Peek At The Off-Ear Speaker Prototypes For Valve’s VR

The Valve Index VR headset incorporates a number of innovations, one of which is the distinctive off-ear speakers instead of headphones or earbuds. [Emily Ridgway] of Valve shared the design and evolution of this unusual system in a deep dive into the elements of the Index headset. [Emily] explains exactly what they were trying to achieve, how they determined what was and wasn’t important to deliver good sound in a VR environment, and what they were able to accomplish.

First prototype, a proof-of-concept that validated the basic idea and benefits of off-ear audio delivery.

Early research showed that audio was extremely important to providing a person with a good sense of immersion in a VR environment, but delivering a VR-optimized audio experience involved quite a few interesting problems that were not solved with the usual solutions of headphones or earbuds. Headphones and earbuds are optimized to deliver music and entertainment sounds, and it turns out that these aren’t quite up to delivering on everything Valve determined was important in VR.

The human brain is extremely good at using subtle cues to determine whether sounds are “real” or not, and all kinds of details come into play. For example, one’s ear shape, head shape, and facial geometry all add a specific tonal signature to incoming sounds that the brain expects to encounter. It not only helps to localize sounds, but the brain uses their presence (or absence) in deciding how “real” sounds are. Using ear buds to deliver sound directly into ear canals bypasses much of this, and the brain more readily treats such sounds as “not real” or even seeming to come from within one’s head, even if the sound itself — such as footsteps behind one’s back — is physically simulated with a high degree of accuracy. This and other issues were the focus of multiple prototypes and plenty of testing. Interestingly, good audio for VR is not all about being as natural as possible. For example, low frequencies do not occur very often in nature, but good bass is critical to delivering a sense of scale and impact, and plucking emotional strings.

“Hummingbird” prototype using BMR drivers. Over twenty were made and lent to colleagues to test at home. No one wanted to give them back.

The first prototype demonstrated the value of testing a concept as early as possible, and it wasn’t anything fancy. Two small speakers mounted on a skateboard helmet validated the idea of off-ear audio delivery. It wasn’t perfect: the speakers were too heavy, too big, too sensitive to variation in placement, and had poor bass response. But the results were positive enough to warrant more work.

In the end, what ended up in the Index headset is a system that leans heavily on Balanced Mode Radiator (BMR) speaker design. Cambridge Audio has a short and sweet description of how BMR works; it can be thought of as a hybrid between a traditional pistonic speaker drivers and flat-panel speakers, and the final design was able to deliver on all the truly important parts of delivering immersive VR audio in a room-scale environment.

As anyone familiar with engineering and design knows, everything is a tradeoff, and that fact is probably most apparent in cutting-edge technologies. For example, when Valve did a deep dive into field of view (FOV) in head-mounted displays, we saw just how complex balancing different features and tradeoffs could be.

3D Printed Speakers With Many Lessons Learned

Although we all wish that our projects would turn out perfect with no hiccups, the lessons learned from a frustrating project can sometimes be more valuable than the project itself. [Thomas Sanladerer] found this to be the case while trying to build the five satellite speakers for a 5.1 surround sound system, and fortunately shared the entire process with us in all its messy glory.

[Thomas] wanted something a little more attractive than simple rectangular boxes, so he settled on a very nice curved design with few flat faces and no sharp corners, 3D printed in PLA. Inside each is an affordable broadband speaker driver and tweeter, with a crossover circuit to improve the sound quality and protect the drivers. The manufacturer of the drivers, Visatron, provides very nice speaker simulation software to select the appropriate drivers and design the crossover circuit. The front of each speaker consisted of a 3D printed frame, covered with material from a cut-up T-shirt. These covers attach to the main body using magnets and really look the part.

After printing, [Thomas] soaked all the parts in water to clean of the PVA support structures but discovered too late that the outer surfaces are not watertight and a lot of water had seeped into the parts. In an attempt to dry them he left them in the sun for a while which ended up warping some parts, so he had to reprint them anyway. The main bodies were printed in two parts and then glued together. This required a lot of sanding to smooth out the glue joints, and many cycles of paint and sanding to get rid of the layer lines. When assembling the different pieces, he found that many parts did not fit together, which he suspects was caused by incorrect calibration on the delta-bot printer he was using.

In the end, the build took almost two years, as [Thomas] needed breaks between all the frustration, and eventually only used one of the speakers. We’re glad he shared the messy parts of the project, which will hopefully spare someone else a bit of trouble in a project.

Listening to a high-quality audio setup is always a pleasure, and we’ve covered several projects from audiophiles, including affordable DML speakers, and 3D printed speaker drivers.

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Patterned Plywood Makes For Attractive Speakers

In the matter of audio, we’re well past the reign of the home hi-fi and the boombox. If you’re not listening on headphones or directly on your phone, you’ve got a brick-sized Bluetooth speaker pumping out the tunes. Still a fan of the old-school, [Amanda Ghassaei] built some bookshelf speakers with a hip aesthetic.

