Abstract:
An educational system for visualizing sound by a student in a laboratory. The system includes a speaker powered by an audio amplifier. A function generator or a microphone controls the amplitude and frequency of pressure waves originating from the speaker. A model of the ear canal is suspended over the speaker, the model having a plastic pipe with two open ends and a membrane stretched taut over one of the open ends with constant tension. A mirror is affixed to the membrane, creating a mass-loaded membrane. A laser pointer emits light directed toward the mirror. A screen receives a light reflection pattern created by the light reflected from the mirror, with the model ear canal, speaker, membrane, and mirror placed equidistant between the screen and the laser pointer. The system is adapted to demonstrate hearing sensitivity to a deaf or hearing-impaired person in an educational setting.

Description:
RELATED APPLICATION 
     This application claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 61/908,234, filed on Nov. 25, 2013, the contents of which are incorporated in this application by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to hearing systems and, more particularly, to an electro-optical eardrum that allows the deaf or hearing-impaired to visualize sound. 
     BACKGROUND OF THE INVENTION 
     The purpose of the auditory system in mammals is to convert sound (pressure) waves into electrical signals that the brain can interpret. The human ear  1  is divided into the outer ear  10 , the middle ear  20 , and the inner ear  30  as shown in  FIG. 1  and explained, for example, in Reece et al.,  Campbell Biology  at pages 1090-94 (9th ed., Pearson Education Inc., 2011). The outer ear  10  includes the pinna  12 , a curved external cartilage which “catches” sound waves and directs them into the auditory canal  14 . At the end of the auditory canal  14 , separating the outer ear  10  and the middle ear  20 , is the eardrum  16 . The eardrum  16  is also known as the tympanic membrane, is taut, and is pushed inward and outward via sound pressure waves. 
     The three bones of the middle ear  20  are collectively called the ossicles or the auditory ossicles. Starting proximate the eardrum  16 , the bones are the malleus  22  (also known as the hammer), the incus  24  (also known as the anvil), and the stapes  26  (also known as the stirrup). The ossicles are contained within the middle ear  20  and transmit sounds from the air to the fluid-filled labyrinth called the cochlea  32 , which is located in the inner ear  30  along with the semicircular canals  34 . The ossicles are arranged so that movement of the eardrum  16  causes movement of the malleus  22 , which causes movement of the incus  24 , which causes movement of the stapes  26 . The ossicles are coupled to the eardrum  16  and consequently vibrate when the eardrum  16  oscillates. All the vibrational energy of the eardrum  16  is concentrated on the much smaller surface area of the ossicles. This increases the pressure about fifteen to thirty times, thereby amplifying the sound. 
     Once a sound propagates through the middle ear  20 , it comes to the faceplate of the stapes  26  resting against the cochlea  32 , which is the starting point of the inner ear  30 . Thousands of hair-like nerve cells line the length of the cochlea  32 . Each hair cell has a particular resonant frequency. When the stapes  26  vibrates in the middle ear  20 , it strikes the faceplate of the cochlea  32 . The round window  36  is one of the two openings into the inner ear  30 . The round window  36  is closed from the middle ear  20  by the round window membrane, which vibrates and moves fluid in the cochlea  32 , which in turn ensures that hair cells of the basilar membrane will be stimulated. Thus, the strike of the stapes  26  sends a compression wave through the cochlea  32  and, as the wave travels, if its frequency matches with the natural frequency of any hair cells, those hair cells will resonate and vibrate with larger amplitude. This increased movement initiates nerve cells to emit electrical impulses to the brain for processing. 
     More specifically, the vestibulocochlear nerve has two branches: the vestibular nerve  52  and the cochlear nerve  54 . The vestibular nerve  52  transmits spatial orientation information from the three semicircular canals  34  to the brain. The cochlear nerve  54  carries signals from the cochlea  32  of the inner ear  30  directly to the brain. 
     The middle ear  20  opens into the Eustachian tube  40 , which connects to the pharynx via the opening  42  and equalizes pressure between the middle ear  20  and the atmosphere. The balance portion of the inner ear  30  includes the three semicircular canals  34 . Arterial supply of blood to the ear  1  is provided, in part, through the internal carotid artery  50 . The styloid bone  56  is a slender pointed piece of bone just below the ear  1 . The styloid bone  56  projects down and forward from the inferior surface of the temporal bone, and serves as an anchor point for several muscles associated with the tongue and larynx. 
