Circular economy 3D printed 3D printing Audio DIY Eco-friendly Loudspeaker Recycling Speakers Sustainable development

Circular Sound – Recycling loudspeakers with the help of 3D printing

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.

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:

  1. Biological cycle: Using bio-based and bio-degradable enclosure materials.
  2. 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.

Size240 mm diameter
Weight~4 kg
ShapeRegular icosahedron
MaterialModified PLA
Amplifier2×30 W
InputsBluetooth 5.0
Power supply19 V laptop charger
Wide-band driver3″ BMR
WoofersUpcycled dual 4-6″
Frequency response60-20000 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.

3D printing a bio-based loudspeaker enclosure
Eco-friendly Circular economy Sustainable development

Circularity is not just about facts, it needs emotions too

Text: Joonas Sirviö
Images: Unsplash

As we know, the World is not the same place if we compare it to the 1980’s when I was born.

Technology, cars, life, culture, basically everything has changed. We are the first generation who must handle this correctly and transfer these elements to the next generation.

The same comes to music. My memories are going back to my childhood, LPs, cassettes then CDs and Minidisc (whose idea was that?). I listened to Kaija Koo ‘yes you read that right’ because there was nothing else to listen to.

Do you remember the first visits to record shops and how interesting it was to get a new CD in your hands! I can still remember that feeling and you don’t get that same feeling playing new albums on your phone.

Joonas Sirviö, CEO at Granulous

My old speaker system still exists in my dad’s warehouse and I haven’t used that since my childhood. It feels sad and I believe I’m not the only one who has a similar situation.

But how can loudspeakers be a perfect example of circularity?

The world’s population has increased from 6,15 billion in 2000 to over 8 billion in 2023. Last year humanity used up all the natural resources the Earth can sustainably regenerate already on the 28th of July. For the rest of the year, mankind was inflicting an unsustainable toll on the planet.

Old loudspeakers are especially problematic due to rare-earth elements found in the magnets of loudspeaker transducers. Rare-earth elements are essential for manufacturing permanent magnets, so this is a super interesting point when aiming for more circular societies.

Despite the changes and forgotten loudspeakers in the world, the basis of the good life has been the same since “back in the days” and it is finding the good feeling.

The feeling is what we are looking for and sustainability isn’t any different. We are usually talking about sustainability in a broad sense. But we need to understand that the changes cannot be huge at the start. They must be easily digested. Governments will do their part to find guidelines, but as individuals, we can make tiny changes in our lives that can turn into huge impacts. You feel good when you do something good, and we must be proud of ourselves when this happens even if it seems like a small thing to do.

Circular Sound loudspeakers are exactly what it is all about; circularity and feeling in their perfect shape. Design can feel good, the truth about reducing the impact on the environment feels good, and the beautiful sound from the speakers, whatever you are listening to, feels good. It gets you where the great dopamine gives you the right tools for happiness.

This is a beautiful piece of life, that can be your impact on the future and the next generations. I know and probably you know as well that we have the responsibility to act for a better future and now you can be the climate hero and listen to good music at the same time.

Joonas Sirviö, CEO at Granulous
About the author:
Joonas is a Co-Founder and CEO of Granulous start-up company who has developed a new plastic replacement material utilizing spent grains from brewing industry. He's mind game is to save the world one grain at a time.
Artificial intelligence AI-generated Audio Loudspeaker MidJourney Speakers

Loudspeakers Generated by Artificial Intelligence – How AI Can Boost Your Creativity

Artificial intelligence in loudspeaker design

Artificial intelligence is a tool that loudspeaker designers can use when they want to think outside the box and come up with modern and unique designs. We will focus on image-based AI in this text because that is easily available to the public and does not require engineering considerations. Although AI-generated images seem to take cues from existing designs, AI can merge features in a novel way. For example, merging loudspeakers and furniture or blending the loudspeakers with the interior design. Instead of specific technical or topological solutions, think of it more like a mood board or general family of concepts. The greatest benefit of artificial intelligence in the design process is generating a multitude of new concepts in a short period of time.

artificial intelligence loudspeaker
Clever combination of furniture and loudspeakers. Posted by Lucas D. on the Facebook group AI Loudspeaker and Stereo Design.

How to get started

One of the most popular tools currently is MidJourney, which creates “unique imagery from short text descriptions”. You can start using AI algorithms like MidJourney to generate new designs by simply coming up with your own unique prompts. The easiest way to start using MidJourney is to join one of their newbie channels, create your own server and invite the bot there (see video at the end of this article).

