Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
  • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
  • H04R1/34—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means
  • H04R1/345—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means for loudspeakers
  • H04R1/347—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means for loudspeakers for obtaining a phase-shift between the front and back acoustic wave
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
  • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
  • H04R1/28—Transducer mountings or enclosures modified by provision of mechanical or acoustic impedances, e.g. resonator, damping means
  • H04R1/2869—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself
  • H04R1/2876—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself by means of damping material, e.g. as cladding
  • H04R1/288—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself by means of damping material, e.g. as cladding for loudspeaker transducers

Definitions

• the present invention is concerned with a loudspeaker which comprises a loudspeaker element and a box, the loudspeaker element being installed on one wall of the said box.
• the solution most commonly used is a dynamic loudspeaker. It has several applications. It can be said that a feature common of hi-fi loudspeakers pro- vided with dynamic loudspeaker elements is the use of two or more elements in order that a sufficiently wide frequency range could be covered by means of the loud ⁇ speaker. Subjects of the most active product develop ⁇ ment in recent years have been uniform frequency response, high efficiency, low harmonic and intermodular dis ⁇ tortion, wide radiation properties, and lack of phase distortion.
• the object of the present invention is to provide a novel loudspeaker whose sound reproduc- tion can be affected by the properties of the room as little as possible.
• a loudspeaker has been designed so that it has a uniform power spectrum, its free-field response unavoidably emphasizes the high frequencies, owing to the properties of directivity of the piston radiator.
• Such a loudspeaker sounds reasonably agreeably in a hard room, but in a room with soft acoustics it is annoyingly sharp with the missing bass and emphasized middle and treble ranges.
• the loudspeaker in accordance with the present invention is mainly characterized in that at least one wall of the loudspeaker box is made of such a material as permits passage of the background radiation of the loudspeaker element as attenuated through the wall into the listening space so that the said radiation is of at least substantially opposite phase (phase difference 180°) , as compared with the frontal radiation of the loudspeaker element, within a wide frequency range.
• the wall con ⁇ cerned may be the rear wall of the box, both of the side walls, or even all the walls of the box.
• One suitable wall material is polystyrene plastic whose density is about 25 to 40 kg/m 3 , but it is also possible to use other so-called lossy materials, e.g. cardboard or thermoplast.
• the sound penetration properties depend on several factors, such as thickness, density, area and internal structure of wall. Correct dimensioning is obtained by experimenting.
• the method increases the directivity at low frequencies considerably, it at the same time dramatically reduces the power radiated by the loudspeaker at these frequencies. In this way it is possible to reach an ideal ratio between sound pressure and power.
• most recent studies have indicated that, among reflections in a room, the so-called early reflections are the most detrimental ones. As early reflections are considered reflections arriving at delays of about 0.1 to 2 ms. These reflections are produced from faces placed in immediate proximity of the loudspeaker, i.e. from the rear wall, the floor, and from the side walls. Accord ⁇ ing to the studies, the early reflections cause the following distortions of reproduction: colouring of sound, attenuation of transients and dynamics, unstable stereo picture, weakened resolution power.
• the loudspeaker radiates rearwards and to the sides as attenuated by up to 20 dB, as compared with the radiation in the direction of the main axis.
• the acoustic advantages obtained can be presented as follows, as condensed:
• Figures 1 and 2 show situations in which the loudspeaker has a wide and a narrow, respectively, directional cone.
• Figure 3 shows a dipole radiator
• Figure 4 the radiation pattern produced by it.
• Figure 5 shows an embodiment of a loudspeaker in accordance with the invention,
• Figure 6 shows its radiation pattern.
• Figure 7 shows a second embodiment of a loudspeaker in accordance with the invention
• Figure 8 shows its radiation pattern.
• Figure 1 shows a normal situation in which the loudspeaker has a wide directional cone.
