An Open Source Wireless Streaming Speaker
The Strøm open source speaker project have been started with the main goal of creating a fully functional “streaming speaker”, but as an open sourced product. One that you can choose to buy fully built and tested, or choose to built it yourself.
Requirements
The main goal of the Strøm open source speaker project are to create a fully functional and open source “wifi speaker”.
The Speaker concept
The primary features of the Strøm speaker are:
Minimalistic design language
Playback via Spotify Connect and Bluetooth
Wall mountable
Sustainable materials
Open Source
Making it a modern, minimalistic and fully capable speaker.
Design Goals
The following parameters are used as design goals. These are not hard requirements, but reflects the ideal characteristics of the final speaker.
Sustainability
It is important to use materials that are produced and sourced using sustainable methods, as well as using sustainable productions methods of the speaker itself. A non exhaustive lists of considerations:
The cabinet must primarily be made out of wood
like MDF and plywood
No plastic
Built to be repairable
Making a 100% sustainable active speaker is, however, not 100% realistic as there isn’t any fully sustainable PCB’s. At least not readable available.
Cabinet
The design of the cabinet must reflect a minimalistic design approach. This means a small physical form factor and a minimalist visual appearance. A non exhaustive lists of considerations:
Small form factor
Shallow cabinet for better on-wall placement
Ultra mat finish of the cabinet
Cloth covered drivers
Acoustics
With this project it is not the goal to create another boombox, with over attenuated lows (bass) and highs (treble) as this will quickly result in listening fatigue. This is also called a smiley face curve.
However a slight bass boost at lower SPL levels to accommodate for the non-linear human hearing will make the speaker sound natural at lower sound pressure levels (SPL). This boost should be less pronounced at higher SPL levels; the dynamic part of this requirement can become hard to realize, but it will make for a much more appealing listening proposition. A non exhaustive lists of further considerations:
Max SPL of 100dB
Frequency range: 80Hz - 17kHz; ±3dB
Reasonable flat response; within ±4dB
High speech intelligibility
SPL dependent bass boost to match the nonlinearity of the human hearing
Below each of the technical design goals are unwrapped to explain what they mean and how the voicing process is used to implemented these requirements.
High maximum SPL
SPL is a measure of “how loud” a sound is. And the maximum SPL of a speaker tells something about how loud a speaker is capable of playing.
Usually the SPL is measured at a distance of one meter [m]. The unit of SPL is decibel [dB].
The Strøm speaker isn’t a large speaker, but it should still be a capable speaker. A speaker that is capable of “playing loud”. But as this can be hard to quantify as the perception of “loud” various a great deal from person to person. It is also highly affected by the distance between the speaker and the listener as well as it’s placement in the room. And finally this perception is impacted by any audible distortion from the speaker. The higher the distortion, the higher the SPL is perceived.
So instead of stating that the speaker must play “loud”, a quantifiable number is needed.
We also want to add a few more limitations to this design goal. The maximum SPL should:
be reachable “anywhere” on the frequency band,
without reaching the mechanical limits of the driver,
and should avoid clipping
We have settle on 100dB of maximum SPL for this small speaker. This will be more than sufficient for most small and medium sized rooms. The implementation of this requirement will affect (limit) the frequency response of the speaker. Most drivers can play down to 20Hz, but maybe not at great volume. So by limitting the frequency band we can push the drivers to higher SPL levels.
Frequency response
It should be pleasent to listen to this speaker and at the same time you should be able to get an “audio experience”. So no smiley curve frequency response, nor overly exaggerated lows; i.e. this is not a boom box. We are looking to implement a “hi-fi” speaker with fairly linear frequency response.
A requirement of a linearity within ±4dB isn’t perfect, but it is a pretty decent middle ground.
The better the low range extension a speaker can achieve, the more of the audio frequency range it is capable of reproducing and the more “convincing” this speaker will sound.
As small drivers are used, subwoofer levels of extension are hard to come by, so a compromise is needed. By setting the targeted -3dB point at 80Hz, this speaker will not be a bass monster, but the bass it will reproduce will be crips and undistorted.
