DK171338B1

DK171338B1 - Circular sound source

Info

Publication number: DK171338B1
Application number: DK117494A
Authority: DK
Inventors: Jean-Dominique Polack
Original assignee: Brueel & Kjaer As
Priority date: 1994-10-10
Filing date: 1994-10-10
Publication date: 1996-09-09
Also published as: DK117494A; AU3604495A; WO1996011558A1

Description

„ DK 171338 B1"DK 171338 B1

Opfindelsen angår en lydkilde omfattende en højttaler, som i én retning udstråler i en hul kobler med en åben indgang, som kommunikerer med og er lukket af højttaleren, og en åben udgang, idet kobleren har stive vægge, der ikke kan reagere på 5 de af højttaleren frembragte lydtryk og har et tværsnitsareal, der aftager i retning bort fra højttaleren, hvorhos højttaleren i modsat retning udstråler i et kabinet.The invention relates to a sound source comprising a speaker which radiates in one direction in a hollow coupler with an open input communicating with and closed by the speaker, and an open output, the coupler having rigid walls which cannot respond to those of the the speaker produced sound pressure and has a cross-sectional area that decreases in direction away from the speaker, the speaker radiating in the opposite direction in a cabinet.

En højttaler, der er udstyret med en kobler og et kabinet, kendes fra US-patentskrift nr. 4.206.831.A speaker equipped with a coupler and cabinet is known from U.S. Patent No. 4,206,831.

10 Formålet med opfindelsen er at tilvejebringe en rundtstrålende lydkilde.The object of the invention is to provide a radiant sound source.

En lydkilde af den indledningsvis nævnte art er ifølge opfindelsen ejendommelig ved, at kabinettets tværsnitsareal aftager i retning bort fra højttaleren. Forsøg har vist, at man derved 15 undgår, at kabinettet skygger for udstråling i bagudgående retning, hvorved der opnås en i hovedsagen kugleformet udstrålingskarakteristik inden for et relativt stort frekvensinterval.According to the invention, a sound source of the kind mentioned initially is peculiar in that the cross-sectional area of the cabinet decreases in direction away from the speaker. Experiments have shown that this avoids the cabinet shading from radiation in the backward direction, thereby obtaining a substantially spherical radiation characteristic within a relatively large frequency range.

Endvidere kan ifølge opfindelsen kabinettet være konusformet 20 eventuelt stubkonisk. ·Furthermore, according to the invention, the housing may be cone-shaped, possibly stub-conical. ·

Det konusformede kabinet kan ifølge opfindelsen have en konusvinkel på højst 15°.According to the invention, the cone-shaped housing can have a cone angle of not more than 15 °.

Endvidere kan ifølge opfindelsen kobleren være konusformet og have en konusvinkel, der er mindre end konusvinklen af kabi-25 nettet.Furthermore, according to the invention, the coupler may be cone-shaped and have a cone angle smaller than the cone angle of the cab net.

I en særlig hensigtsmæssig udførelsesform har den konusformede kobler en konusvinkel på ca. 8°.In a particularly convenient embodiment, the tapered coupler has a taper angle of approx. 8 °.

Opfindelsen skal nærmere forklares i det følgende under henvisning til tegningen, hvor 1 fig. 1 en rundtstrålende lydkilde ifølge opfindelsen, fig. 2 ekstreme afvigelser fra rundtstråling som funktion af frekvensen, idet de internationale standarder er indtegnet, og 2 DK 171338 B1 fig. 3 udstrålingskarakteristikken som funktion af vinklen.The invention will be explained in more detail below with reference to the drawing, in which: FIG. 1 is a circular sound source according to the invention; FIG. 2 extreme deviations from orbital radiation as a function of frequency, the international standards being plotted, and 2 DK 171338 B1 fig. 3 the radiation characteristic as a function of the angle.

Der er et behov for rundtstrålende lydkilder til brug ved 5 kontrol af bygningsakustik. For det ferste angiver nye ret ningslinier for måling af lydisolation, at der skal anvendes en rundtstrålende lydkilde. For det andet er avancerede rumakustiske indicier stærkt afhængige af lydkildens retningsbestemthed, hvilket har ført til anbefalinger med hensyn 10 til direktivitet.There is a need for radiant sound sources for use in 5 building acoustics control. First, new guidelines for measuring sound insulation indicate that a radiant sound source must be used. Second, advanced space acoustic indications are highly dependent on the directness of the sound source, which has led to recommendations regarding directivity 10.

