Voltage presence indicator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology
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The device is designed to check the presence or absence of direct or alternating voltage up to 380 V, determine the polarity of direct voltage and continuity of electrical circuits with a resistance of up to 20 K.
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T1-T5 - any low-power npn type transistors; diodes D1, D2 - for voltage 400 V, current not less than 0.1 A; EP1 - miniature sound transducer resist. - 8 ... 30 Ohm (used in Chinese alarm clocks or toys), resistor R2 selects the maximum resistance of the resistor being tested (about 20 K), at which the device "beeps"; resistors R1, R4, R5 and capacitor C1 adjust the frequency and maximum volume
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| Random news from the Archive Tolerance for dissonance comes with age
05.04.2015
Age-related changes in hearing are usually explained by the fact that special receptors in the inner ear die off, which catch sound vibrations and turn them into a nerve signal. As you know, sound first enters the eardrum, from it it passes to the auditory ossicles (hammer, anvil and stirrup), and from them, in turn, to the inner ear filled with liquid. Here, on the membranes of the organ of Corti, there are hair cells that react to fluctuations in the liquid medium: their hairs deviate, activating ion channels in the cell membrane. As a result of complex neurochemical processes, a mechanical vibration is converted into a neurochemical impulse, which is sent to the brain's auditory analyzer.
If there are few such hair cells, if they break down and work poorly, then hearing becomes worse: for example, we stop distinguishing high frequencies. However, there are other changes that happen in our hearing aid with age - in the brain itself, the cells responsible for processing the sound signal begin to react differently to it. In particular, their temporal activity changes: different groups of neurons, which turn on in a certain sequence in response to sound, suddenly move out of their usual "schedule". How can this affect the perception of sounds?
More recently, Oliver Bones and his colleagues at the University of Manchester have shown that the behavior of neurons over time determines the perception of sound consonances and dissonances. It would be logical to assume that age-related changes in the temporal activity of nerve cells will affect how a person hears music. To test their hypothesis, the researchers asked dozens of volunteers to rate several audio intervals on a scale from "very pleasant" to "very unpleasant". The intervals themselves ranged from a small second, which sounds very sharp, to a harmonious pure fifth (the usual uniform tempered system of European music was taken as the basis).
Then the same intervals were listened to again, but now the participants of the experiment simultaneously recorded the activity of groups of neurons from the brainstem (the same ones that distinguish dissonances from consonances). As the authors of the work in the Journal of Neuroscience write, in young people, the temporal coding of euphonies and dissonances worked perfectly. What could not be said about elderly people or people approaching old age (that is, over 40 years old) - their time differences in neural activity on consonances and dissonances were not too great. And this was reflected in the perception of intervals: older people were not as much irritated by dissonances as young people, and, on the contrary, they received less pleasure from consonances. It is worth noting that none of the participants in the experiment played any instrument and none of them tried to study music for at least the last five years, so it would be interesting to repeat the same experiment, but with professional musicians.
On the one hand, the results obtained suggest that age-related hearing changes are much more complex, that we not only begin to hear worse, but also perceive what we hear differently. On the other hand, does this mean that with age we may suddenly like dissonant music, which XX and XXI centuries. especially rich? Hardly. Indeed, in order to feel dissonance well, we must feel consonance well, and older people, as was said, are generally worse at distinguishing dissonance from consonance. However, the perception of music is still not reduced to just distinguishing between euphonious and dissonant chords, so it would not be entirely correct to say that older people in general hear music worse.
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