Patent Grant
6870935
1. Field of the Invention
The present invention is generally directed toward automobile audio systems and, more particularly, toward partitioned audio systems wherein front passengers and rear passengers listen to different audio sources.
2. Description of the Related Art
Most of the time in automobiles, all of the passengers listen to the same audio source (radio/tape/CD) whereby sounds are emitted to the passenger compartment from the front and rear speakers. However, there are times when the rear passengers cannot agree with the front passengers on the desired music or radio station to be listened to. In these situations, it is desirable to have a partitioned system wherein the front passengers listen to one source via the front speakers while the rear passengers listen to a different source by means of headphones or other personal sound sources.
Such partitioned systems are generally well known in the art. When the system is operated in the single-source mode (i.e., partitioning disabled), the front and rear speaker output is entirely controlled by the conventional controls positioned on or near the front dashboard of the automobile. In this situation, the front passengers have total control over speaker output, the portion of the overall sound attributed to the front speakers and to the rear speakers, and the total overall sound level. When the system is operated in the dual source mode (i.e., when sound partitioning is enabled), adjustment of the dashboard mounted controls by the front seat passengers is only operable to adjust the volume of the front speakers, the rear speakers being turned off. Rear-seat accessible controls are used by the rear passengers to adjust the audio source and volume output by the headphones.
Unfortunately, when the system is disabled/enabled to switch between single source and dual source modes, volume stability problems arise. For example, when switching from a single source to dual sources, the volume perceived by the front passengers drops considerably. Conversely, when switching from dual source to single source modes, the volume perceived by the front passengers increases significantly. This disadvantage with state of the art systems is aggravating and causes the front seat passengers to have to adjust the volume controls each time the mode of operation is changed.
Therefore, there exists a need in the art for a partitioned audio system that maintains the volume, as perceived by the front-seat passengers, at a stable level when the system is switched between single and dual source modes.
The present invention is directed toward an improved partitioned audio system wherein the volume, as perceived by the front passengers, is maintained at a stable level when the system is switched between dual and single source modes.
In accordance with the method of controlling the speaker output according to the present invention, when the partitioned system is switched from single source mode to dual source mode, the system enters a first transition phase wherein the output of the rear speakers decreases to zero while the output of the front speakers increases to compensate for the loss of rear speaker output. The total or overall sound pressure level in the passenger compartment, as experienced by the front passengers, remains substantially constant during the first transition phase. At the end of the first transition phase, the output of the front speakers is essentially the same as the combined output of the front and rear speakers during the single source mode or, alternatively, at some sound level that is greater than the sound level provided by the front speakers only in a conventional system.
In further accordance with the present invention, when the partitioned system is switched from dual source to single source mode, the system enters a second transition phase wherein the output of the rear speakers increases while the output of the front speakers decreases. The total or overall sound pressure level in the passenger compartment, as experienced by the front passengers, remains substantially constant during the second transition phase. At the end of the second transition phase, the combined output of the front and rear speakers, as experienced by the front passengers, is essentially the same as the output of the front speakers during the dual source mode.
These and further features of the present invention will be apparent with reference to the following description and drawing FIGURE which schematically illustrates operation of the volume stability control system according to a first preferred embodiment of the present invention.
Operation of the partitioned audio control system according to the present invention will be described hereinafter with reference to the drawing figure wherein the system is shown to operate in either a first mode or a second mode. The first mode corresponds to the situation wherein audio partitioning is disabled and the overall or total sound pressure level of the passenger compartment is provided by the front and rear speakers. The second mode corresponds to the situation wherein partitioning is enabled and the sound pressure level in the passenger compartment is provided solely by the front speakers. During the second mode, the rear passengers may listen to a second source of music, etc. by means of personal sound sources such as headphones.
As used hereinafter, the sound pressure level is intended to indicate the approximate sound level within the passenger compartment and, more particularly, the sound pressure level experienced by the front passengers. Such sound pressure level may be detected by sensors or may be estimated. Moreover, the sound pressure setting of each automobile may be separately determined to tune the relative adjustments of the sound system to the specific features of the automobile. Many factors are known to contribute to the sound pressure level within the car, including the size of the passenger compartment, the relative distance between the front speakers, the rear speakers, and the area at which the sound pressure level is detected, the type of fabric used in the automobile interior, and the amount of window glass. Therefore, the individual sound characteristics of each automobile may be separately determined to tune the relative adjustments of the sound system to the specific features of the automobile.
