Home Forums DIY Amplifiers and Electronics DSP – how, why, troubleshooting, different hardware, etc.

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    ajc9988
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    So, I decided to open this thread to consolidate work on DSPs here. Regardless if you are using Texas Instruments solution that is similar to SigmaStudio, using DIRAC, using miniDSP’s software alternative to SigmaStudio, etc.

    DSPs and active crossovers have their own challenges. I even considered putting this in the crossover section because of the DSP relation to active crossovers. But there isn’t a neat place to tuck this. @TVOR-Ceasar – if you want, you can add a new topic in that section for DSPs, as it is similar to crossovers, amplifiers (as some DSPs now have amps with them, such as the JAB series among others), pre-amplifiers due to the signal processing, etc.

    @ElliottDesigns – wanted to tag you since you mentioned about this.

    Now, recently, I found the problem I was having with some of my designs for the JAB5. When trying to add the part for external potentiometers for each speaker after the active crossover, it stops playing sound. I am still trying to figure out why, as I have decided to do three independent gain knobs for the 3-way, then the master volume.

    Does anyone have more experience with sigmastudio? Otherwise, I’ll post the solution once I figure it out.

    Edit: turns out it was working, but unlike the master volume which defaulted to full volume, the gain switches defaulted to off. I didn’t plug the potentiometers in because of being lazy, but plugged them in to try. And they work. so now back to figuring out how to import the frequency response (or what I am doing wrong) for the autoEQ. Then is making FIR filters. Then just playing around with different ways to adjust phase, to adjust timing, etc. That way when I build my boxes, I can tune them quickly.

  • DSP – how, why, troubleshooting, different hardware, etc.

  • ajc9988

    Member
    October 13, 2021 at 12:51 am

    @nixem – That is Dacron/PET/Polyester types material. At 0.0003in displacement compared to 0.016 from the Melanine, and with a way higher starting frequency around 621Hz compared to 116Hz for Melanine, and with that only being half an inch of Dacron, I’d say do dacron/polyester before trying with the foam. It is already decently cheap.

  • nixem

    Member
    October 13, 2021 at 2:26 pm

    @ajc9988 

     

    Do you think two 1/8″ tempered hardboard panels laminated with a dampening adhesive would be any good, then add bracing/Dacron? Trying to think of ways to increase cabinet volume by reducing thickness but keep resonance/dampening reasonable.

  • ajc9988

    Member
    October 13, 2021 at 2:40 pm

    @nixem – From my tests to date, Insulation > CLD (which is what a dampening layer or adhesive between two panels is) > bracing.

    I’m on that same mission, now running simulations on 1/2″ (12mm) boards instead of 3/4″ (18mm) which is where I first started, that way to reduce weight (and cost).

    So, first thing is pick an insulation. Whether that is mineral wool or denim or polyester/dacron, how those perform is well known for acoustic properties. Certain foams help (melamine doesn’t seem to be that great). Wool used to be more common, though synthetics are found a lot more in speakers now.

    After you pick the insulation, you then can reduce how much bracing you do as the insulation absorbs the pressure from the drivers better than the bracing reduces the displacement, so you already would be far ahead just by using even 1/2″ (12mm) dacron for furniture. Then do cross bracing (meaning vertical and horizontal across the plane, I’m currently running models on the effects of braces running to the opposing walls) about 2″ toward the center (or less if you have to due to size).

    If you have a reason to do the CLD with a viscoelastic adhesive, then do it. It is much better than bracing, but is less than insulation.

    You can reduce bracing, though, just on the performance of the insulation alone. So, first decide on the insulation and the thickness of said insulation. Then, move onto bracing. If you have a reason to use CLD, like absorbing tons more energy not captured by the insulation due to frequency or something like that (sub-100Hz), then doing that is fine.

  • ajc9988

    Member
    October 13, 2021 at 3:03 pm

    @nixem – yes. When looking up Dacron, it gave me PET, so I plugged those numbers in. When I next looked up polyester, it pointed to PET being a large variety of polyester now used, so I didn’t do a separate polyester run. As such, I group Dacron with PET and Polyester with PET. And it did perform well in the FEA. Further, it looks like what was used with the acclaimed subwoofer from monoprice, the THX one. It has been used for decades in the loudspeaker industry, so is a safe and cheap bet.

  • nixem

    Member
    October 13, 2021 at 3:39 pm

    @elliottdesigns 

    Do you have experience with adding an IR remote to the Teensy? Or, how are you controlling it?

