the present invention will be described in detail now with reference to the attached drawings . fig1 and 2 show an electroacoustic transducer fabricated in accordance with a first embodiment of the present invention . lead terminals 2a , 2b , 2c and 2d are integrally formed of a lead frame 40 . a pole piece portion 4 consists of a plate - shaped yoke 5 and a core 6 attached to the yoke 5 . the lead terminals 2a , 2b , 2c and 2d and the pole piece portion 4 are embedded in a base 8 formed of a synthetic resin in the shape of a rectangular flat plate . a coil 10 is wound around the core 6 , and an annular magnet 12 is disposed so as to surround the coil 10 . the magnet 12 and the pole piece portion 4 are magnetically coupled to form a magnetic path . the coil 10 formed of an air - core one is mounted on the core 6 or directly wound around the core 6 . the base 8 is provided on its upper surface with positioning protrusions 14 , 15 , 16 , 17 and 18 . a support ring 20 is positioned inside the positioning protrusions 14 , 16 and 18 on the base 8 . the support ring 20 has a stepped portion 22 on its inner surface at a position near the upper end thereof , and a diaphragm 24 is seated on the stepped portion 22 of the support ring 20 . a magnetic piece 26 is attached to the central portion of the diaphragm 24 to increase the vibrating mass of the diaphragm 24 . opposite ends 28 and 30 of the coil 10 are pulled outside along the lower surface of the magnet 12 and via a space between the positioning protrusions 16 and 18 , and soldered to the lead terminals 2a and 2b , respectively . a case 32 is positioned in place on the base 8 by the positioning protrusions 14 , 15 and 17 , and the case 32 is fixed to the base 8 by a fixing means , such as ultrasonic welding . the case 32 formed of synthetic resin defines a resonance space 34 extending over the surface of the diaphragm 24 and around the support ring 20 . the case 32 is provided on one side wall thereof with a sound emitting cylinder 36 by means of which the resonance space 34 communicates with the atmosphere . in such an electroacoustic transducer , the pole piece portion 4 having the core 6 and combined with the base 8 by insert molding , the coil 10 and the magnet 12 constitute an electromagnetic transducing portion 38 . when an ac signal is applied across the lead terminals 2a and 2b , the coil 10 is excited and creates an alternating magnetic field between the core 6 and the diaphragm 24 provided with the magnetic piece 26 . consequently , the diaphragm 24 vibrates to generate sound , the resonant space 34 resonates and the sound is radiated outside the case 32 through the sound emitting cylinder 36 . the resonation of the resonant space 34 causes the base 8 and the case 32 to vibrate and generate sounds . since the lead terminals 2a and 2b are formed of the lead frame , the electroacoustic transducer comprises a comparatively small number of component parts , can be efficiently assembled by a reduced number of assembling steps , and can be formed in a flat , compact construction . the support ring 20 is formed of a metal , such as brass , separately from the base 8 , which enhances the accuracy of the support ring 20 , moderates demand for the molding accuracy of the base 8 , and improves the yield of the electroacoustic transducer fabricating process . the method of fabricating the electroacoustic transducer will be described in sequential fabricating steps with reference to fig3 to 14 . referring to fig3 showing an example of the lead frame 40 , the lead frame 40 is formed like a strip and is coated with solder . the lead frame 40 has opposite side bars provided with locating holes 42 . as shown in fig4 a and 4b , the lead terminals 2a , 2b , 2c and 2d are formed so as to slightly protrude by a step 44 from a plane including the side bars . the lead frame 40 as shown in fig3 need not be formed by a single forming cycle but may be formed by a plurality of forming cycles in which the lead frame 40 is located by means of the locating holes 42 . referring to fig5 showing an example of the pole piece portion 4 , the pole piece portion 4 consists of the yoke 5 having a notched portion 7 on a circular material and the core 6 attached to the yoke 5 by caulking the core 6 by the yoke 5 . the core 6 is columnar and is small in diameter at its press fit portion 9 . a circular protrusion 11 is formed on the lower surface of the yoke 5 . referring to fig6 and 8 showing a molding process of the bases 8 on the lead frame 40 , a plurality of bases 8 are formed of synthetic resin on the lead frame 40 by molding . fig6 and 8 show the top side of the lead frame , and fig7 shows the rear side . in the molding , the lead frame 40 and the pole piece portions 4 are held in a mold , and a molten synthetic resin is poured into the mold