When placed on a wall even lower frequency extension will be possible at the same (or higher) SPL.
Drivers
In order to fulfill the requirements of a small form factor speaker, shallow drivers are needed. This makes it possible to minimize the overall depth of the cabinet.
Only a few really larger shallow drivers exists, which also tends to be rather expensive. They usually deliver good performance, but most of them are considered to be too expensive for this project. In stead of using one large driver, 4 miniature full range transducers are targeted instead. This makes it possible to decrease the overall depth of the cabinet.
The following drivers are used:
2.5” full range driver: SB65WBAC25-4.
User Documentation
Maintenance
User Manual
Voicing of the Strøm speaker
Note
One important aspect of developing a speaker are to tune the frequency response, as well as to ensure that the drivers isn’t driven over their capabilities. It is here the sound of the speaker is developed.
This process is called voicing.
The voicing of a speaker consists of several steps and this howto will try to outline a few of them. The following topics will be covered below:
Voicing goals
Measurements
Adjusting the response
Voicing goals
With the Strøm speaker several design goals have been defined (see more in the Requirements section) and those related to sound reproduction should – where applicable – be implemented through the voicing process.
The following acoustic design goals have been set for the speaker:
Max SPL of 100dB
Frequency range: 80Hz - 17kHz; ±3dB
Reasonable flat response; within ±4dB
High speech intelligibility
SPL dependent bass boost to match the nonlinearity of the human hearing
Most of these design goals can be asserted using various measurement techniques.
Measuring the speaker
What you need to measure the speaker:
A measurement microphone like the UMIK-1 (or similar)
Assembled cabinet with drivers
External amplifier
Laptop (or similar) with Camilla DSP installed.
Room EQ Wizard (REW)
In order to measure the speaker, make sure that you can “answer yes” to all of the above bullets.
What do we want to measure?
With REW it is possible to measure a large suite of things, but bare in mind, that this program is initial created to measure rooms and not speakers.
We will use REW to perform the following measurements:
* frequency response
* phase response
* impulse response
Frequency and phase response
We do not have easy access to an anechoic chamber, but that doesn’t mean that we can’t produce some useful results. And for this speaker we actively rely on the walls and boundaries to increase our bass response. So a measurement “in place” isn’t actually that bad.
We have placed the microphone within 10cm from the baffle to limit the impact of reflections.
Here’s the speaker measured before voicing. A single 8th order high pass (HP) filter have been added at 45Hz to protect the driver (from exceeding \(X_{max}\)).
The frequency and phase response are depicted. It is worth noting that the results haven’t been normalize, resulting in that the measured dB can’t be related to anything (other than other measurements using the same setup).
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Measured frequency response of an initial test cabinet. Primarily used for validation of the internal cabinet volume.
Adjusting the response
As a developement workflow I am using the great HEnquist/camilladsp project. This makes it possible to specify the filter banks as a simple YAML config file. For the initial 80Hz target tuning this file have been used: voicing/voicing-80hz-target.yaml.
As we can’t make the bass higher – without additional \(X_{max}\) of the driver - we need to lower the rest of the frequency response. This will lower the overall efficiency of the speaker, but result in a much more linear frequency response. See the below graph for a measurement of the inital filters applied to the signal chain.
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Measurement result when initial filtering have been applied.
The result isn’t perfect but a really good starting point (and a good sounding one of that) which proves that these little drivers are pretty capable in this little cabinet.
Repair
End of life
Speaker Parts and Assembly
The speaker cabinet are constructed from MDF, as this material is well suited for this type of application. Both the low internal damping, as well as the ease of processing, of this material makes it a good choice for constructing speaker cabinets.
To minimize the overall volume of the cabinet, a sealed construction is chosen. Each driver, does in fact, have its own internal cabinet. This is done to minimize the internal interference between the drivers; hence limiting interference artifacts.
Each speaker part have its own unique ID to make it easier to identify the correct part. Externally sourced parts will likely also have a SKU or similar.
