Horn Type Research Articles

Low-Frequency Response of Horn Loudspeakers—An Appraisal

Horn—type loudspeakers show characteristically low-frequency cut-off, depending on the aperture or mouth area. In the conical horn, the aperture area plays an important role whereas in the exponential horn types, the taper of the horn also plays an important role. How the low-frequency cut-off arises is briefly discussed in the paper.

HORMONAL CONTROL OF PROGESTERONE RECEPTORS*

Uterine progesterone receptors are under dual hormonal control. Estrogen increases the concentration of receptor through a mechanism that depends on synthesis of both RNA and protein. Progesterone decreases the concentration of its own receptor, probably by enhancing its inactivation rate. This regulation explains receptor variations during the estrous cycle. In both guinea pig and rat uteri, cytosol receptor concentration is maximal at the preovulatory period and decreases after ovulation. Nuclear receptor was measured in the rat. Its concentration is also maximal at proestrus, but the higher nuclear to cytosol receptor ratio was observed at metestrus. There is a good correlation (r = 0.78) between nuclear receptor concentration, on one hand, and the product of cytosol receptor concentration times the plasma progesterone concentration, on the other hand. Autoradiographic studies show that receptor variations during the estrous cycle occur simultaneously in all cell types of uterine horn, cervix, and vagina, which suggests that similar mechanisms control receptor concentration in all of these cells. Progesterone receptor was also measured during pregnancy in rat uterus. Cytosol receptor concentration is low at the beginning of pregnancy (approximately 6000 binding sites per cell), declines slightly on Day 5 (approximately 4000 binding sites per cell), and then increases progressively during the remainder of pregnancy to attain its highest value on Day 22 (26,000 binding sites per cell). Nuclear receptor concentration is very low on Day 3 (1200 binding sites per cell), increases slightly on Day 5 (1900 binding sites per cell), decreases on Day 6, and then increases again to attain a plateau between Days 9 and 15 (approximately 2600 binding sites per cell). Thereafter, its concentration begins to decrease rapidly. On Day 22, the mean concentration is very low (700 binding sites per cell); in some animals (probably on the verge of parturition), no nuclear receptor can be detected.

Integral representations of functions which belong to weighted Sobolev classes in regions, with applications. I

In the present work for general weighted classes of functions which are anisotropic with respect to the differentiation indices and with respect to the weight indices we isolate classes of regions for which we have imbedding theorems which are of the same nature as those for a half-space. A definitive result of this type for WD(I) spaces was obtained by Besov and II'in in (I0-13). In our case such regions will also be determined by a horn type of condition, but, in contrast to the unweighted case, the form of the horn for weighted classes of functions dePends in an essential fashion on the point in the region. Our conditions on the region are definitive in a certain sense since without the weight the conditions revert to the conditions for the W~ ~)'' classes. A fundamental tool in our investigation is an integral representation of functions which generalizes a known representation due to Win (see (11)). To obtain our integral identity we use a function average with an averaging parameter that is point-dependent. The first such construction was obtained by Kudryav-

The organization of cholinesterase-containing systems of the monkey spinal cord

The spinal cords of the baboon (Papio anubis), Cercopithecus aethiops and Erythrocebus patas monkeys have been studied histochemically by the ‘direct-colouring’ thiocholine technique for cholinesterases. Of the two cholinesterases, acetylcholinesterase (AChE) is a prominent feature in the monkey spinal cord. Pseudo-cholinesterase (ChE) is not. AChE is present in varying quantities, in the grey matter only, at all levels of the cord. Spinal white matter in the normal (unexperimented) animal did not reveal histochemically demonstrable AChE. In the dorsal horn, neurones of laminae I–III react moderately for the enzyme whilst those of laminae IV–VI appear to contain no AChE. Afferent inputs to the dorsal horn also contain no histochemically demonstrable AChE. In the intermediate grey matter there were discrete areas, for instance the nucleus dorsalis and the nucleus cervicalis centralis, containing cells staining weakly to moderately against a background of AChE negative neuropil. Staining of the vascular elements in these nuclei was atypical. Experimental evidence indicates that the dorsal spinocerebellar tract is an AChE projecting tract. A further interesting feature of the intermediate spinal grey matter is the structural ‘ladder’ design of the autonomic complex ( i.e. nuclei intermediomedialis and intermediolateralis) as revealed by their AChE content. The ventral horn contains a considerable number of stained and unstained cells. Four types of stained cells are distinguishable on the basis of cell size and staining intensity. These cell types are correlated as far as possible with physiologically indentified cell types of the ventral horn. A fifth type of cell with moderate AChE activity appears, on the basis of size and anatomical location, to correspond to the so-called ‘Renshaw cell’. The above results have been discussed in the light of existing knowledge of the structural and functional organization of the mammalian spinal cord. Possibilities for further research resulting from this study are emphasized.

