US1878018A - Cone-horn combination - Google Patents

Description

Sept. 20, 1932. G'STEPHENS 1,878,018

CONE-HORN COMBINATION Filed Sept. 29, 1931 Fig. 1.

u a "5* Q 8* E In so 40 Ibo 46o 2800 40 00 Frequency WITNESSES INVENTOR die n Allan a- Stephens AT.T EY

ta p I a p r 1 I If the horn be constructed large enough to bring itsresonant frequency down below the lowest frequency to be received, the high-fre- A eadset 26,19 2.

TES

PTA/TEN T OFFICE a inenousnnrnc'rnxca MANUFACTURING COMPANY, A conrom'rron or BENN- ,OQNE-HQRN, COMBINATION l A ppllic ation ni as t mber 2 s, 1931. Serial in. 565,896.

My inventionrelates to energy translating jdevicespsuch as loud speakers or the like,

wherein; electric energy may be converted 'into sound or sound converted into electric energy. More particularly; my invention relates to improvements in apparatus of the above ,type whereby improved operating characteristics may beobtained.

i In apparatus involving the use of vibrat-- ing air columns to produce sound from electric currents or to convert sound'mto corref spondinfg electriccurrentsfithas been found I that the apparatus amplifies to an undesirable x p and dis'agreeableextent those notes for tones having a frequency which substantially coiincidesfvvith or bears aharmonic relationship to,jthe. resonant Ifrequency'of the air column.

1 T The es l is' h t e ir q el qyfre n e p the apparatus becomes] quitef rregular, the

response at resonant frequencies giving rise fsirable volume changesfiand distortion inthe reproduced 1 I pp ratusiu z n o d p nature whereinahorn is employed for ami fplifyingsound waves,the dilficulties outlined i above are met, inasmuch as {the horn defines [a vibratinglcolumn ofair. Theoretically, it

program, and overloading of the eakers or apparatus a similar would bepossibletoso designthe horn as to bring itsresonant frequency outside of the [frequency limits within which it is desired to receive, but newer and greater disadvantages would arise as a result low such procedure.

of a attempting to foluency response ofthehorn will be impaired. imilarly, if the horn (be made so small as to bring its resonant jfrequencygabove the highest frequencylimitof receptiomthe lowfrequency response ofithe horn will suifer.

Consequently, itbecomes more or less ne'c- ,essary evil'that theresonant frequency of the horn should liefsomewherewithin the range [of frequencies to which theispeakeris de- I signed to respond; The remedy, therefore-,i

111 1 be notin so constructing thehornfas to I "bring its resonant frequency outside of the i translating device.

" panying draw ng wherein "stantially closed chamber.

frequency range of reception but in reducing the effect produced by reason of a resonant condition existing Within the frequency range. 1

It is, accordingly, one object of my invention to provide means for reducing resonant peaks in the frequency response of an energy- It is another object of my invention to provlde an energy-translating device having smooth frequency-response characteristics. "f fAnother object of my invention is to pro .vide meanswhereby the frequency-response characteristics of a horn loud speaker may be substantially smoothed out.

Other objects of my invention will be disclosed in the following-"description of the same, taken in conjunction wi h the accom- Figure 1 is a schematic View, in cross-sec- ;tion, of an energy-translating device constructed according to my invention.

V 2 'is' a curve illustratingthe comparatlve-results obtainedthrough theuse of my invention; i v

Fig; 3 1s a rear View of the driver and cone structure; h a

In practiclng my invention, 1 provide a driving motor and its associated cone diaphragm in spaced relationship to the battle ,board'to which it is customarily aflixedand enclose the driving mechanism within a sub- The space between the driving' meansand the baffle provides an air-passage connection between the horn. v V, a

Referring more particularly to Fig; 1 of the chamber and the air column defined by the behind thebafiie, in spaced relationship thereto, andin axial alignment With-the horn, I provide a driving mechanism 5 comprising a driver and its associated cone diaphragm 9 being maintained or supported against transverse movement by; means of a support '11 mounted on the driver. Spacing members 13 are employed for supporting the driving mechanism in its spaced position'relativeto the bafilel The drivingmechanism is enclosed drawing, my invention comprises a horn 1 ailixed to a bafifle board 3. Mounted directly horn.-

by a boX 15 or other similar structure mounted on the baffle board, thereby defining a chamber which has. connection with the horn by means of the air passage 17 formed by maintaining the driving mechanism in spaced relationship to the baflie board. The-horn,by reason of its physical dimensions, as necessitated by practical requirements, has, by reason of its length, a certain fundamental resonance which,as explained heretofore,will,

. to some extent, impairspeech reproductionand produce overloading of the apparatus at toreduce the response or volume'of the speaker. at the lower'frequencies, particularly at those frequencies at which peaks occur, ap-

parently, by reason of the fact that the air connection betweenthehorn and the enclosed 3 chamber servesto bypass'some of the energy,

at low frequencies, which would otherwise find; an exit through the horn.

