DIY Soundbar With Built-in DSP

Building a modern looking soundbar from 1/2" thick kerf-bent plywood. The soundbar has 2 channels (stereo), 2 amplifiers, 2 tweeters, 2 woofers, and 4 passive radiators to help boost low frequencies in this small cabinet. One of the amplifiers has a built-in programmable Digital Signal Processor (DSP) which I use to create 2-way crossovers, custom EQs, and add dynamic bass boost. The DSP amp uses the ADAU1701 processor which is configurable using Analog Devices SigmaStudio (free software). A separate USBi programmer is needed to download the SigmaStudio program on to the processor. Sure offers a not so stellar one for $20, otherwise a more expensive version from Analog Devices can be used.

Main parts list:

• Woofers (x2): Dayton Audio ND91-4
• Tweeters (x2): Dayton Audio ND20FB-4
• Passive Radiators (x4): Dayton Audio ND90-PR
• Amplifier 1 (feeding tweeters): Dayton Audio Kab-215
• Amplifier 2 (feeding woofers): Sure Electronics Jab3-250
• Enclosure: 1/2" thick plywood (Home Depot)
• Front baffle: 1/2" thick MDF (Home Depot)

Step 1: Kerf Bending the Enclosure

I wanted a unique enclosure which didn't look "boxy" so I decided to use a kerf bending technique to achieve a seamless smooth edge all around the enclosure. I made several (9 per bend) thin-kerf non-through cuts which terminate about ~2mm away from the surface of the plywood sheet. This yielded a rounded edge with a bend radius of approximately 1". Removing material from one face of the wood, allows the plywood to be easily bent. Care must be taken however since this bend is quite fragile. Kerf bending requires knowing the thickness (kerf) of your blade, the thickness of your material, and the radius desired. By knowing these parameters, you can calculate the amount of material removed(number of cuts), outer and inner arc lengths (cut spacing). To make things easier, kerf bending calculators exist but they have a conservative limit on the bend radius. One example can be found here: https://www.blocklayer.com/kerf-spacingeng.aspx

Step 2: Gluing Together

I created a mixture of ~1:1 saw dust and wood glue and used it to fill the cuts in each bend. I tried applying the glue mixture generously since these bend do not have much material left and the bend is fragile. However, once the glue mixture dries, the bend is quite strong (at least strong enough for a speaker). I also created a half-lap joint which is used to join the top piece to the bottom. You could theoretically have one long seamless piece which would be close to 90" long and difficult to handle. Since the bottom is not visible, I opted to split the enclosure in two pieces and have the joints be on the bottom.

Step 3: Making MDF Front Baffle

I used a plunge router and circle cutting jig to cut out the holes for each woofer and passive radiator. I used a large forstner bit and drill press for the tweeter holes. I also used a round-over bit to smooth out the edges of each hole as well as the outer edge of the baffle. I mounted the tweeters as far apart from each other as possible for better imaging but I am not sure how much of an impact this has.

Step 4: Mounting Speakers and Fabric Wrap

To finish the baffle, I rear-mounted all the woofers, passive radiators, and tweeters using 1/2" wood screws. The drivers came with foam gaskets (shipped loose) which created a nice seal when rear mounting. I also used the hole pattern on each gasket to drill my pilot screw holes -- eliminating guessing. I covered the front of the baffle with fabric (attached with staples) and used an adhesive backed foam strip to create a seal between the front baffle and the enclosure.

Step 5: Rear Baffle + Electronics

The rear baffle has a mitered edge which is used to create a flush airtight seal with the enclosure. I used a chamfer bit and a router table to create the 45 degree chamfer and used the same foam strip for creating the seal. The electronics (2 amplifiers, DC power input jack, stereo input jack, and 2 LEDs) are all mounted in the rear baffle. The electronics are mounted in a sealed cavity in the center of the enclosure which separates the left/right channels.

Step 6: DSP Programming/tuning

Digital Signal Processors (DSPs) are widely used in most modern consumer soundbars. Their biggest advantage is that they accept a digital input and can be used for multi-channel sorround sound. For this project, I used the analog inputs because they are easier to design around. The Sure Electronics Jab3-250 amplifier is equipped with an ADAU1701 processor which has 2 input ADCs (analog-to-digital converters) and 4 output DACs (digital-to-analog converters). I used two output DACs to feed each tweeter and two DACs to feed each woofer. Image of my SigmaStudio graphical program is attached and some of the important blocks used are described below:

Input level adjustment: used to decrease the input volume for each channel. I found that this is a critical step that is required for the Dynamic Bass Boost feature to work (described later).

