binaural cues used for localizing sounds in both the horizontal and vertical dimensions. 2. The acoustic effects of removing the external ear structures were measured using probe tube microphones placed in the ear canals. In both baby and adult ruff-cut owls, the spatial pattern of binaural localization cues was dramatically different from normal: interaural level difference (ILD) changed with azimuth instead of with elevation, the rate of change of ILD across space was decreased relative to normal, and the rate of change of interaural time difference (ITD) across frontal space was increased relative to normal. 3. The neurophysiological representations of ITD and ILD in the optic tectum were measured before and > or = 3 mo after ruff removal in adults and beginning at 4.5 months of age in baby ruff-cut owls. Multiunit tuning to ITD and to ILD was measured using dichotic stimulation in ketamine-anesthetized owls. The tectal maps of ITD and ILD were reconstructed using visual receptive field location as a marker for recording site location in the optic tectum. 4. Adjustment of the tectal map of ITD to the altered spatial pattern of acoustic ITD was essentially complete in adults as well as in baby ruff-cut owls. This adjustment changed the magnification of ITD across the tectum, with resultant changes in ITD tuning at individual tectal sites of up to approximately 25 microseconds (approximately 5% of the physiological range) relative to normal values. 5. Adaptation of the tectal ILD map to the ruff-cut spatial pattern of acoustic ILD was substantial but clearly incomplete in both adult and baby ruff-cut owls. Although changes of up to approximately 15 dB (approximately 47% of the physiological range) relative to normal tuning were observed at certain tectal sites, the topography of the ILD map was always intermediate between normal and that predicted by the ruff-cut spatial pattern of acoustic ILD.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of probe insertion depth on real ear measurements

The purpose of this article is to provide an overall summary of the role probe insertion depth has on real ear measurements, and to compare the real ear sound pressure level measured by a probe microphone system, using three methods for positioning the probe in an ear canal. The probe insertion techniques that were compared included: (1) an acoustic method that incorporates use of the quarter-wave antiresonance property of the ear to determine acoustically the location of the probe tube relative to the eardrum in an individual ear; (2) a constant insertion depth method (25 mm from the intratragal notch); and (3) the earmold +5 mm method, which places the probe 5 mm beyond the tip of the individual's earmold in the canal, thereby avoiding problems associated with the transition region, where sound exits from the bore of the earmold into the larger ear canal. Measurements were obtained for each method at 32 frequencies in the unoccluded ears of 17 subjects. Results indicated that the sound pressure levels measured by the acoustic method were significantly larger than those measured by the other two methods. This result was most evident in subjects with long ear canals (> 25 mm) and at high test frequencies (4.0 to 6.3 kHz). For subjects with short or average length ear canals, the three methods provided essentially equivalent results.

The relationship between sound transfer functions from free sound field to the eardrum and temporary threshold shift

Three groups of 12 subjects were utilized for an experiment in which the temporary threshold shift due to a free-field exposure was measured and compared to the sound transfer functions from free-sound field to the subjects' eardrums. Subject selection was based upon their sound transfer functions and the requirement of normal hearing. The subjects were assigned to one of three groups depending on their dominantly sound transfer function frequency: Low, middle, or high. A probe tube with a miniature microphone was used for the measurement of the sound transfer functions in 1/3-oct bands. The measurements were performed in frequency bands from 0.2 to 20 kHz with one direction of sound incidence: 0 degree azimuth and 0 degree elevation. The subjects were exposed twice to a 2-kHz and twice to a 4-kHz narrow-band noise monotonically on four different occasions. Pre- and postexposure sweep Békésy audiograms were recorded and the temporary threshold shift calculated as the difference between the two. The averaged temporary threshold shifts differed significantly among groups.

Value of in situ measurement for evaluating effective hearing aid amplification at high sound pressure levels

A careful hearing aid fitting requires consideration of various characteristics of inner ear pathology. The recruitment phenomenon restricts the dynamic range of the impaired hearing and this increase the demands on the hearing aids for a satisfactory correction of the frequency characteristics as well as for an intensity reduction at higher sound pressure level SPL. For years data from coupler or KEMAR (Knowles Electronics Manikin of Acoustical Research) have served to estimate the real ear gain of a hearing aid at higher input levels. In previous papers we reported on some of the differences between coupler measurement and probe tube measurement. The object of this study was to investigate the differences between these two methods at higher input SPL. Therefore, we measured the real ear insertion gain as well as the output characteristics with a 2 cm3 coupler in 80 patients at input levels of 60 dB, 80 dB and 100 dB. The results show differences between the two methods up to 30 dB in both directions in the single patient. Furthermore, the highest compression rate was found in the middle and high frequency range which are crucial for speech discrimination. Consequently, probe tube measurement should be used not only to adjust the frequency characteristics of the hearing aid but also to characterise the real effect of Automatic Gain Control AGC and Peak Clipping PC on insertion gain at higher input SPL. Multichannel hearing aids should be used whenever possible to reduce the disturbances to speech discrimination at low frequencies.

