The 'Pasobaric 490'

annunaki

annunaki

Moderator
Hello All - Its been a LONG time since I posted a project here. Anyway, wanted to share a project I did as a gift to my daughter for her 7th birthday. Now she has music in her room whenever she wants it!

Build Photos

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!

IMG_7631.jpg
IMG_7632.jpg
 
Alex2507

Alex2507

Audioholic Slumlord
Each pair of woofers is wired in series
That sounds like it's not stereo.

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.
Is this the ND PR you would use if you designed it today?

I used the Dayton DTA-100a amplifier.
That came up as NLA. This Lepai must have better distortion numbers at 50% output still meeting your 50 watt per driver target. That sound about right?

Very nice to see your work. :)
 
annunaki

annunaki

Moderator
That sounds like it's not stereo.



Is this the ND PR you would use if you designed it today?



That came up as NLA. This Lepai must have better distortion numbers at 50% output still meeting your 50 watt per driver target. That sound about right?

Very nice to see your work. :)
hey Alex!

Yes it is in stereo.

Yes that is the PR I would have went with.

As for an amplifier that is currently available, I would have to look around for one. I would also probably do four of the ND90-8 and ran each pair of woofers in parallel. That way I could present a 4ohm load at the amplifier per channel.
 
annunaki

annunaki

Moderator
Here are some of the response models I did in advance of the project:
ND90 project Max SPL at 20w rms.JPG
ND90 project transfer function F6.JPG
ND90 project woofer excursion.JPG
ND90 project PR excursion.JPG
 
Alex2507

Alex2507

Audioholic Slumlord
I'm getting confused here:
Dayton Audio ND90-4 – Quantity 4
Peerless by Tympany SDS-P830878 – Quantity 4
I thought it was two drivers and two radiators. This AM I see a quantity of 4. Yesterday the stereo question came up because I don't understand how 2 speakers wired in series can produce stereo.
Each pair of woofers is wired in series
Oh, I just got it. Yesterday I looked up "isobaric" ... you stacked the drivers you sneak! :D I assume the back of the boombox has the other 2 PRs? Did you not take build pics? That picture being worth a thousand words thing is real, bro. :)

Man, I wish I had more time for this stuff. I've had time for a while but that's about to evaporate and then I won't have time to even read, never mind build. Real life is taking a toll on hobby life. I've said it before and I'll say it again, 'I should have been born rich instead of good looking'.
 
annunaki

annunaki

Moderator
I'm getting confused here:

I thought it was two drivers and two radiators. This AM I see a quantity of 4. Yesterday the stereo question came up because I don't understand how 2 speakers wired in series can produce stereo.


Oh, I just got it. Yesterday I looked up "isobaric" ... you stacked the drivers you sneak! :D I assume the back of the boombox has the other 2 PRs? Did you not take build pics? That picture being worth a thousand words thing is real, bro. :)

Man, I wish I had more time for this stuff. I've had time for a while but that's about to evaporate and then I won't have time to even read, never mind build. Real life is taking a toll on hobby life. I've said it before and I'll say it again, 'I should have been born rich instead of good looking'.
Alex, click the “Build Photos” link in the original post. They are all there. It should give a better understanding of the design.

Two PRs per pair of ND90’s
The PRs are located on the side and rear of the enclosure.
 
Alex2507

Alex2507

Audioholic Slumlord
click the “Build Photos”
I don't know how I miss things like that but it happens all the time. It reminds me of something j_garcia once said about the devil being in the details. It took a few ganders but I my guess about stacking the drivers and rear panel PR placement was a good one. I also now understand why the side mounted PRs are skooched toward the back. Pretty slick.

Thanks for getting my head out of being 'bated by somebody else's problem on the forum. This thread is a lot more fun. The pics are very cool with that bit of motion and audio included. I noticed my phone doing that but I don't have any clue as to how it happens.
 

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