A New Wrinkle On Wooden Ribbon Microphones

March 30, 2022 by Dan Maloney 13 Comments

Not too many people build their own microphones, and those who do usually build them out of materials like plastic and metal. [Frank Olson] not only loves to make microphones, but he’s also got a thing about making them from wood, with some pretty stunning results.

[Frank]’s latest build is a sorta-kinda replica of the RCA BK-5, a classic of mid-century design. Both the original and [Frank]’s homage are ribbon microphones, in which a thin strip of corrugated metal suspended between the poles of magnets acts as a transducer. But the similarities end there, as [Frank] uses stacked layers of walnut veneer as the frame of his ribbon motor. The wood pieces are cut with a vinyl cutter, stacked up, and glued into a monolithic structure using lots of cyanoacrylate glue. The video below makes it seem easy, but we can imagine getting everything stacked neatly and lined up correctly is a chore, especially when dealing with neodymium magnets. Cutting and corrugating the aluminum foil ribbon is no mean feat either, nor is properly tensioning it and making a solid electrical contact.

The ribbon motor is suspended in a case made of yet more wood, all of which contributes to a warm, rich sound. The voice-over for the whole video below was recorded on a pair of these mics, and we think it sounds just as good as [Frank]’s earlier wooden Model 44 build. He says he has more designs in the works, and we’re looking forward to hearing them, too. Continue reading “A New Wrinkle On Wooden Ribbon Microphones” →

Solving Grounding Issues On Switch Audio

March 27, 2022 by Bryan Cockfield 32 Comments

Grounding of electrical systems is an often forgotten yet important design consideration. Issues with proper grounding can be complicated, confusing, and downright frustrating to solve. So much so that engineers can spend their entire careers specializing in grounding and bonding. [Bsilvereagle] was running into just this sort of frustrating problem while attempting to send audio from a Nintendo Switch into a PC, and documented some of the ways he attempted to fix a common problem known as a ground loop.

Ground loops occur when there are multiple paths to ground, especially in wires carrying signals. The low impedance path creates oscillations and ringing which is especially problematic for audio. When sending the Switch audio into a computer a loop like this formed. [Bsilvereagle] set about solving the issue using an isolating transformer. It took a few revisions, but eventually they settled on a circuit which improved sound quality tremendously. With that out of the way, the task of mixing the Switch audio with sources from other devices could finally proceed unimpeded.

As an investigation into a nuisance problem, this project goes into quite a bit of depth about ground loops and carrying signals over various transforming devices. It’s a great read if you’ve ever been stumped by a mysterious noise in a project. If you’ve never heard of a ground loop before, take a look at this guide to we featured a few years ago.

Reverse Engineering Your Own Bluetooth Audio Module

March 26, 2022 by Jenny List 32 Comments

There was a time when we would start our electronic projects with integrated circuits and other components, mounted on stripboard, or maybe on a custom PCB. This is still the case for many devices, but it has become increasingly common for an inexpensive ready-built module to be treated as a component where once it would have been a project in its own right. We’re pleased then to see the work of [ElectroBoy], who has combined something of both approaches by reverse engineering the pinout of a Chinese Bluetooth audio chip with minimal datasheet, and making his own take on an off-the-shelf Bluetooth audio module.

The JL_AC6939B comes in an SOIC16 package and requires a minimum number of components. The PCB is therefore a relatively simple proposition and indeed he’s fitted all parts and traces on one side with the other being a copper ground plane. It’s dangerous to assume that’s all there is to a board like this one though, because many an engineer has come unstuck trying to design a PCB antenna. We’d hazard a guess that the antenna here is simply a wavy PCB line rather than an antenna with a known impedance and bandwidth, at the very least it looks to have much thicker traces than the one it’s copying.

It’s possible that it’s not really worth the effort of making a module that can be bought for relative pennies ready-made, but to dismiss it is to miss the point. We make things because we can, and not merely because we should.

Immersive Stereo Sound Recording With This Binaural Microphone

February 20, 2022 by Jenny List 22 Comments

Sound recording has been a consumer technology for so long now that it is ubiquitous, reaching for a mobile device and firing up an app takes only an instant. Anyone who takes an interest in audio recording further will find that while it’s relatively straightforward to make simple recordings. But, as those among you who have fashioned a pair of Shure SM58s into an X configuration with gaffer tape will know, it can be challenging to create a stereo image when recording outside the studio. In the quest to perfect this, [Kevin Loughin] has created a binaural microphone, which simulates a human head with microphones placed as ears to produce ambient recordings with an almost-immersive stereo image.

