This article describes the Circular Sound loudspeaker models in detail. We will dive into the technical specifications and also go into detail on how you can build your own.
Table of Contents
The Circular Sound Process
All Circular Sound products rely on a circular flow of materials. There are two paths to obtaining circularity, but they are not mutually exclusive:
Biological cycle: Using bio-based and bio-degradable enclosure materials.
Technical cycle: Remanufacturing from old components.
The biological cycle means using bio-materials such as UPM Formi 3D, BrightPlus BrightBio, and Sulapac Flow. Our mono-material design principle allows easy recycling of the bio-materials at end-of-life.
The technical cycle means we disassemble old loudspeakers, inspect and measure the components and use them in a new product. This is called remanufacturing. The components typically have a decade or more of life remaining, but the old product they were in was no longer wanted by users.
We take sound quality very seriously and often this means only woofers can be reused, while wideband transducers need to be of virgin origin. Nevertheless, the majority of the mass resides in the woofers and enclosure, and therefore the recycled fraction of Circular Sound loudspeakers is 70-80%. You can read more about the circular economy and environmental impact in our blog.
Circular Sound Eikosa
The Circular Sound Eikosa gets its name from the Greek word eikosáedron referring to the 20-faced polyhedron. It’s a Bluetooth loudspeaker that uses upcycled woofers for bass frequencies and a virgin wideband transducer for producing mids and highs. The enclosure is 3D printed from a PLA-based polymer. Each Eikosa is slightly different on the inside depending on the old components used, but thanks to our acoustic design, the low-frequency reproduction varies very little from unit to unit. Besides, the user can adjust the bass tuning and level of the bass frequencies based on personal preference and listening space. You can order an assembled Eikosa by backing our crowdfunding campaign.
240 mm diameter
19 V laptop charger
Upcycled dual 4-6″
60-20000 Hz (+-3 dB)
Circular Sound Sfaira (Pair)
Sfaira means sphere in Greek and refers to the shape of the enclosure. The spherical shape has many benefits in loudspeakers. It is made by 3D printing Sulapac Flow material, which is a bio-based and bio-degradable wood-filled plastic. The Sfaira is intended to be used as a stereo pair and supported by a subwoofer, such as the CS-012, if required.
Circular Sound CS-012 Subwoofer
The Circular Sound CS-012 is the first loudspeaker design in the Circular Sound line-up. The donor components come from an old Yamaha YST-SW012 bass-reflex subwoofer, which you can find second-hand for about 50€. Additive manufacturing was used to produce a smaller, sealed enclosure loudspeaker. The material used in the prototype is a bio-based material produced by BrightPlus. It has a natural dye made from woad by Natural Indigo Finland.
The original Yamaha loudspeaker is designed to be used as a single subwoofer unit placed somewhere on the floor out of sight. The new product, on the other hand, is designed to be used in a stereo configuration (2 pcs) and placed under the main speakers. It serves a different function compared to the original product, but no new materials need to be consumed. We are not injecting a new product made from virgin materials into the economy. Instead, we are taking two old ones out and replacing them with one value-added product. This is what Circular Sound is about. You don’t have to wait for distributors to bring sustainable products to your local market. You can start making these today. The files are shared for free under a Creative Commons license on Thingiverse.
The first version of our 3D printed coaxial CX loudspeaker series was made using the Desktop Metal Forust method, which is, at the moment, too expensive for most DIY audio enthusiasts. Therefore, the CX2 was designed based on fused filament fabrication (FFF).
3D printing gives design freedom
The starting point for the design is simple but effective: sealed enclosure and coaxial driver. This inherently gives us controlled cone displacement in the low-frequency region and a coherent radiation source in the crossover region. 3D printing allows to easily implement two more acoustically beneficial geometries: large roundovers and compound curved walls. These translate into a Minimal Edge Diffraction Enclosure (MEDE™) and reduced panel vibrations, respectively. Curved walls mean that the loudspeaker requires a stand. This requirement can be turned into a benefit: the symmetric loudspeaker can be tilted or laid on its side when placed on a so-called Isopodd stand 3D printed from soft TPU material. 3D printing allows complex shapes at no extra manufacturing cost. For example, the front baffle is stiffened on the inside with a honeycomb strucure that acts also as support for the overhangs, but robs very little internal volume.