Another option is using DALL-E, which is oriented more towards generating art, but also image editing. DALL-E is developed by OpenAI, who are known for GPT-4.

A great upcoming alternative is Imagine: AI Art Generator by Vyro AI. It is available for iOS and Android operating systems. The free trial has video ads, limited settings and watermarks.

artificial intelligence loudspeaker
AI-generated image when prompting for a sphere-shaped loudspeaker.

Contrary to what some guides tell you, direct messaging prompts directly to the MidJourney bot does not work in the free trial version. You have approximately 25 free prompts (0.4 hrs GPU time) without a subscription. Upscaling, generating variations and repeating a prompt (“rerolling”) uses up your GPU time quota. The most inexpensive subscription plan is $8/month at the time of writing this and it gives you 3.3 hrs of GPU time and ownership of results.

If You are not a Paid Member, You don’t own the Assets You create. Instead, Midjourney grants You a license to the Assets under the Creative Commons Noncommercial 4.0 Attribution International License./…/By default, Your images are publically viewable and remixable.

MidJourney Terms of Service

Examples of AI-generated loudspeakers

Coming up with useful prompts can be challenging and the output is seldom what you had in mind. That’s the beauty of it though. To give you an idea of what kind of results can be obtained, we have listed some of the more successful prompts and their corresponding results. They are by no means the best that can be achieved, but rather a result of simply experimenting with AI. We have included some comparisons MidJourney vs. DALL-E to give you an idea of what kind of results to expect. First, let’s give both image-generating AIs something ordinary like:

/imagine small loudspeaker with scandinavian design in a livingroom
artificial intelligence loudspeaker
Results from MidJourney
Results from DALL-E
Result from Imagine

Next, let’s ask something more specific:

/imagine studio monitor loudspeaker with waveguide in recording studio environment
artificial intelligence loudspeaker
Result from MidJourney
Result from Imagine

Since RD Physics develops 3D-printed loudspeakers, let’s see how well the AIs understand that and how creative they get:

/imagine 3D printed loudspeaker in livingroom
artificial intelligence loudspeaker

You can also upload images to your Discord server and use the URL of those as part of your MidJourney prompt or upload an image to DALL-E and create variations. Below you see what happened when we uploaded a photograph of our Circular Sound Eikosa speaker and placed it in another environment using MidJourney and asked DALL-E to create variations:

/imagine <image URL> on a table in a scandinavian livingroom white colour
artificial intelligence loudspeaker
Placing into another environment with MidJourney
Asking DALL-E to create variations

As you can see above, MidJourney will often mess up the shape of the original input photograph. For some reason, the pentagonal face of the speaker always becomes hexagonal and the icosahedral shape is also lost. You can also directly ask for a shape in the prompt (with varying success):

/imagine small icosahedron shaped loudspeaker in livingroom
artificial intelligence loudspeaker

Future Outlook

We asked ChatGPT to explain the potential benefits of AI in loudspeaker design and here’s what it had to say (edited for brevity):

Firstly, AI can help to optimize the design of loudspeakers for specific applications. By analyzing data from simulations and experiments, AI algorithms can identify the optimal shapes, sizes, and materials for loudspeakers that are intended for different uses.

Secondly, AI can help to reduce the time and cost of designing and testing loudspeakers. With AI, simulations can be run to test different design parameters, allowing designers to quickly identify the best designs without the need for expensive and time-consuming physical testing.

Thirdly, by analyzing large amounts of data, AI algorithms can identify patterns and correlations that might be missed by human designers. This can result in more precise designs that perform better and are more consistent across different manufacturing runs.

Overall, using AI for designing loudspeakers can result in more optimized designs, faster design iterations, and more accurate and precise designs, all of which can lead to improved sound quality and performance.



The easiest way to implement AI in loudspeaker design is to use a visual tool like MidJourney. It does not consider acoustics, materials, or 3D dimensional structures. Knowledge in those fields is needed to evaluate the feasibility of each concept created. Nevertheless, AI-generated images can be of assistance in the ideation phase when one would typically use sketching or other quick visualization methods to explore new designs.

artificial intelligence loudspeaker
Posted by David M. on the Facebook group AI Loudspeaker and Stereo Design

At first glance, these ideas may seem way too complex to fabricate. That is true if confined to traditional woodworking methods. However, 3D printing is a technology that can help in making these intricate designs become reality. The design freedom that 3D printing allows is not limitless, but unparalleled. Many of the AI-generated loudspeaker designs could not be fabricated economically in any other way. For advice regarding 3D printing in audio, we recommend our DIY blog and the Facebook group 3D Audio and Hi-Fi Projects. Have fun experimenting and remember that the AI only knows what it has been taught and only does what it is told.