Commercial binaural microphones can cost thousands of dollars, but this one opts for a more budget design using an off-the-shelf mannequin head sold for hairdressers. It’s filled with high-density foam, and in its ears [Kevin] placed 3D-printed ear canals with electret microphone capsules. On the back goes a battery and a box for the bias circuitry.

The results as you can hear in the video below the break are impressive, certainly so for the cost. It’s not the first such microphone we’ve shown you, compare it with one using a foam-only head.

Continue reading “Immersive Stereo Sound Recording With This Binaural Microphone” →

Python Web Proxy Convinces Sonos To Stream YouTube

February 4, 2022 by Dave Rowntree 22 Comments

[Maurice-Michel Didelot] owns a Sonos smart speaker, and was lamenting the devices inability (or plain unwillingness) to stream music from online sources without using a subscription service. YouTube Music will work, but being a subscription product there is a monthly fee, which sucks since you can listen to plenty of content on YouTube for free. [Maurice] decided that the way forward was to dig into how the Sonos firmware accesses ‘web radio’ sources, and see if that could be leveraged to stream audio from YouTube via some kind of on-the-fly stream conversion process.

What? No MP4 support for web radio? Curses!

So let’s dig in to how [Maurice] chose to approach this. The smart speaker can be configured to add various streaming audio sources, and allows you add custom sources for those. The Sonos firmware supports a variety of audio codecs, besides MP3, but YouTube uses the MP4 format. Sonos won’t handle that from a web radio source, so what was there to do, but make a custom converter?

After a little digging, it was determined that Sonos supports AAC encoding (which is how MP4 encodes audio) but needs it wrapped in an ADTS (Audio Data Transport Stream) container. By building a reverse web-proxy application, in python using Flask, it was straightforward enough to grab the YouTube video ID from the web radio request, forward a request to YouTube using a modified version of pytube tweaked to not download the video, but stream it. Pytube enabled [Maurice] to extract the AAC audio ‘atoms’ from the MP4 container, and then wrap them up with ADTS and forward them onto the Sonos device, which happily thinks it’s just a plain old MP3 radio stream, even if it isn’t.

Sonos doesn’t have the best reputation, let’s say, but you can’t deny that there’s some pretty slick tech going on inside. Here’s a neat hack we covered last year, adding Sonos support to an old school speaker, and a nice teardown of a IKEA Sonos-compatible unit, which uses some neat design hacks.

Thanks [mip] for the tip!

Featured image by Charles Deluvio on Unsplash.

Know Audio: A Mess Of Cables

February 2, 2022 by Jenny List 99 Comments

We’ve now spent several months in this series journeying through the world of audio, and along the way we’ve looked at the various parts of a Hi-Fi system from the speaker backwards to the source. It’s been an enjoyable ride full of technical detail and examining Hi-Fi myths in equal measure, but now it’s time to descend into one of the simplest yet most controversial areas of audio reproduction. Every audio component, whether digital or analogue, must be connected into whatever system it is part of, and this is the job of audio cables, sometimes referred to as interconnects. They are probably the single component most susceptible to tenuous claims about their performance, with audiophiles prepared to spend vast sums on cables claimed to deliver that extra bit of listening performance. Is there something in it, or are they all the same bits of wire with the expensive ones being a scam? Time to take a look.

What Makes A Nearly Good Cable

In a typical domestic audio system with digital and analogue signals you might expect to find two types of cable, electrical interconnects that could carry either analogue or digital signals, and optical ones for digital signals. We’re here to talk about the electrical cables here as they’re the ones used for analogue signals, so lets start with a little transmission line theory. Continue reading “Know Audio: A Mess Of Cables” →

Woodworking, Blinkenlites, And FFT’s Dance To The Music

January 18, 2022 by Ryan Flowers 5 Comments

We all have that one project on our minds that we’d love to build if we could just find the right combination of time, energy, and knowledge to dive right in. For [Jonathan], that project was a sound sculpture that’s finally made it from concept to complete. [Jonathan] describes the sound sculpture as the culmination of a decade of learning, and in a moment you’ll understand why.

The sculpture itself is a beautiful display of woodwork mixed with what appear to be individually addressable LED’s. The varying length of the individual enclosures evokes the idea that the sculpture is somehow involved in the sound production, which is a nice touch.

An Adafruit microphone module feeds detected audio into a PSoC 5 microcontroller. You’d expect that [Jonathan] just used one of the FFT libraries that are available. But you’ll recall that this was the culmination of a decade of learning- why so? Because [Jonathan] went through the process of procuring his own grey hairs by writing his own FFT function. A homebrew FFT function and blinkenlites? What’s not to love!

You may also enjoy this discussion of Sine Waves, Square Waves, and FFT’s with our own Bil Herd.

Continue reading “Woodworking, Blinkenlites, And FFT’s Dance To The Music” →