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
  • H04R1/22—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
  • H04R1/2807—Enclosures comprising vibrating or resonating arrangements
  • H04R1/2815—Enclosures comprising vibrating or resonating arrangements of the bass reflex type
  • H04R1/2823—Vents, i.e. ports, e.g. shape thereof or tuning thereof with damping material
  • H04R1/2826—Vents, i.e. ports, e.g. shape thereof or tuning thereof with damping material for loudspeaker transducers

Definitions

• This invention relates to port devices for bass-reflex speakers enclosures and more particularly to devices which extend reproduction of sounds down to lower frequencies while providing attenuation and damping such as to minimize boominess and other resonance effects and distortions.
• the devices also improve efficiency and output at low frequencies and at the same time, they are relatively simple and inexpensive in construction and reduce the size of enclosure required to provide high quality sound reproduction.
• the base-reflex ported type of enclosure has been very popular because of its relative s.implicity and low cost co.mbined with ve.ry good performance.
• a port opening is provided in a wall portion of an enclosure, typically in a portion of the front wall which carries the speaker behind an opening therein, spaced from the port opening.
• the mass of the air in the port opening cooperates with the compliance of the Air volume within the enclosure to produce a phase-shift which may approach 180 degrees. Since the sound emanated from the back of the speaker cone is 180 degrees out of phase with that emanated from the front of the speaker cone, the sound emanated from the port opening may approach an in- phase relationship to the sound emanated from the front of the speaker cone.
• the size of the port opening should have the proper relationship to other parameters including the size of the enclosure and the size of the speaker.
• the size of the port opening may approach that of the speaker opening for larger enclosures and is reduced to a fraction of the size of the speaker opening for smaller enclosures.
• This invention was evolved with the general object of further improving upon the bass-reflex ported type of enclosure.
• the invention is based upon the recognition of the nature of problems associated with prior disclosures and upon the discovery of constructions which provide improved results.
• a port device including a cylindrical tube positioned within a ported enclosure with one end thereof at a port opening of the enclosure, the tube being thus positioned in a manner similar to the positioning of tubular ducts in prior enclosures.
• a wall is provided which has a circular central opening in coaxial relation to the tube, the opening being of smaller diameter than the diameter of the tube and having a substantially smaller area.
• the diameter of the opening may be such that the area of the opening is about two-fifths the area of the tube. it is found that with this change, greatly improved results are achieved. .
• the speaker cone is subjected to a more constant or even pressure and the momentum which can be imparted to air in the small opening is reduced.
• the speaker is required to move a larger volume of air in relation to the size of the opening.
• the speaker cone is subjected to additional back pressure to achieve the objectives of the use of a damping material but with much less loss of energy.
• the action is obtained in the absence of conditions which might produce peak resonance effects at certain frequencies.
• the high efficiency and output capabilities of the bass-reflex design are preserved without resonances and without energy absorbing damping material.
• efficiency and output it is noted that the air enters the small opening, moves through the tube and exits from the port opening with no substantial decrease in total energy.
• an important aspect of the invention is that the degree of effective damping obtained is controlled by the ratio between the exit or mouth area at the port opening of the enclosure and the small opening or throat area at the inner end of the tube, the degree of damping being increase by increasing the ratio. It is also noted that the device can be quite short in length and yet produce results which are superior to those obtained with a conventional duct of much larger length. It is further noted that the length of the tube may apparently be reduced by a factor equal to the ratio between the cross sectional areas of the port device at its mouth and its throat.
• Figure 1 is a perspective view of a bass-reflex speaker enclosure in which a port device according to the invention is installed;
• Figure 2 is an elevational sectional view through the speaker enclosure of Figure 1, taken substantially along line II-II thereof;
• Figure 3 is a sectional view on an enlarged scale, taken substantially along line III-III of Figure 2 and showing details of the construction and mounting of the port device;
• Figure 4 is a sectional view similar to Figure 3 but showing a modified device having a generally hemispherical shape
• Figure 5 is another sectional view similar to Figure 3 but showing another modified device having a generally conical shape
• Figure 6 is still another sectional view similar to Figure 3 but showing still another modified device havin a rectangular shape
• Figure 7 is a sectional view taken substantially along line VII-VII of Figure 6;