First, the speaker enclosures were designed in WinISD, a software package specifically made for the task. For given woofers and tweeters, it helps get the enclosure and port sizes in the correct range for good sound. Panels were then fabricated out of plywood to make the enclosures. The plywood was cut and reformed several times to make the panels, using the pattern from the multiple plies to create the zig-zag look. Audio wise, a class D amplifier takes in line-level signals, before pumping them out to a woofer and tweeter through a custom designed crossover network.

It’s a tidy build, and we’d love to experiment ourselves with the fancy patterned plywood technique. Getting your enclosure design right can make a big difference to sound quality, as we’ve seen before. Video after the break.

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Cheap Speakers Sound Great In A Proper Enclosure

It’s possible to pick up a low-cost set of speakers for a few dollars, but by and large, you don’t get a lot of quality for your money. Expect a small pair of drivers, with tinny sound and ugly noises from the enclosure’s cheap materials. [JSK-koubou] has shown us, however, that these speakers can become so much more.

The internal structure helps improve the frequency response.

In this case at least, the basic speaker drivers and electronics inside were passable. Harvesting these, the builder then proceeds to create a stunning pair of tuned wooden enclosures for the speakers. This is achieved with a routing template, large blocks of wood and plenty of elbow grease.

The internal structure makes a huge difference to the bass response of the speakers, allowing them to far more faithfully recreate the music under test. Thanks to the artisan-level craftsmanship, the final product is stunning to look at, too. It’s impressive just how well a cheap pair of drivers can perform with a proper enclosure, and of course, there’s nothing to stop an even better set of drivers being installed, either.

When building your own speakers, your creativity is the limit. Video after the break.

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This MDF Sound Bar Sounds Great

Everyone should build a speaker cabinet at least once in their life, if only so they can realize how much thought goes into building a simple box. [John] of wanted a sound bar for his home theater setup, and that means building a sound bar. The result is beautiful, and a demonstration of how much you can do with just a router and a table saw.

[John] built this sound bar almost entirely out of MDF, which isn’t the best material but it works well enough for a speaker cab that’s meant to be mounted to a wall. The sides were constructed first, with a rabbet holding the front and back on. Both the woofer and tweeter are inset into the front, and a standard piece of plumbing pipe serves as the bass port. Slap a round over bit into the router and do some light sanding, and everything looks great with a coat of black paint.

As with any speaker enclosure, the design is effectively parametric, designed entirely around the drivers being used. In this case, [John] is using a spreadsheet named ‘Unibox’ that gives you all the formulas and graphs for designing a speaker enclosure.

With the box built and the speakers installed, the only matter left were a few aesthetic choices. [John] went with a standard black finish with a very nice wooden grille held onto the front with magnets. It’s a design that pops, but the true test of a speaker is how it sounds. That’s a bit hard to convey over the Internet, but [John] included a few sound samples at the end of the build video, available below.

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Sanding Seashells By The Seashore

We all maintain this balancing act between the cool things we want, the money we can spend, and our free time. When the pièce de résistance is a couple of orders of magnitude out of our budget, the only question is, “Do I want to spend the time to build my own?” [Nick Charlton] clearly answered “Yes,” and documented the process for his Nautilus speakers. The speaker design was inspired by Bowers & Wilkins and revised from a previous Thingiverse model which is credited.

The sound or acoustic modeling is not what we want to focus on since the original looks like something out of a sci-fi parody. We want to talk about the smart finishing touches that transform a couple of 3D printed shells into enviable centerpieces. The first, and most apparent is the surface. 3D prints from consumer FDM printers are prone to layer lines, and that aesthetic has ceased to be trendy. Textured paint will cover them nicely and requires minimal elbow grease. Besides sand and shells go together naturally. At first glance, the tripod legs holding these speakers seemed like a classy purchase from an upscale furniture store, but they are, in fact, stained wood and ground-down bolts. Nicely done.

The moral is to work smarter, take pictures, then drop us a line.

One Man’s Quest To Build His Own Speakers

Why build your own stereo speakers? Some people like to work on cars in their garage. Some people build fast computers. Others seek the perfect audio setup. The problem for a newcomer is the signal to noise ratio among audiophile experts. Forums are generally filled with a vocal group of extremists obsessing on that last tiny improvement in some spec.  It can be hard for a beginner to jump in and learn the ropes.

[Ynze] had this problem. He’d finished a custom amplifier and decided to build his own speakers. He found a lot of spirited debates about what was important for good speakers. He tried to wade through the discussions and determine which things had real practical value. The results and his speaker build are documented in a post that you’ll want to check out if you would like to design and build your own speakers.

Some of the topics ranged from solder type to capacitor construction and 700 Euro capacitors. [Ynze’s] goal was to build something that sounded good while keeping costs in line. He claims he spent about 250 Euro and wound up with speakers equivalent to 750 Euro store-bought speakers.

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