     The human ear can generally hear sounds with frequencies between 20 Hz and 20 kHz (the audio range). Although hearing requires an intact and functioning auditory portion of the central nervous system as well as a working ear  1 , human deafness (extreme insensitivity to sound) most commonly occurs because of abnormalities of the inner ear  30 , rather than in the nerves or tracts of the central auditory system. There are two types of deafness: conductive and sensorineural. Conductive deafness occurs when sound waves cannot enter the inner ear  30 . Usually caused by physical impedance, conductive deafness can result from infection, perforation of the eardrum  16 , loud noises, etc. Sensorineural deafness most commonly involves damaged hair cells, auditory nerves, or auditory processing in the brain. Sensorineural deafness can be caused by genetics, viral infections, inflammation, multiple sclerosis, and stroke. 
     A number of solutions have been proposed to address the problem of deafness. For example, U.S. Pat. No. 8,396,239 issued to Fay et al. discloses an optical electro-mechanical hearing device with combined power and signal architectures. An audio signal transmission device includes a first light source and a second light source configured to emit a first wavelength of light and a second wavelength of light, respectively. The first detector and the second detector are configured to receive the first wavelength of light and the second wavelength of light, respectively. A transducer electrically coupled to the detectors is configured to vibrate at least one of an eardrum or ossicle in response to the first wavelength of light and the second wavelength of light. The first detector and second detector can be coupled to the transducer with opposite polarity, such that the transducer is configured to move with a first movement in response to the first wavelength and move with a second movement in response to the second wavelength, in which the second movement opposes the first movement. 
     Others have addressed the problem of deafness by converting sound signals into other media. In U.S. Pat. No. 3,766,311, for example, Boll teaches a sensory substitution system. The system converts electrically coded information into selective, intelligible, localized cooling of a receptive heat-producing medium, e.g., a human body. In combination with a microphone, amplifier, and filters for producing the electrically coded information, the system enables a deaf person to perceive auditory information in the form of distinguishable localized cooling of the skin. Advantageously, the selective, localized cooling of the skin is achieved by covering a portion of the body with an apertured insulating medium and selectively gating body-produced heat through the medium. In preferred embodiments, the selective gating is achieved by a vibrating disc driven by a vibrating reed which, in turn, is driven by a piezoelectric element. 
     Similarly, in U.S. Patent Application Publication No. 2010/0013612, Zachman discloses an electro-mechanical system designed to help the hearing impaired. The system has a plurality of servo actuators each associated with a particular segment of a predetermined frequency domain. The servo actuators drive tactile stimulators which engage the skin of the hearing-impaired person in patterns that are unique to individual inputs thereby enabling the hearing-impaired person to “hear” signals within the defined frequency domain. 
     Others seek to assist the deaf by proposing methods and devices for image display of sound waves. For example, in U.S. Pat. No. 3,831,434, Greguss discloses an apparatus that uses a piezo-optic cell having a thin layer of aligned liquid crystals which is illuminated by polarized light and viewed through a polarized analyzer to give a real-time visual image in color of the acoustic wave pattern incident on the cell. The acoustic wave pattern is typically an acoustic image of an insonified object such that the resulting device is useful in non-destructive testing for industry and medicine. The acoustic wave pattern can also be the human voice (helpful in teaching speech to the deaf) and music (for pleasurable and informative visualization of the musical sound). By use of a reference acoustic wave this device may be utilized to obtain a holographic image. 
     Despite the existence of the devices summarized above, science educators have yet to address many of the problems that arise when attempting to teach deaf or hearing-impaired students. One of the important responsibilities for such educators is ensuring that students possess the proper tools and accommodations to examine phenomena in a laboratory setting. It is the job of the educator to innovate methods and devices that enable students with disabilities to participate in all aspects of investigations. 