• an abundance of early reflections 11 can be generated from the walls 10 and from the floor, the intensity of the said early reflections being high. Moreover, they come almost straight from the direction of the sound (L, R) , whereby their effect deteriorating the sound is emphasized further.
• Figure 2 shows a loudspeaker whose directional cone is narrow. In such a case, the amount of early reflections 12 is little and their intensity is low.
• a dynamic loud ⁇ speaker can be considered as a piston radiator whose properties of directivity almost exclusively depend on the ratio of the diameter of the radiator to the fre ⁇ quency to be reproduced.
• a good directivity of the bass range i.e. a narrow directional cone, requires a large area of the radiator. This is, of course, not possible in all constructions.
• a dipole radiator con ⁇ sists, e.g., of a loudspeaker element placed in a finite plate.
• Figure 3 shows a dipole radiator, and Figure 4 the radiation pattern 15 generated by same.
• a drawback of a dipole radiator is very poor ability to reproduce low sounds, for when the distance of the loudspeaker 13 from the edge of the plate 14 is less than X/4, below the corresponding frequency, the reproduction starts being attenuated by about 12 dB/oct.
• FIGS. 5 and 7 are schematical sectional views of two embodiments in accordance with the invention seen from above.
• Reference numeral 1 denotes the loud ⁇ speaker element
• 2 denotes the loudspeaker box as a whole
• 3 denotes the front wall of the box, into which the loudspeaker element has been mounted.
• Reference numerals 4 , 5 and 6 denote such walls penetrable by sound as (by vibrating) allow passage of the background radiation 9 of the loudspeaker element 1 , as attenuated, into the listening space so that the background radiation is at an opposite phase, phase difference 180 , as compared with the frontal radiation of the loudspeaker element 1 , within the frequency range of about 40 to about 800 Hz.
• Numeral 7 (in Fig.
• Fig. 7 denotes an additional attenuating part for bass sounds, attached to the middle portions of the walls 5 and 6, which said attenuating part may consist of a piece of wood and which is not in con ⁇ tact with the rigid walls 2 and 3.
• Numeral 8 denotes an ordinary insulation, e.g. mineral wool.
• Fig. 5 the rear wall of the loudspeaker has been replaced by a wall 4 penetrable by sound.
• Figure 6 shows the directional pattern 16 generated as well as, shown by broken line 17, the corresponding situation if the rear wall were traditionally rigid.
• both of the side walls have been replaced by walls 5 and 6 penetrable by sound
• Fig. 7 both of the side walls have been replaced by walls 5 and 6 penetrable by sound
• the apparatus in accordance with the invention operates as follows: the sound material to be repro ⁇ quizzed is passed into the loudspeaker 1.
• the background radiation 9 of the loudspeaker has access, being partly attenuated, through the wall 4 (or walls 5. and 6) pene ⁇ trable by sound into the listening space. Thereby a dipole effect is produced, wherein the back vibra- tion of opposite phase partly annuls the frontal radi ⁇ ation.
• a radiation pattern in accordance with Fig. 6 (or Fig. 8) results, in which pattern the inten ⁇ sity of the radiation in the lateral direction of the loudspeaker is strongly reduced. This results in an efficient attenuation of early reflections caused by the side walls of the room.
• the front wall 3 and the rear wall are made of rigid particle board, thickness, e.g., 18 mm; the side walls 5 and 6 are made of polystyrene board, density about 40 kg/ ⁇ r 3 and thickness about 25 mm; the attenuation parts 7 are made of pine wood, length about 220 to 230 mm, height about 35 to 40 mm, and thickness about 25 mm.
• the wood parts 7 can be sub ⁇ stituted for, e.g., by appropriately dimensioned alu ⁇ minium profiles.
• the walls 5 and 6 are preferably lined with fabric, underneath the loudspeaker 1 , in a way known in prior art, a stationary support between the front wall and the rear wall is fitted, which support is not shown in Fig. 7.

Landscapes

• Health & Medical Sciences (AREA)
• Otolaryngology (AREA)
• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8516169

Family Applications (1)

Country Status (4)

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Family Cites Families (8)

• 1982
  • 1982-10-18 FI FI823540A patent/FI823540A0/fi not_active Application Discontinuation
• 1983
  • 1983-10-17 EP EP19830903296 patent/EP0141813A1/en not_active Withdrawn
  • 1983-10-17 WO PCT/FI1983/000065 patent/WO1984001681A1/en not_active Ceased
• 1984
  • 1984-06-15 DK DK295384A patent/DK295384D0/da not_active Application Discontinuation

Non-Patent Citations (1)

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