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DSP - how, why, troubleshooting, different hardware, etc.

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ElliottDesigns
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@nixem didn't even know that was an option 🤣

Elliott Dyson - Mechanical Engineering Student and 3D printing & Design Freelancer


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ElliottDesigns
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@ajc9988 In regards to the post at this time and date: 19/09/2021 2:38 pm

I don't really like the built in crossovers due to the limitation of not being able to do both linear phase and having a flat response (as far as I am aware), that is why I put my crossovers in rePhase when doing my FIR filters for convolution.

Elliott Dyson - Mechanical Engineering Student and 3D printing & Design Freelancer


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ElliottDesigns
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Seems like a great solution and should work great! 👍

Elliott Dyson - Mechanical Engineering Student and 3D printing & Design Freelancer


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Nixem
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@elliottdesigns @ajc9988

If I understand correctly, by interfacing the Teensy 4.0, it can provide USBi as well as live controls. Ex, volume, source selection, touch display, loudness, etc. 

Basically $20 microcontroller with $40 adau1467, full powerful core. Could make it a preamp, DAC, dsp, whatever. With remote, switches, display, etc.


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ajc9988
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@nixem - I have not, but I can say I am familiar with the concept. I started there when wanting to interface the RPI with the JAB5 from Wondom which has an adau1701 on it.

But, I also noticed that Wondom uses only the i2C connections on their board to interface with the microcontroller, rather than taking up the pins for SPI and I2C. Instead, the SPI on their board is reserved for the MISO and MOSI (Master I/O, Slave I/O, with it telling you the direction in the name) between master and slave boards, using I2S over SPI.

So, although familiar, because of a limitation of how Wondom made the boards, it could only do input from the MISO or output through the MOSI, but not both at the same time. But I can complain some other time about that. No ragretz! lol

As to sigmastudio, one of the ways I learned was taking the base file for my device from Wondom (in case you flash a non-working, for you to flash to), then to walk myself through each thing they did, meaning open a blank file and try to replicate it. That taught me how to do hierarchy boards, etc. I then started taking out what I didn't need, because it would be used in the left or the right, not both. That saved on instructions allowing for more FIR taps. Then I played with the autoEQ, which then required learning how to import the readings from REW and convert those to read correctly in SigmaStudio.

That means, for learning, I just recommend replication, reading in the wiki, and thinking up cool things you want to do with it.


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ElliottDesigns
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@nixem Yeah, sounds pretty cool, but since I'm personally going multichannel and multiroom with my speakers, I'm doing processing on a per speaker basis, and therefore just need the teensy.

Elliott Dyson - Mechanical Engineering Student and 3D printing & Design Freelancer


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ajc9988
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Posted by: @nixem

@elliottdesigns @ajc9988

If I understand correctly, by interfacing the Teensy 4.0, it can provide USBi as well as live controls. Ex, volume, source selection, touch display, loudness, etc. 

Basically $20 microcontroller with $40 adau1467, full powerful core. Could make it a preamp, DAC, dsp, whatever. With remote, switches, display, etc.

What are you using for the ADC on the $40 ADAU1467 board? The core board would need the ADC to input to it. Or are you using the microcontroller as a master?


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Nixem
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@ajc9988 

 

I actually don't have any analog sources. 

You could pick up a nihtila ADC AK5572 if you needed analog in, or something else.

I would not want to use the microcontroller for anything except control, so inputs would be direct to the ADI board and audio flow would be only through the ADI board. Would prefer to keep 48k/24bit or higher with digital volume control, just a personal preference. 

I haven't messed with the microcontroller portion, or tinkered with the programming. For myself, I may just keep it simple and do ddrc-24 -i2s> adau1467 -i2s> ma12070p. I am working on an active 3-way.

The microcontroller portion may be more of a side / 2nd project for me. It would be neat to do a more stand alone all in one control system for less $ and more features than minidsp. There is enough i2s to have whatever audio I/O you could want, and those microcontrollers with ADI boards are powerful.

Edit: adau1467 has spdif pinouts I think.


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ElliottDesigns
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I've given up on the programs for FIR convolution for my teensy that I find on GitHub. So now I'm just going minimum phase biquads. Let's hope I can at least get those working. Soldered up the board and I am happy to say I do get an output with the 7 band parametric that comes on the audio board. I am getting a lot of noise from somewhere though which I'll have to look into, the minimum SNR from the components used is 85db, so at the volumes I was giving it a test at should have made the noise inaudible, but I'll look into it 😉

Elliott Dyson - Mechanical Engineering Student and 3D printing & Design Freelancer


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@elliottdesigns - Sorry to hear about the issues regarding the GitHub files for implementation. I've been busy doing FEA on bracing, constrained layer damping, and insulation. Looking over the numbers I've seen to date, Laurie Fincham was absolutely correct, insulation is king, followed by constrained layer damping, and then bracing itself. Also, how it is braced can definitely impact the resonance of the enclosure. My studies to date, using a constrained 24(width)x48in (height) board (3/4"), have included 1-4 vertical braces, 1-8 horizontal braces, 1-2 vertical braces combined with 1-4 vertical braces, constrained layer damping with 1/4" and 3/4" sheets (and the inverse for which side the pressure is acting upon), CLD with 1/2" on both sides, 3/4" both sides, and 3/8" both sides with 1/4" rubber mat in between the two layers. Then I have run the 2" rockwool and 1" rockwool simulations.

