Part 3
The Car Environment
As most of us will listen to music the majority of the time in the car or at home, I will limit the discussion to these two environment. Music Hall, concerts, natural reproduction can be discuss another time in a more esoteric thread.
Car audio has advantages and disadvantages over conventional home system. The biggest disadvantage and also its’ biggest advantage is the environment in which sound are reproduced. The main disadvantage is where the listener is sitting. Either to the left or to the right of the optimum spot of a typical speakers set-up. There is really no truly cost effective way to correct this problem although new DSP technology has limited this issue. I will not go into the various acoustic properties problem associated with the various materials found in a typical car as it is beyond this thread.
To truly understand this importance, one has to understand how music are recorded. The majority of music recordings are done via a studio with the engineer placing each musical instrument or voice in a precise area to create depth and proper soundstage. This is not a physical placement but rather the use of panning, ambience/delay and level control.
Another method of recording and are mainly used in classical music is binaural recording. These recordings utilizes a dummy head with two microphones either embedded into the ear canals or on the side of the dummy’s head to capture live recordings. The dummy is placed in the optimum (center) position in the amphitheatre to capture all the nuances heard as if a live person was sitting in that very seat thus capturing not only the main sound but also the natural ambient sound from the environment, the same ambience/delay and level typically artificially created in the studio as stated above. This method will also recreate the proper soundstage that engineers strive for and in my opinion, the purest form of recording. Of course this type of recording is only effective for Classical or Operatic performances or in an environment as envisioned by the artist.. Either scenario requires that the listener of these recordings be placed in the center of the two speakers which as stated above, is not feasible in a car.
The problem is distance differences caused by where the listener is in relation to each speaker located in a typical car. Differences in distance create levels and time delays variations and if not angled correctly to the listener, deviances in frequency reproduction as well causing localization issues.
To elaborate, frequency and levels changes dramatically at off-center. For tweeters, there is typically a drastic drop-off at the high end. Occasionally the drop off are not uniform thus creating coloured sound at off-angle. Some designs are better than others when dealing with this issue but we’ll limit our discussion to basic linear drivers and not exotic eletrostatics or ribbons. Thus if you taylor the set up to the driver, it cannot be done for the passenger. Unless you’re the driver in the Mclaren F1, compromise must be accepted.
Some novel ideas has been tried to solve this problem in the past by utilizing a center speaker and Digital Signal Processing (DSP). Its’ effectiveness especially DSP is largely due to our psychoacoustic responses but by no means optimum. In my opinion, there is no way to correct this natural phenomenon to achieve absolute proper soundstage. Thus, the only feasible way is to minimize the effect is by proper placement of speakers, angles of each drivers and at the longest possible distance from speakers to listener as possible as the ratio difference would be lessen.
As such, issue relating to timing and frequency between drivers from each channel must also be taken into consideration. For example when dealing with component setup (Tweeter and woofer), it should always have the same facing angle and distance. Optimally from the same point. Due to the short distance from the drivers to the listener in a typical car installation, poor soundstage would result and at worst, the illusion of musical chairs would result. This phenomenon can be illustrated when an instrument is playing at a lower octave thus a lower frequency then as it move to a higher octave, movement of the instrument is noticed. Sound originally played by the woofer at the door for example, would creeps toward the tweeter on the dash. If both drivers are close to each other this creeping would be minimized.
Fortunately, this creeping is very difficult to detect since crossover frequency between tweeter and woofer are in the frequency range that the brain tends to have difficulty in localization and the majority of all recordings contain many complex notes that masks this movement. Some system mask this phenomenon by overlapping the x-over frequency to make the transition less evident to cover the deficiency in placement.
With the above, we also have to keep in mind that no speakers/driver can produce all the frequencies in the desirable range and at an acceptable level. Now our problems are two folds. Multiple speakers in multiple locations. Concentric design speakers will limit the creeping issue but will still have issues with time delay in a stereophonic setup if not place with diligence. Again, angle and distance must be well researched, something that a home system would not much of an issue, all else being equal. Fortunately localization is of a non issue when we are dealing with low frequencies as it is quite difficult to locate the source with any accuracy below 85Hz hence, subwoofers can placed in the back without the sense bass coming from the back.
As stated, although the space in which the listener is placed in a car is the biggest problem, it is also the biggest advantage since the confined space of the vehicle will allow phenomenal amount of low frequency to be not only heard but felt. The obstacle to achieve desirable bass notes in most listening environment is a non issue in a typical car. When we are dealing with low frequencies the listener is within the space of the wavelength itself. The confined space also allow higher levels with ease.
With the above basic knowledge, let set out each individual component in a typical cars system. Begin in the order of the typical audio chain;
Continue to Part 4
Last edited by zakimak; 11-28-2013 at 05:26 PM.
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