What you need to build your own CX2
3D files for 3D printing, sold on Etsy. Dimensions 210x273x170 mm, ~1200 grams of filament.
SB Acoustics SB13PFCR25-4 COAX or SEAS MP15 (contact us)
Neutrik NL4MPR SpeakON connectors and fastON crimp connectors
4.2 mm wood screws
Bitumen or similar visco-elastic damping sheet and fibrous damping material such as pillow stuffing
Soldering capability (super easy)
How to build it
3D print the enclosures using the files mentioned above. It’s a single-piece print with no support needed. Wood-filled PLA or similar material is easy to sand and no other surface finish besides sanding is needed. If you are using the SEAS drivers you also need to print the TPU gasket/adapter. The speaker can be tilted and rotated when you print a small stand for it from TPU material. Some rubber feet on a plate will do the same job just fine. The assembly order is as follows:
Finish the outside of the enclosure and make sure the driver and SpeakON connector fit.
Line the inside with bitumen damping material and fill it quite densily with wadding.
Solder wires to the speaker drivers and crimp fastON connectors at the other end. Mark woofer and tweeter positive and negative wires.
Feed the wires through the SpeakON connector opening and mount the driver using wood screws. Use gasket/adaptor if you have the SEAS driver.
Connect the fastON connectors to you SpeakON connector and mount it.
Setup your bi-amping and crossover configuration. A good starting point for crossover frequency is 2 kHz. On-axis response will be bright, so keep that in mind when equalizing. Some toe-in may be beneficial.
Circular economy is a model of production and consumption that prioritizes resource efficiency and waste reduction. It involves designing products with durability and repairability in mind, reusing and refurbishing materials and products, and recycling materials at the end of their useful life. The goal is to keep resources in use for as long as possible and minimize environmental impacts. Currently, only 7.2% of the materials we use circulate back into the economy 1. This number needs to increase in all industries, including the loudspeaker industry, in order to reach the Sustainable Development Goals, more specifically SDG 12.5 2:
The current linear model of loudspeaker production
The global loudspeaker market size is anticipated to reach USD 8.48 billion by 20253. Its effect on the circularity gap can not be ignored. Most manufacturers using virgin materials attempt to mitigate their environmental impact by focusing on long lifespans by:
Producing long-lasting products
Offering spare parts and warranty repairs
Facilitating a second-hand market for pre-owned loudspeakers.
However, it does not matter if a product can be used forever if nobody wants it anymore. Our research shows that having a specific need is the main reason for loudspeaker buyers not using the second-hand market. This is confirmed by studying the thousands of near-zero-priced loudspeaker listings in online marketplaces. There is low demand and a high supply of old but fully functional loudspeakers. The current economy has no end-of-life solution.
The importance of loudspeaker magnets
Not having an end-of-life solution for old loudspeakers is especially problematic due to rare-earth elements found in the magnets of loudspeaker transducers. Rare-earth elements are essential for manufacturing permanent magnets. Permanent magnets are critical components in most decarbonisation technologies4 .
Lithium and rare earths will soon be more important than oil and gas. Our demand for rare earths alone will increase fivefold by 2030.
Ursula von der Leyen, President of the EU commission5
The EU imports 98% of its magnets from China and less than 1% is recycled6. Relying on China poses a geopolitical and supply chain risk. China has a history of export restrictions and weaponisation of REEs in trade wars7. Recycling is not commercially viable due to the high cost of manual separation of magnets and the relatively low price of the raw material itself8.
The circular economy approaches to loudspeakers
The circular economy of loudspeakers can be described with the help of the 7Rs.
Rethink: Use fewer components and eco-friendly materials, combine functions, or make the product easy to disassemble and recycle.