Speaker parts
Drive-in Nut
Parts Description
To ensure proper mounting of the speaker drivers, they are fastened using these screws and the already mounted drive-in nuts.
Please see the tables below for dimensions.
Screw type |
Outer dimensions |
Thread |
|---|---|---|
Drive-in nut |
5mm x 13mm |
M3 |
M3 driver mounting screw
Parts Description
To ensure proper mounting of the speaker drivers, it’s not enough to just drive the screws into the MDF of the baffle. We need mounting hardware to ensure that the drivers remain in place. A set of Drive-in nuts are mounted on the backside of the baffle. These screws are fasted into the nuts, holding the drivers in place.
Please see the tables below for dimensions.
Type |
Outer dimensions |
Thread |
|---|---|---|
M3 metal screw; black |
6mm x 16mm |
M3 |
PCB Standoffs
Parts Description
The PCB are mounted inside the main cabinet. There are dedicated support for this on cabinet layer 1. here a set of drive-in nuts are mounted. Using a set (of four) PCB standoffs the PCB are securely mounted to the cabinet. This provides sufficient space on both sides of the PCB.
Please see the tables below for dimensions.
Type |
Outer dimensions |
Thread |
|---|---|---|
Steel PCB standoffs |
6mm X 16mm |
M3 |
Amplifier Module
Part description
The amplifier module is a generally available, but custom, PCB design which are base upon the popular Espressif ESP32 platform.
This is combined with an audio amplifier from Infineon. The MA12040P is a strong candidate.
Sourcing
Todo
sourcing of this module are still TBD.
Back Panel
Part description
The cabinet back panel are the bottom layer in the complete cabinet. This part makes an air tight fit to the rest of the cabinet, sealing the enclosure.
Four counter sunk screw holes – one in each corner – are created in this part for easy assembly.
To ensure a close distance between the back panel and the wall, when wall mounted, a bracket needs to be recessed into this part. This bracket must be fastened with two wood screws.
Finish
To create a small visual seperation between the wall and the speaker, the back panel must be of a dark color. Preferably black. The most important part of the back panel to finish with a black tint, are the 45° angled sides.
Warning
Depending on the requirements with regards to MDF degassing, this cabinet part only needs limited finishing, or a full pain job.
Downloads
Download the drawing as a PDF back-panel-drawing.pdf.
Download the CAD file in .STEP format back-panel.step.
Fusion 360 Source Files
The model is developed in Fusion 360. To access the original Fusion 360 source files, follow the link below.
Cabinet Baffle
Part description
The baffle are where the speaker drivers are mounted. They are counting sunk into the baffle, so the top of the driver matches the top of the baffle. For each driver four screw holes are made to fasten the driver to the baffle.
Three assembly-guiding holes are also cut in to the baffle. This helps aligning the different layers with each other.
See also
For further details about the assembly, take a closer look at the assembly description.
Todo
Add feature to ensure proper mounting of the soft top frame to the baffle.
Finish
The top of the baffle must be finished with a paint, complementary to the hue of the soft top fabric. If the fabric are of a light hue, then a white paint must be applied – RAL9010 for instance – and when are darker hue of fabric are used, then a black finish must be applied – something like RAL9005 will suffice.
The surface finish of the paint are allowed to be a rough and matte finish, as the top of baffle are covered by the soft top fabric under normal operation.
Warning
Depending on the requirements with regards to MDF degassing, this cabinet part only needs limited finishing, or a full pain job.
Downloads
Download the drawing as a PDF baffle-drawing.pdf.
Download the CAD file in .STEP format baffle.step.
Fusion 360 Source Files
The model is developed in Fusion 360. To access the original Fusion 360 source files, follow the link below.
Dowels
When assembling the cabinet dowels are needed for easy alignment of the different layers.
Parts description
These woods dowels comes in many assortments, lengths and diameters. For this project the following dimensions dowels are needed:
Material |
Diameter |
length |
|---|---|---|
Wood |
8mm |
40mm |
An example of such as dowel are this one from HABO: 63009.
