Allan J. Rosenheck

Choice of frequency weighting for the evaluation of weapon noise

This paper describes a laboratory study to choose an appropriate frequency weighting network for predicting the annoyance caused by the noise from small, medium, and large weapons. The results indicate that the annoyance of all three weapon types is the same if the blasts are heard at identical A-weighted SELs. On the other hand, equal C-weighted SELs result in large differences in annoyance between the weapon types. The implications of these results for outdoor noise criteria depend on the assumption concerning window condition. If one assumes that people hear the blasts predominantly through open windows, then A-weighted criteria should be appropriate for all the weapon types without any correction (penalty or bonus) for weapon type. On the other hand, if the blasts are heard predominantly through closed windows a penalty of about 5 dB should be applied to the outdoor levels of the large weapons to account for the poorer low-frequency attenuation of the windows.

External‐Ear Replica for Acoustical Testing

As part of the development of an acoustical manikin, an artificial ear was designed to simulate the mechanical and acoustical properties of the external ear, up to and including the impedance of the eardrum. The sensing element is a B&K 4132 electrostatic microphone terminating a simulated ear canal with an acoustical impedance‐matching network that, combined with the microphone, furnishes the eardrum impedance. The canal proper has dimensions approximating those of the real ear and is placed inside a skull of polyester‐impregnated fiberglass, provided with a plastisol pinna of realistic dimensions and texture. The head is mounted on a fiber torso. The new artificial ear is suitable for testing all types of receivers and ear enclosures under realistic conditions. The inner portion of the artificial ear is made of reproducible metallic components, making it suitable for consideration as an artificial‐ear standard.

Head‐Contact Microphone for Efficient Speech Transmission

Work was undertaken to develop a microphone that would provide highly intelligible speech reception by direct contact with the head. Since investigation (Paper 7D4) showed that the forehead provided the bighest quality speech, efforts were concentrated in this region. In order to avoid a loss of high‐frequency response owing to flesh compliance, the total mass of the transducer had to be limited to below 1 g for a unit of small size. This was most readily accomplished with a miniature, inertial‐type transducer, which, additionally, provides the proper response‐frequency characteristics. Articulation tests, with the microphone located on the forehead, indicated an average PB word score of 90% in quiet surroundings. Good rejection of ambient acoustical noise was observed. The ultimate noise rejection is limited by noise‐induced vibrations transmitted through the head. The microphone totally frees the mouth area of obstacles located in front of the lips, and its miniature size suggests several applications. ...

Speech Intelligibility by Head Contact as Function of Location on Head

A study was made to determine the level, spectrum, and intelligibility of speech available for contact transducers, as a function of head location. A specially designed head‐contact microphone was developed for use in these tests. The output of the head‐contact microphone and that of a “flat” acoustical microphone were simultaneously recorded for 10 talkers reciting phonetically‐balanced test sentences. The recorded data were then played back, and trained listeners subjectively evaluated the intelligibility of the contact speech versus the acoustically received speech. Several head areas showed highly intelligible speech with good consonantal pickup, while other regions were notably poor even when equalization techniques were employed. Spectral analysis showed that regions that had adequate high‐frequency energy generally corresponded to those that had exhibited good intelligibility in the listening tests. The head was grouped into four regions—forehead, ear, cheek, and top and back of head. The over‐all ...

Transmission of Directional Perception

In a previous paper [B. B. Bauer, “Stereophonic Earphones II,” presented before the 13th Ann. Convention Audio Eng. Soc., 1961], one of the authors described a scheme for transmitting directional information using crossed dipole receptors connected to dichotic earphones through a stereo‐binaural network [B. B. Bauer “Stereophonic Earphones and Binaural Loudspeakers,” J. Audio Eng. Soc. 9, No. 2, 148–151 (1961)]. In the paper, it was predicted that improved realism would be obtained by using receptors having a limacon characteristic. Recently, experimental work with cardioid pattern receptors has been performed, confirming the above prediction. This paper describes the new apparatus and the orientation ability afforded by it. Applications of the directional transmission scheme to aerospace and underwater communications are discussed. [Work supported in part by the Avionics Laboratory, Research and Technology Division, ASD, W‐PAFB, Ohio, under contract AF 33(357)‐10737.]