Reduce: Spend less material and energy. Generate less waste.
Reuse: Sell in the second-hand market.
Repair: Fix broken loudspeakers by re-coning transducers, replacing components, and refurbishing the enclosure.
Remanufacture: Disassemble old loudspeakers and use the materials to make a new product.
Recycle: Use raw materials, such as plastic and metal, again.
Recover: Burn the enclosure for energy.
All of the approaches are a step forward from the current linear economy. The first two (Rethink and Reduce) are effective since they occur already at the design stage. However, they still rely on virgin materials and do nothing about the current levels of waste. The last two (Recycle and Recover) are not recommended, because they do not preserve added value and hardly generate any jobs or social well-being. Reuse and Repair are great if there still is demand for that product. Remanufacturing allows for meeting new user needs using existing materials. An example of remanufacturing is the RD Physics Circular Sound loudspeakers.
Benefits of circular economy
The benefits of a circular economy include reducing the extraction of virgin materials, reducing greenhouse gas emissions, creating new job opportunities, and improving the resilience of the economy. It also has the potential to create a more sustainable and profitable industry, reduce resource costs, and improve social and environmental outcomes. By introducing a circular economy for the loudspeaker transducers specifically, we can achieve:
Independence of imported magnets
Reliable supply chains
Reduced need to mine rare-earth elements
Preservation of added value in existing products
Utilization of electronics waste
Life-cycle impact assessment of loudspeakers
Life-cycle analysis can be used to quantify the impact of the circular economy of loudspeakers. The majority of the impact comes from magnets and the chemical processing of the rare-earth elements in them. For example, the Circular Sound Eikosa loudspeaker contains approximately one kilogram of magnets in the upcycled transducers it uses. The life-cycle impact assessment of 1 kg of magnet reported here is an average of several sources reported in two studies 9,10.
kg CO2 eq.
mol H+ eq.
kg P eq.
kg N eq.
mol N eq.
Human toxicity (carcinogenic)
kg CFC-11 eq.
kg PM2.5 eq.
kBq U235 eq.
Impact per kilogram of rare-earth permanent magnet
All industries need to transform into a circular economy in order to close the circularity gap and reach the Sustainable Development Goals. The current loudspeaker industry operates in a linear fashion and trusts that a long product life will mitigate environmental impact. However, there is no end-of-life solution available and precious raw materials found in the loudspeaker magnets end up in landfills.
Various circular economy solutions exist. Minimizing material use and swapping one material for another is an incremental improvement, but still involves virgin materials. Repairing and relying on a second-hand market assumes there is still a demand for the old product. Recycling the raw materials destroys the added value of the product and is not economically viable due to manual disassembly steps. Remanufacturing, on the other hand, offers a way to meet new customer needs using components and materials from old products.
Upcycling old loudspeaker transducers and using them in a new product keeps the magnets in our economy and reduce the need to produce virgin magnets. This has quantifiable environmental impacts, such as avoiding 70 kg of CO2 equivalent in greenhouse gas emission per one kilogram of magnet.
Life cycle impact assessment (LCIA) is a tool used to evaluate the environmental impact of products or services across their entire life cycle. To measure these impacts, a variety of impact categories and units can be used. Here are some examples:
Global warming: This impact category measures the amount of greenhouse gases (primarily carbon dioxide) that are emitted over the life cycle of a product or service. The unit used is typically kilograms of carbon dioxide equivalent (kg CO2e).
Acidification: This impact category measures the amount of acidifying substances (such as sulfur dioxide and nitrogen oxides) that are emitted over the life cycle of a product or service. The unit used is typically moles of hydrogen ions (mol H+).
Eutrophication: This impact category measures the amount of nutrients (primarily nitrogen and phosphorus) that are released into the environment and contribute to the growth of algae and other aquatic plants. The unit used is typically moles of phosphate (mol PO43-).
Particulate matter (PM): This impact category measures the amount of fine particulate matter (PM2.5) that is emitted over the life cycle of a product or service. The unit used is typically micrograms of particulate matter per cubic meter (μg/m3).