Ved de kendte tilnærmelser til rundtstrålende lydkilder anbringes et stort antal højttalere på en kugleflade. Kuglen tilnærmes af et regulært polyeder. Der findes lydkilder, produkter, som er baseret på tetraeder, kuber (hexaeder), oktae-15 der og ikosaeder. En højttaler er da monteret på hver flade af polyhedronen, og alle højttalere fødes i fase. Som følge af spredning i højttalerkarakteristikker, fasevariation, især i frekvensområdet over 1kHz opstår der interferensmønstre, der påvirker retningskarakteristikkerne. De forskellige standarder 20 kræver imidlertid kun 'direktivitetsmålinger i brede bånd (1/3 oktav eller én oktav) til tilvejebringelse af 30° glidende middelværdier. 12 eller 20 højttalere optager forholdsvis meget plads, og dette resulterer i voluminøse kilder, der er tunge og typisk vejer mere end 12 kg og har en diameter på ca. 50 25 cm.By the known approximations to radiant sound sources, a large number of speakers are placed on a ball surface. The ball is approximated by a regular polyhedron. There are audio sources, products based on tetrahedra, cubes (hexaedes), octahedrons and icosedes. A speaker is then mounted on each surface of the polyhedron, and all speakers are born in phase. Due to scattering in speaker characteristics, phase variation, especially in the frequency range above 1kHz, interference patterns occur affecting the directional characteristics. However, the various standards 20 require only broad band directivity measurements (1/3 octave or one octave) to provide 30 ° moving averages. 12 or 20 speakers take up quite a bit of space and this results in bulky sources that are heavy and typically weigh more than 12 kg and have a diameter of approx. 50 25 cm.

Ifølge opfindelsen er der tilvejebragt en rundtstrålende lydkilde med en karakteristik, der kan sammenlignes med karakteristikkerne af de kendte polyederkilder. Den perfekte rundtstrålende kilde er en punktkilde. Diameteren af den lyd-30 emitterende åbning af kilden er derfor reduceret, indtil afvigelserne fra rundtstråling ligger inden for tolerancerne.According to the invention there is provided a radiant sound source having a characteristic comparable to the characteristics of the known polyhedral sources. The perfect radiant source is a point source. The diameter of the sound-emitting orifice of the source is therefore reduced until the deviations from circular radiation are within the tolerances.

En lydkilde, der er opbygget efter dette princip, er vist i DK 171338 B1 3 fig. 1. Lydkilden består af 4 elementer nemlig a) en kraftig højttaler 6 b) en hul kobler med stive vægge i form af et horn 4, som kommunikerer med og er lukket af højttaleren og kon- 5 centrerer lyden og transmitterer denne til en apertur 2 c) en apertur 2, som diffrakterer lyd i alle retninger d) et kabinet 8, som indsnævres i bagudgående retning og mindsker diffraktionen.A sound source constructed according to this principle is shown in DK 171338 B1 3 fig. 1. The sound source consists of 4 elements namely a) a powerful loudspeaker 6 b) a hollow coupler with rigid walls in the form of a horn 4 which communicates with and is closed by the speaker and concentrates the sound and transmits it to an aperture 2 c) an aperture 2 which diffractes sound in all directions; d) a housing 8 which narrows in the backward direction and reduces the diffraction.

Disse elementer undersøges hver for sig, og det har vist sig, 10 at der.derved kan tilvejebringes en rundtstrålende lydkilde, der i hovedsagen virker som en punktkilde. En kraftig højttaler 6 er imidlertid forholdsvis dyr, men i forhold til de 12 højttalere, der tidligere var nødvendige, er der ikke tale om nogen fordyrelse. Anvendelsen af kun én højttaler 6 øger desu-15 den pålideligheden.These elements are examined separately, and it has been found that thereby a radiant sound source can be provided, which essentially acts as a point source. However, a powerful speaker 6 is relatively expensive, but compared to the 12 speakers that were previously needed, there is no price tag. The use of only one speaker 6 further enhances reliability.

Den rundstrålende lydkilde må imidlertid være omhyggeligt dimensioneret. Ikke blot er størrelsen af kabinettet 8 væsentlig for dækningen af det ønskede frekvensområde. Også den ydre form er væsentlig for tilvejebringelse af retningskarakteri-20 stikkerne ifølge de internationale standarder.However, the radiant sound source must be carefully dimensioned. Not only is the size of the enclosure 8 essential to the coverage of the desired frequency range. Also, the outer shape is essential for providing the directional characteristics according to the international standards.

