There was a time when consumer electronics were statement items, designed to resemble quality furniture that would be shown off as a centerpiece of the home. Televisions in ornate wooden cabinets, or stereos looking for all the world like sideboards. [Zethus] had just such a huge record player and radio combo in a sideboard, and having little use for the cream of 1950s home entertainment technology, he rebuilt it as a concealed liquor cabinet with electronic controls and a much more modern stereo that forms part of a Logitech Media Server multi-room system.
After removing the tube-based radio chassis and Garrard jockey-wheel turntable it was time to gut their supporting woodwork and install the platform derived from a standing desk. With suitably impressive lighting and a pair of VFD displays for the music choice, there is the inevitable Raspberry Pi running the show. Control is achieved by a set of hidden capacitive buttons, and there’s a Web interface to allow both music and magical appearance of alcohol from the comfort of a smartphone. The whole can be seen in the video below the break.
Whenever a piece of vintage electronics is gutted in this way there will always be people who find it disquieting, but the truth is that these all-in-one stereos were made in huge quantities during the mid-century period and do not have a significant value. This one may have lost its original electronics, but it lives on safe from the dump that has claimed so many of its brethren. Happily this isn’t the first one we’ve seen saved with a Pi.
When you go by a handle like [Simplifier], you’ve made a mission statement about your projects: that you’ll take complex processes and boil them down to their essence. So tackling the rebuilding of the humble speaker, a device he himself admits is “both simplified and optimized already,” would seem a bit off-topic. But as it turns out, the principle of magnetostriction can make the lowly speaker even simpler.
Most of us are familiar with the operation of a speaker. A powerful magnet sits at the center of a coil of wire, which is attached to a thin diaphragm. Current passing through the coil builds a magnetic field that moves the diaphragm, creating sound waves. Magnetostriction, on the other hand, is the phenomenon whereby ferromagnetic materials change shape in a magnetic field. To take advantage of this, [Simplifier] wound a coil of fine copper wire around a paper form, through which a nickel TIG electrode welding filler rod is passed. The nickel rod is anchored on one end and fixed to a thin brass disc on the other. Passing a current through the coil causes the rod to change length, vibrating the disc to make sound. Give it a listen in the video below; it sounds pretty good, and we love the old-time look of the turned oak handpiece and brass accouterments.
We love the world of audiophiles here at Hackaday, mostly for the rich vein of outrageous claims over dubious audio products that it generates. We’ve made hay with audiophile silliness in the past, but what we really like above that is a high quality audio project done properly. It’s one thing to poke fun at directional oxygen free gold plated USB cables, but it’s another thing entirely to see a high quality audio project that’s backed up by sound design and theory to deliver the best possible listening. [Davide Ercolano]’s transmission line speakers are a good example, because he’s laid out in detail his design choices and methods in their creation.
Starting with the Thiele-Small parameters of his chosen driver, he simulated the enclosure using the Hornresp software. As a 3D-printed design he was able to give it paraboloid curves to the convoluted waveguide, making it a much closer approximation to an ideal waveguide than a more traditional rectangular design. In the base is a compartment for an amplifier module, with additional Bluetooth capability.
We’d be curious to know how well 3D printed plastic performs in this application when compared for example to something with more mass. However we like these speakers a lot; this is how a high quality audio project should be approached. We’ve delved into speakers more than once in the past, but if you’re looking for something really unusual then how about an electrostatic?
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.
Everyone has a stack of old infra-red remote controllers lying around, for devices that have long since shuffled off this mortal coil. Containing little more than an application-specific encoder chip, keyboard, and IR LED, they’re of little use unless you happen to have another device that uses the same encoding scheme. For [RiYa] though they represent an opportunity, to be repurposed into controllers for other devices. How? Hijack the bitstream with an ATtiny13 microcontroller, re-encode it, and send it out afresh into the ether from the LED. It’s a gloriously simple solution which we can’t help applauding, and has the potential to cheaply replace all those universal remotes.
The ATtiny itself along with a buffer to drive the LED is mounted on a small breakout board and concealed within the shell of the remote. We don’t learn much about the power supply arrangement, but we’d expect the ATtiny to be on its most power-sipping behaviour as anything which would shorten the battery life of a remote would be unlikely to be popular with a couch potato forced to change AA cells every few weeks. There’s a plan for a learning mode to make it more like a commercial universal remote, but for now the translation is hard coded.
A lot of projects we feature use video in some form or other, but that video is invariably digital, it exists as a stream of numbers in a computer memory or storage, and is often compressed. For some of us who grew up working with composite video there is a slight regret that we rarely get up-close and personal with an analogue stream, so [Kris Slyka]’s project putting video on a conventional audio cassette is a rare opportunity.
It’s fair to say this isn’t the highest quality video.
Readers with long memories may recall the Fisher-Price PixelVision toy from the late 1980s which recorded black-and-white video on a conventional cassette running at many times normal speed. This system does not take that tack, instead it decreases resolution and frame rate to a point at which it can be recorded at conventional cassette speeds. The result is not particularly high quality, but with luminance on one side of a stereo recording and chrominance on the other it does work.
The video below the break is a run through the system, with an explanation of how video signals work. Meanwhile the code for both encoder and decoder are available through the magic of GitHub. If you’re interested further, take a look at our examination of a video waveform.
As a writer, I have long harboured a dream that one day an editor will buy me a top-of-the-range audio analyser, and I can set up an audio test lab and write pieces debunking the spurious claims made by audiophiles, HiFi journalists, and the high-end audio industry about the quality of their products. Does that amp really lend an incisive sibilance to the broader soundstage, and can we back that up with some measurable figures rather than purple prose?
An Audio Playground You Didn’t Know You Had
An Audio Precision APx525 audio analyser. Bradp723 (CC-BY-SA 3.0)
Sadly Hackaday is not an audio magazine, and if Mike bought me an Audio Precision he’d have to satisfy all the other writers’ test equipment desires too, and who knows where that would end! So there will be no Hackaday audio lab — for now. But that doesn’t mean I can’t play around with audio analysis.
Last month we carried a write-up of a Supercon talk from Kate Temkin and Michael Ossmann, in which they reminded us that we have a cracking general purpose DSP playground right under our noses; GNU Radio isn’t just for radio. Once I’d seen the talk my audio analysis horizons were opened up considerably. Maybe that audio analyser wouldn’t be mine, but I could do some of the same job with GNU Radio.
It’s important to stress at this point that anything I can do on my bench will not remotely approach the quality of a professional audio analyser. But even if I can’t measure infinitesimal differences between very high-end audio circuitry, I can still measure enough to tell a good audio product from a bad one.
