Designing Speaker Systems from the Ground Up

Designing Speaker Systems from the Ground Up

Kneading bread dough, hands dusty with flour, you wish you turned on some tunes. If only you could ask your oven, as it heats up to 350 degrees, to play U2's "Joshua Tree" album.

Voice control and internet connectivity are bringing a variety of formerly placid products to life. With its June announcement that its Siri voice assistant would get its own internet-connected speaker, Apple is finally joining the likes of Amazon and Google. Since Amazon began shipping its Amazon Echo devices in June 2015, the company has sold more than 10 million units, according to industry analysts. And Amazon, working together with GE, has enabled its Alexa virtual assistant to bring voice control to Wi-Fi-enabled GE appliances. So, you could tell your oven to preheat itself, or ask your washing machine when the cycle will be finished. Maybe someone is devising a way to play music from ovens.

Sound is no longer just for speakers in traditional stereo systems and boomboxes (remember those?). Of course, standalone speakers still have a role in our world. Even record players are seeing a resurgence with renewed interest in vinyl. But now we have the opportunity to integrate sound into a wider range of devices. You might be designing speakers for a radio, an MP3 player, an appliance, or something that no one else has even considered. As with any kind of design engineering, there are best practices to follow when you're designing a speaker system from the ground up. For these audio design tips, I consulted with three of Maxim's experts in the company's Mobile Solutions Business Unit: Michael Tuason, a principal member of the technical staff; Greg Mow, a business manager; and Robert Polleros, also a principal member of the technical staff. 

Defining Your Audio Design

According to the experts, your first step is to answer some defining questions about your design. For example: how big or small can the system be? What kinds of interactions will it have to support (i.e., voice activation, high-fidelity audio content)? Will the system plug into an electrical outlet or be battery powered? Is it mobile or stationary? Once you’ve defined your end product, you'll need to consider various parameters:

  • Audio subsystem: size, shape, and location of the components such as drivers, PCBs, and batteries will influence your selection of underlying ICs
  • Voltage rail considerations
  • Content type: voice, music, or other sounds?
  • Environment: will your system be designed to operate in a quiet, noisy, or mixed location?
  • User experience
  • Cost
  • Manufacturability
  • Materials

Choosing the Right Audio ICs

Once your product is fully defined, it's time to select the audio ICs that help your systems deliver beautiful music (or voice, or other sounds). First order of business, the experts tell me, is to choose your speaker drivers. The parameters you've already defined will determine the type of drivers you want. Evaluate the drivers’ sensitivity, excursion, impedance, power rating, and frequency response. Test selected drivers via a subjective listening test using a wide range of content to cover all use cases for your application. Use a consistent and overpowered amplifier to ensure that you are testing the limits of the speakers and not the amplifier itself. Next, select your audio amplifier ICs. For these components, considering that so many things are getting smaller and lighter, important considerations include power, cost, battery life, and size. See our tutorial, "How to Select the Best Audio Amplifier for Your Design," for more details. Finally, you'll want to test your speakers using a test enclosure design. Factors such as the acoustic design of the box, material/weight of your enclosure, the volume behind the speaker enclosure, and the suspension will all impact sound quality. Test with different people. Test in different types of environments—inside, outside, large rooms, small rooms.

Addressing Mobile Design Challenges

Many of today's designs featuring sound are mobile. If you're designing speakers for mobile devices, you must generate great sound from micro speakers. Micro speakers do have some inherent challenges:

  • They're not particularly loud
  • They lack bass response
  • They can be easily overdriven, such that the sound becomes distorted
  • They also break easily

Maxim's Dynamic Speaker Management (DSMTm) technology overcomes these micro speaker challenges, helping you deliver louder, richer sound. The technology provides voice coil thermal protection and excursion limiting, minimizes hardware DSP redundancy, provides rich bass via true bass extension frequency response, and features a battery-tracking function that reduces the output swing as the supply voltage. You can find DSM technology in Maxim's IV sense boosted Class D speaker amplifiers, which provide up to 2x loudness improvement over standard Class D amps.

Now, how about bringing the sounds of Bono and company to my oven?