【Introduction】As vehicle fuel consumption standards continue to increase (according to the U.S. Environmental Protection Agency, the mileage per gallon will increase to 40 miles per gallon in 2026), the challenge for car audio designers is how to provide immersive audio experience while reducing vehicle weight and improving overall efficiency.
If it is necessary to design an automotive external amplifier, the user experience can be enhanced by upgrading the audio system architecture by increasing output power, utilizing higher impedance speakers, and implementing Class H control in the system. This article will detail each method, including its impact on audio system weight and performance.
Supports higher output power using higher supply voltage and higher output current
In addition to the original equipment manufacturer (OEM) demands to reduce vehicle weight, consumers also expect superior audio performance to be able to enjoy an immersive audio experience in the car. To develop systems that deliver this experience, designers like to integrate more powerful subwoofers: these subwoofers deliver deafening bass consistently and provide greater dynamic range (measured in decibels between the lowest sound and the highest sound) difference) sound reproduction.
To increase dynamic range and increase output power, consider increasing the input supply voltage. Table 1 shows the supply voltage and output current values required to maintain the 75W output power as the speaker impedance increases.
Table 1: Relationship between various channel requirements (same power)
Table 2 shows the correlation between increased power demand and supply voltage/output current. In this example, to increase the output power, it is necessary to increase the supply voltage and output current at the same speaker impedance.
Table 2: Relationship between various channel requirements (increasing power)
Why High Impedance Speakers Can Reduce Overall Weight
As shown in Table 1, one benefit of using high-impedance speakers is that the output current drops significantly while maintaining the same output power. Furthermore, the relative size (diameter) of the copper wire can also be reduced due to the reduction in the required output current. For example, an 8Ω speaker can use a smaller diameter copper wire than a 4Ω or 2Ω speaker at the same output power, which helps reduce the weight of the audio cable. The simplified installation diagram shown in Figure 1 shows a six-speaker car audio system with a midrange speaker in each door and two additional speakers in the rear, requiring a total of about 76 feet of copper wire to connect all speakers.
Figure 1: Length of copper wire required to connect a typical six-speaker car audio system
One benefit of increasing the speaker impedance is that the cable diameter can be reduced. Coupled with the fact that the cabling typically used to connect all the speakers to the audio external amplifier is very lightweight, it can really reduce the overall weight of the audio system.
Implement Class H controls to optimize system efficiency and further reduce weight
As shown in Figure 2, in a traditional audio system, to provide the peak power required by the audio load, the power solution typically sets the audio amplifier supply voltage (labeled PVDD) for all speakers to the highest voltage required.
Figure 2: PVDD in a conventional audio system without Class H control
Implementing a “Class-H control” technique (using an automotive Class-D audio amplifier such as the TAS6584-Q1) can optimize the PVDD voltage supplied to the amplifier (see Figure 3) and dynamically track the envelope of the audio waveform. Class H control can significantly improve the efficiency of audio designs and save power that would otherwise be dissipated when the PVDD voltage was fixed at 42V.
Figure 3: PVDD with class H control
To further illustrate the effect of class H controls on efficiency, let’s look at the data in Table 3. Table 3 compares power input (Pin) versus power consumption (Pout) in the system using the TAS6584-Q1-based automotive Class-H audio and tracking power supply reference design to enable or disable Class-H control. With class-H control, the system efficiency gain between the boost power supply controller and the audio amplifier is close to 10%.
Table 3: Improving Efficiency Using Class H Controls
As shown in Figure 4, improving efficiency can also reduce the overall power loss of the external amplifier.
Figure 4: Reducing Overall Power Loss Without Using Class H Control
To illustrate this further, let’s take a look at a thermal image of the TAS6584-Q1 audio amplifier and LM5123-Q1 boost controller power supply with Class H control enabled and disabled, and compare their thermal signatures. Figure 5 shows how the implementation of Class H controls can significantly reduce the total heat load.
As shown in Figure 5, the improved efficiency of Class H control (by reducing power loss) helps reduce thermal load, allowing the choice of a smaller heat sink to dissipate the internal heat.
Figure 5: Temperature comparison without and with class H control
Table 4: Temperature comparison table for LM15123-Q1 and TAS6584-Q1 thermal imaging
Hopefully this article has given you a clear overview of how utilizing higher impedance speakers and implementing Class H controls can help you develop a lighter weight audio system and how the weight savings of external amplifiers translates into the benefit of extended vehicle range. This will help you incorporate a greater number of speaker channels into your overall audio design and increase the overall average output power per channel for the existing number of car speakers.
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