     None of the existing devices summarized above can be used in an educational setting to demonstrate hearing sensitivity to a deaf or hearing-impaired person. To overcome the shortcomings of the existing devices, a new electro-optical eardrum is provided as part of an experimental educational system. An object of the present invention is to provide a real-time display of the sound suitable for educational applications and the like. A related object is to reproduce adequately sounds with frequencies between 20 Hz and 20 kHz (the audio range). Another object is to avoid physically contacting the student, and particularly the skin of a person, especially via a device that must be worn or carried on the person. It is still another object of the present invention to use relatively simple and inexpensive components, which fall within the limited budgets of educational institutions, while avoiding components that are complex, expensive, or both. 
     An introductory physics laboratory experiment at a typical university guides students through several computer simulations investigating the properties of waves and wave interference. After the simulations, students are prompted to determine the minimum and maximum frequencies they can hear using a basic function generator and headphones. Educators have inadequately addressed, to date, the problem of how they would include a deaf student in the experiment while the other students are listening to headphones to determine their personal hearing sensitivities. Therefore, a need exists to allow a student, particularly but not limited to a deaf student, to determine the hearing sensitivity of an electro-optical eardrum when unable to do so personally and without assistance. 
     BRIEF SUMMARY OF THE INVENTION 
     To meet this and other needs, and in view of its purposes, the present invention provides an electro-optical eardrum that allows the deaf to visualize sound. More particularly, in a specific embodiment of the invention an experimental accommodation allows a deaf student to determine and plot the sensitivity of an electro-optical eardrum in a particular sound range (e.g., 10-150 Hz). 
     The educational system for visualizing sound by a student in a laboratory, according to an embodiment of the invention, includes a speaker powered by an audio amplifier. A function generator or a microphone controls the amplitude and frequency of pressure waves originating from the speaker. A model of the ear canal is suspended over the speaker, the model having a plastic pipe with two open ends and a membrane stretched taut over one of the open ends with constant tension. A mirror is affixed to the membrane, creating a mass-loaded membrane. A laser pointer emits light directed toward the mirror. A screen receives a light reflection pattern created by the light reflected from the mirror, with the model ear canal, speaker, membrane, and mirror placed equidistant between the screen and the laser pointer. The system is adapted to demonstrate hearing sensitivity to a deaf or hearing-impaired person in an educational setting. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures: 
         FIG. 1  illustrates the human auditory system; 
         FIG. 2A  illustrates an experimental system for visualizing sound with an electro-optical eardrum including an exploded view of an ear canal model, according to one exemplary embodiment of the present invention; 
         FIG. 2B  illustrates a non-exploded view of the ear drum model of  FIG. 2A , according to one exemplary embodiment of the present invention; 
         FIG. 3  illustrates circular membrane modes generated using the experimental system shown in  FIGS. 2A and 2B , according to one exemplary embodiment of the present invention; 
         FIG. 4  illustrates light reflection using the experimental system shown in  FIGS. 2A and 2B  when the system is at equilibrium; 
         FIG. 5  illustrates Mode (0, 1) light reflection using the experimental system shown in  FIGS. 2A and 2B , according to one exemplary embodiment of the present invention; 
         FIG. 6  illustrates Mode (1, 1) light reflection using the experimental system shown in  FIGS. 2A and 2B , according to one exemplary embodiment of the present invention; and 
         FIG. 7  is a sample hearing sensitivity graph produced by the system shown in  FIGS. 2A-2B , according to one exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawing, in which like reference numbers refer to like elements throughout the various figures that comprise the drawing,  FIG. 2A  shows a system  100  for conducting experiments including visualizing sound with an electro-optical eardrum, according to one exemplary embodiment of the present invention. A model  110  of an ear canal is placed over a speaker  120 . The speaker  120  may be a subwoofer, i.e., a woofer, or a complete loudspeaker, which is dedicated to the reproduction of low-pitched audio frequencies known as bass. 