Below is a video explaining how to set up MidJourney with Discord.

3D printing Audio DIY Loudspeaker Speakers Technology

A versatile 3D printed coaxial loudspeaker – RD Physics CX2

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)
  • Active crossover, miniDSP recommended
  • Two channels of amplification per speaker, ICEpower module recommended
  • 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:

  1. Finish the outside of the enclosure and make sure the driver and SpeakON connector fit.
  2. Line the inside with bitumen damping material and fill it quite densily with wadding.
  3. Solder wires to the speaker drivers and crimp fastON connectors at the other end. Mark woofer and tweeter positive and negative wires.
  4. Feed the wires through the SpeakON connector opening and mount the driver using wood screws. Use gasket/adaptor if you have the SEAS driver.
  5. Connect the fastON connectors to you SpeakON connector and mount it.
  6. 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.


Bluetooth speaker 3D printing Audio Circular economy DIY Loudspeaker Recycling Speakers Sustainable development

Bluetooth loudspeaker without an internal battery

What’s wrong with having batteries in your portable boombox?

Wireless electronics, such as bluetooth speakers, are extremely popular nowadays. All such devices must have a power source and typically it is a lithium-ion battery. However, the demand for battery raw materials is rising at an alarming rate:

The supply of some of these [battery] materials, in particular cobalt, natural graphite and lithium, is of concern today and for the future in view of the large quantities needed and/or very concentrated supply sources.

European Battery Alliance (EU)

As we have discussed earlier, when launching our Circular Sound program, the best solution for reducing reliance on critical raw materials is to reduce their use. The RD Physics BB1 boombox enables you to do just that. It is designed to use existing external power sources and therefore no new batteries are needed. Battery service-life or battery replacement is no longer a concern.

Alternatives to dedicated batteries

The BB-project started by looking at how power tools are sold without accompanying batteries. The idea being that the user needs only one battery (plus spares) that fits all tools. While this approach reduces the amount of batteries needed, it is also used to tie the customer to a specific brand. We wanted a universal solution and therefore the USB-C standard was chosen. The BB1 and BB2 boomboxes use a USB-C port as an interface to feed power to the amplifier. The boombox can be connected to any USB port: power banks, phone chargers, laptops, extension cords, solar panels etc. Obviously, the input voltage and current draw is limited, which leads to limited sound pressure level (SPL).

The weather-proof USB-C port is located at the top.
Frequency responce of 3D printed bluetooth speaker.
Frequency response of BB1 at maximum drive level.
BB2 boombox with Dayton Audio RS100 drivers.
Frequency response of BB2 at arbitrary drive level.


What you will need to build your own batteryless boombox:

  • Geometry files for 3D printing (free under Creative Commons License at Thingiverse)
  • 3D printer big enough to fit a 235 mm diameter sphere
  • Slightly over 1 kg of filament depending on your settings
  • Two active drivers. Either Peerless 3″ (BB1) or Dayton Audio 4″ (BB2)
  • One 6½” Dayton Audio passive resonator
  • A Sure (Wondom) bluetooth board with additional cables set
  • USB-C panel mount plug (from eBay) and 6 mm DC plug
  • Wood screws (4.2 mm for the drivers and resonator, 3 mm for the BT board)
  • Drawer handle, IKEA Eneryda 703.475.16
  • Damping material (bitumen or similar automotive damping mat and fibrous wadding, for example pillow stuffing)
  • Optional: Wall mount bracket, Genelec 4000-410B
  • Minimal soldering capabilites

The enclosure for the BB1 and BB2 can be downloaded from the link above. Assembling everything takes 30 minutes.

3D printed boombox enclosure
3D printed enclosure ready for assembly.

How to build the BB1/BB2 bluetooth speaker

  1. Start by soldering the 6 mm DC plug to the USB connector. Red (+) goes to center pin and black (-) to outer shell.
  2. Connect DC power and speaker cables to bluetooth board and fasten the board inside the enclosure by tightening the screws via the driver openings.
  3. Mount the USB connector and handle.
  4. Line the inside of the enclosure with bitumen or similar visco-elastic damping material. Heat will aid in conforming to internal shapes. Make sure the damping material is fully bonded to the walls.
  5. Bring the speaker wires through the driver openings and solder them to the drivers. Make sure polarity is the same for both drivers. Then fasten the drivers using wood screws.
  6. Fill the enclosure with fibers (cotton, polyester, wool etc.) and fasten the passive resonator.
  7. Optional: Attach the wall mount bracket.
  8. Connect a USB port and the bluetooth board powers on automatically. Pair your signal source with the device (“WONDOM”). Enjoy!
BB1 portable bluetooth speaker with 3D printed enclosure.
BB1 ready to rock.

