reception- the ability of the body to perceive information from the external and internal environment. The primary perception of all stimuli in the human body is carried out receptors- specific cells that perceive the effects of external and changes in the internal environment of the body.
Sensitivity- the ability of the body to perceive information (stimuli) from the external and internal environment and respond to it with differentiated forms of reactions.
Analyzer- a functional association of structures that performs the perception and analysis of information (receptor - pathways - cortical center).
2. Sensitivity classification:
Kinds sensitivity by modality:
1)Simple
- exteroception:distant- hearing, vision; contact- pain, tactile, temperature, feeling of pressure (pyesthesia), taste; mixed(?) – sense of smell
- interoception(chemo-, baro-, osmoreceptors),
- proprioception(joint-muscular feeling - kinesthesia, feeling of movement of the skin fold - dermatokinesthesia, vibration - seismoesthesia, sense of weight - baroesthesia).
2)Complex
- localization(topesthesia),
- discriminatory,
- two-dimensional-spatial(graphesthesia, dermatolexia),
- three-dimensional-spatial(stereognosis).
Types of sensitivity according to the level of information processing:
1)protopathic(thalamic or vital) - perceives gross influences that threaten the life of the body - fibers of type B and C.
2)epicritical(cortical, gnostic) - provides subtle recognition and differentiation of various influences - fibers of type A.
Gued-Scherer law(1905) - in the process of regeneration of the sensory nerve, first the restoration of protopathic, and then epicritical sensitivity occurs.
3. Peripheral components of the sensitivity system:
Types of contact exteroreceptors:
1)Painful: nociceptor - nociceptive system (see below).
2)Temperature: warm - Ruffini's ending and cold - Bulb Krause.
3)Tactile(1 type of receptors - with small, delineated fields) : Merkel disc (slowly adapting) and Meissner corpuscle (rapidly adapting).
4)pressures and weights(type 2 receptors - with extensive fields) : the body of Golgi-Mazzoni (slowly adapting) and the body of Vater-Pacchini (quickly adapting).
5) vibrations- periosteal receptors
Types proprioceptors (for details, see the topic "Reflex-motor sphere"):
1)muscle spindles 1 and 2 types.
2)tendon receptors(Golgi body).
Types sensitive fibers:
1)thick myelin type A-alpha(40-50 m/s) - proprioception;
2)thick myelin type A-beta(30-40 m/s) - tactile;
3)thick myelin type A-gamma(20-30 m/s) - pressure;
4)thin myelin type B(10-14 m/s) - pain and temperature;
5)unmyelinated type C(2 m/s) - pain (protopathic).
Sensitivity: morphophysiology
1. General features of the three-neuronal pathways of superficial and deep sensitivity
First the neuron is located in the spinal (cranial) node.
axons second neurons cross over.
Third neuron located in the ventrolateral complex of the thalamus, its axon - thalamocortical path passes through the posterior third of the posterior leg of the internal capsule and the radiant crown, ends in the posterior central gyrus and the upper parietal region.
Do you know anyone with heightened sensitivity and heightened perception? Have you ever paid attention to highly sensitive, emotional people among colleagues, friends or relatives? Or maybe you belong to their circle?
For those who hear about it for the first time, I will talk about the terms "high sensitivity" and "highly sensitive person." They were offered in the mid-90s American psychologist and psychotherapist Elaine Ayron. It is not a diagnosis or a disorder. This is an innate feature of temperament and personality. Such a person perceives any incoming information very intensively. Most often, these people are very emotional, they have increased both physical and emotional sensitivity.
We are all sensitive to one degree or another, we receive information from our nervous system and somehow react to it. What is the difference between ordinary people and highly sensitive people? The latter perceive information as if it is not filtered.
I am sometimes asked, is being highly sensitive and emotional the same as being an introvert? Hypersensitivity has nothing to do with introversion or extraversion. Some highly sensitive people are closer to introverts, while others can be considered extroverts.
What do they perceive and feel more intensely? Noises, smells, touches, emotions and behavior of others, emotional connection with others, "energy" of the environment.
Instead of accepting my features, I resisted, ignored them, moved away from my true nature.
Such people think deeply, love deep conversations. They often ask themselves the question of the purpose in life, starting from early childhood to ask themselves: “Why do I live on this Earth?” Often they have a deep connection with nature, they have developed intuition, they are very spiritual.