Fig. 2 viser resultaterne af den endelige udformning af lydkilden, hvor kabinettet 8 er indesluttet i et konisk eller stubkonisk hus svarende til et horn med en forbindelsescylinder mellem de to konusser, der er reduceret til 10 mm. Resul-25 taterne ligger inden for tolerancerne af de internationale standarder, idet det antages, at centerfrekvensen af hvert bånd afspejler hele båndets adfærd.FIG. 2 shows the results of the final design of the sound source, wherein the housing 8 is enclosed in a conical or stub-conical housing corresponding to a horn with a connecting cylinder between the two cones reduced to 10 mm. The results are within the tolerances of international standards, assuming that the center frequency of each band reflects the behavior of the entire band.

Lydkilden udformes på følgende måde: DK 171338 B1 4 i) Først vælges aperturdiameter: For et givet sæt af ret ningstolerancer enten for oktav- eller trediedels oktavbånd må den optimale aperturradius og den maksimale afvigelse for hvert bånd bestemmes.The sound source is designed as follows: DK 171338 B1 4 i) First, aperture diameter is selected: For a given set of directional tolerances either for octave or third octave bands, the optimum aperture radius and maximum deviation for each band must be determined.

5 ii) Dernæst vælges højttaleren 6. Eftersom kun nogle få procent af lydeffekten udstråles, skal den valgte højttaler være så følsom og så effektfuld som overhovedet muligt indenfor det bånd, som er af interesse. Dette kræver imiderltid en tung lydkilde af en stor diameter, dvs. øgede vanskeligheder med at 10 tilfredsstille retningskrav i skyggeområdet bag kabinettet 8. Valget af højttaler 6 er derfor et kompromis imellem følsomhed, effekt og størrelse.5 ii) Next, select the speaker 6. Since only a few percent of the sound power is radiated, the speaker selected must be as sensitive and as effective as possible within the band of interest. However, this requires a heavy source of large diameter sound, ie. increased difficulty in satisfying directional requirements in the shading area behind the cabinet 8. The choice of speaker 6 is therefore a compromise between sensitivity, power and size.

iii) Derefter fastlægges dimensionerne af det koniske horn 4.(iii) Then the dimensions of the conical horn 4 are determined.

To dimensioner af konussen er allerede fastlagt under de for- 15 udgående trin nemlig diameteren af aperturen 2 og den samlede diameter af højttaleren 6. Den sidste dimension er længden af hornet 4, som skal tilfredsstille to krav nemlig, at den halve åbningsvinkel ved spidsen af konussen skal være mindre end 15°, idet man ønsker at minimere skyggearealet, og at Helmholtzre-20 sonansen af kilden skal afstemmes til den laveste frekvens, som er af interesse. Eftersom fastgørelsen af højttaleren 6 ved bunden af hornet 4 svarer til en forøgelse af den tilsyneladende længde af hornet 4, vil det sidste krav nødvendiggøre beregninger af hornets 4 længde evt. ved successive ap-25 proksimationers metode, indtil Helmholtzresonansen er korrekt. Dette sker ved hjælp af det efterfølgende trin iv.Two dimensions of the cone are already established during the preceding steps, namely the diameter of the aperture 2 and the overall diameter of the speaker 6. The last dimension is the length of the horn 4, which must satisfy two requirements namely that the half opening angle at the tip of the the cone must be less than 15 °, wishing to minimize the shadow area, and the Helmholtz resonance of the source to be tuned to the lowest frequency of interest. Since the attachment of the speaker 6 at the bottom of the horn 4 corresponds to an increase in the apparent length of the horn 4, the last requirement will necessitate calculations of the length of the horn 4. by successive ap-25 approximations until the Helmholtz resonance is correct. This is done by the following step iv.

iv) Derefter vurderes udformningen. Dette sker ved hjælp af simuleringer, som gør det muligt at beregne den elektriske impedans og kontrollere kabinettets 8 resonans og hele fre- 30 kvensgengivelsen for at kontrollere lavfrekvensafskæringen, det samlede lydniveau og hornresonanserne. Det skal bemærkes, at Thiele-Small parametrene kun beskriver lavfrekvensgengivelsen af en højttaler. Højfrekvensområdet af lydkilden, hvor hornet 4 spiller en afgørende rolle, kan derfor ikke simuleres DK 171338 B1 5 nøjagtigt.iv) Then the design is evaluated. This is done by means of simulations which allow the electrical impedance to be calculated and check the resonance of the cabinet 8 and the entire frequency reproduction to control the low frequency cut, the overall sound level and the horn resonances. It should be noted that the Thiele-Small parameters only describe the low frequency reproduction of a speaker. Therefore, the high frequency range of the sound source, where the horn 4 plays a crucial role, cannot be accurately simulated DK 171338 B1 5.

