US 1774706 A
Description (OCR text may contain errors)
Patented Sept. 2, 1930 UNITED STATES PATENT OFFICE TONE AMPLIFIER Application filed April 9,
This invention relates to a tone amplifier such as used in conjunction with radio loud speaker units, phonographs and the like.
It is known from actualexperience and investigation that the average tone reproducing instrument in use to-day is not capable of amplifying with equal efficiency all the possible frequencies within the range ot1 hearing. The amplification curves of even the best horns, for example, show very great irregularities. Horns usually amplify the upper ranges of frequencies more or less satisfactorily but give only selected' amplification to the lower frequencies. Cones amplify the lower frequencies more efficiently but fail usually to handle the upper tones so well.
The object of the present invention is to generally improve and simplify the construction and operation of tone amplifiers, and particularly to provide a. tone amplifier which Will combine the better vqualitiesl of the horn and conety es of tone amplifiers.
The invention, briey stated, comprises a tone amplifier in which is formed a flat resonance chamber having a. constant dimension or spacing between its walls in one .direction and a gradually increasing space between its walls in a. direction at right angles to the first dimension. The/apex or narrow end of they chamber is connected with the speaker unit and the wider eind of the resonance chamber is provided With a series of openings through which the sound waves discharge. y y
The invention is shown by wayof illustration in the accompanying drawings in which:
Fig. l is a front View of the tone amplifier, y
Fig. 2 is a vertical cross section taken on line ,II-II, Fig. 1.
Referring to the drawings in detail, A indicates a base member of suitable shape on the central upper portion of which is mount- 1928. Serial No. 268,406.
ed the tone amplifier. The tone amplifier' may assume varying` shapes but in this instance shown as circular or disc shaped. It consists ofr a back plate B around which formed an annular flange or rim 7.' Set forward of the back plate and spaced therefrom to form a` resonance chamber' 9 is a front plate S. This plate is provided `with a number of slots, such as indicated at 10, and a number of peripheral openings such as `indicated at 11, the openings l0 Yand ll forming openings through which the sound waves discharge, as will hereinafter be described. The base A and the plates B and S may be constructed of a number of different materials, such as plaster of Paris, cement, papier-mche, vulcanized rubber, etc. A number' of tone amplifiers, such a here illustrated, have been cast of plaster of Paris and in that instance, a reinforcing wire mesh is placed within the front and rear plates, as indicated at 1Q, to reinforce and strengthen the same. The surfaces of the plates may be finished in any suitable man-- ner, for instance with vai sh, shellac or the like, and they may be colored or finished to suit varying conditions. lf the tone amplifier is constructed of plaster of Paris, an internally threaded sleeve such as indicated at 6 is secured in the lower end of the resonance chamber, this sleeve being provided with projecting arms or wire which is wound about the same so as to thoroughly anchor it and secure it in the cast material. The sleeve serves the function of se ring and supporting a loud speaker unit, such as indicated at C. Any suitable type of unit having a diaphragm such as indicated at e may be employed. The diaphragu'l is mounted within a casing, as shown, and it is actuated by a magnet in an armature which is connected with the diaphragm in the usual manner.
The tone amplifier here illustrated might be likened unto a horn which has been flattened as it provides a resonance chamber which .is flat, the spacing` betr-.cen the Vtrout and rear Valls B and S being the same while the spacing between the opposite Walls ol' the rim 'i' increases i'rom the 'fnrulc or entrance opening 6 due to the circular shape ot the plates 8 and B. ln other words, a flat resonance chamber is provided which has a constant dimension or spacing in depth and which g adn-ally increases in Width 'trom an entrance point to a discharge point.