PHOTO-OPTICAL MEASUREMENT OF GASTRIC MOTILTY

The present study was made to investigate the difference of gastric motility between hypertonic and hypo- or atonic type of stomach in healthy adults. The subjects studied were 10 adults consisting of two groups of every 5 persons with hypertonic steer horn and hypo-or atonic long stomach respectively.Cinefluorogram of gastric motility of these subjects was taken on 16 mm cinefilm by means of an image intensifier. The size of longitudinal axis (L) and transverse diameter (T) of the gastric peristalsis was measured on each frame of the obtained film by a film motion analyzer.In the hypertonic steer horn type the reduction of L was greater than T, and the velocity of peristalsis was fast. On the contrary the reduction of T was greater than L and the velocity of the peristalsis was slow in the case of hypo- or atonic type of the stomach.The changes of the L and T seem to be related to the contractions of the longitudinal and circular muscle of the gastric wall respectively.Therefore, it is conceivable that participation of the longitudinal muscle to the gastric motility is greater than that of the circular muscle in the hypertonic type, while participation of the circular muscle is greater than that of the longitudinal muscle in the hypo- or atonic type.

Match optimization of a two-port phased array antenna element

A systematic method for designing a phased array element that is matched over a wide scan region is presented. Measured coupling coefficients from a small array of trial elements, combined with computer simulation, yield the design parameters of an individual element matching obstacle. These obstacles will optimize the match versus scan characteristics when properly inserted within the element channels. The method presented has been used to optimize the match versus scan characteristic of a circularly polarized coaxial horn type of element over a 15 percent bandwidth. A close agreement between the predicted and measured returned powers has been observed over the frequency band for a broad scan region.

Launching a surface wave over the Earth

Proposals are made for a ferrite-loaded horn type of antenna capable of launching a 1.5 MHz surface wave over the Earth. The use of a ferrite coating on the conductor laid parallel with the ground, and forming one side of the horn, makes provision for a surface reactance which can be tapered up to reduce the size of the radiating aperture, and thence tapered down again to match the reactance of the ground.

Formulation of the Brass-Instrument Bore Problem

The boundary conditions for waves in a brass instrument require a pressure amplitude large in the mouthpiece and small at the open end. The nth vibrational mode of the air column therefore consists of (2n−1) standing quarter-wave segments For a horn whose cross section is given by πr2(x), Webster's equation is [∂2/∂x2−U(x)]ψn=−(ωn/c)2ψn. Here, ψn=πr2pn(x), and pn(x) is the pressure distribution for the nth mode, whose oscillation frequency is ωn. U(x)=(d2r/dx2)/r is the product of the longitudinal and transverse curvatures of the horn at x. The similarity with Schrödinger's equation gives considerable insight. WKB methods show a useful relation between the length Ln of a cylindrical pipe (whose nth frequency matches that of the horn) and the value of x at the point where U(x)=(ωn/c)2. For music, the resonances should approximate a harmonic series, so Ln=L1⋅(2n−1)/n. The choice of useful horn types is discussed, including effects of bell shape on starting and maintaining self-sustained oscillations. Effects of bore discontinuities and estimates of radiation and wall damping are described. Experimental data are presented and musical implications drawn.

Study of Underwater Horns—Single-Loading Exponential and Pseudohemispherical Horns

Single-loading, axisymmetric exponential, and pseudohemispherical horns were tested under water by pulse techniques over the frequency range from 1000 to 22 000 cps. The sound source was a piezoelectric bender-type transducer in the shape of a circular disk. Both impedance and radiation measurements were made. The results are discussed in terms of the separate and joint effects of horn geometry, modes of radiation, back radiation, and the pistonlike action of the transducer. A theory is proposed to predict the behavior of the horns. Separate predictions of cutoff frequency, impedance, and radiation characteristics were made for each type of horn. The predicted behavior and the measured results are compared and found to be in reasonable agreement over the frequency range above. Planned extensions of the current work are discussed. [This work is supported by the U. S. Office of Naval Research.]

