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How To Get The Best Listening Experience From Your Micro Speakers?

As the technology evolves, integrated circuits are getting smaller and smaller, allowing developers to pack more features into miniature handheld, portable, and wearable devices. With new multimedia features becoming available, the demand for higher quality playback on such devices is increasing. However, product consumers don’t care for trade-offs that have to be made due to small form-factor; they still demand a high-fidelity listening experience with high sound volume. Faced with the physical limitations of embedded micro speakers, designers have to rely on a narrow and expensive range of design options that are currently available.

The developers at Maxim Integrated didn’t want to let the physics of a micro speaker disrupt the listening experience on small, portable devices. They came up with the DSM™ technology – a technology that can be used to maximize the performance of micro speakers. Their DSM™ series smart amplifiers such as the MAX98390, provide a significantly better low-frequency (LF) response with an increase in the perceived loudness of up to 2.5 times.

What Is DSM™ And How Does It Work?

The Dynamic Speaker Management (DSM) technology is optimized for driving small, 1 – 3W micro speakers in a sealed box enclosure, up to their absolute maximum. This technology uses current and voltage (I/V) sensing feedback in combination with Maxim’s patented DSM™ speaker protection algorithm to extend both the perceived output volume and frequency response of a typical micro speaker setup (a micro speaker within an enclosure). The DSM™ algorithm is implemented inside a fixed-function DSP core and requires no additional programming; only a set of speaker response parameters that are specific to each particular micro speaker setup. These parameters can be easily extracted using the dedicated DSM Sound Studio GUI, which significantly reduces time to market.

What Is a Micro Speaker, And What Can It Be Used For?

By their design, micro speakers are very similar to conventional, regular-sized speakers with a moving coil. However, their performance is greatly affected by their small size: the voice coil cannot withstand more than a couple of watts, while the diaphragm excursion range is very low, negatively affecting the LF response. The voice coil can quickly overheat to its melting point, while excessive excursion of the speaker diaphragm may cause a lot of sound distortion and irreversible mechanical damage. Speakers can be safely operated only within their electro-mechanical Safe Operating Area (SOA), so the main task of the DSM™ is to precisely determine the inner boundaries of a micro speaker’s SOA and keep the operational parameters within these boundaries. 

Micro speakers can be found in a wide range of handheld and wearable products that can reproduce sound, such as smartphones, tablets, gaming consoles, portable medical devices, smartwatches, toys… They also have some other uses in applications related to Smart City and Infrastructure, including smart home and IoT devices, doorbells, AV intercoms, parking and elevator voice interfaces, and any other similar applications.

Figure 1) Exploded view of a typical micro speaker

DSM™: The Best Option For More Power

Designers have only a limited set of options for protecting micro speakers in their designs: the first and the cheapest option is to operate the amplifier with an ample safety margin for the worst-case scenario. The second option would be to undergo a rather complicated speaker characterization procedure and create own compensating algorithms and accompanying circuitry, which negatively impacts overall time to market and development costs. Unfortunately, the first option is very often the choice of many designers due to its low cost, and both options produce a less-than-ideal outcome. However, Maxim’s DSM™ technology now offers the third option.

Maxim’s DSM™ technology relies on using a proprietary algorithm running on a fixed-function DSP core. With the help of the integrated I/V sensing amplifiers, it is possible to create a precise model of the micro speaker based on the temperature of the voice coil, and its DC resistance. With this information, the DSP algorithm can dynamically maximize the output power through the voice coil while preventing it from overheating. This is especially useful for some high-pitch and narrow-band frequency sounds, commonly used as doorbells and alarms. Such sounds do not cause too much speaker diaphragm excursion; however, they can still be devastating for the voice coil. By using the DSM™ technology, power output can be increased to realistic limits, resulting in much higher sound pressure levels (SPLs), and thus better performance of those devices.

The speaker characterization process is easy and straightforward. It can be performed by using the DSM Sound Studio GUI application. Once the speaker parameters have been extracted and fine-tuned by the software, the entire setup can be submitted to Maxim for a final step: a high-precision laser characterization process. The laser characterization process creates a highly accurate electro-mechanical model of the entire micro speaker setup. The excursion of the diaphragm is closely monitored over the frequency and power range, and its response is accurately captured and stored. The accurate electro-mechanical response model of the speaker enables the DSM™ algorithm to extend the LF range down to two octaves below the resonant frequency, while driving it up to its realistic power limit, without having to wild-guess the optimal parameters. The result is an unusually natural and present sound from a tiny micro speaker setup, with up to 2.5 times higher sound volume and unexpectedly rich LF content.

Figure 2) SPL-Frequency diagram: conventional vs. DSM-enabled smart amplifier

Additional Features:

Besides DSM™, several other features are also incorporated within the DSP algorithm. All of these features can be enabled or disabled, and their operating parameters can be fully adjusted by accessing the corresponding control registers via the I2C interface. These additional features include:

  • Stereo Bass Management: provides an even, centered bass experience for stereo systems.
  • Dynamic Range Compressor (DRC): attenuates loud signals and amplifies low signals, preventing unpleasant and abrupt changes in the sound level. It can also be used to maximize speech volume.
  • 8-band Parametric EQ: seven different filter types are provided. This fully parametric EQ can be used to precisely shape the frequency response of the sound.
  • Debuzzer: Maxim’s Debuzzer technology employs a programmable dynamic notch filter, attenuating only when signal levels are high enough to stimulate buzzing, and thus maximizing the SPL.
  • Perceptual Power Reduction (PPR): a patented algorithm that saves up to an additional 25% of power, with no loss in audio fidelity. 

MAX98390: Boosted Class D Amplifier With Integrated DSM™

The MAX98390 integrated Class D amplifier is the latest product from Maxim Integrated, which features their highly acclaimed DSM™ technology. It is a perfect, high-efficiency solution for powering micro speakers in many different applications. The MAX98390 integrates a programmable boost converter, allowing it to use supply voltage down to 2.65 V and convert it up to 10 V for the output stage. An extensive set of power-saving functions is also available, including an advanced envelope tracking function, which automatically adjusts the output voltage for maximum efficiency, output stage FET scaling function, and more. The result is a peak efficiency of up to 86% while using only a 3.7 V power supply.

The DSM™ technology significantly improves the rest of the specs for this IC: the MAX98390 smart amplifier can efficiently deliver 5.1 W into 4 or 8 Ω load while retaining an excellent THD ratio of only 1%. And since we’re talking about the advanced output power management, it is possible to achieve these numbers even with the speakers rated at lower output power, typically around 1 to 2 W, making the MAX98390 a particularly useful for applications working in a noisy outdoor environment. Finally, a set of most commonly used digital audio interfaces offers a high level of flexibility for designers: the MAX98390 includes the I2S, PDM, and TDM audio interfaces. A fine-tuning of the configuration parameters can be performed via the standard I2C interface, as already mentioned.

Figure 3) Max98390 block diagram

The list of features goes much further, so be sure to check the official MAX98390 datasheet. An Evaluation Kit is also available, offering not only a chance to evaluate the performance of the MAX98390 Class D smart amplifier but also a free DSM Laser Characterization coupon (one per kit). You can find more information about the Dynamic Speaker Management technology on Maxim Integrated official DSM landing page

MAX98390EVSYS – Audio demonstration