Baby Boomer

Baby Boomer

Mark Rivera

Project Category:
Portable Speakers

Project Level:

Project Time:
1-8 Hours

Project Cost:
$100 – $500

Project Description:
This is an aluminum fabricated sheet metal enclosured Bluetooth boombox using Dayton ND-91 drivers and the Dayton 50w Bluetooth boards and accessories.

Design Goals:
Goal was to design a good sounding, medium sized boombox around one of my favorite speakers and the newly available Dayton boards with BT circuitry built in. This one uses 2 of the battery boards available with three 18650’s each.

Enclosure Design:
Aluminum formed, welded and shaped construction, stainless steel back cover

Crossover Design:
Full range

This is a nice sounding unit that plays for 4-8 hours depending on use, and will work really well for camping or whatever portable sound solution is necessary. The lower voltage supply of the lithium batteries and the low sensitivity of the drivers don’t make it the loudest box available, but it hits nice and low, has very smooth midrange, and the highs are adequate if you stay mostly in front of it or a decent distance away. Overall satisfied, but dreaming bigger and louder…

About the Designer:
I’m a tinkerer whose designed and built several systems for personal use, from home theater to car audio to portable… I work in metals daily and have been exploring more nontraditional enclosures for some time, with decent success…

Project Parts List

Dayton Audio ND91-8 3-1/2″ Aluminum Cone Full-Range Driver 8 Ohm
Dayton Audio KAB-250 2x50W Class D Audio Amplifier Board with Bluetooth 4.0


Add yours
  1. 2
    Philip Carter

    Wait a minute. I do not get it. Sounds like you not satisfied with how loud they are. The post does not state the driver-wiring configuration. If they were in series parallel, it would result in an 8-ohm load. The max input power is 30 Watts for each driver for a net of 120 Watts. The sensitivity of each driver at 1-W SPL is 81.8 with a net sensitivity of 87.82 dB. If you push them with 100 watts, you should get 110 dB. That is loud. I get this from 87.82+ (10*LOG (2*100)), and verified with BaseBox 6 Pro. Even with 87.82+ (10*LOG (100) you should get 107 db. That is still very loud. These drivers should be capable of this. Something is wrong somewhere unless you are dreaming bigger and louder yet.

  2. 3
    Mark Rivera

    Thanks for the comments, guys… I was a little surprised at the lack of volume. I think the issue is, this amplifier board isn’t putting out near 50wpc. The Lithium ion battery boards are only at ~11V fully charged, and this amp is rated for around double that I think. I wanted the safe and easy charging capabilities that the boards support, so I’m guessing it’s closer to 20Wpc or perhaps less. These are the 8 ohm version of the ND-91, and they are wired in parallel, 2 drivers per channel, of course, for a net of 4 ohm per channel. I accidentally hooked them up in series the first time around, and that was way quieter. The sound quality is good and doesn’t distort much when cranked, but they definitely need more amp. That was apparent the first time I used them in another project as well.

  3. 4

    As a metalworker, I applaud your unique and skillfully fabricated cabinet. Unrelated: could you tell me more about the antenna? Does it extend the range of the bluetooth?

  4. 5

    Awesome build! I really like the retro look as well. I am shocked, you are not getting the volume out of it. You should be. I am assuming you are wiring them in parallel to get them down to 4 ohms? If you wired them in series, you would be getting 16 ohms and your speakers would not get loud at all. However, this really isn’t why I wanted to comment. I think your design is great, but you could really use a baffle step circuit to bring out that bass. Without it, the ND91’s lack a lot of low end. Something like a 0.6 solid core inductor and a 4 ohm resistor should do the trick would work for those speakers wired in parallel. Solder the inductor and resistor together (parallel) and in series with your positive wire that goes to your first woofer from the amp. It should really open up your low end.

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