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The 'Pasobaric 490'

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  • The 'Pasobaric 490'

    The ‘PasoBaric 490’
    Components:
    Dayton Audio ND90-4 – Quantity 4
    Peerless by Tympany SDS-P830878 – Quantity 4
    Dayton Amplifier DTA-100a – Quantity 1
    Design:
    My main objective in this project was to achieve a small enclosure design with adequate bass output using the Dayton ND90-4 Full range drivers. My design started a number of years back. In fact, it predated the introduction of the ND series passive radiators hence why I have the Peerless models used. My goal was to achieve usable response to near 40hz. That is a tall order for a 3.5” woofer. The ND90 was a good selection due to it’s high Xmax, reasonably clean looks, and wide frequency range capability.
    My goal for the enclosure was to keep the size down as much as possible. Obviously when engineering enclosures everything is a compromise. I looked for the best balance between size, output/response goals, cost, etc. Because of these limitations I decided to try a route I had not seen executed in a tabletop/Bluetooth type design.
    Vented Isobaric, or in this case an Isobaric PR alignment. Hence where most of the name comes from.
    When I started modeling the woofers I realized the vent was going to take up too much space in my design. Though the vent is small, every tenth of a cubic foot matters to help achieve my design F3/F6 goals. That is why I decided to go the Isobaric PR route. Because amplifier power is cheap, the loss in efficiency going the isobaric route did not matter since it offered a significant help in reducing enclosure size and lowering the F3/F6. Check and Check.
    Using the modeled SPL with rated power of 20w RMS per driver the F6 is at 39hz at over 85db. Definitely effective for the goals I am after since this is ultimately a gift for my daughter in her bedroom.
    Each pair of woofers is wired in series to present an 8ohm load on the amplifier making the system very easy to drive, even should we change or upgrade amplifiers in the future.
    Enclosure Design & Construction:
    For the enclosure I arrived at a 5.5” x 15” x 6-7/8” external. For the Isobaric section I opted for the inline approach versus a clamshell option, primarily for aesthetic reasons. In such a design the chamber separating the woofers needs to be as small as possible. I ended up at a net of 0.02ft^2 in that chamber with the design. I did add a small piece of acoustical foam where it would not come into contact with either woofer to cut down on reflections some. I could probably have gone smaller still but needed room to wire the driver through to the rest of the enclosure. The mounting baffle for the internal woofers also helps to brace the enclosure.
    I made the main portion of the enclosure out of ¾” MDF and the interior baffle, rear and front baffles out of ½” 11ply & 7 ply birch. This allowed me multiple finish options for the project.
    Being that I have not built some enclosures for some time, I unfortunately made a small mistake as I neared completion of the construction. I misread the cutout for the woofer at 85mm when it was actually 76.5mm. This left my opening oversized. Rather than start the baffle over again, I decided to improvise and add some nice ½” thick “cups” if you will around the woofers. An advantage to doing it this way is that it will allow for optional grilles to be added easily. When life gives you lemons, make lemonade.
    Lastly I used some denim fiber for a light stuffing of the rear chamber to help tame reflections there as well.
    Amplifier Housing:
    With space in the enclosure such a premium, and at the time of my purchases few if any small chip-based amps being available, I used the Dayton DTA-100a amplifier. It has a rather large outboard power supply so hiding it was ideal. I crafted a quick housing for the speaker to sit on which holds the amplifier and power supply. This way she will have a nice clean look to everything when it is in her room It also serves as a platform for the speaker as a whole.
    Finish:
    My daughter’s favorite colors are a teal blue and purple. Not my first picks for a speaker mind you, but they are hers. I decided I would use a base color for the center section of black and make the baffles teal. I also opted to try and go for a classier take rather than just painting. I purchased some mica powder/dye on Amazon and tested it in the Poly prior to application to get the right ratios and color. With this being a first attempt, the plus side of it is a decent color and a bit of a shimmer. I was hoping the pigment would have dyed the poly better to get more of the wood grain to pop. I think my next attempt there would be to get a liquid dye to add into the poly or find a stain that I can mix the dye into without darkening the natural wood too much. For the main section I used a roll-on enamel black and then mixed a purple mica powder/dye into the poly. That worked rather well. Photos don’t quite capture the overall look.
    Initial Impressions:
    Overall it sounds rather nice. Midrange is clear and tonal balance is decent, more so at moderate volumes if in an open space. At moderate volumes it sounds quite good and full on axis. When placed near a boundary or corner it has ample output to the mid 40hz range and you don’t need to have the volume up as high to have the sound be nice and full. At high volumes near a boundary it gives the impression of a sub being involved. It is rather impressive when you consider it is just two 3.5” woofers! The woofers are running full range with no eq or any circuit applied. I don’t plan to do any tweaking there until I get a measurement mic.
    I need to invest in a measurement mic soon to hopefully provide some actual response measurements. I will try and get a few using the SPL/FR app I have on my phone as well to ballpark. This was a fun project that my sons assisted with as a gift for their sister. It was fun to teach them about how a fairly complex design works and what the yield can be.
    I am pretty happy with how everything turned out. There were a few mistakes along the way that I learned from so that is always helpful. It was good practice as I continue to prepare for a full active reference build. In the end my daughter is really happy to have great sounding music in her room and her being happy is what matters. Thanks for looking!