• Figure 8 is another sectional view similar to Figure 3, showing yet another modified device according to the invention, having a stepped construction.
• Reference numberal 10 generally designates a bass reflex speaker enclosure to which the invention is applied, the enclosure 10 including bottom and top walls 11 and 12, side walls 13 and 14, a rear wall 15 and a front wall 16.
• the front wall 16 has a speaker opening 17 therein and supports a speaker 18 on its rearward side behind opening 17 - the speaker 18 including a cone 19 and a driver structure 20.
• the front wall 16 also has a port opening 21 therein, below the speaker opening 17, and a port device 22 is mounted on the front wall 16 behind the port opening 21.
• the port device 22 is constructed in accordance with the principles of the invention and includes a cylindrical tube 23, the forward end of which is fitted in the port opening 21, a suitable adhesive being provided between the outer surface of the forward end portion of tube 23 and the inner surface of the wall 16 at the opening 21.
• the cylindrical tube 23 is similar to tubes as ducts used in certain prior art enclosures, but in the device 22 the inner end of the tube 23 is not completely open. Instead, a circular wall member 24 secured to the inner end of the tube 23 as by providing an adhesive between the outer surface of member 24 and an inner surface portion of tube 23.
• Wall member.24 has an opening 25 therein which may preferably be centrally located in alignment with the axis of tube 23.
• the enclosure 10 in the illustrated arrangement nay have an inside height dimension of 15 inches, an inside width dimension of 14.5 inches and an inside depth dimension of 14 inches to provide a volume (excluding construction members) of 2830 cubic inches.
• the speaker 18 may be a 12 inch unit of a type such as generally used in bass-reflex enclosures. A unit with a cloth roll suspension sold as Radio Shack Model No. 40-1304 is suitable, but is only one example of a unit which might be used.
• the tube 23 may be a cardboard tube having a length of 4.25 inches and an inside diameter of 3 inches.
• the wall 24 may be a fiberboard insert and the diameter of the opening 25 may be 1.87 inches to provide an area equal to about two-fifths the internal cross-sectional area of the tube 23.
• the size of the port device 22 in relation to the size of the enclosure should be in approximately the same proportions as in the example. Best results are achieved by so selecting approximate dimensions for a device and then making adjustments by trial and error until an operation is obtained in which the response is both extended to as low a frequency as possible and increased as much as possible without producing response peaks or booming effects.
• the size of the opening 25 is critical. In the example, its area is equal to two-fifths of the crosssectional area of the tube 23 and such a ratio is recommended as a starting point but it should preferably be adjusted until the low frequency response is extended and increased as much as possible without producing booming.
• FIG 4 illustrates a modified device 27 which comprises a hollow generally cup-shaped hemispherical member 28 having a rim portion secured within a port opening 21a in an enclosure wall 16a and having an opening 29 in centered relationship on the axis of the port opening 21a.
• Figure 5 illustrates another modified device 30 which comprises a member 31 of frusto-conical shape having a larger end secured within a port opening 21b in an enclosure wall 16b, a throat opening 32 being provided at the smaller end of the member 31.
• Figure 6.and 7 illustrate yet another modified device 34 which comprises a hollow rectangular member 35 having a forward peripheral portion secured within a port opening 21c in an enclosure wall 16c.
• a rearward wall member 36 is secured within the rearward end of member 35 and has central opening 37 therein, forming the throat opening of the device.
• Figure 8 illustrates still another modified device 38 which includes a cylindrical tube 39, the forward end of which is secured in a port opening 21d in an enclosure wall 16d.
• a circular wall member 40 is secured to the inner en of tube 39 and has a central opening 41 therein.
• a second tube 42 which is smaller than tube 39 has a forward end secured in the opening 41.
• the device 38 is similar to the device 22, but with the addition of a second smaller tube to provide a stepped construction.
• device 38 can be carried forward to provide additional steps, if desired. It will also be understood that shapes other than those illustrated may be used and that in each case, dimensions are chosen and established in the manner as set forth in the foregoing discussion to extend and increase the low frequency response as far as possible without producing booming or other resonance effects. It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of this invention.

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• Health & Medical Sciences (AREA)
• Otolaryngology (AREA)
• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Details Of Audible-Bandwidth Transducers (AREA)

Applications Claiming Priority (1)

Publications (1)

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• 1981
  • 1981-04-28 EP EP19810901632 patent/EP0077324A1/de not_active Withdrawn
  • 1981-04-28 WO PCT/US1981/000554 patent/WO1982003961A1/en not_active Ceased
  • 1981-04-28 AU AU73244/81A patent/AU7324481A/en not_active Abandoned

Non-Patent Citations (1)

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