Personally, I remember that from early childhood I began to think about the meaning of life and my purpose. At some point, I realized that I perceive emotions, smells, noises, touches sharply and have amazing intuition. Sometimes all this disorientated me. For a long time I did not trust myself, my intuition, receptivity. Instead of accepting my features, I resisted, ignored them, moved away from my true nature, because it seemed to me that something was wrong with her. It took me a long time to accept this gift.
I once came across Dr. Elaine Ayron's book on hypersensitivity. I immediately fell in love with this book - it gave me the opportunity to learn more about the gift that I was endowed with. The book opened my eyes and allowed me to look at myself from a different perspective.
I began to look for information about these features and learned a lot about myself. It was the first step towards overcoming resistance and accepting the real you. Curiosity pushed me to go further along the path of self-exploration, and I learned to better understand my inner self and appreciate increased emotional sensitivity.
From that moment I was able to accept myself and understand that my features are both a gift and a source of vulnerability. I have learned a lot! For example, I often began to arrange "dates with myself", carefully studying myself, learning to be more balanced. I know that taking care of myself is my responsibility, and I take it seriously, further training self-discipline.
1. They have very strong intuition.
2. They have developed emotional empathy - they understand well what the other person thinks and feels.
3. They are great at listening.
4. They notice flaws and gaps in various systems.
5. They are generous and thoughtful.
6. They are responsible and reliable.
7. They are ready to talk openly about what others are afraid to talk about.
8. They are spiritually advanced.
9. They are close to nature.
10. They are good at noticing emotional imbalances in relationships in families, between partners or friends, in various groups and teams.
11. They have a developed sense of beauty.
12. Justice is important to them.
13. They have fast thinking.
14. They are able to analyze problems instantly.
15. They are innovators.
16. They have a special understanding of harmony - in colors, sounds, music.
17. They are often very talented in one or more areas.
18. They have developed deep emotional bonds with friends, partners, relatives, nature, animals, and the world.
19. They are usually very devoted.
All this sounds great. But it often happens that highly sensitive people who have not yet realized all the benefits of their gift, really suffer from it. And at the same time they put themselves in the position of a victim.
How to stop feeling like a victim?
First of all, understand that you have such a personal feature. It must be recognized and accepted. You need to learn more about yourself and your features, show curiosity in order to better understand yourself. Learn to treat yourself with kindness and compassion.
Connect with that vulnerable part of yourself that is associated with hypersensitivity. Accept your vulnerability and realize that it is a valuable gift. When taking it, do not forget to take care of yourself, taking into account your own characteristics. It is important to take responsibility for your life, to maintain energy balance. I hope that most highly sensitive people will be able to perceive their features not as a curse, but as a gift worth sharing with the world!
about the author
Coach, psychotherapist, osteopath, naturopath and yoga instructor with over 20 years of experience.
Sensitivity (we consider the concept in the framework of physiology) is one of the most important properties, which is possessed by both a person and any other living organism. Therefore, it requires detailed consideration. In the article we will present the types of sensitivity according to a number of classifications, as well as the types of its violations.
What is this?
All types of sensitivity in physiology are:
- Part of the reception perceived by the psyche. Reception - afferent impulses entering the departments of the central nervous system.
- The ability of a living organism to perceive various stimuli that come from both its own organs and tissues, and from the environment.
- The ability of the organism, preceding a differentiated response to a stimulus - reactivity.
And now - the classification of types of sensitivity.
General sensitivity
Several groups stand out here at once - we will present their content separately.
The exteroceptive type (superficial sensitivity) within itself is divided into:
- tactile (rough);
- painful;
- temperature (cold and heat).
Proprioceptive type (deep sensitivity) - a sense of oneself in space, the position of one's body, limbs relative to each other. This view has the following categories:
- feeling of own body weight, pressure;
- vibration;
- sense of touch (tactile light);
- joint-muscular;
- kinesthesia (the so-called determination of the movement of skin folds).
Complex types of sensitivity:
- The feeling is two-dimensional and spatial - with its help we determine the place of touch to our body. It helps to find out what symbol, number or letter is "written" on the skin with the finger of another person.
- Interoceptive - this sensitivity causes irritation of internal organs.
- Discriminatory - helps to distinguish between touches, skin injections that are applied at a close distance to each other.
- Stereognosis - this type of sensitivity helps to recognize a particular object by touch.