    Photo Log

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  • #2
    Interesting looks great, I've always wanted to try an isobar but generally get persuaded otherwise on forums. Saying that the full range driver in a small enclosure makes me want to have an actual shot at it

    Comment


    • #3
      Originally posted by 3rutu5 View Post
      Interesting looks great, I've always wanted to try an isobar but generally get persuaded otherwise on forums. Saying that the full range driver in a small enclosure makes me want to have an actual shot at it
      It is definitely more expensive. The advantage is a speaker that can hit the mid 40hz range (though not at high spls) in a rather small enclosure. It was definitely a bit of an experiment and I still need to do some further measurements but I am very pleased with the outcomes.

      Comment


      • #4
        Do you happen to have the transfer graph? I wouldn't mind seeing how it looked, I don't know but sometimes I think I might be trying something too extreme for the driver. I have one peerless PR in my garage already I wonder how it would fair as a portable battery setup

        One thing people mentioned on other forums was the lack of the high end frequencies and you would need a tweeter, assuming using these drivers you dont and completely sufficient?
        Last edited by 3rutu5; 01-20-2020, 03:43 PM.

        Comment


        • #5
          Originally posted by 3rutu5 View Post
          Do you happen to have the transfer graph? I wouldn't mind seeing how it looked, I don't know but sometimes I think I might be trying something too extreme for the driver. I have one peerless PR in my garage already I wonder how it would fair as a portable battery setup

          One thing people mentioned on other forums was the lack of the high end frequencies and you would need a tweeter, assuming using these drivers you dont and completely sufficient?
          I will get it for you when I can access my laptop again.

          Comment


          • #6
            Originally posted by 3rutu5 View Post
            Do you happen to have the transfer graph? I wouldn't mind seeing how it looked, I don't know but sometimes I think I might be trying something too extreme for the driver. I have one peerless PR in my garage already I wonder how it would fair as a portable battery setup

            One thing people mentioned on other forums was the lack of the high end frequencies and you would need a tweeter, assuming using these drivers you dont and completely sufficient?
            Click image for larger version

Name:	ND90 project Max SPL at 20w rms.JPG
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Name:	ND90 project woofer excursion.JPG
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            Attached Files

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            • #7
              Very nice boombox there.

              I'm also planning on doing something similar to you but with a two 6-1/2" inside in two band-pass compartments for bass, and two 6-1/2" 2-Way's as mid/high, feeded by standard 12v.


              Regards

              Comment


              • #8
                Originally posted by anunnaki View Post

                Click image for larger version

Name:	ND90 project Max SPL at 20w rms.JPG
Views:	441
Size:	156.7 KB
ID:	1429872Click image for larger version

Name:	ND90 project woofer excursion.JPG
Views:	424
Size:	154.0 KB
ID:	1429874
                Thanks mate, me not knowing much really about these charts thought going under the zero line was a bad thing, but more and more I read I notice people referring to F3, F6, F10 etc which shows me I was wrong. Good to know that's how a PR models will have to reconsider a few scrapped project ideas now lol

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