Full Range Driver
Parts Description
This is the full range driver used in this project. For each speaker a total of four drivers are needed.
These drivers are primarily chosen for their extremely small height – of only 38mm overall height – and for their relative high power handling of 20W.
Sourcing
Todo
sourcing of this module are still TBD.
Downloads
Download the driver specification as a PDF 2.5in SB65WBAC25-4.pdf.
Cabinet Layer 1
Part description
This is the first layer of the cabinet, connecting directly to the baffle. To make room for the DC barrel power plug and it’s wires, a mounting hole and a tapering slot are cut. This helps guide the DC power cables from the DC socket.
The three larger holes (Ø8,4mm) are for dowels, used for aligning the three layers during cabinet assembly.
Finish
This part doesn’t require any finish.
Downloads
Download the drawing as a PDF cabinet-layer-1-drawing.pdf.
Download the CAD file in .STEP format cabinet-layer-1.step.
Fusion 360 Source Files
The model is developed in Fusion 360. To access the original Fusion 360 source files, follow the link below.
Cabinet Layer 2
Part description
This is the middle layer of the cabinet. To make room for the DC barrel power socket, a matching DC socket mounting hole is cutout. Half of this hole are counter sunk at a wider diameter (Ø11,5) to accommodate for the wider diameter of the DC plug itself - to ensure that this plugin can be fully consealed within the cabinet (for on wall placement).
The small holes (Ø2mm) are used when mounting the back plate to the main cabinet. The larger holes (Ø8,4mm) are for dowels, used for aligning the three layers during cabinet assembly.
Finish
This part doesn’t require any finish.
Downloads
Download the drawing as a PDF cabinet-layer-2-drawing.pdf.
Download the CAD file in .STEP format cabinet-layer-2.step.
Fusion 360 Source Files
The model is developed in Fusion 360. To access the original Fusion 360 source files, follow the link below.
Cabinet Layer 3
Part description
This is the third layer of the cabinet - counting form the baffle. Here a large keyhole slot a cut to make room for the DC jack, an L-bracket adaptor and a little wire. All in all to make sure that the power connections are consealed when mounted to a wall.
The small holes (Ø2mm) are used when mounting the back plate to the main cabinet. The larger holes (Ø8,4mm) are for dowels, used for aligning the three layers during cabinet assembly.
Finish
This part doesn’t require any finish.
Downloads
Download the drawing as a PDF cabinet-layer-3-drawing.pdf.
Download the CAD file in .STEP format cabinet-layer-3.step.
Fusion 360 Source Files
The model is developed in Fusion 360. To access the original Fusion 360 source files, follow the link below.
Power Brick
Parts Description
When creating an active speaker, it will need power. For this project we have settled on a barrel styled power plug. These type of power supplies readable available are relatively inexpensive, but not any old power supply will do. There’s are few requirements that is required to be met. Please see the tables below for further details.
Mains range |
Output Voltage |
Output Wattage |
|---|---|---|
100V - 240V |
18V |
60W |
Plug type |
Plug dimensions |
Cable length |
|---|---|---|
Barrel, male |
5,5mm x 2,1mm |
>=1,5m |
Sourcing requirements
Warning
When sourcing a power brick (power supply), it is really important that set power supply is CE approved, as well as RoHS compliant. Therefore only approved power supplies must be used and supplied to the end customer.
Currently the only approved power supply is this one from Mean Well: GST60A18-P1J.
DC Power Socket
Parts Description
In order to maintain an airtight cabinet we have taken a bit of a different approach to the DC socket. In fact this socket is a overmold jack. We are then using the cabinet as the overmold.
How this socket are integrated in the cabinet are described in detail in the assembly description as well as in the description of layer 2 and 3.
Todo
the assembly section needs to be updated.
Sourcing
Todo
sourcing of this module are still TBD.
Downloads
Download the specification as a PDF 50-00541.pdf.
Download the CAD file in .STEP format 50-00541.step.
Soft Top Fabric
Soft Top Frame
Part description
The soft top frame holds the fabric that covers the drivers. This is a simple part. The soft top frame are friction fit to the pretuding dowels in hte baffle of the main cabinet. This ensures a tight fit of the frame but at the same time allow for its removal in case of service or repair.
