In Harry F. Olson’s book entitled, “Acoustical Engineering” which was originally published in 1947, he discusses a radio placed in an automobile. It is interesting to see the “acoustical thought” that was in use in 1947 and compare that thinking and application with current acoustical trends.
Rather than paraphrase his book section and make comparisons to modern day applications, I will just quote the entire section below and let you, the reader, make the modern day similarities and differences. Any parentheses inserted are by myself to improve understanding when text refers to a graphic:
Acoustical Engineering – Automobile Radios
The primary loudspeaker in an automobile is usually located in one of four locations, namely in front of instrument enclosure (this would be a front panel mounted speaker), in the top of the instrument enclosure (this would be a dash mount speaker firing into the windshield), in the fire wall or dash, and in the header above the windshield. The header location gives somewhat better distribution of the high frequency response in the back seat than the three other locations. However, the low frequency response of a loudspeaker mounted in the header is usually attenuated due to the small volume behind the loudspeaker.
The dash or firewall location gives fair distribution of the high frequency response in the front seat, but very poor distribution in the rear seat. The low frequency response in this position can be made very good by employing a large loudspeaker case or by venting the back of the case into the engine department. Sometimes a combination of a low frequency dash loudspeaker and a high frequency header or instrument panel loudspeaker is employed. At the present time, the favored position for the loudspeaker appears to be in the instrument panel because in this location the radio receiver, loudspeaker, and controls may be combined into a single compact unit.
The distribution of sound is excellent in the front seat and good in the back seat. The stiffness presented to the back of the cone because the entire radio receiver case volume is used to enclose the back of the loudspeaker. In this manner, the response can be maintained in the low frequency range. In order to improve the reproduction of sound in the rear seat, a secondary loudspeaker is used in the rear. (header area between rear seats and windshield)
The conditions under which an automobile radio receiver operates differs widely from those of a loudspeaker in the living room. It will be seen that the automobile is a small enclosure with short distances between the loudspeaker and the listener. This is fortunate because wind,road rumble, and engine noise mask the reproduced sound. The power output of the receiver should be powerful enough to override these noises and give intelligible reproduction of speech and pleasing reproduction of music.
In view of the fact that the sound level delivered to the loudspeaker is quite high under the noise conditions, it is important that the frequency response characteristics be smooth and free of peaks, otherwise the reproduced sound will be disagreeable due to the high level of peaks relative to the general level. It is also important that the nonlinear distortion be kept at a low value because spurious components in the reproduction of sound are more apparent at the higher sound levels.
Speaker locations today, differ slightly from those represented in this book chapter. Now, we do most of the speaker and sound manipulation in the digital domain and bounce the sound around between the speakers inside the vehicle to try and produce some order to our sound presentation. It is difficult in a “glass bowl” for even a computer.