As for the above examples, their identification will be possible only with further input and processing of the impulse from the primary cortical layer of the analyzer (it will be the central posterior gyrus) into associative or secondary cortical fields. The latter are predominantly located in the parieto-postcentral zones, in the lower and upper parietal lobes.
Let's move on to the next classification.
General and special sensitivity
The same concepts are used here, only for a slightly different classification.
General sensitivity is divided into simple and complex.
Special sensitivity is represented by the following categories:
- visual;
- taste;
- olfactory;
- auditory.
Complicated Sensitivity
In this classification, we will consider different kinds sensitivity - characteristic not only for humans, but for all living beings in general.
It's the following:
- Vision is the body's perception of light.
- Echolocation, hearing - perception by living systems of sounds.
- Smell, taste, stereochemical sense (typical for insects and hammerhead sharks) - the chemical sensitivity of the body.
- Magnetoreception - the ability of a living being to feel a magnetic field, which allows you to navigate the terrain, determine the height, plan movement own body. The type of sensitivity is characteristic of some sharks.
- Electroreception - the ability to sense the electrical signals of the surrounding world. Used to search for prey, orientation, various forms of biocommunication.
According to phylogenetic criteria of formation
The classification was proposed by the scientist G. Head. There are two kinds of sensitivity of a human being, a living being:
- Protopathic. A primitive form that has its center in the thalamus. Cannot give a precise definition of the localization of the source of irritation - neither external nor inside one's own body. It no longer reflects objective states, but subjective processes. Protopathic sensitivity ensures the perception of the strongest, coarsest forms of stimuli, pain and temperature, which are dangerous to the body.
- Epicritical. Has a cortical center, is more differentiated, objectified. Phylogenetically considered younger than the first. Allows the body to perceive more subtle stimuli, evaluate their degree, quality, localization, nature, and so on.
Location of receptors
This classification was proposed in 1906 by the English physiologist C. Sherrington. He proposed to divide all sensitivity into three categories:
Varieties of skin sensitivity
Classical physiology distinguishes the following types of skin sensitivity:
- Pain. Occurs under the influence of stimuli that are destructive in their strength and nature. She will talk about a direct danger to the body.
- Thermal (temperature) sensitivity. It allows us to determine hot, warm, cold, icy. Its greatest importance is for the reflex regulation of the body.
- Touch and pressure. These feelings are connected. Pressure, in fact, is a strong touch, so there are no special receptors for it. Experience (with the participation of vision, muscle feeling) allows you to accurately localize the area affected by the stimulus.
In some classifications, the varieties of skin sensitivity will be divided in this way:
- Pain.
- Feeling cold.
- Touch.
- Feeling warm.
Types of sensation thresholds
Now consider the classification of types of sensitivity thresholds:
- The absolute lower threshold of sensation. This is the smallest strength or magnitude of the stimulus at which its ability to cause nervous excitation in the analyzer is preserved, sufficient for the occurrence of one or another sensation.
- The absolute upper threshold of sensation. On the contrary, the maximum value, the strength of the stimulus, beyond which the body no longer perceives it.
- The threshold of discrimination (or difference threshold of sensation) is the smallest difference in the intensity of two identical stimuli that a living organism can sense. Note that not every difference will be felt here. It needs to reach a certain size or strength.
Varieties of disorders
And now - types of disorders of sensitivity. The following stands out here:
- Anesthesia is the name given to the complete loss of some type of sensation. There is thermal (thermoanesthesia), tactile, pain (analgesia). There may be a loss of a sense of stereognosis, localization.
- Hypesthesia - this is the name of a decrease in sensitivity, a decrease in the intensity of certain sensations.
- Hyperesthesia is the opposite of the previous phenomenon. Here the patient has an increased sensitivity to certain stimuli.
- Hyperpathia - cases of perversion of sensitivity. The quality of sensation changes - point irritations crumble, some qualitative differences between the stimuli in the patient are erased. The sensation is painted in painful tones, it can be purely unpleasant. The aftereffect is also diagnosed - the sensation continues to remain after the cessation of the stimulus.
- Paresthesia - a person experiences any sensations without the presence of their stimuli. For example, "crawling", a sharp sensation - "as if thrown into a fever", burning, tingling, and so on.
- Polyesthesia - with such a violation, a single sensation will be perceived by the patient as multiple.
- Dysesthesia is a perverted perception of a particular stimulus. For example, touch feels like a blow, cold feels like heat.