All of this, except for the front baffle design, means I may step down to 1/2" for the enclosure, change the bracing design, then use 1" rockwool in the sub chamber, then change the bracing slightly of the upper chamber and keep the 2" planned for there.

I still have studies to do on Dacron (PET) and a couple other common insulation materials.

Also, the cheaper pre-made DSPs from China could really make it worth it to consider, although there is a cost. And if a person wanted, they could do 3-4 out that could connect to the other speaker and have one master speaker and the other slave, driven by the same DSP (Splitting the $150 among 2 speakers is $75, as an example).

In any case, good to see you making headway, even if not working out as you have planned.


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ElliottDesigns
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@ajc9988 That's really interesting about the damping. Have you had a look to see what different materials do to different frequencies (e.g. rockwool being better for low frequencies for example), or even the performance of different fillers. I'm interested to know because I have a bunch of long haired sheep's wool since my dog's raw food always comes wrapped in the stuff as a thermal insulator. I'm particularly interested since I'm designing a quarter wave transmission line for my GRS 8sw-4 since the driver has such a high QTS, and damping is crucial in the way such an enclosure performs. In my design there's a small section of line (at the opposite end to the opening and before the driver) that has to be totally filled with absorption to work correctly, stopping higher harmonics in their tracks and allowing the drivers excursion to be massively lowered with even more output. Not entirely sure how stuffing can do so much but that's what hornresp said. So, effectively, I need the most effective absorber I can find! (Or combination of absorbers for the matter)

Elliott Dyson - Mechanical Engineering Student and 3D printing & Design Freelancer


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ajc9988
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Posted by: @elliottdesigns

@ajc9988 That's really interesting about the damping. Have you had a look to see what different materials do to different frequencies (e.g. rockwool being better for low frequencies for example), or even the performance of different fillers. I'm interested to know because I have a bunch of long haired sheep's wool since my dog's raw food always comes wrapped in the stuff as a thermal insulator. I'm particularly interested since I'm designing a quarter wave transmission line for my GRS 8sw-4 since the driver has such a high QTS, and damping is crucial in the way such an enclosure performs. In my design there's a small section of line (at the opposite end to the opening and before the driver) that has to be totally filled with absorption to work correctly, stopping higher harmonics in their tracks and allowing the drivers excursion to be massively lowered with even more output. Not entirely sure how stuffing can do so much but that's what hornresp said. So, effectively, I need the most effective absorber I can find! (Or combination of absorbers for the matter)

I have not yet. What my assumption was using 0.5% critical damping (1% structural, approximately), constraining the edges in a structural position, then applying pressure over the whole on the one side (assuming in the system, you would have the internal and external air pressure cancel out as vectors, thereby simplifying the model at the moment). This also does not take into account the sinusoidal nature of the speaker's pressure, at the moment, where you only get that high a pressure in peaks, then a vacuum to pull air back in in a vented enclosure, meaning you will have swings in pressure acting upon the bracing and insulation (although the spring sinusoidal analysis of this type is always present for the type of analysis being done; I'm doing a crap job of explaining the limits of my current modeling). I'm saving the more complex modeling for later, instead just examining frequency vs mode and frequency vs displacement to understand which modes have the largest effect on certain designs.

Towers Freq vs Magn displacement

This is the current design I showed using roughly similar assumptions. I know I can do better than that.

I can look for material properties for long haired sheep's wool, and can say that it has been used in speakers before for damping. But until I find the physical properties to estimate it's behavior, I cannot yet give a clear answer.

Edit: I also have some restrictions on rotational behaviors, etc., currently being used. I'll update the modeling later, as I've learned a fair amount about FEA modeling since running that first simulation on my speaker design. So the actual behavior may differ down the road as I change the conditions of the model.

 

Edit 2: I am also using 20 Pascal, which is 120dB, which is 0.0029007548 psi.


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Nixem
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@ajc9988 

 

This is really interesting!!

Lately I have been looking at foam board - dampening adhesive - 1/4" plywood, with possible bracing. I vaguely recall something from Tech Ingredients about certain dimensional ratios, maybe 3/5ths, I think 2-3 iterations of 3/5ths bracing would be interesting. I have no idea if any of this would actually work or be better, the idea just sounds good to me.

Keep us updated on what all you learn!


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