Technology history Horn loudspeaker

1 technology history

1.1 megaphone
1.2 exponential

1.2.1 multicell
1.2.2 radial, sectoral, , diffraction


1.3 tractrix
1.4 constant directivity

1.4.1 mantaray
1.4.2 bi-radial
1.4.3 twin bessel
1.4.4 cd horn characteristics


1.5 multiple entry horn
1.6 waveguide horns
1.7 quadratic-throat waveguide
1.8 oblate spheroid waveguide

technology history

francis barraud s original painting of nipper looking edison bell cylinder phonograph.

the physics (and mathematics) of horn operation developed many years, reaching considerable sophistication before wwii. known horn loudspeakers on mechanical phonographs, record moved heavy metal needle excited vibrations in small metal diaphragm acted driver horn. famous example horn through nipper rca dog heard master s voice . horn improves loading , gets better coupling of energy diaphragm air, , pressure variations therefore smaller volume expands , sound travels horn. kind of mechanical impedance matching absolutely necessary in days of pre-electrical sound reproduction in order achieve usable sound level.

megaphone

a collapsible cone horn removable flared bell. horn patented in 1901 gramophone record playback

the megaphone, simple cone made of paper or other flexible material, oldest , simplest acoustic horn, used prior loudspeakers passive acoustic amplifier mechanical phonographs , human voice; still used cheerleaders , lifeguards. because conic section shape describes portion of perfect sphere of radiated sound, cones have no phase or amplitude distortion of wavefront. small megaphones used in phonographs , loudhailers not long enough reproduce low frequencies in music; had high cutoff frequency attenuated bottom 2 octaves of sound spectrum, giving megaphone characteristic tinny sound.

exponential

a three-way klipsch loudspeaker late 1970s employing different exponential horn @ each bandpass

the exponential horn has acoustic loading property allows speaker driver remain evenly balanced in output level on frequency range. benefits of design first published c.r. hanna , j. slepian in 1924 american institute of electrical engineers (aiee). major drawback exponential horn allows narrowing of radiation pattern frequency increases, making high frequency beaming on axis , dull sound off axis. concern throat of small diameter needed high efficiency @ high frequencies larger throat best low frequencies. common solution use 2 or more horns, each appropriate throat size, mouth size , flare rate best performance in selected frequency range, sufficient overlap between frequency ranges provide smooth transition between horns. solution tried in late 1930s harry f. olson of rca use multiple exponential flare rates, either connecting increasingly larger horns in series or subdividing interior of single horn. exponential horns continue used designers, , in applications.

multicell

altec multicell horn models 1978 product catalog

a number of symmetrical, narrow dispersion, exponential horns can combined in array driven single driver produce multicell horns. patented in 1936 edward c. wente of western electric, multicell horns have been used in loudspeakers since 1933 address problem of directivity @ higher frequencies, , provide excellent low frequency loading. directional control begins beam both vertically , horizontally in middle of target frequency range, narrowing further @ high frequencies level changes great 10 db between lobes. multicell horns complex, difficult fabricate , have higher associated expense. persisted in public address applications many years because, faults, sounded relatively good. revolutionary coaxial driver, altec lansing duplex 601 , 604, used multicell horn high frequency component 1943 1998.

radial, sectoral, , diffraction

a jbl model 2397 diffraction horn 1978. 2397 contained internal sectoral vanes divided throat 6 exponential sections

radial horns have 2 surfaces based on exponential flare rate, , 2 straight walls determine output pattern. radial horn exhibits of beaming of exponential horn. altec sectoral horns radial horns vanes placed in mouth of horn stated purpose of pattern control. ease in mounting loudspeaker cabinets, flat front radial horns have been used, instance community in sq 90 high-frequency horn. jbl s diffraction or smith horn variation on radial design, using small vertical dimension @ mouth method of avoiding mid-range horizontal beaming of radial horns have larger vertical dimension @ mouth.

the diffraction horn has been popular in monitor designs , near-field public address applications benefit wide horizontal dispersion pattern. counterintuitively, narrow vertical dimension provided expansive vertical output pattern approaching 90° frequencies of wavelength equal narrow vertical dimension. small version of diffraction horn designed in 1991 jbl model 2405h ultra-high frequency transducer, yielding 90° x 35° output pattern @ 20 khz.

tractrix

the tractrix horn similar in many respects exponential horn , has gained adherents among diy horn enthusiasts, audiophile consumers, , manufactures well. uses curve formula derived assuming tangent point on horn s inner curve reach central axis of horn line segment of set length. @ mouth, tangent line segment becomes perpendicular axis , describes radius of mouth. horn concept studied paul g.a.h. voigt in mid-1920s , patented in 1927. size of tractrix horn generated specifying desired low frequency cutoff or limit determine mouth diameter. 2 incremental improvements on exponential horn include better support low frequency extension , broader high-frequency coverage pattern.

constant directivity

don keele s first constant directivity horn patent assigned electro-voice in 1978

in may 1975, address problems of beamwidth changing @ different frequencies, d. broadus don keele, jr. of electro-voice introduced hybrid horn exponential expansion rate near throat followed conical expansion section , ending rapidly flaring flange @ mouth. flange @ mouth solved remaining problems lobing @ higher frequencies. don keele specified in 1 version of design wider horizontal flare pattern control appropriate public address purposes. keele s paper set forth relationships between mouth size, frequency , coverage angle, providing basis many future developments of horn design. 1 problem found constant directivity horns horizontal coverage pattern cannot narrowed without making vertical coverage pattern small useful.