- Synesthesia - a person will perceive the stimulus not only in the location of its direct impact, but also in a different zone.
- Allocheiria - a violation, something related to the previous one. The difference is that a person feels the impact of the stimulus not in the location of its impact, but in a symmetrical area of the opposite part of the body.
- Thermalgia - cold, heat are painfully perceived by the patient.
- Dissociated sensory disorder - a case in which a certain sensation is disturbed, but all others are preserved.
Types of disorders
Types of sensory impairment can be divided into the following categories:
- Cortical type. This is a sensory disorder that will be observed on opposite side body.
- Conductor type. Defeat of the conducting ways of sensitivity. Disorders will be found downward from the location of this lesion.
- Dissociated (segmental). It will be observed in case of damage to the sensitive nuclei of the cranial nerve of the brain stems, as well as in case of damage to the sensitive apparatus related to spinal cord.
- Distal (polyneuric) type. Multiple lesions affecting peripheral nerves.
- peripheral type. It is characterized by damage to the peripheral nerves and their plexuses. Here there is a disorder of all kinds of sensations.
Sensitivity is a fairly broad phenomenon in understanding. Evidence of this is the large number of classifications that internally divide it into multiple groups. Also today, a variety of types of sensitivity disorders have been established, the gradation of which is associated with the localization of the lesion, the manifestation of sensations in the patient.
Naturally, we are interested in reducing the probability of a type II error as much as possible, that is, increasing the sensitivity of the criterion. To do this, you need to know what it depends on. In principle, this problem is similar to the one that was solved in relation to type I errors, but with one important exception.
To evaluate the sensitivity of a test, you need to specify the amount of difference that it should detect. This value is determined by the objectives of the study. In the diuretic example, the sensitivity was low - 55%. But, perhaps, the researcher simply did not consider it necessary to detect an increase in diuresis from 1200 to 1400 ml / day, that is, by only 17%?
As the data scatter increases, the probability of both types of errors increases. As we will see shortly, it is more convenient to account for the magnitude of the differences and the spread of the data together by calculating the ratio of the magnitude of the differences to the standard deviation.
The sensitivity of a diagnostic test can be increased by reducing its specificity - a similar relationship exists between the level of significance and the sensitivity of the test. The higher the significance level (that is, the smaller a), the lower the sensitivity.
As we have already said, the most important factor that affects the probability of both type I and type II errors is the sample size. As the sample size increases, the probability of error decreases. In practice, this is very important, since it is directly related to the design of the experiment.
Before proceeding to a detailed consideration of the factors affecting the sensitivity of the criterion, we list them again.
Significance level a. The smaller a, the lower the sensitivity.
The ratio of the size of the differences to the standard deviation. The larger this ratio, the more sensitive the criterion.
Sample size. The larger the volume, the higher the sensitivity of the criterion.
Significance level
To get a visual representation of the relationship between the sensitivity of the criterion and the level of significance, let's return to Fig. 6.3. By choosing the significance level a, we thereby set the critical value of t. We choose this value so that the proportion of values that exceed it - provided that the drug has no effect - is equal to a (Fig. 6.3A). The sensitivity of the criterion is the proportion of those values of the criterion that exceed the critical one, provided that the treatment has an effect (Fig. 6.3B). As can be seen from the figure, if the critical value is changed, this share will also change.
Let's take a closer look at how this happens.
On fig. 6.4A shows the distribution of Student's t-test values. Difference from fig. 6.3 is that this is now the distribution obtained for all 1027 possible pairs of samples. The top graph is the distribution of t values for the case when the drug does not have a diuretic effect. Suppose we chose a significance level of 0.05, that is, we took a = 0.05. In this case, the critical value is 2.101, which means we reject the null hypothesis and accept the differences as statistically significant at t > +2.101 or t. Now look at Fig. 6.4B. It shows the same distributions of t values. The difference in the chosen significance level is a = 0.01. The critical value of t has increased to 2.878, the dotted line has shifted to the right and cuts off only 45% of the lower plot. Thus, when moving from 5% to 1% significance level, the sensitivity decreased from 55 to 45%. Accordingly, the probability of a type II error increased to 1 - 0.45 = 0.55.
So, by reducing a, we reduce the risk of rejecting the correct null hypothesis, that is, finding differences (effect) where there are none. But by doing so, we also reduce sensitivity - the probability of detecting differences that actually exist.