Performance Characteristics of a 160 000-W Acoustic Siren

A series of tests was conducted by the Acoustics Section of Test Laboratory at MSFC to determine the performance characteristics of a large acoustic siren. This siren will be used to study long-range sound propagation and is capable of generating either random noise or discrete frequencies. The measurement program and the methods used to analyze the data collected during these tests are briefly discussed. From these tests, it was found that the directivity of the siren was independent of the operating conditions in the frequency range between 31 and 125 cps. A maximum power oulput of 161 000 W was calculated while the siren was being operated at 125 cps. The basic limitation of the present system is its inability to efficiently propagate low-frequeucy sounds (below 31 cps). However, this is a characteristic of the exponential horn and not of the siren. The efficiency of a catenoidal horn at low frequencies is briefly discussed to illustrate the advantage of using this type of horn with the siren.

Note on Underwater Horns

Various types of free-flooding finite horns are used to load both faces of a piezoelectric transducer. The general axisymmetric configuration of each horn type tested is the same; it is comprised of a straight, frontloading horn and a folded, back-loading horn, such that the mouths of the two loading horns are concentric. Each horn type tested has the same throat dimension, folding geometry, theoretical cutoff frequency, and was tested with the same piezoelectric transducer. Experimental data taken over the frequency range of 1000–20 000 cps are presented and compared with those which theory would predict from the design geometry. [This work supported by the U. S. Office of Naval Research.]

A Synopsis of the Cave Beetles of the Genus Pseudanophthalmus of the Mitchell Plain in Southern Indiana (Coleoptera, Carabidae)

Thirteen species and subspecies of cave beetles of the genus Pseudanophthalmus Jeannel have been reported from the Mitchell Plain of southern Indiana. Horn (1871, 1883), Jeannel (1931, 1949), and Krekeler (1958) have described and illustrated the majority of these forms in considerable detail. The present paper is intended to be used in conjunction with the papers of Jeannel (1949) and Krekeler (1958), and no attempt has been made to repeat descriptions of forms which have been adequately treated by these authors. The discovery of a lost species in Wyandotte Cave and a nearby cavern necessitates a new combination and the changing of several trinomials. A new species, from Lawrence County, is described. For reasons stated in an earlier paper (Barr, 1959) the writer has applied the polytypic species concept to the systematics of Pseudanophthalmus and other genera of troglobious carabids. An alternative taxonomic approach was offered by Krekeler (1958), who regarded each morphologically distinct cave population (or group of similar populations in closely associated caves) as genetically isolated. The specimens upon which the present paper is based were collected in Crawford, Harrison, Lawrence, Monroe, Orange, Owen, and Washington Counties, Indiana, during the summer of 1957 and the fall of 1958. Dr. Carl H. Krekeler, Valparaiso University, whose recent (1958) paper is the most important single contribution to our knowledge of Indiana anophthalmids, provided a topotype P. morrisoni and a paratype P. youngi donaldsoni for examination. One P. morrisoni and six P. youngi donaldsoni were collected for the writer by Mr. Thomas L. Poulson. Deep appreciation is expressed to Mr. Lewis D. Lamon, Corydon, Indiana, and to Miss Leona Hert, Springville, Indiana, for assistance in collecting the material discussed below. Mr. Robert Louden, manager of Wyandotte Cave, was most courteous and helpful. Dr. Harold J. Grant, Academy of Natural Sciences of Philadelphia, kindly compared the writer's topotypes with Horn's types of Anophthalmus eremita and A. tenuis. Five species groups and six species are recognized in the present study, four of the groups being monotypic. The species may be separated by the following key.

An Investigation of the Air Chamber of Horn Type Loudspeakers

The air chamber is treated as a boundary value problem which results in the solution of the wave equation for the general case in which the horn throat enters the air chamber in any circumferentially symmetrical manner. The following specific cases are analyzed: (1) the case in which the horn throat enters the air chamber by means of a single orifice, (2) the horn throat enters the air chamber by means of a single annulus of radius r and width w, and (3) the horn throat enters the air chamber in “m” annuluses of radii r1⋯rm and widths w1⋯wm. The analysis reveals that the radial perturbation caused by the horn throat excites higher order modes. At the resonant frequencies of these modes the horn throat pressure becomes zero and the loudspeaker does not radiate. By suitable choice of annulus radii and widths the first “m” modes may be suppressed and the corresponding nulls in the output pressure eliminated.

