Speakers and smart amplifiers, what makes amplifiers smart
Time:2023-12-27
Views:195
Compared to standard Class D amplifiers, smart amplifiers can improve your audio solution
Do you remember the day you strung two tin cans together and made a phone call? Unfortunately, due to the miniaturization of devices (including speakers), mobile phone audio sounds much like those tin cans. Unless you upgrade your phone to a top of the line phone in the past few years, you will struggle to use speakers for voice or audio. This is because mobile phone manufacturers have made slow progress in making audio unique among high-end phones, and there is almost no low-frequency audio (usually referred to as bass).
Now, due to the technology we call smart amplifiers or smart amplifiers, this situation is changing because unlike traditional amplifiers, they can safely and temporarily push the speaker to its limit. By sensing the operation of the speaker while playing music and applying advanced algorithms, smart amplifiers can obtain a large amount of sound from the phone‘s miniature speakers without harming your ears.
What are the speakers today?
Before discussing the working principle of smart amplifiers, it is important to understand another crucial part of the audio signal chain: the speaker. No matter what the amplifier is, if the speaker is not designed properly, it will not overcome any audio processing or amplification issues. This is like injecting rocket fuel into a lawn mower engine - all of this power is unusable. However, if you start with a reasonable engine, adding an intelligent amplifier is like adding a turbocharger, pushing it to its limit in a controllable way.
The speaker consists of a frame, magnet, voice coil, and vibrating film (Figure 1). The current flows through the voice coil, causing it to react with the fixed magnet of the speaker and magnetize it. The electric motor moves the film attached to the coil up and down, and emits an audible sound wave. We refer to the motion of the vibrating diaphragm as the limit, which has limitations. When the offset limit is exceeded, auditory distortion occurs. In extreme cases, damaged speakers may cause malfunctions. Traditional amplifiers use simple equalization (EQ) to limit offset. However, in order to protect all speaker changes, operating conditions, and audio signals, these filters are usually conservative - abandoning the ability to push speakers to their true limits.
Anatomy of the speaker
The second issue with speakers is that when current passes through the voice coil, some energy is converted into heat instead of sound. Pushing the speaker forcefully may melt the varnish on the electromagnetic wire and damage the voice coil. When the voice coil is heated from the energy transmitted by the amplifier, it must be cooled into the surrounding structure through a magnet. In traditional amplifiers, the maximum power is limited to a single value, and if continuously provided, it will not damage the speaker. The maximum power value must cover all speaker variations, operating conditions, and signals. Therefore, this value is usually lower than the value that the speaker can handle, so it is relatively conservative.
What makes amplifiers intelligent?
How do we extract the maximum sound pressure level (SPL) from a given speaker while still ensuring safe operation? We can use smart amplifiers. Audio has peak to average ratio (PAR), which allows us to drive real-time peaks while maintaining an average or safe level. Intelligent amplifiers are divided into two categories. The first one is feedforward, where speaker models are created and audio is fed through these models to predict speaker behavior. Feedforward is often suitable for larger speakers, with smaller variations and more linear operation. Even with larger speakers, we must consider changes in the speakers in the headroom, but the dynamic system can temporarily push the speakers to their limits to produce loud audio.
The commonly used micro speakers in smartphones require more advanced smart amplifiers. The second type is feedback smart amplifiers, which add current and voltage (IV) sensing to Class D of digital to analog converters (DACs) and feedforward solutions. This IV induction allows us to directly measure the voice coil temperature of the speaker and detect changes in the speaker caused by changes between units, ambient temperature, and speaker load (such as placing hands on the speaker port). This information allows the algorithm to extract other SPL from the speaker, otherwise it will be lost by limiting the output to cover these changes.
In order to utilize voltage and current sensing information, smart amplifiers require a processor (preferably a digital signal processor or DSP) to parse this data and apply complex algorithms to extract optimal performance and sound while maintaining safe operating conditions for the speaker. Smart amplifiers with or without integrated DSP can meet the cost, time to market, and performance requirements of designers.
Meet your speaker
Based on a basic understanding of how speakers and smart amplifiers work together to provide better sound at higher volumes, we can discuss how to use this technology to bring your product to the market. The first step is to create a speaker feature and measure multiple aspects of the speaker to identify its limitations. It is necessary to fully understand these limitations in order to achieve maximum sound and highest quality sound for the speaker without causing damage. Conduct detailed measurements to develop accurate speaker models. One method is to use TI‘s PurePath Console 3 (PPC3) and the accompanying learning board. This combination can use an easy to follow program to perform these measurements.
These measurements include but are not limited to system checks, offset characteristics, thermal characteristics, and SPL measurements. Although the parameters in the speaker data table can be used to measure the offset, a more accurate method is to use a laser displacement sensor to measure the offset and extract the required parameters. TI‘s intelligent amplifier learning board can provide all the required data collection by using lasers and microphones for SPL measurement, allowing engineers to easily characterize the speakers. After completion, users can quickly view different measurement data graphs, including offset and frequency, as well as safety work area restrictions.
TI‘s PPC3 can simplify the adjustment process. Its advanced tool kit can automatically merge low-end impedance measurement results with high-frequency microphone measurement results. This will create a clean full frequency SPL measurement to begin tuning. By easily selecting various alignment filters and allowing software to automatically generate the required compensation filters, it is possible to quickly adjust the low-frequency bass area to drive the bass. The smart amplifier will dynamically adjust this filter to push the maximum bass without exceeding the offset limit. Next, SmartEQ can be used to easily produce sound from speakers. Users only need to specify the target EQ curve, and PPC3 will calculate the necessary filters to adjust the measured SPL response of the speaker to the target EQ. This tool will perform all mathematical operations,
Put them all together
After completing the characterization and fine-tuning of the speaker, it is important to ensure that your selection can operate safely and reliably in larger speaker samples. Reliability testing is an important step before bringing your product into the assembly line. Regardless of the speaker manufacturer, there are always differences between speakers. Although the tuning sounds good and seems within a safe operating range, other speakers may not be as powerful as the goal you have been striving for in the previous steps. We suggest that you obtain a larger speaker sample through lifespan testing. This sample should have at least 20 spokespersons, and you should test it for longer periods of time and extreme temperatures to simulate expected customer use cases.
If you are using the TI TAS2555 smart amplifier, there is no need to integrate the sorting and settings of the smart amplifier into the host processor, as the DSP is fully integrated into the smart amplifier. This greatly reduces software development time. In addition, if your application processor has been upgraded or changed, there is no need to re integrate sorting and settings.
When you move to the production line, you can implement fast and powerful testing programs to ensure that the final product meets the parameters set during development. Production line software can help filter speakers, ensuring that they are within the preset range and not damaged during assembly. Additionally, impedance changes between speakers can be measured and stored. This step ensures that all the heat dissipation space of each speaker can be used.
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