Size of difference
Considering the influence of the significance level, we took the magnitude of the differences constant: our drug increased the daily diuresis from 1200 to 1400 ml, that is, by 200 ml. Now let's accept
constant significance level a = 0.05 and see how the sensitivity of the test depends on the magnitude of the differences. It is clear that large differences are easier to identify than small ones. Consider the following examples. On fig. 6.5A shows the distribution of t values for the case when the study drug does not have a diuretic effect. Hatched are 5% of the largest absolute values of t located to the left - 2.101 or to the right +2.101. On fig. 6.5B shows the distribution of t values for the case when the drug increases the daily
Increase in daily diuresis, ml
diuresis by an average of 200 ml (we have already considered this situation). Above the right critical value lies 55% of the possible values of t: the sensitivity is 0.55. Next, in fig. 6.5B shows the distribution of t values for the case when the drug increases diuresis by an average of 100 ml. Now only 17% of t values exceed 2.101. Thus, the sensitivity of the test is only 0.17. In other words, the effect will be found in less than one out of every five comparisons between the control and experimental groups. Finally, fig. 6.5D represents a case of increased diuresis by 400 ml. 99% of the values of t fell into the critical region. The sensitivity of the test is 0.99: differences will almost certainly be detected.
By repeating this thought experiment, one can determine the sensitivity of the test for all possible effect values, from zero to "infinite". Plotting the results on a graph, we get Fig. 6.6, where the sensitivity of the test is shown as a function of the magnitude of the differences. From this graph, you can determine what the sensitivity will be for a particular effect size. So far, the graph is not very convenient to use, because it is only suitable for this group size, standard deviation, and significance level. We will build another chart soon, more suitable for research planning, but first we need to understand more about the role of dispersion and group size.
Scatter of values
The sensitivity of the test increases with the observed differences; as the spread of values increases, the sensitivity, on the contrary, decreases.
Recall that Student's t-test is defined as follows:
where X1 and X2 are averages, s is the combined score of the standard
deviations a, n1 and n2 are sample sizes. Note that x1 and
X2 are estimates of two (different) means - p and p2. For simplicity, we assume that the volumes of both samples are equal, that is, n1 = n2. Then the computed value of t is an estimate of the quantity 
P1-P2 P-P
Thus, t depends on the ratio of the effect size to the standard deviation.
Let's look at a few examples. The standard deviation in our study population is 200 ml (see Fig. 6.1). In this case, an increase in daily diuresis by 200 or 400 ml is equal to one or two standard deviations, respectively. These are very noticeable changes. If the standard deviation were 50 ml, then the same changes in diuresis would be even more significant, amounting to 4 and 8 standard deviations, respectively. Conversely, if the standard deviation were, for example, 500 ml, then the change in urine output in 200 ml would be 0.4 standard deviation. Finding such an effect would be difficult and hardly worth it at all.
So, the sensitivity of the test is affected not by the absolute magnitude of the effect, but by its ratio to the standard deviation. Let's denote it f (Greek "phi"); this ratio φ = 5/a is called the noncentrality parameter.
Sample size
We have learned about two factors that affect the sensitivity of a test: the significance level a and the non-centrality parameter φ. The more a and the more f, the more feeling
validity. Unfortunately, we cannot influence at all, and as for a, its increase increases the risk of rejecting the correct null hypothesis, that is, finding differences where there are none. However, there is one more factor that we can, within certain limits, change at our discretion without sacrificing the level of significance. We are talking about the sample size (number of groups). With an increase in the sample size, the sensitivity of the test increases.
There are two reasons why increasing the sample size increases the sensitivity of the test. First, increasing the sample size increases the number of degrees of freedom, which in turn reduces the critical value. Secondly, as can be seen from the formula just obtained
the value of t grows with the sample size n (this is also true for many other criteria).
Figure 6.7A reproduces the distributions from fig. 6.4A. The upper graph corresponds to the case when the drug does not have a diuretic effect, the lower one - when the drug increases daily diuresis by 200 ml. The number of each group is 10 people. Figure 6.7B shows similar distributions. The difference is that now each group included not 10, but 20 people. Since the size of each of the groups is 20, the number of degrees of freedom is V = 2(20 - 1) = 38. From Table 4.1, we find that the critical value of t at the 5% significance level is 2.024 (in the case of samples of size 10, it was 2.101). On the other hand, an increase in the sample size led to an increase in the values of the criterion. As a result, not 55, but 87% of the values of t exceed the critical value. So, increasing the size of the groups from 10 to 20 people led to an increase in sensitivity from 0.55 to 0.87.