Miniature microphone probe tube measurements in the external auditory canal

The use of a miniature microphone probe tube for sound-pressure level measurements in the outer earcanal was studied in four experiments. The main reason was to evaluate this method for clinical applications and for measurements of hearing protector attenuation. All measurements were registered in 1/3-oct bands. The dynamic range, frequency response of the microphone system, the insertion loss of the probe tube walls, and the influence of the probe tube in the ear canal on the sound-pressure level were examined. The first experiment attempted to determine an optimal placement of the probe tube in the earcanal. Sound-pressure levels resulting from a known free-field sound stimulus were measured at 12 different positions in the earcanal of human subjects. The results indicated that the position which is least sensitive for small movements of the probe tube on the measure was within 1 to 3 mm of the tympanic membrane. In a second experiment the changes in sound transfer function to the tympanic membrane caused by the microphone itself, when positioned just outside the ear canal entrance, were studied for 72 angles of sound incidences in ten subjects. A few minor but significant changes were observed with the microphone in this position. In a third experiment, sound transfer functions were measured from free sound field to the tympanic membrane in 19 subjects. The measurements were performed in 1/3-oct frequency bands (0.2 to 20 kHz) with sound incidences from 24 azimuthal positions and for each of these, three different elevations. The inter- and intrasubject-variability are analyzed and discussed. Finally, the reliability of probe tube microphone measurements was evaluated by repeated measurements of the sound transfer function, five times in ten subjects with the sound incidence from one position. The results indicated very small variations between repeated measurements.

Signal Delivery/Real Ear Measurement

This report describes a signal delivery/real ear measurement system for application in the hearing aid selection and fitting process. This signal delivery/real ear measurement system provides a means for quantifying a listener's auditory characteristics (e.g., thresholds, loudness discomfort levels) in a manner that is compatible with electroacoustic measures of hearing aid performance. The signal delivery/real ear measurement system consists of a button-type hearing aid receiver coupled to the listener's personal earmold, and a probe tube microphone system to measure the signal level within the occluded ear canal. This signal delivery/real ear measurement system was used to measure detection thresholds and loudness discomfort levels in severe/profoundly hearing-impaired school-age children, with results indicating good test-retest reliability in behavioral responses. The findings presented in this report relate to the intersession electroacoustic variability associated with this instrumentation. In addition, the potential application of this or a similar system for measuring real ear to 2-cc coupler difference values is illustrated and discussed.

Real Ear Sound Pressure Levels Developed by Three Portable Stereo System Earphones.

Differences in real ear sound pressure levels (SPLs) with three portable stereo system (PSS) earphones (supraaural [Sony Model MDR-44], semiaural [Sony Model MDR-A15L], and insert [Sony Model MDR-E225]) were investigated. Twelve adult men served as subjects. Frequency response, high frequency average (HFA) output, peak output, peak output frequency, and overall RMS output for each PSS earphone were obtained with a probe tube microphone system (Fonix 6500 Hearing Aid Test System). Results indicated a significant difference in mean RMS outputs with nonsignificant differences in mean HFA outputs, peak outputs, and peak output frequencies among PSS earphones. Differences in mean overall RMS outputs were attributed to differences in low-frequency effects that were observed among the frequency responses of the three PSS earphones. It is suggested that one cannot assume equivalent real ear SPLs, with equivalent inputs, among different styles of PSS earphones.

Flow characteristics of slot jet impingement on a wedge

An experimental investigation is made to study the flow characteristics of slot jet impingement on a wedge whose included angle is 90 degrees. The aim of this investigation is to study the characteristics of the flow field near the wedge surface for various parameters. The different parameters like, jet velocity, slot width, distance of wedge vertex from the jet exit and the inclination of the wedge to jet axis are systematically varied to see their effect on the flow field. The flow field near the wedge vertex is similar to stagnation point flow. Far away from the vertex, the flow field is like that of wall jet. Near the vertex, very large variations of static pressure are observed in streamwise and transverse directions. This is due to large streamwise curvature and stagnation of flow. The transverse pressure gradient slowly decays in the streamwise direction, as a result, the velocity profiles are different from the similarity profiles of stagnation point flow and wall jet in the respective regions. Experiments are conducted for slot widths of 10 mm, 15 mm and 30 mm each for the distance between slot and wedge vertex of 80 mm, 120 mm and 240 mm. The static pressure and velocity profiles are measured by calibrated disk type static pressure probe and pitot tube respectively at various streamwise locations.