Ecotoxicity (aquatic): This impact category measures the potential harm that a product or service may cause to ecosystems and their inhabitants. The CTUe (Characterization Factor Toxicity Unit – ecotoxicity) unit is based on converting the amount of a substance emitted during a product’s life cycle into a standardized ecotoxicity value. The ecotoxicity value is expressed in CTUe per kilogram (kg) of the emitted substance. The characterization factor takes into account various parameters such as the chemical properties of the substance, its persistence in the environment, its toxicity to aquatic organisms, and the extent of the area affected by the emissions.
Human toxicity (cancer): This impact category measures the potential harm that a product or service may cause to human health. The human toxicity value is expressed in CTUh per kilogram (kg) of the emitted substance. The characterization factor takes into account various parameters such as the chemical properties of the substance, its toxicity to humans, and the extent and duration of exposure. When the CTUh unit is used to assess cancer risk, it is often expressed as cancer cases per million people per year (cases/million/year), rather than CTUh/kg. The cancer risk is calculated by multiplying the amount of the substance emitted by its cancer potency factor, which represents the likelihood that the substance will cause cancer in humans. The resulting value is then converted into cancer cases using demographic and exposure data.
Ozone depletion potential: The ODP of a substance is determined by comparing its potential to deplete ozone to that of CFC-11. Many ozone-depleting substances, including CFCs, are banned. The use of CFC-11 as a reference substance is only relevant for historical analysis or for assessing the impact of new substances that may have similar properties to CFCs.
Ionizing radiation: It is used to represent the potential harm a substance can cause to human health through exposure to ionizing radiation. The unit kBq U235 represents the activity of uranium-235, which is a measure of the rate at which the material emits ionizing radiation. The unit kBq stands for kiloBecquerel, which is a unit of radioactivity. One kBq corresponds to 1,000 disintegrations per second.
Water consumption: This impact category measures the amount of water used over the life cycle of a product or service. The unit used is typically cubic meters (m3) of water.
Land use: This impact category measures the amount of land required over the life cycle of a product or service. The unit used is typically square meters (m2) of land.
There are many other impact categories that can be used in life cycle assessment, depending on the specific environmental and social impacts of interest.
3D printed loudspeakers do not have to be made out of plastic anymore. There is a new way of 3D printing wood called Forust. It is a binder jetting process where upcycled sawdust is used together with a binder to form the closest thing we have to 3D printed wood. We are particularly interested in the possibilities this offers loudspeaker manufacturers.
RD Physics CX1 – A coaxial loudspeaker
RD Physics has been developing speakers with full-range drivers for some time now and while they have their inherent benefits, it is time to look what coaxial drivers have to offer. The starting point was a spherical shape, which is known for its benefits. However, the limitations in build volume favored a shape closer to a rectangular cuboid. The shape of the CX1 has the largest possible roundovers, with the constraints imposed by driver size and maximum baffle dimensions. This is to reduce edge diffraction. The sides are compound curved to maximize stiffness. There is also internal ribbing to stiffen the enclosure without taking up internal volume like a sandwich structure would. The enclosure is made in two parts; the front baffle has a separate cover that conceals the driver flange and mounting screws. The driver is a proprietary SEAS unit designated MP15 (15 cm diameter). The idea is to have an external active crossover and bi-amp the loudspeaker via the Neutrik SpeakOn 4-pin connectors at the back.
3D printing a loudspeaker using Desktop Metal Forust method
The geometry files were sent to Forust for 3D printing. The chosen colour is “natural” with the artificial wood grain introduced during manufacturing. The result is a structure that looks like plywood. Parts can be ordered without the grain and with darker colours, too. The grain is more interesting, however, because various surface texture effects can be achieved by aligning the layers at low angles relative to the principal axes of the printed shape giving a zebra stripe effect.