Going through all possible sample sizes, you can plot the sensitivity of the test as a function of the size of the groups (Fig. 6.8). With increasing volume sensitivity
is growing. At first, it grows rapidly, then, starting from a certain sample size, the growth slows down.
Sensitivity calculation is the most important component planning medical research. Now, having become acquainted with the most an important factor, which determines the sensitivity, we are ready to solve this problem.
How to determine the sensitivity of a criterion?
On fig. 6.9 the sensitivity of the Student's test is presented as a function of the non-centrality parameter f = 5/s at a significance level a = 0.05. The four curves correspond to the four sample sizes.
The samples are assumed to be of equal size. What if it's not? If you refer to Fig. 6.9 when planning a study (which is very reasonable), then you need to consider the following. For a given total number of patients, it is precisely the equal number of groups that ensures maximum sensitivity. So, an equal number of groups should be planned. If, however, you decide to calculate sensitivity after the study, when, having found no statistically significant difference, you want to determine the extent to which this can be considered evidence of no effect, then you should take the size of both groups equal to the smaller of them. This calculation will give a somewhat underestimated sensitivity, but will save you from being overly optimistic.
Let's apply curves from fig. 6.9 for example with a diuretic (see fig. 6.1). We want to calculate the sensitivity of Student's t-test at a significance level of a = 0.05. The standard deviation is 200 ml. What is the probability of detecting an increase in daily diuresis by 200 ml?
The number of control and experimental groups is ten. We choose in Fig. 6.9 the corresponding curve and find that the sensitivity of the criterion is 0.55.
So far, we have been talking about the sensitivity of the Stew test.
Sample size
Halothane and morphine in open heart surgery
In ch. In Table 4, we compared the cardiac index during halothane and morphine anesthesia (see Table 4.2) and did not find statistically significant differences. (Recall that the cardiac index is the ratio of the minute volume of the heart to the surface area of the body.) However, the groups were small - 9 and 16 people. The mean CI in the halothane group was 2.08 L/min/m2; in the morphine group 1.75 l/min/m2, i.e. 16% less. Even if the differences were statistically significant, such a small difference would hardly be of any practical interest.
So let's put the question this way: what was the probability of detecting a difference of 25%? The combined variance estimate is s2 = 0.89, so the standard deviation is 0.94 l/min/m2. Twenty five percent of 2.08 l/min/m2 is 0.52 l/min/m2.
Thereby,
5 _ 0.52 o ~ 0.94
Since the sizes of the groups do not match, we will choose the smallest of them - 9 - to estimate the sensitivity. 6.9 it follows that in this case the sensitivity of the criterion is 0.16.
The chances of detecting even a 25% difference were very small. Let's summarize.
The sensitivity of a test is the probability of rejecting the false hypothesis of no difference.
The sensitivity of the test is affected by the significance level: the smaller a, the lower the sensitivity.
The larger the effect size, the greater the sensitivity.
The larger the sample size, the greater the sensitivity.
Sensitivity is calculated differently for different criteria.
Of all the characteristics of the speakers and acoustic systems the concept of "sensitivity" is perhaps the most interesting and attractive (in this it competes with the power characteristic). One would like this concept to be directly dependent on the quality of the speaker, i.e. the larger this parameter, the better the speaker sounds. After all, an acoustic system is a device for playing music, and its quality is often determined only in a subjective way, and sensitivity - from the word feel, feeling well, subconsciously merges with the word quality. However, we know that this is not the case. First of all, this concept is purely technical, reflecting the efficiency of the speaker. According to GOST 16122-78, the characteristic sensitivity of the speaker is the ratio of the average sound pressure developed by the speaker in a given frequency range (usually 100 ... 8000 Hz) on the working axis, reduced to a distance of 1 m and the input electrical power 1 W. Of course, if we have a speaker with a higher sensitivity, then by supplying 1 W we will get more sound pressure than from a speaker with a low sensitivity, less non-linear distortion and, probably, more high quality sound. However, it is worth considering how this sensitivity is obtained?
We have several legal (real) and illegal (marketing) ways to increase sensitivity.
Real ways to fight for sensitivity
Acoustic systems with big amount speakers
When connecting several speakers (acoustic systems) in parallel (in series), the volume level increases (and the power also increases). It is used for sound systems and due to the variability in the characteristics of broadband speakers, the sound quality remains low. Often the method is used in acoustic systems where 2 or more woofers are used for one tweeter. In this case, the main problem is the features of the directivity characteristic of such a system.
Increasing the sensitivity of single speaker systems
The speaker, acoustic system is an electro-mechanical-acoustic transducer and, as a result, it is possible to increase the efficiency of the system at each stage of this transformation.
Electro-mechanical coupling factor (BL) speaker
The first stage is electro-mechanical transformation. For this, the coefficient "BL" is introduced. It depends on "B" - induction in the gap and "L" - the length of the conductors in this gap (or the number of conductors on which the magnetic field acts). "B" can be increased by increasing the volume and strength of the magnets, reducing the magnetic gap both in height and in width. "L" - increasing the diameter of the coil and the number of turns in height in the gap. If you increase the value of "BL", without changing the other characteristics of the speaker, then the sensitivity in the area above the main resonance of the speaker will increase, and the low-frequency capabilities will remain unchanged.
Mass of the moving system
By reducing the mass of the moving system, we can create more pressure than with a larger mass. This improves the impulse and transient characteristics, but reduces strength (power), stiffness (nonlinear distortion may increase) and will require the use of new materials and technologies. Receiving low frequencies, especially deep ones, requires a lot of effort.
Radiation area
Increasing the area of the diffuser leads to an increase in the level of sensitivity, but there are problems with the reproduction of high frequencies and the strength of the structure.
Acoustic transformation - horn
This method allows you to get low frequencies from a small and light speaker by matching it with environment. It requires a lot of effort in terms of building buildings. The most competent, but also the most expensive way.
Well-designed loudspeakers with really high sensitivity use the last four methods, and sometimes the first. As shown, this requires spending large amounts of money, increasing the cost of the system and increasing its size, however, you can do it easier.
Illegal way
Recall that the sensitivity is measured on the axis, at a distance of 1 meter when summing up 1 W of power. How to get this 1W? To do this, you need to determine the nominal resistance. It is selected from a range of 2, 4, (6), 8, 16, 25 and 50 ohms. Since the speaker is a complex resistance with a complex dependence of the total electrical resistance from frequency, the definition of this resistance obeys the law. For example, this is written in GOST 9010-84 “The measured minimum value of the electrical impedance modulus in the range lying above the fundamental resonance frequency should not differ from the nominal electrical resistance by more than minus 20%.” Thus, the value of the total electrical resistance modulus of a 4-ohm system cannot be less than 3.2 Ohm, and of an 8-ohm system - 6.4 Ohm, etc. Then, according to Ohm's law, to measure a speaker with a nominal resistance of 4 Ohms, we must bring 2 Volts (root of 4) to it, 8 Ohms - 2.82V, and for 16 Ohms - 4 V.
In Western descriptions and passports, the “sensitivity” column is often found, with a characteristic of 1m / 2.8V, in combination with “resistance”, for example, 6 ohms. When measuring, it turns out that the minimum resistance of such a product is 3.4 Ohm. So the system turns out to be really 4 Ohm, and we apply 2 W to it (According to Ohm's law 2.8V2 / 4 \u003d 2W) and we get a sensitivity increase of 3 dB. In addition to this, frequency response, especially the speakers separately, has areas of dips and rises, which allows you to fix the sensitivity in the area of this rise. Not to mention the possibility of a simple postscript. As a result, we easily get an increase in the sensitivity value of 4-8 dB. The measurement of acoustic systems of Western manufacturers, including eminent ones, unfortunately, showed that this practice is common and is used, with rare exceptions, everywhere.
What is it for?
It's all about low frequencies, because. the level of low frequencies when indicating the frequency range in the passport, and when listening, is measured precisely from the average sound pressure level - sensitivity and, therefore, systems with real low sensitivity have a gain in the number and depth of low frequencies. And getting deep low frequencies and high sensitivity with a certain size of speakers and acoustic systems is very difficult. After all, you can’t write a sensitivity of 80dB in your passport, no one will buy it! It is much easier to write a normal level of sensitivity and when listening to give the client a mighty bass.
This text is not written to accuse someone of falsification, but to provide the consumer with more complete information.
