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Project "Anomalies", started doing some preliminary modeling...

Being the premise of next InDIYana being the 'Inner Sanctum', and surveying the projects I have to place on the burner that would suit that premise, I have done some preliminary modeling to meet that pending goal.

There aren't many modelers that can accomplish the multichamber and multitunings of a DCR/DBR/ABC(WinISD) alignment and do it justice. To top it off, this pending project with a 4" long throw Kartesian SUB120 has to take really long and large ports or PRs to tune low enough. Furthermore, it has to take 2x DSA135PRs to keep all the elements somewhat happy. The Double Chamber Reflex alignment type entertained here is likely to keep the elements a little happier still by making the tuning range broader and reduce excursion further. It just has to be done with PRs for the low tunings required. I have not done a DCR with PRs, so this is another one on the bucket list I've wanted to go for.

Using the measured T/S for the Sub120;


The online program that Jurgen Micka created and placed online is pretty powerful, and a versatile tool for such a thing. I think it is Akabak based. You can access it here:
https://www.micka.de/en/advanced.php#
I wish I could download it and not have to be used on the 'net, but oh well...

I figured out the only way the parts would fit in the initial PR box would be to side mount the DSA135PR and front mount the SUB120. Since that is the case, I could not use 1 or 2 more DSA135 and make them fit in any reasonable fashion or placement as normal DCR alignments go. I figured out I could use an 8" PR for the secondary unit and likely place it on the back by using a U shaped secondary chamber.

Modeling with Micka's program shown in the next post...

Tagged:
6thplanet
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Comments

  • edited August 2023

    I am posting below screenshots of the entered parameters, the box criteria, and the results this program generated. I had to use some math to substitute in the dual PRs as a single entity. Unibox helped with the length calculation as if the PRs were ports and finding the length required for the tunings I implemented at the PR diameter.

    If you use this online program, make sure you read the examples page for best use. For example, large unused chambers must be set as 10000000. Used ports must have Rap=0 and unused ports must have Rap=1.0E+30. This is so the program calculates only what is desired. Selection of the proper Enclosure Variant button is also important. Then hit "calculate" to see the results below.

    I tried calculating with Port1 in use, but i could not fill in the dip in the rolloff by doing so. Excursion was better without this in play, so just omitted its use. In past multichamber implementations i've done, this port was peaky and noisy anyway, and i plugged it off with some foam. This is not the case with all of them, but another possibility for negating its use.

    The normal ROT for DCR states to use a model for 2 ports at the right frequency, then divide into 1/3 and 2/3 volumes and place the driver and one port in the larger, the second port in the smaller, and a 3rd and equal port to breach the divider. When i did the 3CR, i used 5 equal ports and volumes divided by half and a pair of quarters.

    Using this program allows modeling different Fb tunings and eliminating the ROT. I tried with the same Fb and the rolloffs were too peaky for my liking. Granted, the volumes are estimated at this stage, so this is all preliminary anyway. I just felt i should show the process. Staggering the tunings at 40 and 35Hz did the trick. F3/10 = 55/40Hz, according to the model.




    6thplanetjohnny5jzugly_woofer
  • This project is definitely an outlier from the norm, Wolf - your chosen name of "Anomalies" is quite appropriate.
    (Watching with great interest).

  • It’s definitely going to be an interesting build

  • This driver is likely the cleanest and longest xmax 4" on the market, short of its neodymium sibling. It is also a tall order for any 4" to yield a 50-55Hz F3 in 3 ltrs, take 75-80W in stride getting there, require a pair of 5.25" PRs to do it cleanly, and put out close to 100dB down to there without breaching xmax. That is pretty impressive to me! I felt I really needed something special and different to implement them, and it appears this is the path I'm taking. 6 ltrs is not huge either.
    When I announce the tweeter, it will also reinforce the name. There just seemed to be no other mate for the SUB120 that I wanted to use. It had to be an upper tier tweeter or wide range, just so i did not feel i was short-changing the woofer. I have looked at many drivers since getting those little behemoth woofers, and nothing has clicked for me like the intended.
    More later....