Finish
This part is painted black to match the shadow created where the drivers are located. It is important to lightly sand this part after painting, as the raised grain can in fact tare any fragile fabric.
Downloads
Download the drawing as a PDF softtop-drawing.pdf.
Download the CAD file in .STEP format softtop.step.
Fusion 360 Source Files
The model is developed in Fusion 360. To access the original Fusion 360 source files, follow the link below.
Generate a parts ID when adding a new part
To generate a ID for a part, follow the below example. The following tool is used: Short UUID.
suid -l 6 -d utils/uuid-dict.json
Please note that a simplified dictionary have been used to ensure only uppercase characters are used.
Cabinet Assembly
Todo
Still missing these sections:
linoleum
drivers
back panel
soft top
Assembling the main cabinet
The main cabinet is assembled using the following 5 parts:
Each of the three cabinet layers are glued together using standard indoor wood glue. To easily lineup the individual layers with each other, a set (3) of guide holes are bored in each layer. These are for the dowels.
Exploded view of all the parts needed to assemble the main cabinet.
Following the steps below to assemble the main cabinet.
Start with layer 1 and place it, so the cable ducts and layer numbering faces downwards
Add wood glue to the guide holes and mount the dowels inside them. Make sure that go all the way through, but do not pertrude further than the face of this layer - otherwise the back panel can’t be mounted correctly.
Now we are ready to add the second layer.
Apply glue to layer 1 in order to the second layer to adhere to it.
Now take layer two and ensure that the layer identification holes faces up.
Add glue to the guiding holes and place it over the dowels and press down. Make sure to press the layer all the way down so it mates with layer 1.
The third layer can now be mounted. This is done in the same way as in point 3 above.
Clamp all the layers firmly together and let the glue set.
Finally we can mount the DC power socket. This is down with a couple of screw.
Add some hot glue over the wires, to ensure they do not come off. We are encapsulating this socket inside the cabinet, so we do not want any faults.
Place the wire harness in the cable duct and secure it with hut glue.
The main cabinet are now ready for the next stage: mounting the baffle.
Assembly video
To make it more clear how all these parts comes together, a short video showing an exploded view of the speaker can be found below. This highlights how all the parts fit together with each other.
Downloads
Download the drawing as a PDF main-cabinet-assembly.pdf.
Mounting the baffle
The baffle and the main cabinet are now ready to be mated.
The baffle needs to be mated to the main cabinet. This is a relatively simply process, but first it needs to finished.
Exploded view of all the parts needed to mount the baffle to the main cabinet.
Following the steps below to mount the baffle to the main cabinet.
Start by finishing the top of the baffle - see parts description for additional details.
Add glue to the main cabinet and place the baffle on the main cabinet, using the dowels guide holes for proper placement.
The top of the dowels should pertrude about 6mm out of the main cabinet. Enough to properly align the baffle on the cabinet.
Clamp down the parts while the glue sets.
Assembly video
To make it more clear how all these parts comes together, a short video showing an exploded view of the speaker can be found below. This highlights how all the parts fit together with each other.
Downloads
Download the drawing as a PDF mounting-the-baffle.pdf.
Cabinet construction
To ensure an easy assembly of the speaker cabinet, a sandwish construction is used. This makes it easy to construct the different layers and, at the same time, simplifying the construction of this semi complex cabinet. This also makes it possible to machine all the individual layers on a CNC. This comes in handy when utilizing decentrilized manufactoring.
Further details on the cabinet assembly can be found in the assembly section.
The Software Platform
This speaker is capable of playing audio through Bluetooth and Spotify Connect, as well as other sources. All of this are handled by the software platform called Euphonium. This is a separate project on GitHub and it can be used for other types of platforms. Not just this ESP32 based setup. Read more in this projects documentation.
Bluetooth
“A short-range wireless technology standard that is used for exchanging data between fixed and mobile devices over short distances”
Over The Air (OTA) Updates
Spotify Connect
“Listen on your speakers or TV, using the Spotify app as a remote.”