     Although various models of the ear canal are suitable, the model  110  of  FIG. 2A  includes a pipe  112  with a first open end  112   a  proximate to the speaker  120  and a second open end  112   b  opposite the first open end  112   a  to model the ear canal. The pipe  112  may be, for example, a plastic pipe typically used to convey drinking water, waste water, chemicals, heating fluid and cooling fluid, foodstuffs, ultra-pure liquids, slurries, gases, and compressed air and in vacuum system applications. The pipe  112  is preferably polyvinyl chloride (PVC). 
     As shown in  FIGS. 2A and 2B , a membrane  114  (which may be an exercise resistance band) is stretched over the second open end  112   b  of the pipe  112  with constant tension. The membrane  114  may be held in place by any typical fastening element such as a hose clamp  115 .  FIG. 2A  depicts the model  110  in an exploded view;  FIG. 2B  depicts the membrane  114  held in place by the hose clamp  115 . 
     A reflective surface is formed on the center of the membrane  114 . In one embodiment, the reflective surface is a small circular mirror  116  delicately attached to the membrane  114 , for example by glue, effectively creating a mass-loaded membrane. As described below, the reflective surface may alternatively include a reflective silver surface painted on the membrane  114 . 
     The model  110 , the speaker  120 , the membrane  114 , and the mirror  116  are placed equidistant between a screen  210  and a laser pointer  310 . The laser pointer  310  may emit a light  314 , for example, a red light. The light  314  from the laser pointer  310  is directed at the mirror  116  and reflected on to the screen  210 . The screen  210  may be supported by, and can be positioned in space using, a first stand  214 , such as a ring stand. Similarly, the laser pointer  310  may be supported by, and can be positioned in space using, a second stand  316 . The spatial arrangement of the mirror  116 , the screen  210 , and the laser pointer  310  is described in greater detail below in conjunction with  FIG. 4 . 
     The system  100  further includes a sound signal-producing device such a function generator  410  in communication with the speaker  120 , the output of which allows the user to control the amplitude and frequency of pressure waves originating from the speaker  120 . The laser pattern seen on the screen  210  depends on the mode that the pressure wave of the speaker  120  produces on the mass-loaded membrane  114 . The output of the function generator  410  is sent to an audio amplifier  420  powering the speaker  120 . Alternatively, a microphone  415  can be connected to the audio amplifier  420 . In other embodiments, any other suitable sound signal producing device may be connected to the audio amplifier  420 . Although a wireless connection between the audio amplifier  420  and the speaker  120  is possible, wires  430  connect the audio amplifier  420  to the speaker  120  in the embodiment illustrated in  FIG. 2 . Wires  430  may also connect the function generator  410  and/or the microphone  415  to the audio amplifier  420 , or they may be connected wirelessly. 
     The system  100  can produce at least two circular membrane modes based on the amplitude and frequency of pressure waves originating from the speaker  120 : Mode (0, 1) and Mode (1, 1). Modes are classified as Mode (m, n) with “m” as the number of nodal diameters and “n” as the number of nodal circles where there is no displacement. As illustrated in the top left image of  FIG. 3 , Mode (0, 1) contains one large anti-node at the center of the membrane  114  effectively raising and lowering the mirror  116  and never changing its orientation (as shown in  FIG. 5 ). As illustrated in the top right image of  FIG. 3 , Mode (1, 1) contains a nodal diameter with one circular node along the edge of the membrane  114 . This causes the mirror  116  to change orientation in a “see-saw” like pattern which changes the surface normal angle of the mirror  116  (as shown in  FIG. 6 ). 
     When the surface normal angle of the mirror  116  changes, the direction of the light ray path also changes by that same angle. Therefore, the vertical height of the laser or light reflection pattern on the screen  210  is the range of motion for the membrane  114 . To increase the magnification of the range of motion, the mirror-to-screen horizontal distance can be increased. If the laser pattern is not vertical due to the see-saw effect of the mirror  116  not aligning with the direction of the light ray path, the pipe  112  contains a slip union allowing the pipe  112  to rotate and re-align the mirror  116 . There is no volume displacement in Mode (1, 1) likely causing little to no movement of the ossicles in a real ear, but for the purpose of the system  100  as an educational tool any movement of the membrane  114  is used to simulate hearing. In addition to Mode (0, 1) and Mode (1, 1) discussed above, Mode (0, 2) and Mode (1, 2) are also illustrated in  FIG. 3  as the bottom left image and the bottom right image, respectively. 