Assembly instructions

Concept and sound test

Circular economy 3D printing Audio Eco-friendly Loudspeaker Recycling Speakers Sustainable development

Circular Economy of Loudspeakers – Reducing Waste and Creating Value

Introduction to circular economy

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:

“By 2030, substantially reduce waste generation through prevention, reduction, recycling, and reuse”

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.

Old loudspeakers with negligible market value.

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.

Loudspeaker transducers have large magnets containing precious materials.

The circular economy approaches to loudspeakers

The circular economy of loudspeakers can be described with the help of the 7Rs.

  1. Rethink: Use fewer components and eco-friendly materials, combine functions, or make the product easy to disassemble and recycle.
  2. Reduce: Spend less material and energy. Generate less waste.
  3. Reuse: Sell in the second-hand market.
  4. Repair: Fix broken loudspeakers by re-coning transducers, replacing components, and refurbishing the enclosure.
  5. Remanufacture: Disassemble old loudspeakers and use the materials to make a new product.
  6. Recycle: Use raw materials, such as plastic and metal, again.
  7. 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.

Circular economy loudspeaker
A new loudspeaker using components from old 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.

Impact categoryQuantityUnit
Global warming69kg CO2 eq.
Acidification0.63mol H+ eq.
Eutrophication (freshwater)0.015kg P eq.
Eutrophication (marine)0.09kg N eq.
Eutrophication (terrestrial)1.26mol N eq.
Ecotoxicity (aquatic)331CTUe
Human toxicity (carcinogenic)3.4CTUh
Ozone depletion4.2*10-6 kg CFC-11 eq.
Particulate matter0.12kg PM2.5 eq.
Ionizing radiation4.19kBq U235 eq.
Water consumption0.63m3
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.

Sustainable loudspeaker
A remanufactured loudspeaker 3D printed from bio-based materials and using components from an old subwoofer.

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.

Appendix A: Life-cycle impact assessment categories

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:

  1. 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).
  2. 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+).
  3. 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-).
  4. 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).
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. 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.
  10. 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.


Audio 3D printing Circular economy DIY Loudspeaker Speakers Technology

3D printed wood – A revolutionary way of making loudspeakers

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.


Technology Audio DIY DSP Loudspeaker Speakers

Acoustic panels and DSP – Both are beneficial

It is tempting to consider “room correction” with Digital Signal Processing (DSP) as a substitute for acoustic treatment. We implemented both in the same room to see what the effects actually are.

Experimental setup: DSP and acoustic panels

The setup used is a normal living room/home theater. The loudspeakers are Genelec 8351A active monitors with DSP and automatic calibration using a microphone and frequency sweeps.

Home theater with active DSP speakers
The test setup with Genelec active monitors.

Five acoustic panels were placed in the room. They are mineral wool panels measuring 60x60x10 centimeters. Two of them were placed at the side walls in order to address first sidewall reflections and three of them were placed behind the listener by the back wall. The measurement point is also the normal listening point. Measurements were done with REW software:

The effect of acoustic panels and DSP on room response

Effect of acoustics panels and DSP on frequency response.
Effect of acoustic panels (top) and DSP (bottom).

From the magnitude response we see that the acoustic panels bring down some of the peaks in the mid-range. When we then apply DSP and automatic calibration, we get attenuation of the low-frequency peaks caused by room modes. DSP does not really affect the mid-range and the highs. It only raises their level back to where it was earlier. Using DSP and equalizing for mids and highs would be very difficult, because notches and peaks are very narrow.

Waterfall chart showing reduced decay time with acoustic panels
Waterfall charts show faster decay at mid-range frequencies when acoustic panels are applied.

Spectrograms show massive amounts of energy in the bass domain, where we have room modes affecting. Panels this size should not be very effective at long wavelengths according to the manufacturer and our magnitude plot. Yet, adding acoustic panels brings down the energy across the frequency range according to the spectrogram. DSP reduces the bass peaks which, of course, reduces the energy in that region. DSP brings up the mids and highs, so we can see slightly increased energy in that region, which leads to an evenly distributed energy across the spectrum of frequencies.

Effect of acoustic panels and DSP on acoustic energy content
Spectrograms of the reference condition (top), with acoustic panels (middle), with acoustic panels and DSP (bottom).


