An In-Depth Look Into HTC BoomSound Speakers, Part 1



Quality audio output tends to be farther down the list of priority features we look for when buying a new phone. We get sucked into the allure of the camera, the user interface, or the phone’s silhouette before we even consider sound.

But these days our phones double as our TVs and computers with increasing frequency, and watching videos, playing games, or listening to music on our phones has become second nature. And that means good sound, regardless of whether or not we as users think about it, is a requirement that device manufacturers can’t ignore.

Our BoomSound front-facing speakers have been a point of pride for us ever since they debuted on the One M7. Now our partnership with Dolby brings 5.1 surround sound to the One M9 and other select HTC devices, so you can have a cinema-worthy surround-sound experience, without headphones or external speakers, right from your phone.

The work and thought that went into the BoomSound audio system is worth exploring and sharing with you. Lucky for us, HTC Community team member Jude Wang took the time to do an in-depth interview with the BoomSound designers to understand how these speakers came to life.

HTC BoomSound speakers have been praised for offering the world’s best audio experience in the industry. What was the motivation driving the design?

It all started with the HTC One M7. Smaller bodies have always been the pursuit of smartphones; the ideal was to fit all of the parts into the smallest space possible. Compared to features such as camera functions and screen size, speaker size and sound quality took a backseat in terms of priorities, and thus they were usually the first things to go. But in reality, we use the phone’s speakers every single day, for activities like listening to music in a car or while playing games.

Our first thought was, “Could we make it any better and reinvent the reason for its existence? Could we challenge the thinking of smartphone companies, and tell them that there is still room for the evolution of smartphone speakers?”

Why are smartphone speakers always placed on the back or sides?

Back then, everyone made speakers on the back of phones or, in some instances, directed toward the sides. This was because front-facing speakers would increase the length of the phone, affecting the structure and shape of all internal parts.

Before the HTC dual front-facing speakers came around no one expected more than a voice receiver on the upper part of a phone, because replacing it with a micro speaker required trying to fit a sound box in an already packed space while dealing with other technical difficulties to satisfy various (international) volume standards.

Let’s put it this way: it’s not as difficult to install speakers on the bottom part of the phone—almost all smartphones place their speakers at the bottom—because the upper part is already crowded with front-facing and back-facing cameras, the headphone jack, and more. Placing the speaker at the upper part of the phone means you are going to have to try and fit it in a really crowded and uncomfortable neighborhood.

Due to the limited space, we were forced to change the shape of the sound box for the speakers, but this would result in an unpredictable sound output. This is why you rarely see odd-shaped speakers—they’re usually rectangular, circular, or cylindrical to avoid distorting sound quality and effects. Which brings us to the greatest challenge of BoomSound: the shape of the speakers is weird.

When we first saw the design we really wanted to snip off some corners here and there, but doing so would be cutting into our workspace. We had no choice but to stick with it. But what were we going to do about the sound box? How could we induce proper sound wave refraction in such a tight space?


The layout of the bottom part of the phone was relatively normal, but the upper part would appear irregular, as shown in the sketch. We had to think of ways to go around, even punching holes in the front and back to bring it across or guide it to the back…very much like making a sandwich. Putting it simply, we were pushing for as much space as we could, by any means possible.

We came up with several ideas, one of which was to change the material, so we started adding some filler to the sound box. The filler is made of a high-polymer material that is very much like a sponge. This “sponge” would slow down the speed of the air that travels into the sound box, thus slowing down the reflection and refraction of sound. The speed of sound refraction is really just fixed within a sound box that cannot get any bigger. However, if the sound that goes in has to travel through a greater distance, this simulates the space of a bigger sound box, tricking your ears into hearing louder music.

This was a solution with really noticeable results and it also had the benefit of providing better soundproofing. But manufacturing was challenging! We were fitting material into an irregular shape, sealing one end with breathable wool and the other with plastic to ensure free airflow, and all of this had to be done within a little over 1mm of space.

The assembly of the speakers posed a great challenge during manufacturing, as the material could easily be damaged, broken, or even scattered across the table like powder. So we set many ground rules with the manufacturing team, like using very little pressure when handling each component and monitoring every step to ensure things didn’t break. This took a gigantic bite out of our time.

To squeeze a speaker into an already jam-packed space is a very tough thing to do, which is why most smartphone manufacturers don’t do it. Still, we aren’t the only ones attempting dual front-facing speakers—it’s not impossible, it just means spending a great deal of time and effort.

When we first started to discuss BoomSound speakers we faced numerous dead ends and bottlenecks, held discussions and considered just how massive the manpower and cost would be. In the end HTC valued delivering a good user experience more than anything else; we insisted that this was a good and worthwhile investment, so we went for it and never compromised.

Due to the in-depth nature of this interview we’ve broken it into two pieces and will be posting part 2 later this week!

  • Kwadwo Boadu

    That sounds right, followed by devices like the Samsung Note 10.1 and Nexus 10.

    • Adrianus Albert Jonathan Nadea

      True but those are all tablets so space is far less of a concern compared to a phone with 4.7-5.0 inch screen.

  • Kwadwo Boadu

    The R&D that was put into Boomsound is great to read about, looking forward to part 2! I’m sure it will always get better with each new generation, whether hardware wise or through software.

  • EarlyMon

    I saw the backwave damping material being made fun of in a teardown. Obvious to any speaker maker what its point was. Kudos for getting public with this.


    This article adds more insight to why the devices are longer and have the bezel that everyone complains about. You can’t have your cake and eat it too.

  • Leonard

    I believe that HTC can accomplished some really good and fantastic heights in the mobile industry… this was one time that they have proven their strength and ability to do so. They can do better, although we can’t have the both of two world like having a smaller phone while still retaining the awesome speakers, which btw takes up space, I believe that HTC will get around this problem a deliver a fix to mitigate the problem. Also, to HTC, keep up with the awesome innovations but make sure your phones that you guys roll out really when through great amounts of reviewing, phones like M9 will not get you guys through… Hope next year will be better… don’t just keep improving and boasting about Boom sound… time to move on.