Ambi-Alice Goes Down The Rabbit Hole Of Ambisonic Microphones

August 27, 2021 by Kristina Panos 2 Comments

Theoretically, ambisonic microphones allow you to perfectly encode the soundscape around you and recreate it from the focal point of any direction. To do this, you need at least four microphone capsules and some math. Ambisonic microphones have been around for 50 years, but [DJJules] wanted to bring ease of use to these tools and push them into the open source fold.

As you’ll see in the video below, there were a few iterations before this one. Everything changed for the better when [DJJules] found out about TSB25905 capsules. These are electret condenser mics with 1″ diaphragms and built-in EMI/RFI-suppressing capacitors. Another big help was deciding to color code everything from the XLR cable boots to the cable sleeves to the electrical tape that’s protecting each of the P48 resistor-capacitor pairs inside the XLR plugs.

[DJJules]’ buddy [Tom] designed and printed a single piece that holds the four capsules in a perfect tetrahedral array, and an elegant two-piece basket that protects the mics and provides a base for a one of those furry windscreens. The mics and the basket are separated with four silicone plugs designed for quadcopters that provide both isolation and vibration dampening.

If you want to make one of these yourself, [DJJules] has STLs for both a normal microphone stand and another for GoPro mounts. Check out the build video after the break and the sound demos on Instructables.

No need for a rich soundscape? Build a USB microphone instead, or if that’s too cold and modern, whittle up a wooden a ribbon mic.

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Stereo Recording Made Easy With A 3D-Printed Mount

August 1, 2021 by Jenny List 15 Comments

When making a recording it can be surprisingly difficult to capture a good stereo image. A well-known technique is the ORTF microphone arrangement in which two cardoid microphones sit at 110 degrees to each other and 17cm apart, and thus pick up a readily reproducible stereo separation. It’s something that we’ve been known to do in our student days with a pair of Shure SM58s and a stack of Post Office elastic bands, but [marsairforce] has done a much nicer job with a very neat 3D-printed microphone clip.

Designed in OpenSCAD, the first iteration printed on a resin printer proved to be too brittle for the task, so a second version was printed on an FDM machine. This incorporated significant strengthening, as well as a screw mount for a microphone stand. The result is an extremely useful and cheap addition to any recording set-up, and anyone who has wrestled with achieving a good stereo image will appreciate it. You can see some of what went into it in the video below the break.

If this is your field of interest, you might also wish to look at a binaural microphone.

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DIY USB Microphone Seems Overkill; Is Surprisingly In-Depth

June 2, 2021 by Erin Pinheiro 4 Comments

Those of us who have been working from home through video calls for the past year can attest to the rising demand for conferencing gear such as webcams and microphones. Not wanting to spring for a boring off-the-shelf solution, serial hacker [Andy Brown] decided to design his own USB solution from scratch and show us the process from start to finish.

Deciding to go for a full digital design for the circuitry, the peripheral is based off of a MEMS microphone and an STM32 microcontroller doing the heavy lifting between it and a USB connection. [Andy] notes that MEMS microphones are very delicate and you have to design the PCB around the hole where the sound enters, which is why he went with a breakout board which has the component already soldered onto it.

As for the MCU, he reasons that since this is a off-one project which won’t be produced in large numbers, the 180 MHz ARM core shouldn’t be seen as overkill, since it also gives him more than plenty of headroom to do signal processing to make the sound clearer before sending it through to a computer by the USB audio device descriptor.

Once the components are chosen and the board designed, [Andy] goes into detail explaining the firmware he wrote for the STM32 to translate the PCM samples from the microphone’s I²S interface into a format better suited for the computer. He also describes how it then processes the audio, applying a graphic equalizer to reduce noise and then ST’s own Smart Volume Control filter, which works more like a compressor than a simple amplitude multiplication.

Finally, all files for the project, including board gerbers and the STM32 firmware are available at the bottom of his post, and to boot, a video demonstrating the project which you can check here after the break. [Andy]’s choice of microcontroller for this project is no surprise to us, given he’s already made his own development board for the STM32 G0 series. But if this digital microphone project is a bit too modern for you, why not try your hand at building a ribbon microphone instead?

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Wood Enclosure Lends Warmth To This DIY Ribbon Microphone

May 14, 2021 by Dan Maloney 7 Comments

We love it when someone takes an idea they’ve seen on Hackaday and runs with it, taking it in a new and different direction. That’s pretty much what we’re here for, after all, and it’s pretty gratifying to see projects like this wooden ribbon microphone come to life.

Now, we’re not completely sure that [Maya Román] was inspired by our coverage of [Frank Olson]’s homage to the RCA Model 44 studio mic rendered in walnut veneer, but we’re going to pat ourselves on the back here anyway. The interesting thing with [Maya]’s build is that she chose completely different materials and design styles for her project. Where [Frank] built as much of his mic from wood as possible, [Maya] was fine with a mixed media approach — CNC-milled plywood for the case and stand, laser-cut acrylic for the ribbon motor frame, and 3D-printed pieces here and there as needed. The woven brass cloth used as a windscreen is a nice detail; while the whole thing looks — and sounds — great, we think it would be even better with a coat of dark stain to contrast against the brass, as well as a nice glossy coat of polyurethane.