Web Radio
There’s integration to web radio playback, making it easy to select most online available web radios.
Simply search in the UI, for your favorite station and select play.
Contribution Guideline
The following document describes how to contribute to the STRØM 1.0 project.
Contributing to Stroem 🔊 (Open Source Speaker)
We’re glad you’re considering contributing to Stroem! 🎉 Whether you’re a first-time contributor or a seasoned open source veteran, we’re here to help make your contribution experience as smooth and enjoyable as possible. 💻
Please note that this is an open source speaker project, so some contributions may require specialized knowledge or equipment. 🔧 We appreciate any and all contributions, big or small, and are here to help you get started. 💡
Getting Started 🚀
Before you start, make sure you have a GitHub account. If you don’t have one, sign up for free here. 💻
Take a look at the existing issues to see if there’s anything you’d like to work on. If you have an idea for a new feature or improvement, feel free to open a new issue to start a discussion. 💡
If you’re ready to start coding or working on hardware, fork the repository and clone it to your local machine. 💾
Make your changes and test them thoroughly. 🔧
When you’re ready to submit your changes, create a pull request. Make sure to include a clear and concise description of what you’ve done and why. 📝
Code of Conduct 🤝
At Stroem, we believe in creating a welcoming and inclusive environment for all contributors. 🙏 We follow the Contributor Covenant Code of Conduct, which outlines our expectations for behavior and the consequences for unacceptable behavior.
Help and Support 💬
If you need help or have any questions, feel free to reach out to us by opening an issue or joining our community chat. 💬 We’re here to help and will do our best to support you in your contribution journey. 💪
Thanks for considering contributing to Stroem! We can’t wait to hear what you’ll add to this amazing open source speaker project! 🔊
Project Licensing
The STRØM 1.0 project consists of several open source projects. One for the software platform, one of the hardware (PCB) and this project.
The license listed below only covers what is committed to this GitHub repository: LydByDissing/stroem. The other projects are licenced seperately.
You can read the licens below or in the GitHub repo: LydByDissing/stroem/LICENSE.
The CC BY-SA 4.0 license
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Todo list
Todo
Still missing these sections:
linoleum
drivers
back panel
soft top
(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/stroem/checkouts/latest/docs/source/speaker/assembly/index.rst, line 6.)
Todo
sourcing of this module are still TBD.
(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/stroem/checkouts/latest/docs/source/speaker/parts/amp-module.rst, line 18.)
Todo
Add feature to ensure proper mounting of the soft top frame to the baffle.
(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/stroem/checkouts/latest/docs/source/speaker/parts/baffle.rst, line 27.)
Todo
sourcing of this module are still TBD.
(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/stroem/checkouts/latest/docs/source/speaker/parts/driver.rst, line 25.)
Todo
the assembly section needs to be updated.
(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/stroem/checkouts/latest/docs/source/speaker/parts/power-socket.rst, line 24.)
Todo
sourcing of this module are still TBD.
(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/stroem/checkouts/latest/docs/source/speaker/parts/power-socket.rst, line 29.)
Changelog
Read on below to get a high level Introduction to the project as a whole.
Strøm speaker in conifer linoleum and blue fabric on the soft top.
Introduction to the project
The primary features of the Strøm speaker are:
Minimalistic design language
Playback via Spotify Connect and Bluetooth
Wall mountable
Sustainable materials
Making it a modern, minimalistic and fully capable speaker.
Motivation for starting the STRØM 1.0 project
Project goals
Project history
Initially started as an OPEN!NEXT demonstrator project in December 2021. The project was started by Tue Dissing.
Contributing to the project
Interested in contributing to the project? Then please take a quick look at the contribution guideline beforehand. You find the contribution guide here and in the GitHub repo as well: LydByDissing/stroem/CONTRIBUTING.md.
Last updated
The mainline documentation have last been updated at 2023-02-02.
License
This project is licenced under the Creative Commons ShareAlike 4.0 license.