Before describing the operation ot' the device, it might be stated that a horn is essentiall)Y a resonance chamber which amplidcs 'the sound ot the loud .speaker diaphragm by virtue ol the fact that the air column conlined Within the resonance chamber is i'orced int-o vibration in unison with the yibratioi ot the diaphragm. It a horn should happen to be cylindrical in shape, it would respond only to tones ivhose wave lengths are twice the length otI the tube or to tones` Ylos-e rave lengths are such that the tube is exa( u one-third, one-fourth, one-titth -oi them, etc., tor example it' the. tube or cylinder is approximately 2T inches in length, it will respond to medium C, 25o ribrations per second, to C (IMQ), to G (zitti), etc. The intermed'ate tones Would in that instance not be amplified.
Since a cylindricz l resonance tube responds only to selected tones, in order to reproduce the Whole range ot audible tones with cylindrical resonators, it would ret nire a series ot resonance pipes like a concert pipe organ. Such a tone amplii'ier would, ot course,` be out oi the question in the average residence. The eiilectot a multiple series o1 resonance tube may, however, be secured by gradually increasing the diameter oil 'the tube from its mouth outivard toivard the bell and the horn type of speaker or horn am is the result. However, horns vfill not give true reproduction unless they are built in sizes up to twenty-live or thirty ifcet in length and this is, accordingly, impr-actie; l tor arci age home use.
The cone type ot loud speaker depends upon another principle ot' sound amplilication. The loudness of the tone or sound at a given distance from its .source may be increased by increasing the amplitude of the vibration, i. e., increasing the actuating forces or by increasing the ar ai ci the vibrating obliect. The cone accomplishes` this purpose by presenting a large sur'lace oit coupling with the air and as such does away with the necessity of using a horn. The surface of the cone must in reality vibrate in nu nerous irregular segments if it is to amplify all the elements of the complex tones. The higher the 'frequency `of the notes sounded. the smaller must be the vibrating segment. Since the tactors ot texture and elasticity establish a limit to which the segments maY be duced, a vibrating cone lannot amplify sounds Whose frequencies pass a lined upper limit it it is at the same time to amplify the bass notes ior which it is especially suited. rllhe upper partials in sound reproduced by c. cone, are accordingly absent Where it desired to bring out the lower tonl` i. 'the horn, on the other hand, reproduces the higher frequencies and it is accordingly evident that it would be desir; ble to combine the adi'antages ot the cone with those ol the horn.
rthe tone amplilier 'forming the subject matter ot the present application combines these Yfeatures as it provided with a resonance chamber u'itl such a rate ol increase in its Width that the best advantages ot the horn are retained. 'the liront and bach walls of the chamber which are equally spaced torni sounding boards. These sounding boards preservel the ainplili :ation 'atio lor the loiver notes While the rapid rate of increase in Width ot' the resonance chamber in the other direction, amplities the upper notes, and taith't'ul, harmonious touc a1nplilication is the result.
Thilo certain tentures ot the present invention are more or less specilically dcsi'fribed, l wish it understood that various changes may be resorted to Within the scope ot the appended claims; similarly. that the materials and finishes ot the several parts eniployed may be such as the manufacturer may decide or varying conditionf-'s or uses may den mand.
Hating thus Ydescribed my invention, what I claim and desire to secure by Letters Patent is l. A tone amplifier comprising a bacli plate, a front plate spaced therefrom and parallel with the back plate, a flange surrounding the plates and connecting the same, said flange and plates enclosing a resonance chamber, said flange having an inlet openingl termed at its 3 a, adapted to be connected With a speaker unit, and one oi the plates having a plurality ot sound outlet openings formed in its peripheral edge and in com munication with the resonance chamber.
2. A tone amplilier comprising a :troutl and baci: plate, said plates being;` spaced apart and parallel, a flange surrounding the plates and connecting the same, said 'flange and plates enclosing a resonance chamber, said front plate having a plurality oit out away portions in its periphe 'al edge and adjacent one end of the flange said cut away portions forming outlet. openings t'or the resonance chamber. and said tlaiige having an opening formed in its opposite end` to form a connection for a speaker unit.
3. A tone amplifier connarising a frontant back plate, said plates being spaced apart and parallel, a flange surrounding the plates and connecting the same. said flange and plates enclosing?r a resonance chamber, a plurality of cut away portions in the peripheral fi t)