mantaray

subsequent keele s work , using principles, clifford a. henricksen , mark s. ureda of altec designed strikingly different hybrid horn displaying constant directivity traits, horizontal diffraction or mantaray horn. mantaray separated desired vertical coverage pattern horizontal, making possible design horns variety of coverage patterns. mantaray shape starts vertically oriented jbl-style diffraction horn leading conical waveguide (earliest designs) or square or rectangular horn 4 planar sides. midrange beaming control, outer mouth expanded further short, flared flange in keele style, or added planar sides of greater flare angle. low frequency efficiency not pronounced constant directivity design. unlike previous designs, apparent apex, focal point of pattern dispersion, not same every frequency, making ellipsoidal wavefront rather spherical. because of this, mantaray arrayed satisfactorily in 1 plane. abrupt breaks in flare rate caused diffraction, reflection , distortion components.

bi-radial

a 1996 jbl model 2344a bi-radial butt-cheeks horn 100° x 100° output pattern 1 khz 12.5 khz

by 1980, keele @ jbl took both , altec s designs step further. mated jbl-style diffraction horn secondary horn consisting of exponentially curved sides derived using 2 radial formulas. resulted in hybrid constant directivity horn free distortion components associated abrupt angle changes. market responded design in products such jbl model 4430 studio monitor 100° x 100° model 2344 bi-radial high frequency horn called butt-cheeks . bi-radial design had problems apparent apex , arrayability in same manner mantaray.

twin bessel

ramsa, professional audio division of panasonic corporation, introduced twin bessel constant directivity horn shortly after mantaray appeared. design similar mantaray , bi-radial used dual series bessel expansion formula determine flare rate of secondary horn section.

cd horn characteristics

most popular constant directivity horns (also known cd horns) suffer non-spherical wavefronts, limitations in arrayability, distortion @ high sound pressure levels reflections , distortions related transition diffraction slot secondary horn. tend toward narrowing of dispersion pattern @ higher frequencies wavelengths approach width of throat or width of diffraction slot.

because cd horn s high frequencies more spread out on coverage pattern, appear attenuated relative other horns. cd horn requires equalization boost of approximately 6 db per octave filter knee centered between 2 , 4 khz (depending on horn design) in order sound neutral , balanced. manufacturers of active electronic audio crossovers responded requirement adding optional cd eq boost filter or high frequency shelf filter. instance, such circuitry provided via internal jumper links bss in fds-310 crossover , rane in ac 22s , ac 23b crossovers. rane allowed greater front panel control of 2 bandpasses ( hi-mid , high ) using cd horn equalization including sweepable frequency range on ac 24 crossover. further refinements of filtering process available in dsp-based crossovers.

multiple entry horn

a three-way multiple entry horn in each passband enters same horn

in 1996, ralph d. heinz of renkus-heinz received patent multiple entry horn incorporated multiple drivers 2 bandpasses, high , mid, sound waves exited single horn @ differing distances depending on bandpass. marketed coentrant horn. mid- , high-frequency drivers in renkus-heinz st/stx product line both exited through complex conic waveguide. in late 1990s, thomas j. tom danley of sound physics labs (also known servodrive ) began working on three-way multiple entry horn, bringing spl-td1 market in 2000. design used 7 drivers, 1 high frequency driver @ horn s throat, 4 mid-frequency drivers near throat , 2 low frequency drivers ported closer horn mouth. in 2001, tom danley began developing unity horn yorkville sound, patenting improvement in 2002. following 2003 release of yorkville s unity line, danley formed danley sound labs , developed significant improvement on spl-td1 called synergy horn, yielding substantially better phase , magnitude response along smoother polar pattern. synergy horn design promises greater power output achieved smaller loudspeaker enclosure. because design retains pattern control through crossover regions , on large range of total bandwidth, , because acoustic center of design near rear of enclosure, more combined in arrays public address applications.

waveguide horns

the term waveguide used describe horns low acoustic loading, such conic, quadratic, oblate spheroidal or elliptic cylindrical horns. these designed more control radiation pattern rather gain efficiency via improved acoustic loading. horns have pattern control, , waveguides provide degree of acoustic loading, difference between waveguide , horn matter of judgement.

quadratic-throat waveguide

in 1999, charlie hughes of peavey electronics filed patent on hybrid horn called quadratic-throat waveguide. horn simple conic section throat curved in circular arc match desired throat size proper mating speaker driver. instead of increasing horn mouth size flare control midrange beaming, relatively thin layer of foam covering mouth edge found suit same end. qt waveguide, when compared popular cd horns, produced 3-4 db lower levels of second harmonic distortion across frequencies, , average of 9 db lower levels of more annoying third harmonic distortion. being without diffraction slot, qt waveguide free problems apparent apex, making arrayable needed public address purposes.

oblate spheroid waveguide

oblate spheroid waveguide (oswg) horn designs improve directivity pattern control, provide lower frequency of directivity (the lower better match woofers , mid-woofers directivity), and--as claimed inventor -- dr.earl geddes mitigate higher order modes (hom), form of linear phase/amplitude-distortion. major contribution said comb-filter effects, namely practically limited hornlength explicitly not addressed theory of oswg. realized specimen attempt constant directivity , smooth transition between compression driver , horn. oswg designs applied higher frequency range, above 1 khz.