An Investigation of the Air Chamber of Horn Type Loudspeakers

The classical horn loudspeaker theory is reviewed briefly, and the inadequacy of the classical air chamber analysis for “tweeters” is indicated. The air chamber is treated as a boundary value problem which results in the solution of the wave equation for the general case in which the horn throat enters the air chamber in any circumferentially symetrical manner. The following specific cases are analyzed: (1) when the horn throat enters the air chamber by means of a single orifice, (2) when the horn throat enters the air chamber by means of a single annulus of radius r and width w, and (3) when the horn throat enters the air chamber in “n” annuluses of radii r1⋯rn, and widths w1⋯wn. The theory is verified experimentally.

Spectra and Loudness of Modern Automobile Horns

Measurements were made of the sounds of three types of commonly used automobile horns. Over-all sound levels on the axis at three feet ranged from 108 to 125 db. Loudnesses ranged from 125 to 140 phons. One type of horn gave sound levels of 88 db at 50 feet and 74 db at 300 feet, with corresponding loudness levels of 104 and 81 phons. Fundamental frequencies of all horns ranged between 160 and 380 c.p.s. Two types had harmonic overtones, with large amplitudes below about 2000 c.p.s. and smoothly decreasing amplitudes at higher frequencies. The third type, with the most unpleasant sound, had inharmonic overtones, some of which were greater in amplitude than the fundamental. Sound from a pair of horns at various distances was measured inside a closed automobile The over-all level was 60 db (loudness, 72 phons) at 50 feet and 50 db (loudness, 53 phons) at 300 feet. Filtering out overtones above 1200 c.p.s. reduced the annoying character of horn sounds markedly and reduced the loudness by four phons at 50 feet and only one phon at 300 feet. Since the typical horn is louder than necessary at close range, use of a low pass acoustic filter on automobile horns appears desirable.

A field-strength meter and standard radiator for centimetre wavelengths

The paper describes the development of a field-strength meter and standard radiator for operation at a wavelength of about 9 cm. Details are given of a modified form of Wheatstone Bridge which can be calibrated to give direct readings of the power absorbed in a bolometer. The field-strength meter takes the form of an electromagnetic-horn receiver in which the received power is measured by means of a bolometer. It is shown how the gain of such an aerial may be determined experimentally, and how, knowing this gain, the field-strength existing at the aperture of the horn may be found. The range of power measurable by the bolometer used limits the field-strength range of the equipment to 0.1–50 V/m. The standard radiator consists of the same type of horn as the field-strength meter but with small modifications.A description is given of the application of the two instruments to the determination of the power radiated by a transmitter, and to the estimation of the over-all sensitivity of a receiver.

Generalized Plane Wave Horn Theory

Horns are primarily used with moving coil loudspeaker units to obtain sound radiators possessing satisfactory electro-acoustic energy transfer characteristics. The contribution of the horn to the over-all efficiency, as expressed by the acoustic driving point admittance, will be obtained by a generalized dimensionless treatment of Webster's equations. Numerical solution of the differential equation for the pressure may be effected by the Hartree method widely used in problems involving atomic wave functions, enabling an estimate of the behavior of any horn of reasonable flare. Some new types of horns suggested by certain solutions of the differential equation will be compared to the well-known exponential horn.

A Horn Consisting of Manifold Exponential Sections

The expressions for the throat impedance of a horn with two rates of exponential flare have been derived. This expression is applicable to any number of sections by considering two sections at a time. The impedance frequency characteristic of specific multiple horns shows the possibility of obtaining a large variety of impedance characteristics suitable for improving the efficiency characteristic over that possible with a single rate of flare. The efficiency of a horn type loudspeaker having a horn with three rates of flare shows an efficiency within a few percent of the ultimate efficiency.

A Horn Consisting of Manifold Exponential Sections

The expressions for the throat impedance of a horn with two rates of exponential flare have been derived. This expression is applicable to any number of sections by considering two sections at a time. The impedance frequency characteristic of specific multiple horns shows the possibility of obtaining a large variety of impedance characteristics suitable for improving the efficiency characteristic over that possible with a single rate of flare. The efficiency of a horn type loudspeaker having a horn with three rates of flare shows an efficiency within a few percent of the ultimate efficiency.

The Amplification of Sound Received by Horns

1. The known equations for the amplification of sound received by conical, exponential, hyperbolic and parabolic horns are deduced on the basis of Webster's theory using a more direct method than is generally employed. 2. Representative theoretical and experimental amplification curves are given for each type of horn. 3. The variation with frequency of the ratio of sound pressure at the closed end to that just inside the mouth for the various type short horns having the same length, throat and mouth areas is calculated to show the superiority of the exponential horn. 4. The amplification of a short conical horn with exponential listening pipe is also considered.