The video below shows the whole design and build process, which was a final project for [Maya]’s audio production class this semester at college. Here’s hoping that it got as good a grade as we would give it.

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A HALO Of LEDs For Every Ear

April 17, 2021 by Kerry Scharfglass 28 Comments

Few things get a Hackaday staffer excited like bunches of tiny LEDs. The smaller and denser the better, any form will do as long as we can get a macro shot or a video of a buttery smooth animation. This time we turn to [Sawaiz Syed] and [Open Kolibri] to deliver the brightly lit goods with the minuscule HALO 90 reactive LED earrings.

The HALO 90’s are designed to work as earrings, though we suspect they’d make equally great brooches, hair accessories, or desk objects. To fit this purpose each one is a minuscule 24 mm in diameter and weighs a featherweight 5.2 grams with the CR2032 battery (2.1 g for the PCBA alone). Functionally their current software includes three animation modes, each selectable via a button on device; audio reactive, halo (fully lit), and sparkle. Check out the documentation for details on expected battery life in each mode, but suffice to say that no matter what these earrings will make it through a few nights out.

In terms of hardware, the HALO 90’s are as straightforward as you’d expect. Each device is driven by an STM8 at its maximum 16MHz which is more than fast enough to keep the 90 charliplexed 0402 LEDs humming along at a 1kHz update rate, even with realtime audio processing. In fact the BOM here is refreshingly simple with just 8 components; the LEDs, microcontroller and microphone, battery holder and passives, and the button. [Sawaiz] even designed an exceptionally slick case to go with each pair of earrings, which holds two HALO 90’s with two CR2032’s and includes a magnetic closure for the most satisfying lid action possible.

As with some of his other work, [Sawaiz] has produced a wealth of exceptional documentation to go with the HALO 90’s. They’re available straight from him fully assembled, but with documentation this good the path to a home build should be well lit and accessible. He’s even chosen parts with an eye towards long availability, low cost, and ease of sourcing so no matter when you decide to get started it should be a snap.

It was difficult to choose just a few images from [Sawaiz]’s mesmerizing collection, so if you need more feast your eyes on the expanded set after the break.

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Wooden You Love To Build A Ribbon Microphone?

March 18, 2021 by Dan Maloney 11 Comments

Carbohydrate foams derived from dead trees are not the first material that springs to mind when considering building audio equipment. But really, there’s no reason not to explore new materials for jobs normally reserved for metal or plastic, and when pulled off right, as with this wooden ribbon microphone, the results can both look and sound great.

To be fair, there are plenty of non-wood components in [Frank Olson]’s replica of a classic RCA model 44 microphone. After all, it’s hard to get wood to exhibit the electromagnetic properties needed to turn acoustic energy into electric currents. But that doesn’t mean that wood, specifically walnut veneer, isn’t front and center in this design. [Frank] worked with thin sheets of veneer; cut into shape with a commercial vinyl cutter and stacked up with alternating grains, the wood was glued up with copious cyanoacrylate adhesive to form a plywood of sorts. The dogbone-shaped body was fitted with two neodymium magnets, leaving a gap just wide enough for the microphone’s ribbon diaphragm. That was made from a thin piece of aluminum foil that was corrugated using a DIY crimp roller. Suspended between the magnets and connected to leads, the mic element was adorned with a wood and fabric windscreen and suspended from elastic bands in a temporary frame for testing. The narration on the video below was recorded with the mic, which sounds quite nice to our ears.

We’ve seen ribbon microphones before, as well as wooden microphones, but this is the first time we’ve seen a wooden ribbon microphone. It looks as though [Frank] has more work he wants to do to finish it off properly, and we eagerly await the finished product.

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“Alexa, Stop Listening To Me Or I’ll Cut Your Ears Off”

February 2, 2021 by Dan Maloney 88 Comments

Since we’ve started inviting them into our homes, many of us have began casting a wary eye at our smart speakers. What exactly are they doing with the constant stream of audio we generate, some of it coming from the most intimate and private of moments? Sure, the big companies behind these devices claim they’re being good, but do any of us actually buy that?

It seems like the most prudent path is to not have one of these devices, but they are pretty useful tools. So this hardware mute switch for an Amazon Echo represents a middle ground between digital Luddism and ignoring the possible privacy risks of smart speakers. Yes, these devices all have software options for disabling their microphone arrays, but as [Andrew Peters] relates it, his concern is mainly to thwart exotic attacks on smart speakers, some of which, like laser-induced photoacoustic attacks, we’ve previously discussed. And for that job, only a hardware-level disconnect of the microphones will do.

To achieve this, [Andrew] embedded a Seeeduino Xiao inside his Echo Dot Gen 2. The tiny microcontroller grounds the common I²S data line shared by the seven (!) microphones in the smart speaker, effective disabling them. Enabling and disabling the mics is done via the existing Dot keys, with feedback provided by tones sent through the Dot speaker. It’s a really slick mod, and the amount of documentation [Andrew] did while researching this is impressive. The video below and the accompanying GitHub repo should prove invaluable to other smart speaker hackers.

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