     In one design of the system  100 , the model  110  is attached directly to the speaker  120 . The direct contact and subsequent direct transfer of energy from the speaker  120  produces several more modes on the membrane  114 . Also produced is an interesting phenomenon coined “periodic mode switching.” At fixed time intervals, the membrane  114  spontaneously alternates between two modes of oscillation. Without wishing to be bound thereby, it is hypothesized that a thermal hysteresis effect is the cause. 
     In another design of the system  100 , the model  110  is suspended over the speaker  120 , as shown in  FIG. 2A , using, for example, a hose clamp and ring stand. With this suspended position, fewer modes are observed than the initial direct-contact system. Because the weight of the mirror  114  is the likely culprit for dampening or preventing the formation of higher membrane modes, other embodiments might use a circular mirror of less mass to view more modes or possibly replace the mirror  114  with silver paint for reflection. Other parameters that might be investigated are the effects of different pipe diameters, mirror masses, and membrane tensions on the frequency range of the system  100 . 
     EXAMPLE 
     The following example is included to more clearly demonstrate the overall nature of the invention. This example is exemplary, not restrictive, of the invention. The example refers to  FIGS. 4-6 . In  FIG. 4 , the system  100  (illustrated, for example, in  FIG. 2A ) is depicted at equilibrium. In  FIG. 5 , the system  100  is depicted at the maximum amplitude of the membrane  114  ( FIG. 2 ) when it deforms according to Mode (0, 1) (the top left image of  FIG. 3 ). In  FIG. 6 , the system  100  is depicted at the maximum amplitude of the membrane  114  when it deforms according to Mode (1, 1) (the top right image of  FIG. 3 ). 
     Referring to  FIG. 4 , the center C of the mirror  116  is placed at an equal horizontal distance L between the screen  210  and the laser pointer  310 . The mirror  116  has a diameter m. The laser pointer  310  is placed at a height H above the center C of the mirror  116 . The laser pointer  310  is oriented so that the light  314  emitted by the laser pointer  310  reaches the center C of the mirror  116 . The angle θ of the laser pointer  314  is defined as the angle between the path of the light  314  and a vertical line intersecting the path of the light  314  and will vary based on the height H and the distance L. As used in this document, “vertical” and “horizontal” refer to the orientation of the figures. A person of ordinary skill in the art will understand that the system  100  ( FIG. 2A ) will function equally well in any orientation. Before the output of the speaker  120  ( FIG. 2A ) is applied to the membrane  114 , the mirror  116  occupies a first position  116   a  at equilibrium. In the first position  116   a , the mirror  116  is in a substantially horizontal position so that light  314  reflects off the mirror  116  and forms a first reflected beam  316   a  which intersects with the screen  210  at the same angle θ as the angle between the path of the light  314  and a vertical line intersecting the path of the light  314 . 
     Referring to  FIG. 5 , as a result of the membrane  114  entering Mode (0, 1), the mirror  116  moves upward into a second position  116   b . At the maximum amplitude, the mirror in the second position  116   b  is still substantially horizontal but at a height above the first position  116   a  equal to the amplitude A. Because the raised position of the mirror  116  results in the light  314  reflecting off the mirror  116  at a point offset from the center C, a second reflected beam  316   b  intersects the screen  210  at the same angle θ but at a height E above the intersection of the first beam  316   a  and the screen  210 . If the membrane  114  produces Mode (0, 1), the user measures the height E to obtain the membrane amplitude A, which is equal to half the height E (i.e., E=2A). 
     Referring to  FIG. 6 , the membrane  114  ( FIG. 2A ) is oscillating based on the output of the speaker  120  ( FIG. 2A ) in the Mode (1, 1) (see the top right image of  FIG. 3 ) so that the mirror  116  changes orientation in a “see-saw” like pattern about the center C of the mirror  116  between the first position  116   a  at equilibrium and a third position  116   c . At the greatest amplitude of the oscillation, the mirror  116  occupies the third position  116   c , where the end of the mirror  116  deflects by an amplitude A, resulting in a third reflected beam  316   c . The angle between the mirror  116  in the first position  116   a  and the mirror in the third position  116   c  is defined as α. As a result of the deflection of the mirror  116 , the third reflected beam  316   c  intersects the screen  210  at a distance D below the intersection of the first beam  316   a  and the screen  210  and at an angle equal to θ+2α. 
     For Mode (1, 1), the user calculates the amplitude A by measuring the distance D, incorporating the system constants (defined above), and applying Equation (1) below to calculate A. 
     