v) Derefter vurderes direktivitet og kabinetdesign. Nogle få principper i designet skal overholdes. Højttalerens 6 diameter skal være så lille som muligt, og kabinettet 8 skal udformes 5 med et gradvist aftagende tværsnit i bagudgående retning. Kabinettet 8 er fortrinsvis konisk, evt. stubkonisk med en konusvinkel, der er større end konusvinklen af hornet 4, der fortrinsvis er på ca. 8°.v) Then directivity and cabinet design are assessed. A few principles in the design must be observed. The diameter of the speaker 6 should be as small as possible and the housing 8 should be formed 5 with a gradually decreasing cross section in the backward direction. The housing 8 is preferably tapered, e.g. stub-tapered with a cone angle greater than the cone angle of the horn 4, preferably of approx. 8 °.

Lydkilden ifølge opfindelsen fremstilles på følgende måde: 10 Man anskaffer en højttaler og måler Thiele-Small parametrene.The sound source according to the invention is prepared as follows: A speaker is acquired and the Thiele-Small parameters are obtained.

De af fabrikanterne angivne Thiele-Small parametre er ofte for høje. Man foretager derefter en simulering med aktuelle data for opnåelse af en vurdering af kildens effektniveau. Man tegner en prototype af lydkilden og fremstiller denne.The Thiele-Small parameters specified by the manufacturers are often too high. A simulation is then carried out with current data to obtain an assessment of the source power level. One draws a prototype of the sound source and produces it.

15 For at at kontrollere om lydkilden tilfredsstiller kravene skal der foretages følgende målinger.15 In order to check whether the audio source meets the requirements, the following measurements must be taken.

i) Kilden vejes.i) Weigh the source.

ii) Impedanskurven måles for at bestemme Helmholtz- og kabinetresonanserne .ii) The impedance curve is measured to determine the Helmholtz and cabinet resonances.

20 iii) Frekvensgengivelsen måles, hvorved hornresonanserne vil kunne bestemmes.20 iii) Frequency reproduction is measured whereby the horn resonances can be determined.

iv) Afvigelser fra rundstråling måles i et lyddødt rum. De bedste resultater opnås i store afstande fra kilden. Ifølge standarderne skal afstanden imidlertid være 1,5 m.(iv) Deviations from radiated radiation are measured in a sound dead room. The best results are obtained at great distances from the source. However, according to the standards, the distance should be 1.5 m.

25 v) Effektniveauet måles i et efterklangrum.V) The power level is measured in a reverberation room.

I en konkret udformning har lydkilden en samlet længde på 353 mm, idet kabinettet har en længde på 23 mm, og hornet har en DK 171338 B1 6 længde på 330 mm. Aperturdiameteren er typisk 38 mm. Såvel hornet som kabinettet kan eventuelt indeholde lyddæmpende materiale.In a specific embodiment, the sound source has a total length of 353 mm, the housing has a length of 23 mm and the horn has a length of 330 mm. The aperture diameter is typically 38 mm. Both the horn and the cabinet may contain sound-absorbing material.

Fig. 3 viser udstrålingskarakteristikken ved 500 Hz som funk-5 tion af vinklen Θ i forhold til længdeaksen svarende til, at lydkilden vender opad som vist i fig. i. Det ses, at udstrålingskarakteristikken er i hovedsagen cirkulær.FIG. 3 shows the radiation characteristic at 500 Hz as a function of the angle Θ with respect to the longitudinal axis corresponding to the sound source facing upwards as shown in FIG. i. It is seen that the radiation characteristic is essentially circular.

Claims

An audio source comprising a speaker (6) radiating in one direction a hollow coupler (4) with an open input communicating with and closed by the speaker (6) and an open output, the coupler (4) ) has rigid walls that cannot respond to the sound pressure produced by the speaker (6), and has a cross-sectional area that decreases in direction away from the speaker (6), the speaker (6) radiating in the opposite direction in an enclosure (8) , Characterized in that the cross-sectional area of the cabinet (8) decreases in a direction away from the speaker (6).

Sound source according to claim 1, characterized in that the housing (8) is cone-shaped, possibly stub-conical.

Sound source according to claim 2, characterized in that the cone-shaped housing (8) has a cone angle of not more than 15 °.

Sound source according to any one of the preceding claims, characterized in that the coupler (4) is tapered and has a taper angle smaller than the taper angle of the housing (8).

Sound source according to claim 4, characterized in that the 20 tapered coupler (4) has a taper angle of approx. 8 °.

Sound source according to one or more of the preceding claims, characterized in that the coupler (4) contains a sound attenuating material.

Sound source according to one or more of the preceding claims, characterized in that the housing (8) contains a sound attenuating material.