    Steve_Lee
  • Nice little design. You really know how to shoe-horn alot of elements into a very small space! :+1: As you point out, this will be a real challenge due to the lack of modeling software that can cover all the bases.

  • I'll have to build the inner portion and measure the tuning first. Then do the secondary portion and match the impedance curve.

  • Pretty awesome looking little driver. I'm sure you'll do it justice.

  • I think your Ral for Vr2 is possibly wrong.

  • I replied to this and the message was erased when the site crashed earlier. Thanks for catching that, and I will reevaluate. It's pretty difficult to get everything entered into this program "just so" in terms of accuracy.

  • I agree.

  • Did some fiddling with another driver in the database, and it is very apparent I have too high a number there. The manual of examples states typical RAL values of 42000 to 224000. I'll report more later. I think I still have the page loaded on the tablet with the T/S entered and number alignments as before. It will save on setup time if this is the case...

  • That program is really cool but kind of a pain since you can't save projects. I wish it was a stand alone download program like you mentioned. Anyway, I tried your parameters with Ral = 100000000 and 224000 and there was a pretty big difference.

  • Okay, did some more realistic fiddling. I measured the boxes intended, and made sure everything physically would fit. Then i adjusted the program filters for as they should be, 224000 on both volumes, and double checked the cells to the previously entered values.

    The tunings i ended up with really sound funny, but this is the first tim ive ever done an alignment like this.

    The 2x DSA135 PRs are collectively tuned to 50Hz in the 3 ltr chamber with the SUB120. This is almost where the sim in Unibox led me, and it has good xmax control. In fact, this tuning has the best xmax control from 40 to 80Hz. Suffice that these PRs are serving that function mostly.

    The DSA215PR on the back is tuned to 70Hz in the 2.8 ltrs, and variance from 2.8-3.0 ltrs really made no difference. This is singly tuned, but added in combo with the tunings of the other 2 PRs. This tuning brought a little more output, and lent the SUB120 a little more xmax control.

    The collective system has an F3/10 of 65/38 with the output at 100dB via 75W, and keeps the SUB120 happy to about 40Hz. Xmax is 6.5mm at 40Hz, and it rises dramatically below there.



  • And then I realized I have to rotate the box to fit the tweeter above the woofer. At least since the dims are the same reference points that a simple 90° shift won't matter much...

  • edited August 2023

    You’re pretty good with a shoe horn (packed a lot into your previous couple of builds)

    Mission style (and others) woofer above tweeter. But then that plays into Xover selection / design.

  • No, these will be conventional T/W. I do have have another pending build that will be flipped though.
    I think it must be the way my brain works. I seem to have the knack for it....

    tajanes
  • I sorta see a design preference/ style to a few builders here on this forum, and at the events.

    Thinking many could match up build with builder w/o the nameplates.

  • This is the same 3 ltr PR box without the extra chamber and DSA215:



    At the same power input, it requires quite a bit more excursion. I think the DCR should operate a little more safely.

  • edited August 2023

    Someone wrote to me about this driver.

    It is is nice looking with a great motor and cone, but apparently has no ventilation under the dust cup at all. There are no holes in pole piece, voice coil former or cone body. So all air movement is through the gap.

    As a result, I'm told the driver makes high pitched air noise around +/- 4mm, which is well below it's x-max. Even in its enclosure the high pitched air noise can is still audible.

    Have you done any free air testing @Wolf ? Did you experience any audible noises?

  • I have not done that as yet, but maybe I should. The cone is spun aluminum, and has a carbon fiber dust cap. No pole vent, but the under spider is very open.

  • I'll have to look at the cap cavity for clarification.

  • You are correct, there is no decompression method behind the dustcap.
    I will see what happens when I run it hard....

  • So, that should be +35g added to each DSA135PR, and +60g on the single DSA215PR; according to spec in the Unibox model. This is with lined main driver cavity and minimal fill in the secondary volume.

  • edited September 2023

    I guess I've got alot of learning to do. I'm messing about in that tool and am only getting limited results that aren't much better than standard single chamber bass reflex.

    Billet
  • Oh no you didn't! :p

    BilletNicholas_23
  • Nicholas_23Steve_LeeWolf
    I'm not deaf, I'm just not listening.
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