       
         
           
             
               
                 
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     In an exemplary embodiment, the physical properties of the membrane  114  suitable for use in the system  100  include a radius of about 5.8 cm, a mass density of about 0.020 g/cm 2 , and a thickness of about 0.011 cm. The horizontal distance L between the mirror  116  and the screen  210  is about 100 cm. The height H from the center C of the mirror  116  to the center of the laser pattern on the screen  210  is about 28 cm. The angle θ of the laser pointer  310  is about 60 degrees. And the diameter m of the mirror  116  is about 5 cm. For purposes of this example, these numbers are constant for the system  100 . Although these constants are used in the following calculations, a person of ordinary skill in the art will understand that these values may vary for different systems and understand how to adjust the following calculations accordingly. Because m, θ, and H are held constant, Equation (1) simplifies, using the system constants, to approximately:
 
 A= 2.17× D /(112− D )  (Equation 2)
 
     The largest distance D measured for a system having the above properties was never as large as 112 cm, making Equation (2) continuous for the range of D values. Equation (2) can be used with introductory students so they are not discouraged by the relative complexity of Equation (1). The given system constants were chosen to yield values for the distance D which range from 1.0 to 20 cm and which correspond to membrane amplitudes of 0.5 to 6.5 mm. The derivation of Equation (1) uses only the law of reflection, geometry, and basic trigonometry. 
     With reference to  FIGS. 4 and 6 , Equation (1) can be derived as follows. 
     
       
         
           
             
               
                 
                   
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     The hearing sensitivity of an individual can be determined by a simple test. First, a reference tone at a specific frequency and loudness level is chosen. Next, the frequency is changed from the reference but the loudness level is kept constant. The individual then relays if the new sound is perceived as of equal, higher, or lower loudness than the reference tone. If the loudness at this new frequency is not perceived equal, the loudness level is changed until the individual perceives the new frequency tone as the same loudness level as the reference. From this collected data, the hearing sensitivity of an individual can be plotted on a graph of frequency versus equal loudness. The graph displays the individual&#39;s perceived equal loudness contours at different frequencies. 
     The system  100  gives a hearing-impaired student or another person the ability to create a simple plot of hearing sensitivity. The first step is to determine a fixed membrane amplitude value (also known as a “reference tone”). A membrane amplitude value of 1.0 mm, which corresponds to a distance D of 2.5 cm or a laser pattern total height of 5.0 cm, was used in the original experiment. The user determines the lowest frequency to which the membrane  114  responds with this predetermined amplitude while at maximum power. Next, the user increases the frequency (5 Hz increments are suggested) and changes the speaker power (also known as the “loudness level”) until the system  100  responds with the same predetermined amplitude. This process is repeated for the entire frequency range of the system  100  while recording frequency and speaker power. These steps to determine the range of hearing for the electro-optical eardrum simulate playing tones of equal loudness to determine a person&#39;s range of hearing. 
     The lowest speaker power recorded is used as a reference value for the calculation of a re-normalized sound pressure level (SPL) data set. The power values are re-normalized based on the sound frequency to which the membrane  114  responds with minimum effort (minimum power). To re-normalize the data, simply divide all of the power values by the lowest speaker power value. To obtain a graph of hearing sensitivity, the user plots the re-normalized SPL data set versus the frequency data set.  FIG. 7  shows a sample hearing sensitivity graph produced by the system  100 , which is an analog to the hearing sensitivity of a human being. The connecting line does not represent any specific fit of the data. The data point representing the lowest speaker power is shown as the circled diamond. 
     Although illustrated and described above with reference to certain specific embodiments and examples, the present invention is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the invention. It is expressly intended, for example, that all ranges broadly recited in this document include within their scope all narrower ranges which fall within the broader ranges.