Directivity of a car speaker refers to the ability of the speaker to radiate sound in different directions. Directivity is important for defining the size of the listening area and adjusting the frequency balance according to the listening position. Here are some key points about directivity of car speakers:
1. Frequency response variation
Directivity can be described as the frequency response in relation to the listening position. The sound pressure level is measured by placing microphones at different points, which usually form a circle around the speaker to obtain the sound dispersion at different frequencies.
2. Polar plots
The sound dispersion at different frequencies can be read through polar plots. These graphs show the sound dispersion on the vertical and horizontal axes. The central axis corresponds to 0°, which is the front of the speaker.
3. Physical limitations
Since the wavelength of high frequencies is much smaller than that of low frequencies, car speakers cannot maintain the same dispersion angle across the entire spectrum. This means that the further off-axis, the faster the high frequencies decay compared to the low frequencies, resulting in a more direct and different sound of the room's reverberant sound at the speaker position.
4. Frequency and wavelength relationship
Many efforts have been invested in solving these problems, especially in tweeter design, to offset their natural hyper-directivity. At the low frequency end, the idea of coupling multiple units to simulate a larger speaker has been used for some time.
5. Speaker size
To maintain control over directivity, the size of the speaker needs to be large enough relative to the wavelength of the frequency it reproduces. For example, to control the dispersion angle of low frequencies, a huge and difficult to carry speaker is required.
6. Directivity and listening position
In the automotive environment, speech intelligibility (SI) is also affected by the directivity or direction of the source/speaker in addition to background noise, binaural effect and the acoustic conditions of the space. Studies have shown that the direction of the speaker has little effect on speech intelligibility in the car unless the speaker is facing the listener because of the rich early reflections in the car.
7. Directivity and speaker design
The directivity of the speaker is an important feature in the design, which affects how the sound propagates in the car space. The design of the speaker needs to take into account its directivity at different frequencies to ensure that the sound can provide good distribution and clarity in the car.
8. Directivity and acoustic environment
In a closed space such as a car, the directivity of the speaker has a significant impact on the propagation and clarity of the sound. Research shows that the directivity or orientation of speakers has an impact on speech intelligibility in cars, especially when the speakers are turned away from the listener.
Understanding speaker directivity is critical to optimizing the performance of a car audio system, helping to improve sound quality and speech clarity, ensuring passengers enjoy a clear sound experience in all driving conditions.