Speech enhancement apparatus configured for attachment to a respirator mask that attenuates acoustic energy passed through the respirator mask at one or more frequency ranges of speech, the speech enhancement apparatus comprising: a microphone (34, 134) configured to detect acoustic energy within a clean air envelope of a respirator mask; a speaker (36, 136) configured to produce acoustic energy outside of the clean air envelope within which the microphone is configured to detect acoustic energy; a controller (30, 130) operably connected to the microphone and the speaker, wherein the controller is configured to: receive a speech signal from the microphone, wherein the speech signal is indicative of acoustic energy detected by the microphone within a first frequency range; and deliver an output signal to the speaker to compensate for the attenuation of acoustic energy passed through the respirator mask, wherein the output signal is configured to cause the speaker to emit compensating acoustic energy, wherein the compensating acoustic energy is emitted in one or more predetermined attenuated frequency ranges that cover less than all of the first frequency range, wherein the compensating acoustic energy comprises a predetermined attenuated amplitude profile over each predetermined attenuated frequency range of the one or more predetermined attenuated frequency ranges; and wherein the speech enhancement apparatus further comprises a selector, the selector being operably connected to the controller (30, 130) and configured to select the one or more predetermined attenuated frequency ranges from two or more different predetermined attenuated frequency ranges, and wherein the one or more predetermined attenuated frequency ranges are selected in response to one or more frequency ranges of speech attenuated by the respiratory mask. a microphone (34, 134) configured to detect acoustic energy within a clean air envelope of a respirator mask; a speaker (36, 136) configured to produce acoustic energy outside of the clean air envelope within which the microphone is configured to detect acoustic energy; a controller (30, 130) operably connected to the microphone and the speaker, wherein the controller is configured to: receive a speech signal from the microphone, wherein the speech signal is indicative of acoustic energy detected by the microphone within a first frequency range; and deliver an output signal to the speaker to compensate for the attenuation of acoustic energy passed through the respirator mask, wherein the output signal is configured to cause the speaker to emit compensating acoustic energy, wherein the compensating acoustic energy is emitted in one or more predetermined attenuated frequency ranges that cover less than all of the first frequency range, wherein the compensating acoustic energy comprises a predetermined attenuated amplitude profile over each predetermined attenuated frequency range of the one or more predetermined attenuated frequency ranges; and receive a speech signal from the microphone, wherein the speech signal is indicative of acoustic energy detected by the microphone within a first frequency range; and deliver an output signal to the speaker to compensate for the attenuation of acoustic energy passed through the respirator mask, wherein the output signal is configured to cause the speaker to emit compensating acoustic energy, wherein the compensating acoustic energy is emitted in one or more predetermined attenuated frequency ranges that cover less than all of the first frequency range, wherein the compensating acoustic energy comprises a predetermined attenuated amplitude profile over each predetermined attenuated frequency range of the one or more predetermined attenuated frequency ranges; and wherein the speech enhancement apparatus further comprises a selector, the selector being operably connected to the controller (30, 130) and configured to select the one or more predetermined attenuated frequency ranges from two or more different predetermined attenuated frequency ranges, and wherein the one or more predetermined attenuated frequency ranges are selected in response to one or more frequency ranges of speech attenuated by the respiratory mask.