  • nixem

    Member
    October 13, 2021 at 3:40 pm

    @ajc9988 

    Man, this will be super interesting, keep us updated!!

  • elliottdesigns

    Member
    October 13, 2021 at 4:23 pm

    @nixem I’m programming it through usb and then running it off of usb power. It doesn’t need to be controlled after that since the profile has been applied and it’s just a processor, the main volume will be controlled using the device outputting the audio, the teensy just processes it and passes it through.

  • nixem

    Member
    October 14, 2021 at 2:05 am

    @elliottdesigns @ajc9988

     

    Just thought I would share.

     

    The first half of this video about audio is interesting.

     

    This one is also interesting.

     

  • nixem

    Member
    December 5, 2021 at 4:26 am

    @ajc9988 

     

    Hey, not sure if you saw Tech Ingredients – Anechoic Chamber – DIY Sound Absorption Panels on youtube, but roxul / stone wool insulation might be worth a go. 

     

    I wonder if those rock wool starter cubes for planting would be any good. They are super cheap and would be easy for DIY.

     

    $6.99

     

  • tvor-ceasar

    Moderator
    December 5, 2021 at 6:24 am

    @nixem if you want to see a really good demonstration of just how effective it is, check out the build videos that PS Audio is putting up about the new home of Octave Records studio. Paul takes you into some of the rooms that are fully insulated and the way his voice changes is astounding.


  • ajc9988

    Member
    December 5, 2021 at 10:16 am

    @nixem – Although I have seen from them, I would point toward a couple other resources on information on insulation materials and would recommend getting other than $7 per sq. ft.

    Insulation changes a LOT. Especially in the modeling of box absorption (Qa). Absorption losses being accounted for in winISD, BassBoxPro, and Unibox suggests that anywhere from a Qa = 20 for lining all walls with insulation to a Qa =5 for heavily stuffed means you can then go between 10-25% more wattage before Xmax, depending on the driver (some, due to suspension, etc., gain less).

    Because of that, and because I have more size in my room than sense, I intend on using 2″ insulation on all walls and splitting it to glue to glue to braces spanning the center.

    ATS Acoustics is one of the few places to easily find insulation for this purpose.
    https://www.atsacoustics.com/cat–Fiberglass-and-Mineral-Wool-Batts-and-Boards–106.html

    Specifically the 2″ denim and the Roxul 60, which has equivalents out there.

    https://www.atsacoustics.com/recycled-cotton-batts.html

    https://www.atsacoustics.com/item–Roxul-Rockboard-60-Case-of-6–RB60.html

    Now, if you really had more room than sense, I would actually recommend the cotton 3.5″ batts from Lowe’s. This will basically even be effective tested down to 125Hz, nearly fully.

    https://www.lowes.com/pd/UltraTouch-R-13-Recycled-Denim-Batt-Insulation-with-Sound-Barrier-15-in-W-x-93-in-L/3731875

    Here is a good resource on different types of materials on the market and their acoustic coefficients

    http://www.bobgolds.com/AbsorptionCoefficients.htm

    But, remember, Polyester is fairly transparent. Sure, it helps, and you can get it in 2″ versions, but at some point, you may just go denim or rockwool.

    https://fabricwarehouse.com/2-inch-upholstery-batting-poly-2-inch-loft-30-w-2-oz-extra-extra-dense?sku=DACRON2MAX10yp

  • nixem

    Member
    December 5, 2021 at 2:47 pm

    @ajc9988 

     

    Is denim / rock wool ever used inside a speaker?

  • nixem

    Member
    December 5, 2021 at 2:55 pm

    @ajc9988

     

    Do you know of an easy way to identify i2s signals (SCK, WS, SD, etc) without any schematic or reference identifiers?

     

  • nixem

    Member
    December 5, 2021 at 3:02 pm

    @ajc9988

     

    Or do you have any suggestions on an inexpensive 4 channel scope?

     

  • ajc9988

    Member
    December 5, 2021 at 3:47 pm

    @nixem – First, yes, insulation is used in speakers. Polyester/Dacron/PET is more common (up to 1″), but you can use different thicknesses and materials and that does effect how well it works.

    As to identifying without a schematic or reference, no good recommendation. For a 4-channel scope, maybe check out these recommendations:

     

    edit:

    Also, if you want 48″x24″x2″ x 6 panels, here is another vendor: https://www.acoustimac.com/acoustic-insulation-materials/acoustic-insulation/mineral-wool-acoustic-insulation/roxul-rb6-2in

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