3.0L R/T

3.0L R/T


Designer:
Dynamo

Project Category:
Portable Speakers

Project Level:
Intermediate

Project Time:
8-20 Hours

Project Cost:
$100 – $500

Project Description:
A small powered desktop speaker designed to have good range and pleasant sound. An upgrade to standard plastic PC speakers.

The design is 3 liters internal volume and tuned with a passive radiator to eliminate port noise and eliminate a long port due to the small enclosure.

Design Goals:
The design should be a sound quality upgrade to most pc speakers, while offering Bluetooth ability.

The cabinet was to be made quickly and easily with basic tools.

Driver Selection:
I chose the Dayton ND91 for its long throw abilities and small cabinet requirements. Physics says this results in low sensitivity however as the trade off.

I chose the OT19 tweeter for its small size and because I enjoy the ring radiator sound.

Enclosure Design:
A simple enclosure made of a stick of mahogany and some hobby plywood, with rounded over driver openings. Nice and easy

Enclosure Assembly:
Cut and glue, real easy and quick. Finished mine with danish oil and shellac.

Crossover Design:
See the attached schematic. All resistors are 10w, all caps are poly except the 47uf. Note the reversed tweeter polarity.

I initially had a 2nd order electrical on the tweeter but bumped it to 4th, resulting in an 8th order slope at 2600 on the ttweeter.

Tips & Tricks:
Use rubber feet on the bottom to keep them in place as that little woofer and passive radiator really move.

There are a few odds and ends not listed you will need such as a fuse holder, dc jack, terminal cups for wiring the other (passive) speaker.

Placement of the woofer, passive radiator, and other internal parts should be checked to ensure the passive radiator doesn’t hit them.

From what I have read, the smaller 30 watt Dayton amp board has more output due to its design, so if I did it again I may try out that board.

Conclusion:
I feel they are very pleasant to listen to. The Bluetooth is easy to connect to although wired is preferred.

Very enjoyable, however due to the low sensitivity and crossover design they are not made for a big room. They are designed to be used on a tabletop or desktop for nearfield use.

About the Designer:
I have been dabbling in diy audio for many years. Always learning something new. The techtalk forum is very helpful to me.

Project Parts List:

Dayton Audio ND91-4 3-1/2″ Aluminum Cone Full-Range Neo Driver 4 Ohm
Peerless by Tymphany OT19NC00-04 3/4″ Fabric Dome Tweeter 4 Ohm
Dayton Audio KAB-250v3 2x50W Class D Audio Amplifier Board with Bluetooth 4.0
Dayton Audio KAB-FC Function Cables Package for Bluetooth Amplifier Boards
Dayton Audio KAB-AB L-type Aluminum Bracket for Bluetooth Amplifier Boards
Parts Express 24 VDC 5A Switching Power Supply with 2.5 x 5.5mm Plug
Dayton Audio DS175-PR 6-1/2″ Designer Series Passive Radiator

2 Comments

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  1. 2
    Dynamo

    An added suggestion. Due to the amount of wasted energy below the tuning frequency, I ended up adding 800uf in series with the woofer after the crossover. I suggest using four 200uf npe caps in parallel.

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