So do you need both digital signal processing and acoustic treatment? Yes. Looking at the magnitude response, we see that DSP addresses the peaks in the bass region and adjusts for the overall level, while the acoustic panels address the mid-range frequencies. Looking at the energy spectrum, we can see that actually both acoustic panels and DSP even out the energy distrubtion across the frequency range. It is encouraging to see that placing only five panels has a measurable effect. Headphones are immune to room acoustics, but benefit from DSP. Check out our post on headphone DSP:


This blog post can be found in video format as well.


Technology Audio DIY DSP Headphones

Digital Signal Processing – Improve your headphones for free

Using a computer as your signal source gives you immense DSP possibilities. It does not cost a thing and reverting back is easy in case you do not like it. There is really no reason not to give it a try. A good place to start is here:
There you will find EQ presets for most headphones and links to applying equalization in your operating system using Equalizer APO. Some users may like the Peace add-on which can be found together with Equalizer APO. If you have issues with system-wide equalization, you may want to try a plug-in for your music player. We can recommend Foobar2000 (oldie but goldie) and Math Audio Headphone EQ.

Math Audio preset files for Porta Pro and HD800S headphones

Here’s the preset file to be used in the Math Audio plug-in when listening to Koss Porta Pro headphones. It’s based on Oratory1990’s EQ profile.

Equalizing curve for Koss Porta Pro headphones
EQ for Koss Porta Pro based on Oratory1990’s measurements

We found the equalizing curve for Sennheiser HD800S to be too harsh, brightening up the sound too much. Therefore, the gains of the peaking EQ were halved and entered into the Math Audio plug-in. You can download it here:

Equalizing curve for Sennheiser HD800S headphones
Modified Sennheiser HD800S EQ

We have got to remember that the EQ files found online are obtained using a measurement head and aiming at a flat frequency response. However, each individual has physically different ears 
and a flat frequency response may not be what we actually want. The recordings that we listen to vary and the type of music varies. The presets are a good starting point, but they should be tweaked to make sure the sound is to your liking. Are there any downsides to processing the signal? There could be some artifacts from filtering such as pre-echo and you could get added distortion from excessive bass boost, but as long as it sounds better to you then that’s all that matters. Give it a try!


This post is available in video format.
Technology Audio DIY DSP Headphones Loudspeaker Speakers

Headphones are better than loudspeakers – One factor is behind it all

The argument for headphones instead of loudspeaker as your main sound system is one that you don’t hear too often. Which is why we think it’s important to make it here. It all boils down to one root cause, and that root cause is the room. Let’s divide the consequences of the room into two categories: cost and sound.


First, speakers are played in a room you need more power. Power means power amplifiers. You need to buy expensive amps to power your loudspeakers. Second, you need to place those loudspeakers somewhere, so you need to buy stands. Or if they are floor-standing speakers you need to buy feet. You need to connect them with cables and buy other accessories. Third, you need to acoustically treat your room, so you need to buy acoustic panels, diffusers, bass traps etc. Fourth, you need to buy presents to your spouse because you’re placing the speakers in the middle of the room.


You can buy good loudspeakers and ruin them by placing them in a bad listening environment. Optimally, you would have the loudspeakers and the listening position at least two meters away from the nearest wall. However, that is seldom even possible in the available space. You would need a large room. And with this kind of placement, a livingroom quickly becomes a listening room only. Headphones, on the other hand, have multiple benefits compared to loudspeakers:

  • Single point source
  • No crossovers
  • No sweet spot or particular listening position
  • No room effects
  • Tonal balance can be fixed using only DSP

Some of the drawbacks often stated include poor sound stage or imaging. People say that it sounds like the sound is coming from inside one’s head and it doesn’t feel like you’re at a concert. It is a matter of personal preference, but we suggest looking at headphone listening as something separate and different from live events or loudspeaker listening. It is our subjective opinion that crossfeed will not correct for this phenomena and only makes the sound worse. Another common argument is that there’s no physical sensation of bass. While that is true, the pros outweigh the cons.

Recommended hardware

Which ever headphones you use, applying equalizing with the help of DSP is definitely worth considering. Check out our post on the topic:

Sennheiser HD800S open headphones.

 Enthusiast level:

Hobby level:

  • Sennheiser HD650
  • DAC/amp in price range 200-300€
  • DSP at signal source

Budget level:

  • Koss Porta Pro
  • Analog jack or DAC/amp in 100-150€ price class (get one second-hand, for example)
  • DSP at signal source


The contents of this post can be found in video format