Parameteric EQ: I used a phone app called "Advanced Spectrum Analyzer" to record a frequency sweep (20Hz - 20kHz) and to roughly measure the frequency response of the speaker without any equalizing. This is not the most accurate approach, however, it is fast and it gives me a good starting point without investing in more accurate tools such as a measurement microphone and soundcard for my laptop. I plan to take better measurements in the future and use additional software such as Room EQ Wizard (https://www.roomeqwizard.com) to help me calculate the right EQ. For now, I created a custom parametric EQ which decreases the volume between 500hz and 4000hz. My ears perceived this frequency range louder than the rest. The speaker sounded better (to me) with the volume in this range decreased. Before and after frequency response curves are attached. These are not a true measurement of the speaker's response and most likely very inaccurate but I chose to include them so that I can highlight just how effective a DSP is at altering sound. In the attached graphs, the orange line represents the recorded peak response and the white line represents real-time level (which can be ignored).

Crossover: I used a 4th order Linkwitz-Riley filter set at 3,000 Hz for the low pass filter on the woofers and high pass filter on the tweeters. One of the huge benefits of a DSP is that it can create complex filters such as this with ease. Making a passive 4th order Linkwitz-Riley crossover would require additional components which could easily add up to the cost of the DSP ($35).

Dynamic Bass Boost: Dynamic Bass Boost block provides boost that varies with input-signal level: lower levels require, and receive, more bass than higher levels. Using a variable-Q filter, this block dynamically adjusts the amount of boost. The input level must be decreased in order for the boost to work. This means that the speaker is no longer as loud, however I believe the trade-off is worth it. At 50W / channel, there's plenty of power.

This is my first project with a DSP and SigmaStudio and I am still learning. I will continue to update this Instructable as I fine-tune the sound. I hope you enjoyed the build!

Comments

[fglohr]

Nice project I discovered, please can you post the size of the different wood parts ?

[mastersapm]

Without a wiring diagram this is just an exercise in bending wood!

[Marzouk22]

The output from my TV is only HDMI or Fiber optic. How will I connect it to the board??

[M97122]

The board supports an output via 3.5mm jack. Does your tv have this input ?

[MartínM271]

Awesome! I just wonder if you could share the electronic connections. I saw you mentioned a crossover but I don't see it in the instructions. Thank you for sharing your project!

[beavis0001]

Awesome build, I love how you added dsp.

Have you had hissing problems when the unit is plugged in with no signal? I've read that it originates from the amp and power supply but I've had no luck in getting rid of it

[Papi1978]

Hello team,i am highly impressed by your work and i have just registered to your site. Heavenly speaking i'm a beginner and i'm gonna try this project after i will email everything.
Thank you

[the-l]

Hi !
Nice project and good explanations. Thank you !
I just have a question : how do you connect the JAB3 to your 4 drivers ? I readed the documentation of this DSP, and I only saw 2 audio outputs…
Can you provide some wirering diagrams ?
Thanks !

[ralf_k]

hello! in order to connect 4 speakers in the same configuration (4.0) i have shown here, you will need to connect two amplifiers via a 6-pin cable that is included with the amplifier. Output from the DSP board goes to two sets of woofers and the output from the other board goes to the tweeters. The link to the second amp is below as well as a useful instructional video. Please note that I do not use the on-board potentiometers because I reprogramed the DSP such that a custom filter can be used. You can use the configuration shown in the video but this application is limited.

Amp #2: http://store3.sure-electronics.com/aa-ja32472-1797
Instructions:

[therealburk]

Thanks for a great project! That link leads to the Sure JAB2, while in the project intro you linked to a Dayton Audio KAB-215. Are they both compatible with the JAB3? Would you rather recommend the JAB2? Thanks!

[Barzar]

Hey great job
sorry when I have missed it but how did you make this awesome Ikea like front?

[PeterRP]

Excellent Instructable. I have just ordred a Wondom DSP, and looking forward to tweaking the different possibilities with SigmaStudio. Anything new to add in this deoartment?

[JacksonF28]

amigo poderia me mandar todas as medidas em centimitros ou milimetros

[grahamgamer2447]

How long is the soundbar in total? I just want an estimate so before I make it I know if it can fit where I would like it to go.

[perec3]

Great building skills and great looking (and probably sounding) bar! I wanted to ask you what jig you use for cutting the holes with the router; I even slowed down the video to 0.25 and couldn't make it out. Thanks!

[ralf_k]

Hi there, I believe it's the Jasper 200J (Jasper 200J Model 200 Circle Cutting Jig for Plunge Router https://www.amazon.com/dp/B00009K77A/ref=cm_sw_r_cp_apa_i_zSG4Bb2XQ4RYV).

A bit pricey but it has nicely marked holes every 1/16" which makes it very easy to cut out accurate holes with a 1/4" diameter bit. I like to keep it mounted on my plunge base and use the fixed base or table for most other router work.

[perec3]

Thanks so much!

[ArthurJ5]

I use the heck out of my Jasper jig. It’s a great product and cuts an endless number of different circle sizes. I’m constantly wondering what to do with all the circles left from speaker building.

[ralf_k]

Yes I agree, I didn't go into much detail about the electronic connections. You may think it's complicated but it's actually quite simple. The amplifiers I used are pretty much plug and play. I'll update the instructable with some instructions that came with the amplifiers. Believe it or not, the DSP can be used without programming, right out of the box, but not in the way I wanted.

[biglouie]

Beautiful work! Hope to see more as your fine tuning progresses.