to form the bases 8 over the pole piece portion 4 and the lead terminals 2a , 2b , 2c and 2d so that the upper surface of the pole piece portion 4 , and the upper portions of the lead terminals 2a , 2b , 2c and 2d to be subjected to soldering are exposed on the bases 8 . referring to fig9 after the coil 10 is mounted on the core 6 of the pole piece portion 4 embedded in the bases 8 on the lead frame 40 while the support ring 20 , the magnet 12 and the diaphragm 24 are formed in advance , the support ring 20 is fitted in a space of the base 8 and is attached adhesively to the base 8 . the magnet 12 is fitted in the support ring 20 , and then the diaphragm 24 is placed on the support ring 20 . as shown in fig1 , opposite ends 28 and 30 of each coil 10 mounted on the core 6 of the pole piece portion 4 are pulled outside via the space between the positioning protrusions 16 and 18 , and then caught by protrusions 15 and 17 so that they are extended in the direction perpendicular to the lead frame 40 and held under an appropriate tension , and finally they are soldered to the terminals 2a and 2b , respectively . when an adhesive means , e . g . silicon adhesive is applied to a gap defined between the protrusions 16 and 18 , the opposite ends 28 and 30 of the coil 10 are protected and a groove 50 ( fig1 and 8 ) is sealed . fig1 is a cross - sectional view taken on lines 11 -- 11 in fig1 , showing a state of completion of processing of the opposite ends 28 and 30 of the coil 10 . the case 32 is formed of a synthetic resin by molding and it is disposed on the base 8 formed on the lead frame 40 as shown in fig1 . as shown in fig1 , the base 8 and the case 32 are jointed to each other by ultrasonic welding . the case 32 may be attached adhesively to the base 8 with an adhesive . with such a joining step , a plurality of such electroacoustic transducers are assembled on the lead frame 40 . after the lead terminals 2a , 2b , 2c and 2d are cut off from the lead frame 40 , the lead terminals 2a , 2b , 2c and 2d are subjected to a forming process as shown in fig1 to complete the electroacoustic transducer . since the lead terminals 2a to 2d are integrally molded on the lead frame 40 and the base 8 is also molded to embed the pole piece portion 4 therein , the number of component parts that need to be assembled can be reduced . further , since all the processes can be carried out on the lead frame 40 , it is not necessary to reverse the lower case every assembling step which has been made in the conventional method of fabricating the electroacoustic transducer , and hence the electroacoustic transducer can be easily assembled by simple assembling work . although the core 6 is mounted on the coil 10 in the first embodiment , the coil 10 can be directly wound around the core 6 . although the support ring 20 and the magnet 12 are formed separately in the first embodiment , a magnet 120 constituting a support ring may be formed of a plastic magnet or a metal magnet or the like as shown in fig1 . the magnet 120 has the stepped portion 22 like the support ring 20 so as to place the diaphragm 24 thereon . if the magnet 120 serving as the support ring 20 is used , it is possible to constitute the magnet 12 and support ring 20 as mentioned in the first embodiment by a single component , which reduces dimensional error caused by two components and enhances accuracy of the product . a . since the bases are formed on the lead frame by molding and the pole piece portions can be integrated with the bases by the same molding , it is possible to perform continuous operation starting from mounting to assembling of the component parts on the lead frame . further , since the lead frame need not be reversed , the fabricating steps can be simplified and accuracy of assembly of the product can be enhanced . b . since the lead frame may be formed of a strip of material and intervals between products can be assured on the continuous lead frame , and the plural products can be subjected to an automatic assembling process when the lead frame is carried , fabricating time can be shortened , the number of carriage of the products by a pallet can be reduced , and working areas involved in assembling and molding processes can be reduced so as to enhance productivity of the electroacoustic transducer . c . if the support ring is made of the magnet , the number of component parts can be reduced , the number of components and dimensional error caused by two components can be reduced , and further the accuracy of product can be enhanced . although the invention has been described in its preferred form with a certain degree of particularity , obviously many changes and variations are possible therein . it is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein without departing from the scope and spirit thereof .