Post-processing of 3D printed wood
The parts printed with the Forust method can be sanded smooth, but it is not like sanding natural wood. The surface can be varnished, but not stained. The Forust material does not absorb wood stain. It does not tolerate ethanol and perhaps other solvents either. Long-term exposure to water should be avoided, otherwise there will be is a sticky brown residue on the surface. Although a wooden look can be mimicked, post-processing is not similar to wood. Instead, it resembles the wood-filled polymers used in our previous builds. This is not a serious drawback, it just means that 3D printing skills are more useful than woodworking skills. In terms of aesthetics this is the closest thing available for increasing the acceptance of 3D printed loudspeakers in the audio community, where wood veneer is the go-to solution.
Our previous 3d printed subwoofer, the SW1, is a 13 liter subwoofer with a 6.5″ driver, a matching passive radiator and a plate amp. We wanted to develop something smaller that would still offer the bass extension that satellite speakers so badly need. The result is the SW2 using a Tang Band W5-1138 5″ long-throw driver and the same Dayton Audio DSA175 passive radiator as in the SW1. The enclosure is now only 5 liters and much easier to fit on a desktop. The passive resonator allows tuning the resonance frequency to avoid overlap with room modes, for example. The spherical shape is optimal for material use and stiffness. Combined with the small diameter driver with large surrounds, the appearance is quite unique. If a traditional box is what you want, then this build is not for you.
The measured resonance frequency of the passive radiator indicates that some air-coupling occurs due to the downward firing placement. Simulated resonance frequency matches the measured value (53 Hz) when 16 grams of added mass is used. Mass can be further added using washers to tune the response. In practice, the frequency response starts to drop below 50 Hz. The Arylic amplifier offers DSP capabilites and using a computer as the source allows unlimited DSP with zero cost. Therefore, frequency response in not that meaningful especially when considering the room effects, but we have included some measurements to give an idea of the natural response especially around the lower cut-off.
The enclosure is printed in one part (234 mm diameter) and takes approximately 1.5 kg of filament. Print time is about 48 hours. The mass can be increased by lining the walls with sound deadening mat. Although the external wall is spherical, there is a cylindrical inner wall that braces the woofer to the passive resonator and, thanks to a single curvature surface, allows easy installment of thick sound deadening mat. The drivers are fastened using 4.2 mm wood screws. There is a geometry file for a gasket for the woofer which can be printed from TPU. Traditional gasketing methods will work, but the 3D printed gasket is seamless and has the screw hole pattern accurately incorporated. The binding posts are recessed deep into the enclosure and only accept banana plugs in that configuration. An O-ring under the binding post washer is recommended and there is a chamfer for it. 3D printing using a wood-filled filament allows easy sanding for a smooth surface finish. The photos show 15 minutes worth of post-processing making this a very easy and fast build without compromising in function and looks.
The subwoofer was compared to the much larger, THX certified Logitech Z623 subwoofer. The sound is very similar, but in a much smaller package. The SW2 is a great companion for small satellite speakers and brings fullness to the bass. Electronic music will benefit from the “boom” offered by this small unit, while other types of music may require turning down the level a bit for a tighter bass.
Our 3D printed full-range speakers needed something to beef up the lower end of the frequency spectrum. We set out to design a compact subwoofer that can be used together with our FR3 speakers. The result is a 13 liter enclosure with a 6.5″ driver, a matching passive resonator and a plate amp. The passive resonator allows tuning the resonance frequency to match room modes, for example. The plate amp can power satellite speakers and has a fixed high-pass filter. The low-pass cut-off frequency for the subwoofer can be adjusted and the level too, which means that this system can be easily mated with signal sources that do not have equalizing or DSP capabilities in themselves.
The enclosure consists of two parts, which are glued together after printing. Total print time is about 100 hours and uses about 4 kg of filament. Support is only needed for the small recess where the plate amp is mounted. Dual-material printing is not needed. The mass of the enclosure can be increased by filling the walls with epoxy through the holes in the back. A geometry file for 3D printing a matching funnel is provided, too. 2 kg additional mass can be obtained this way.
The 3D files can be found on Thingiverse for free: