Broad-band acoustic speaker

In an acoustic transducer, the combination of:

• a magnetic assembly having an annular flux gap formed between a cylindrical center pole having a free end and an outer pole disposed around the center pole, the cylindrical center pole having a constant diameter for at least the length of the flux gap and no greater diameter than the constant diameter between the flux gap and the free end of the center pole, the constant diameter forming a continuously cylindrical bearing surface extending into the flux gap;
• a coil assembly including a voice coil wound on a tubular coil form and reciprocally disposed in the flux gap, the coil form having an internal Teflon bearing surface in continuous sliding contact with the cylindrical bearing surface including a portion of the bearing surface within the flux gap to guide the coil form means relative to the magnetic assembly, the Teflon bearing surface being formed by a substantially continuous ring of Teflon and the bearing surface having an axial length substantially shorter than the coil form means and being disposed near the end of the coil form remote from the means forming the radiating surface;
• means forming an acoustic radiating surface attached to the end of the coil assembly beyond the free end of the center pole and reciprocated by the coil assembly when an electrical signal is passed through the coil;
• and
• means for providing a peripheral air seal between the radiating surface and a stationary baffle and radial support for the radiating surface.

In an acoustic transducer, the combination of:

• a magnetic assembly having an annular flux gap formed between a cylindrical center pole and an outer pole disposed around the center pole;
• a coil assembly including a tubular coil form means reciprocably disposed in the flux gap, said coil form means being in continuous sliding contact with the magnetic assembly to guide the coil form means relative to the magnetic assembly;
• means forming an acoustic radiating surface attached to the coil assembly and reciprocated by the coil assembly when an electrical signal is passed through the coil;
• and
• means for providing a peripheral air seal between the radiating surface and a stationary baffle and radial support for the radiating surface, said means also axially biasing the radiating surface to a predetermined axial position and providing essentially the only axial bias to the radiating surface and the coil assembly, and including a plurality of spring metal members cantilevered from the peripheral support flange and extend toward the peripheral edge of the means forming the acoustic radiating surface.

The acoustic driver comprising:

• magnetic means forming an annular flux gap having an axis;
• a tubular coil form having a voice coil thereon disposed in the flux gap for reciprocation coaxially with the flux gap;
• a thin, acoustic radiating membrane fastened to the coil form having an axis coaxial with the axis of the flux gap and coil form;
• and
• a plurality of rib members coupled to the coil form by means for transmitting acoustic energy at frequencies above about 8,000 Hz and radiating outwardly from the coil form, each rib member being coupled along its length to the membrane by means for transmitting acoustic energy at frequencies above about 8,000 Hz to the adjacent portion of the membrane, each rib being fabricated from a material of high rigidity and having its major cross sectional dimension disposed substantially at a right angle to the membrane surface, each rib having, when coupled to the membrane, a longitudinal transmission velocity at least near the coil form for acoustic vibrations parallel to the axis of reciprocation between 8,000 Hz and 16,000 Hz that is equal the velocity of acoustic energy in standard air.

The acoustic transducer comprising the combination of:

• magnetic means for producing an annularly shaped magnetic field including a cylindrical center pole member and a circular outer pole member disposed around and spaced from the center pole to form the annularly shaped magnetic field therebetween;
• coil means forming an annularly shaped alternating current field disposed in the annularly shaped magnetic field for reciprocation axially of the center pole;
• one of the fields being continuous and the other field being divided into axially spaced rigidly interconnected subfields of substantially equal frequency response, the subfields being spaced such that as the current field moves in one direction relative to the magnetic field, one of the subfields is coupled to said one field to an increasing degree and the other of the subfields is coupled to said one field to a decreasing degree, and as the current field moves in the other direction relative to the magnetic field, said one of the subfields is coupled to said one field to a decreasing degree and said other subfield is coupled to said one field to an increasing degree to thereby maintain a substantially constant degree of coupling between the two fields over a substantial distance of relative movement;
• an acoustic radiating surface attached to and reciprocating axially with the coil means and having an outer periphery;
• a rigid support member attached to the magnetic means and including an annular flange disposed adjacent the outer periphery of the acoustic radiating surface;
• and
• axially flexible means providing an annular air seal between the periphery of the radiating surface and the annular flange while providing radial alignment for the radiating surface.

The acoustic driver comprising a tubular coil form the axis of which is disposed on an axis of reciprocation, a voice coil disposed on the coil form, permanent magnet means establishing a magnetic field which intersects the wires of the voice coil, means forming an acoustic radiating surface connected to the coil form and disposed at an angle to the axis, said means comprising a membrane section and a plurality of elongation transmission rib sections coupled to the coil form and extending radially outwardly along the radiating surface and continuously coupled to the membrane section, the transmission rib sections having a transverse dimension normal to the radiating surface of the membrane that is about an order of magnitude greater than the dimension of the membrane normal to the radiating surface,

• a support flange disposed around and spaced from the peripheral edge, and a plurality of metal spring members extending between the peripheral edge and the support flange for providing radial alignment of the means forming the radiating surface and for providing an axially directed spring force tending to bias the member forming the radiating surface to a predetermined axial position, and
• a flexible membrane forming an air seal between the means forming the acoustic radiating surface and the support flange, the membrane being attached to each of the spring members to dampen resonance of the spring members.

The acoustic transducer comprising the combination of:

• magnetic means for producing an annularly shaped magnetic field including a cylindrical center pole member and a circular outer pole member disposed around and spaced from the center pole to form the annularly shaped magnetic field therebetween;
• coil means forming an annularly shaped alternating current field disposed in the annularly shaped magnetic field for reciprocation axially of the center pole, the coil means being in sliding contact with at least one of the poles to guide movement of the coil means relative to the magnetic means;
• one of the fields being continuous and the other field being divided into axially spaced rigidly interconnected subfields of substantially equal frequency response, the subfields being spaced such that as the current field moves in one direction relative to the magnetic field, one of the subfields is coupled to said one field to an increasing degree and the other of the subfields is coupled to said one field to a decreasing degree, and as the current field moves in the other direction relative to the magnetic field, said one of the subfields is coupled to said one field to a decreasing degree and said other subfield is coupled to said one field to an increasing degree to thereby maintain a substantially constant degree of coupling between the two fields over a substantial distance of relative movement;
• an acoustic radiating surface attached to and reciprocating axially with the coil means and having an outer periphery;
• a rigid support member attached to the magnetic means and including an annular flange disposed adjacent the outer periphery of the acoustic radiating surface;
• and
• axially flexible means providing an annular air seal between the periphery of the radiating surface and the annular flange while providing radial alignment for the radiating surface.