Return Wave Research Articles

Pyramid loudspeakers with twin cross-phased midrange speakers

A truncated, open top, pyramid housing is provided containing a downwardly propagating woofer mounted near the base of the pyramid; a forwardly and slightly upwardly propagating tweeter mounted on the front side of the pyramid; and a pair of rearwardly propagating, crossed polarity, mid-range speakers mounted on opposed sides of the pyramid housing. The push-pull propagation between the opposed mid-range speakers, within a single housing, and similar cooperation between stereo loudspeaker pairs, provides a generally phase distortion free, wide dispersion sound circulation. A polarity switch is provided for establishing the desired cross-phase relationship. The nonparallel side configuration of the housing reduces internal resonance by preventing standing wave formation. The open top functions as an unidirectional port which also reduces internal resonance. The upward portion of each sound cycle is guided out of the speaker housing towards the ceiling by the funneling action of the slanted, tapered sides. The return wave, however, is not guided back into the port, thus reducing the feedback energy required to support internal resonance. The housing may be packed with acoustical material to increase its effective acoustical volume.

Extraction of ocean wave height and dominant wavelength from Geos 3 altimeter data

The Geos 3 satellite radar altimeter has the capability to provide accurate, low‐noise measurements of the significant wave height of ocean waves through their effect on the shape of the return pulse. When the amplitude and timing biases are removed from the Geos 3 sample and hold (SH) gates, the mean return wave forms can be excellently fitted with a theoretical template which represents the convolution of the radar point target response, the range noise (jitter) in the altimeter tracking loop, the sea surface height distribution, and the antenna pattern as a function of the range to mean sea level. In computing the wave height, tracking loop jitter may be removed by realigning the SH gates to their actual positions with respect to mean sea level before averaging, by using the observed standard deviation on the altitude measurement to remove the integrated effect of the tracking loop jitter, or by using a lookup table to correct for the expected value of range noise. Analysis of skewness in the Geos return wave form demonstrates the potential of a satellite radar altimeter to determine the dominant wavelength of ocean waves. When the jitter in the Geos range tracker is large, a significant reduction in range noise can be achieved through reprocessing the data. However, when the tracker noise is small, only marginal improvement is possible.

The Propagation of Potential in Discharge Tubes

The propagation of potential in a long discharge tube containing air was investigated as a function of pressure (0.017 to 0.24 mm Hg) and applied potential (74 to 171 kv). Impulsive potentials were applied to one end of the tube while the other end was grounded. By means of a high speed cathode-ray oscillograph, it was found that in the case of both positive and negative applied impulses a definite potential wave traversed the tube from the high voltage electrode to ground, immediately followed by a much faster return wave from ground back to the high voltage electrode. The wave velocity, voltage attenuation, wave form and energy carried in the wave front of the initial impulse were investigated and found, in general, to vary with both pressure and applied potential. The similarity of these results to the observations on the propagation of luminosity in long discharge tubes and in the lightning stroke are discussed. With the higher applied voltages the wave shows practically no observable distortion or attenuation so that the long discharge tube provides an excellent transmission line for many purposes.

The wave antenna: A new type of highly directive antenna

Determination of Constants from Input Impedance. Fig. 61 shows a generator (or oscillator) supplying alternating current to a line. This results in waves which travel from A to B. Assuming for the time being that there is no reflection at B and no return waves, the relation of voltage to current is E/I = Z in which Z is the surge impedance of the line. When the generator makes the point A positive with respect to ground it supplies a current in the direction A — B. Let us now imagine the generator and the absorbing terminal circuit interchanged so that the generator supplies current to the end B and the waves travel from B to A. The impedance measured at the terminals of the generator will be the same as before, but when the line is positive with respect to ground the current will be flowing in the direction B — A. Therefore if we define the voltage as positive when the line is positive with respect to ground, and the current as positive when in the direction A — B, then for waves traveling in the direction A — B the voltage is E = + Z I, but for waves traveling in the direction B — A the relation is E = — Z I.