1 .While it is very beneficial to remove the I peak 'effect characteristics of energy-translat- 3 ing devices, it would at the same' time, be

very desirable-to otherwise increase. the re- 'spons'e ofuthedevice at thelow-frequency end of the. frequency spectrum. In. other words, it isiny object to simultaneously decreasethe response at the *resonant'frequencies of the horn and increase the. response at the other frequencies-toward the lower end of the scale and thereby smooth out the 'frequency rej spo'nse ofthe device. i

. The apparatus, as. described by me, is capablezof functioning, toobtain .the above beneficial results; "The leakage path provided between the horn and the chamber servesto by-pass energy at the peak frequencies, in

1: particular, to. thereby materially reduce the energy output of the device at those frequencies; ,At'the same time, by reason of'the fact thatthe chamber-about the driving mechanism is substantially closed, a certain amount 1:. Of resonance is'introduced, the closed cham:

ber defining aconfined air column which is --normall caused to resonate with the cone "mass. his resonancephenomenon isa-broad one, that is, it extends throughout a substantial' range of-frequencies and, at those frequencies atwhich the chamber resonates, the normal'zdamping.eflecting. onthe energy ,de-

lilvered to the device willbe reduced,"thereby.

causing the device to. partake of the charac- :rs', ma ses" or a tape-P sus; Thiswill lead to. an increase in output energy and a corre sponding increase in the elficiency of the device at those frequencies.

I have found it possible to tune the chamber, so to speak, to bring about a resonant condition within apredetermined band of frequencies. According'to my invention, this band of frequencies will be selected to substantially coincide with a band of frequencies within which the response of the device happens to be poor and inefficient. This tuning effect may be accomplished by altering the characteristics of the enclosed chamber, either by changing the sizeof the same or by providing means whereby the stiffness of the air column may be altered. Qne way of accomplishing this would be to provide the sound chamber'with a resilient or permeable wall. Rubber or felt is sug- ..gested as a material suitable for the purpose.

Itis characteristic of horn loudspeakers,

M general, that the response at the lower- "frequency end of the spectrum, except at the resonant frequency of the horn, is poor.

Consequently, the sound chamber. will .be tuned toproduce a resonance condition at those frequencies. While, by reason of the leakage path connecting the chamber with thehorma certain amount of the energy emitted at, the lower frequencies will be diverted away from the horn, the resonance condition which. occurs "at these poor- 7 response frequencies will more .than compensate for the lost energy. ...The ultimate result arising out ofthe. use of my invention, therefore, is to: reduce the peak responses. and build 'up the response at the frequencies where the response is normally poor.

By reason of. the fact that loudspeakers :of the presentld'ay. vary in characteristics, it isimpossible to setforth definite figures I which I willapply equally well for all of them. The constants best suited for any particular loudspeaker are easily found by varying the physical dimensions of the 1 sound chamber and the s acing between the diaphragm. and, the ba e. For a speaker the horn of which'is resonant at a frequency of approximately 100 cycles, I have. found that a space of approximately 4 is'sufficient to obtain the desired result 7 I In Fig. 2, Ihave illustrated the important results obtained in the practice, of my invention as applied to a speaker having aresonant condition atv approximately 100 cycles.

, The. solid 1 line represents the energy'cu'tput, as plotted against the frequency for a speaker which does. not embody my invention. The dotted or broken line represents the energy output. of the same speaker, as

constructed according't'o myi-nvention. It

will'be noted that the horn frequencypeaks 'at'35 'cyclesiandat the.100 cycles. have been materially." reduced' by reason of the; leakage path existing gbetween the enclosing chamer and the horn. Itwill also be noted that, by reason of the broad resonant condition existing within the enclosed chamber, the

frequency response of the speaker has been appreciably improved between the 150- and 400: frequency limit, and also between the 800- and2000-, frequencylimit. The

ultimate resultis that the frequency response of the speaker has been materially smoothed I out, as clearly shown by the broken'line.

The. speaker, described above, the output curve of which is illustrated in Fig. 2, cm-

' a parent, however, that advantageous results .may be obtained, regardless of the design of the horn structure. a

. Various modifications may be made Within the scope ofmyinve-ntion and, while I have described my improvement in the art in great detail, I do notidesire to be limited to such details except insofar as may be required by theprior art and by the appended claims.

I claim as myinvention:

I 1. An energy-translating device comprising a horn, driving means associated therewith. said horn andfdriving means being deficient n frequency response over a range of l frequencies, and means for increasing the output of said device at substantially those frequencies at which it is normally deficient.

2; An energy-translating device comprising a'horn, driving means associated there- I with andmeansfor smoothing out the frel 1 quency response of said device, said means comprising a chamber connected to said horn by anair pathg. I i 3. .An energy-translating devlce comprls- 1ngahorn, drivlng means associated theref with and means for 'smoothingout the frequency response of said device, said means 1 comprising a chamber substantially enclosjing said driving means and age path tosa d horn.

providing a leak- 74. An energy' translating device comprisahorn, driving means associated therewith a and means for smoothing out the frequencyresponse of said device; said means comprising a chamber substantially enc1os ing said drivingmeans, "said driving means i being spaced fromsaidvchamber to provide i chamber. I

a leakagepath from. said horn to said 5. An energytranslating device comprising means less responsive to certain frequencies than to others and means associated therewlth for improving the response of said first means at substantially those frequencies.

6. An energy-translating device comprising means less responsive to certain fre-' quencles than to others, and means associated therewith forimproving the response of said first means, said means being resonant at those frequencies.

7. An energy-translating device compris ing means having a frequency response which is over-emphasized at certain frequencies and under-emphasized at other frequencies and means associated therewith for reducing the response at the over-emphasized frequencies and increasing the response at the under-emphasized frequencies.

8. An energy-translating device comprising means having a frequency response which is over-emphasized at certain frequencies and under-emphasized at other frequencies and means associated therewith for simultaneously reducing the response at the over-emphasized frequencies and increasing the response at the under-emphasized frequencies.

In testimony whereof, I have hereunto subscribed my name this 23rd day of May 1931.

ALLAN G. STEPHENS.

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