rear cover can also be of metallic material e g nickel plated brass to help electromagnetically screen the transducer and its connections to the plug a stereo plug would permit separate connections to sender transducer and receiving transducer separate parallel tubes or co axial tubes or a single tube would act as the transmission path between plug and operator this would be particularly useful when u2018 patching u2019 between mobile or normal landline telephones and for example a radio transmitter with suitable input circuitry electronic circuitry to alter the volume level or to modify tonal response or to compensate for the tonal alterations due to the tubing may be placed inside the plug cover using microelectronic techniques the mouthpiece hole 2 a can have a flexible tube thinner than the sound tube 2 passed through it acting so as to convey speech down next to the microphone capsule 3 the extra tube to tun internal to the sound tube and entering through a hole made in the sound tube at about mouth distance from the ear end of that tube the lower end of the inner sound tube can extend only a short distance down inside the outer sound tube or it can extend all the way down almost making contact with the microphone capsule 3 this additional inner sound tube will act so as to alter the sound balance between the ear end of the outer sound tube.