Sometimes a project takes longer than it should to land in the Hackaday in-tray, but when we read about it there’s such gold to be found that it’s worth sharing with you our readers despite its slight lack of freshness. So it is with [Andrew Back]’s refurbishment of his Quad electrostatic speaker system power supply, it may have been published back in August but the glimpse it gives us into these legendary audio components is fascinating.
An electrostatic speaker is in effect a capacitor with a very large surface area, of which one plate is a flexible membrane suspended between two pieces of acoustically transparent mesh that form the other plates. A very high DC bias voltage in the multiple kilovolts region is applied across the capacitor, and the audio is superimposed upon it at a peak-to-peak voltage of somewhere under a kilovolt through a step-up transformer from the audio amplifier. There are some refinements such as that the audio is fed as a push-pull signal to the opposing mesh plates and that there are bass and treble panels with different thickness membranes, but these speakers are otherwise surprisingly simple devices.
The problem with [Andrew]’s speakers became apparent when he took a high voltage probe to them, one speaker delivered 3 kV from its power supply while the other delivered only 1 kV. Each supply took the form of a mains transformer and a voltage multiplier board, so from there it became a case of replacing the aged diodes and capacitors with modern equivalents before applying an insulating layer for safety.
For professional-level sound recording, you’ll need professional-level equipment. Microphones and mixing gear are the obvious necessities, as well as a good computer with the right software on it. But once you have those things covered, you’ll also need a place to record. Without a good acoustic space, you’ll have all kinds of reflections and artefacts in your sound recordings, and if you can’t rent a studio you can always build your anechoic chamber.
While it is possible to carpet the walls of a room or randomly glue egg crate foam to your walls, [Tech Ingredients] tests some homemade panels of various shapes, sizes, and materials against commercially available solutions. To do this he uses a special enclosed speaker pointed at the material, and a microphone to measure the sound reflections. The tests show promising results for the homemade acoustic-absorbing panels, at a fraction of the cost of ready-made panels.
From there, we are shown how to make and assemble these panels in order to get the best performance from them. When dealing with acoustics, even the glue used to hold everything together can change the properties of the materials. We also see a few other cost saving methods in construction that can help when building the panels themselves as well. And, while this build focuses on acoustic anechoic chambers, don’t forget that there are anechoic chambers for electromagnetic radiation that use the same principles as well.
Speakers are one of those components that are simple to use, but difficult to simulate. Most of us have used a simple resistor to do the job. But a speaker’s response is much more complex, and while that might be enough for a simple simulation the fidelity is nowhere near close. [Sourav Gupta] recently shared his technique for modeling speakers and it looks as though it does a credible job.
[Sourav] shows how a simple resistor and an inductor can do the job, but for better fidelity you need more components to model some mechanical effects. The final model has six components which keeps it easy enough to construct but the problem lies in finding the values of those six components. [Sourav] shows how to use the Thiele-Small parameters to solve that problem. Speaker makers provide these as a guide to low frequency performance, and they capture things such as Q, mass, displacement, and other factors that affect the model.
There are few limits to the extent audiophiles will go in their quest for the perfect sound. This applies in particular to the loudspeaker, and with that aim [Heine Nielsen] has created an eye-catching set of 3D-printed egg-shaped enclosures.
The theory of a loudspeaker enclosure is that it should simulate an infinite space behind an infinite plane in which the speaker driver is mounted, and the reasoning behind spherical or egg-shaped enclosures goes that they better achieve that aim through presenting a uniform inner surface without the corners of a more conventional rectangular enclosure. [Heine]’s enclosures 3D-printed ported enclosures achieve this more easily than traditional methods of building this shape.
A loudspeaker enclosure is more than just a box though, whatever material it is made from must adequately dampen any resonances and absorb as much energy as possible. Conventional speakers try to achieve this by using high-mass and particulate materials, but 3D-printing does not lend itself to this. Instead, he created a significant air gap between two layers which he hopes will create the same effect.
This is an interesting design and approach to speaker cabinet construction, but we think from an audio perspective its one that will be well served by more development. What would be the effect of filling that air gap with something of higher mass, for example, and should the parameters of the egg shape and the port be derived for a particular driver by calculation from its Thiele-Small parameters. We look forward to more on this theme.
Speakers used to be largish electromechanical affairs, with magnets, moving coils, and paper cones all working together to move air around in a pleasing way. They’ve gotten much smaller, of course, small enough to screw directly into your ears or live inside the slimmest of smartphones and still delivery reasonable sound quality. The basic mechanism hasn’t changed much, but that doesn’t mean there aren’t other ways to make transduce electrical signals into acoustic waves.
Take these speakers made from flexible printed circuit boards, for instance. While working on his flexible PCB soft actuators, [Carl Bugeja] noticed that the PWM signals coursing through the coils on the thin PCB material while they were positioned over a magnet made an audible beeping. He decided to capitalize on that and try to make a decent speaker from the PCBs. An early prototype hooked to a simple amplifier showed promise, so he 3D-printed a ring to support the PCB like a diaphragm over a small neodymium magnet. The sound quality was decent, but the volume was low, so [Carl] experimented with a paper cone attached to the PCB to crank it up a bit. That didn’t help much, but common objects acting as resonators seemed to work fairly well. Check out the results in the video below.
At first glance, this fire engine red speaker box built by [NoshBar] looks straightforward enough. Just an MDF case and couple of drivers recovered from a trashed stereo. But the array of controls and connectors on the front, and a peek on the inside, shows there’s more to this particular project than meets the eye.
Built almost entirely from parts [NoshBar] found in the trash, construction started with some salvaged MDF IKEA shelves and their corresponding twist lock cam fittings. We don’t usually see those style cam fittings used to build DIY enclosures, but if it works for all those furniture manufacturers why not?
A pair of Sony stereo speakers he found gave up their internals, and a TPA3116 amplifier board off of eBay drives them. He’s wired up an audio pass-through mode for using headphones when the amplifier is powered off, and dual inputs so he can switch between PC and PS4.
But the audio components are only half of what’s inside that shiny red exterior. [NoshBar] packed in an ATX PSU and broke out the 3.3 V, 5 V, and 12 V lines to the front panel so he can use it as a bench power supply for his Arduino projects. It’s also home to a gigabit Ethernet switch and a Raspberry Pi acting as a file server.
These days you’d very likely use your phone as the audio source so he included a 20 watt stereo class D amplifier which could be disconnected at the throw of a switch if not needed. To power the amplifier he used 16 18650 lithium-ion batteries which were leftover from previous projects. He estimates they should give him around 100 hours of enjoyable tunes. And to make further use of the batteries, he also added a USB charger so that he could charge up his phone from it, something else which is nice to be able to do when on the road.
A battery management system (BMS), an XT60 connector for charging the batteries, his battery level indicator circuit which we talked about before, a new passive audio crossover, and some rather nice work on that case all round out the boombox. Check out his full construction in the video below and make sure to stay until the end when he gives a taste of its awesome sound (you may even swear your desk is vibrating from the bass despite wearing earbuds, like we did).