Outline of theory of impulse currents

In Part I it is shown how, from the integral of the general differential equation of the electric circuit, which has been discussed in a previous paper, all the types of electric currents are derived as special cases, corresponding to particular values of the integration constants. The equations of the circuits with massed constants, that is, the usual electric circuits, are derived by substituting zero for the (electrical) length of the circuit. Besides the general transients, discussed in a previous paper, three main classes of currents are shown to exist, corresponding to different values of the time exponent b: The alternating currents, corresponding to b = imaginary, which are the useful currents of our electric circuits. The impulse currents, corresponding to real values of b, which may be called harmful currents of our electric circuits. And, as limit case, for b = 0, the continuous-current circuit with distributed constants. The last case, a continuous current in a circuit with distributed resistance and leakage, is discussed, and it is shown that such continuous-current circuit has many features which are usually considered as typical of alternating-current wave transmission. It consists of a main current and a return current; complete reflection occurs at the end of the circuit; partial reflection at a transition point; a surge resistance exists, which, connected to the circuit, passes the current without reflection. In Part II an outline of the theory of impulse currents is given. They comprise two classes, the non-periodic and the periodic impulse currents. The equations of both are given in different form, by exponential and by hyperbolic or trigonometric functions. Their characteristics are: Impulse current and voltage may be resolved into a main wave and a return wave. The return wave is displaced from the main wave in time and in position. A time displacement exists between the two current waves and their corresponding voltage waves. This time displacement may be a lag of the current behind the voltage, or a lead, depending on the circuit constants. In the periodic impulse currents, the displacement between main wave and return wave is represented by a position angle, and the two current waves are in quadrature in position, to their respective voltage waves. A few special cases are discussed.

Capillary electrometer records of the electrical changes during the natural beat of the frog's heart. (Preliminary communication.)

It was shown, in 1880, by Burdon-Sanderson and Page, that when the ventricle of the excised frog's heart is connected with a capillary electometer by two contacts, one lying on the base and other on the apex, then every contraction of the heart was associated with electromotive changes of the following type. The electrometer meniscus was displaced in a given direction, the displacement occurred in the opposite direction, which returned slowly; the recorded displacements are therefore of the type shown in fig. 1 of the annexed diagram. Most of these earlier experiments were carried out on the excised heart rendered motionless by a suitable ligature around the sino-auricular junction, and excited to activity by an induced current which was applied to the tissue, near one of the electrometer contacts. The observed effects were demonstrated to be due to the algebraic sum of an active process under one contact, of the propagation of this process to the tissue under the other contact, and of the occurrence of a similar active process at this further point. The two phases, such as occur in fig. 1, were further shown to be indicative of the time relations of these active processes. The electromotive change during the active process causes this tissue to become relatively negative as compared with the inactive tissue. This negativity commences under the proximal contact, nearest to the seat of excitation; its development is, however, cut short by a similar change occurring under the distal contact situated further off from the seat of excitation, thus giving the first electrometer displacement the character of a single spike. Whilst both changes are in full progress there is no electrical difference between the contacts, and thus an iso-electrical interval occurs; finally, the change outlasting the porximal one, a terminal displacement of opposite sign is produced. All these well-known results have been supposed, with little experimental warrant, to occur in the beating frog's heart in situ , and a discrepancy thus exists between the assumed electromotive phenomena of the beating frog's heart and the electrical changes actually observed in the beating heart of mammals and of man. Numerous records have been obtained in man and mammals by making use of Waller's discovery that the electrometer, when appropriately connected with the surface of the body, shows the electromotive changes which accompany each beat of the heart in situ . These have been supplemented by observations upon the exposed beating heart (Bayliss, Starling, etc.). The latest records of this type in the case of man are those which Einthoven has obtained by the use of his delicate string galvanometer. All these records differ fundamentally from the records obtained by Burdon-Sanderson with the excised heart of both the frog and the tortoise, for, although the effects are diphasic, the second phase in the mammalian heart is of the same sign as the first (as in fig. 2), instead of being of opposite sign. It has thus been suggested that there is a want of parallelism between the activities of the mammalian heart and those of the heart in the frog and the tortoise. The present experiments show that the changes observed when the frog's heart remains in situ and supplied by blood are precisely similar to those known to occur in the mammalian heart, they also bring out a further new point of no little interest, since, under certain conditions, a return wave of activity proceeding from the apex to the base is clearly demonstrable; this wave succeeds that which proceeds from the apex. It is this return wave which is largely responsible for the extensive terminal phase of the whole electromotive effect in the beating heart.