The insurmountable popularity of smartphones, tablets and handheld mobile audio devices is not the least surprising. These devices provide a means to an end that was otherwise reserved for in-home entertainment, granting access to music and Internet on the go.
However, the most off-putting factor common to all these devices is arguably the reliance on headphones for an acceptable sound quality. Due to their small size built-in speakers are far too low in fidelity and power to offer a functional alternative. Fortunately, Bluetooth speakers are the middle ground solution, capable of producing high-quality sound without forcing the user to carry an entire assembly of home audio equipment to every picnic or excursion, but rather, a small, portable device.
Bluetooth speakers are small enough to stash in a backpack, laptop bag, or even a vehicle’s glove compartment, making them extremely inviting devices to bring on day trips. This ease of access is further magnified when the low power consumption and connectivity, inherent to Bluetooth are thrown into the mix.
Since Bluetooth capability has become a standard feature of contemporary mobiles devices, the speakers are compatible with most smartphones and tablets, including those of the Android, iOS, and Windows families. Furthermore, they are completely wireless and do not require a Wi-Fi connection to link with the host device to play music; tethering is as easy as enabling Bluetooth mode and selecting the nearest speaker. No special installation is necessary.
Bluetooth speakers are quickly become popular consumer electronic devices. One need only glimpse at the daily news feed of any tech publication to notice the growing buzz. Yet the speakers are still a nascent product, and not without their issues regardless of how popular as they may be. These issues include:
1. Bluetooth connectivity is limited to approximately 30 feet, making it impossible to stream music in other rooms.
2. Bluetooth speakers are smaller than traditional speakers and lack the same level of hardware robustness; they cannot match the power of traditional speakers.
3. Wireless devices are limited by a finite power supply.
When designing Bluetooth wireless speakers or portable media devices, engineers must take every precaution to reduce power consumption as much as possible. For this reason, Class D amplifiers or switching amplifiers are the optimal choice. They are 90% efficient compared to other types of amps because they operate as binary switches; that is, the output transistors are either fully on or fully off during operation, thereby allowing the amp to completely eliminate the use of the linear region of the transistor responsible for the inefficiency in the other amp types.
Modern Class D amps such as Maxim Integrated’s MAX98400, MAX98502, and MAX98357 are respectable choices that are able to achieve fidelity comparable to Class AB amps. This is a substantial feat in and of itself, considering that Class AB amps are one step below Class A amps.
Class D audio amps are highly efficient, exhibiting output transistors that are either fully on or fully off .
MAX98400
The high-performance and thermally efficient MAX98400 family of Class D amplifiers consists of the MAX98400A and the MAX98400B. The MAX98400A delivers 2 x 20 W into 8-Ω loads or 1 x 40 W into 4-Ω loads, whereas the MAX98400B delivers 2 x 12 W into 8 Ω. The ICs operate from a single 8 to 28-V supply and provide a high 67-dB PSRR, eliminating the need for a regulated power supply. They offer up to 90% efficiency from a 12-V supply.
MAX98502
Similarly, MAX98502 is also a high-efficiency Class D audio amplifier. Unlike the MAX98400 the MAX98502 features an integrated 5.5V boost converter that delivers a constant output power over a wide range of battery supply voltages. The boost converter operates at 2 MHz and requires only a small (2.2-µH) external inductor and capacitor. The automatic level control has a battery-tracking function that reduces the output swing as the supply voltage drops, preventing collapse of battery voltage.
MAX98357
The MAX98357 IC is an easy to use digital pulse-code module (PCM) input Class D power amplifier that requires no programming and provides Class AB audio performance with Class D efficiency. Five selectable gain settings (dB, 6 dB, 9 dB, 12 dB, and 15 dB) are available I2S/left-justified mode set by a single gain select input and a fixed 12-dB gain in TDM mode.
As the demand for Bluetooth speakers continues to gain momentum, engineers will be given ample opportunities to distinguish their products from that of their competitors. Gaining the edge at such an early stage is crucial and utterly dependent on component selection. Fancy marketing can only go so far.
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