Pinna-based spectral cues for sound localization in cat

The directional dependence of the transfer function from free field plane waves to a point near the tympanic membrane (TM) was measured in anesthetized domestic cats. A probe tube microphone was placed ≈ 3 mm from the TM from beneath the head in order to keep the pinna intact. Transfer functions were computed as the ratio of the spectrum of a click recorded near the TM to the spectrum of the click in freefield. We analyze the transfer functions in three frequency ranges: low frequencies (< 5 kHz) where the interaural level differences vary smoothly with azimuth; midfrequencies (5–18 kHz) where a prominent spectral notch is observed; and high frequencies (> 18 kHz) where the transfer functions vary greatly with source location. Because no two source directions produce the same transfer function, the spectrum of a broadband sound at the TM could serve as a sound localization cue for both elevation and azimuth. In particular, we show that source direction is uniquely determined, for source directions in front of the cat, from the frequencies of the midfrequency spectral notches in the two ears. The validity of the transfer functions as measures of the acoustic input to the auditory system is considered in terms of models of sound propagation in the ear canal.

Probe Tube Systems

In probe tube measures, the method used to equalize the sound field will determine the reference value used in calculating real ear insertion gain (REIG) and real ear aided gain (REAG). Several equalization methods are available with current probe tube systems. This study determined the effects of three equalization methods (substitution, modified comparison, and ipsilateral comparison) on REIG and REAG measures using open and closed earmolds for ear canals varying in circumference. Twelve subjects were selected representing a wide range of ear canal circumferences. Results revealed significant differences for REIG and REAG among the three equalization methods. These differences appear to be due to the different acoustic components included or excluded for each method. The results of this study suggest that the sound field equalization method used for probe tube measures needs to be considered when interpreting the hearing aid gain reported among various probe microphone units. Also, canal circumference may be a quick method for categorizing canal cavity size and appears to influence measured hearing aid gain.

Sound transmission through a high-temperature acoustic probe tube

An investigation was conducted of acoustic transmission through a tube subjected to an intense thermal gradient along its axis. The results are of interest in the interpretation of acoustic data from probe tube configurations designed to measure fluctuating pressures in high temperature environments. The measured transfer function across a localized heated region in the tube was compared to a computed transfer function based on a theoretical analysis of propagation through strong temperature gradients. Over the frequency range 0.4 kHz to 6.0 kHz, generally good agreement was obtained between the measured and calculated attenuation across the heated region with some discrepancy occurring at the attenuation minima. Agreement between measured and calculated phase difference was excellent to within the measurement resolution.

Evaluation and Assessment of FM Systems

In the past, frequency modulated (FM) systems were recommended for use only in educational settings for children with severe or profound hearing losses. Recent studies, however, have suggested that FM systems may be appropriate in nonacademic settings and also may benefit children with minimal hearing loss. In addition to the more widespread application of FM use, advances in amplification technology have provided audiologists with a variety of devices and coupling options, resulting in more variables to evaluate in the fitting process. There are three commonly used methods of evaluating FM systems: functional gain measures, probe tube microphone measures, and coupler measures. This paper is intended to provide the audiologist working with FM systems with an overview of the complexities involved in selecting and setting FM systems and the benefits and limitations of each evaluation method. Each evaluation method is examined in view of how well it answers three basic questions related to frequency response, maximum output, and distortion in FM systems. Finally, other issues which may impact on the selection of an FM system for a given individual are discussed.

A frameless, armless navigational system for computer-assisted neurosurgery

A computer-assisted neurosurgical navigational system has been developed which displays intraoperative manipulation on the preoperative computerized tomography (CT) scans or magnetic resonance (MR) images. The system consists of a three-dimensional digitizer, a personal computer, and an image-processing unit. Utilizing recently developed magnetic field modulation technology, the three-dimensional digitizer determines the spatial position and orientation angles of the resin probe, triangle-shaped pointer, or suction tube with a small attached magnetic field sensor. Four fiducial markers on the scalp were used to translate the spatial data of the probe onto the preoperative CT scans or MR images of the patient. With this frameless, armless navigational system, CT or MR-imaging stereotaxy can be applied to conventional open neurosurgery without limiting the operative field or interfering with the surgical procedures.

Ear canal cross-sectional pressure distributions: Mathematical analysis and computation

Cross-sectional pressure distributions, natural acoustic modes, and associated cutoff frequencies are determined for real ear-canal geometries using an asymptotic theory in combination with a numerical method. The technique is particularly well suited to obtain the higher modes, which are trapped near both ends of the ear canal. Results detail the influence of the canal geometry and frequency on the spatial distribution of the pressure. Adult ear-canal geometries are determined near the concha from ear-mold sections using a light microscope interfaced to a video-data-acquisition system. Computed results compare favorably to the exact solutions for circular and square acoustic waveguides. The cutoff frequency of the two adult ear canals studied averaged 20% less than the cutoff frequency of a circular tube of identical cross-sectional area. Inserting a probe microphone into the canal decreases the rate of decay of circumferential nonplanar modes while increasing the rate of decay of radial modes. Relative to the pressure beyond the tube, insertion increases the plane-wave component of the pressure around the tube by a multiplicative factor approximately equal to the square root of the original area divided by the occluded area. Eccentric placement of the probe tube has a relatively small influence on the cutoff frequency. The transition of the pressure distribution at the entrance to a simple plane wave in the core region of the canal is calculated and shown graphically for the actual geometry of two adult subjects.