As shown in the drawing FIGURE, the system generally is operated in the first mode, and then is switched at time t1 to the second mode for an indefinite period of time. At time t2 the control system is returned to the first mode of operation. The first mode corresponds to single source operation, whereas the second mode corresponds to dual source operation.
According to the present invention, time t1, marks the beginning of a first transition phase wherein the outputs of the front and rear speakers gradually change. More specifically, during the first transition phase the system changes from single source to dual source operation. Accordingly, the output of the rear speakers decreases gradually toward zero while the output of the front speakers gradually increases to a level such that the total sound pressure level in the passenger compartment remains constant. The time period Δt1, that it takes for the gradual decrease of the rear speaker output and gradual increase of the front speaker output is predetermined, and preferably is between about 1-5 seconds. Likewise, the output of the personal sound sources or headphones may also be controlled to gradually increase (from zero to a user-selected setting) as the rear speaker output gradually decreases during time period Δt1.
Time t2 marks the beginning of the second transition phase wherein the outputs of the front and rear speakers again gradually change. More specifically, during the second transition phase the system changes from dual source to single source operation. Accordingly, the output of the rear speakers increases while the output of the front speakers gradually decreases. The rate of increase of the rear speaker output and the rate of decrease of the front speaker output is such that the total sound pressure level in the passenger compartment remains constant. The second transition phase time period Δt2 (i.e., the time that it takes for the gradual increase of the rear speaker output and gradual decrease of the front speaker output) is predetermined, and preferably is between about 1-5 seconds. Likewise, the output of the personal sound sources or headphones may also be controlled to gradually decrease (from the user-selected setting to zero) as the rear speaker output gradually increases during time period Δt2.
Although the illustrated rate of change of the front and rear speaker output is relatively linear, it is considered apparent that the rate of change may vary during the first and second transition phases. For example, the rate of change may be relatively slower at the beginning of the transition phases and may be relatively faster at the end of the transition phases. Also, the time periods Δt1 and Δt2 may be identical and static, or may be adjustable, either individually or collectively, to satisfy user preferences.
It is noted that the rate of change of the front speaker output during the first and second transition phases Δt1 and Δt2 is not equal to the rate of change of the rear speaker output. This is due to the fact that the sound pressure level of interest is the sound pressure level at the front seat area. Accordingly, due to proximity, at the front seat area the impact of the front speaker output may be relatively greater than the impact of the rear speaker output. Hence, the front speaker output will change relatively less during the first and second transition phases while the rear speaker output will change relatively more during these transition phases.
In experiments conducted by the inventors, it was found that, assuming that the contribution of the front and rear speakers was the same at the measurement location, the front speaker output level would increase by about 3 dB to maintain the overall sound pressure level constant when the system was switched from single source mode to dual source mode. Preferably, the adjustment level will be a constant in the control software, and will be tuned or calibrated to each vehicle. For example, the adjustment level or constant will be relatively larger if the contribution of the rear speakers is relatively more than that of the front speakers. Conversely, the adjustment level or constant will be relatively smaller if the contribution of the rear speakers is relatively less than that of the front speakers.
Naturally, if the system was at a very high sound level when switched from single source to dual source, the front speakers alone may not be able to maintain the overall sound pressure level. Moreover, in most automobiles, the rear speakers contribute relatively more of the low or bass frequencies than do the front speakers. Therefore, in order to maintain relatively constant frequency components when switching from single source mode to dual source mode, the equalization of the front speakers could be adjusted. In such circumstances, particular frequency components of the front speaker output will change relatively more (or less) than other frequency components. The amount of front speaker low frequency output adjustment to maintain the overall sound quality could be a set amount, or could be variable in dependence upon many factors. Such factors include the specific vehicle tuning as well as the user settings prior to switching modes. Naturally, these adjustments would be reversed when switching from dual source mode to single source mode.
While the preferred embodiments of the present invention are shown and described herein, it is to be understood that the same is not so limited but shall cover and include any and all modifications thereof which fall within the purview of the invention as defined by the claims appended hereto.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5661811 | Huemann et al. | Aug 1997 | A |
| 6330337 | Nicholson et al. | Dec 2001 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 20020131605 A1 | Sep 2002 | US |
