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Construction Article

dB61

Last updated: 1/18/04 (This version includes a revision to the crossover), 4/30/05 (pics and information about the dB71 upgrade).

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I built the first pair of dB61s in 1999 to be a basic two-way average performing speaker with some bass. After hearing the speakers, several of my fellow employees at work became interested. So I set up a weekend DIY project and we built about 12 pairs.

The first version used a straight first order crossover with an L-pad on the tweeter. After that, I went through a dozen or so different crossover designs -- first order, series, etc. -- until I ended up going with the second order crossover in this version which includes built in baffle step compensation. I have also listened to them using the crossover Wayne Jaeschke designed for his Dayton II speakers, the "revised version" to be exact, and they work very well. This is the latest design and was done using SpeakerWorkshop to measure and simulate the crossover.

This speaker provides full, tuneful bass, a decent midrange, and an extended frequency response with lots of detail. I highly recommend that they be placed on stands so as to put the tweeter about 36" above the floor. If possible, they should be positioned away from walls behind and to the sides.

The bass will go down into the 40Hz range, in-room. A subwoofer can add more kick or more low frequency extension -- depending on the subwoofer used.

A shielded version of the dB61 can also be built using the 295-306 woofer and 275-075 tweeter.

 

The photos on the left (apologies for the poor quality) are of the prototype. The corners were rounded with a 1/2" round over bit and the enclosure was painted with a satin black enamel using a spray gun. Other versions have been veneered and look better. The terminal cup on this version is a bi-wire type -- I used it to be able to run an external crossover during the design process. Use of a single wire terminal will work fine. The pic on the right shows projects built by Jeff Delys. The speaker with the light color (ash?) finish is Jeff's dB61. The speaker on the right with the dark mahogany finish is Jeff's dB71 project which is a great upgrade using the Dayton RS180 aluminum cone woofer and the Vifa D25AG-35-06 tweeter. (I hope to post this project soon, both as a driver upgrade version of the dB61 and as a separate project with the larger enclosure specific to the RS-180 woofer). Jeff really likes these speakers, especially the upper detail in the dB71s.

 

A pair of dB61s can be built for roughly $150, depending on the finish. This includes the drivers, crossover parts, MDF and miscellanous parts -- see table below:

 

 

Cost for One Speaker

Item

Qty

Cost/ea

Cost

 

 

 

 

 

 

 

Dayton 6 1/2" Woofer

1

$15.20

$15.20

Dayton 1 1/8" Tweeter

1

$15.50

$15.50

MDF

1/4 Sheet

$18.65

$4.66

Acoustic Foam

1/2 sheet

$1.00

$.50

Terminal Cup

1

$3.95

$3.95

Crossover Parts

1

$14.00

$14.00

Glue

1

 $0.25

$0.25

Screws

8

$0.10

$0.80

Grille Cloth

0.11

$7.50

$0.83

Grille Guides

0.33

$2.40

$0.79

Veneer

1

$15.00

$15.00

Contact Cement

1

$2.00

$2.00

Wire

1

$0.10

$0.10

Total

1

 

$73.58

             

 

 

 

 

 

 

 

Enclosure

 

 

 

 

 

The enclosure is 0.55 cu. ft. internal net volume. Construction is straightforward using butt joints. Two braces are used.

 

 

 

 

 

The drawing shows dimensions for cutting the front, back and sides oversize. Once the box is assembled, the excess 1/8" is trimmed with a straight cutting router bit with bearing. The result of this process will be very square, even corners and there will be no need to sand or fill gaps caused by minor misalignment of the parts. This is a highly recommended technique which many experienced do-it-yourself speaker builders use.

 

 

 

 

 

The assembly sequence is

 

 

 

 

 

 

Cut front baffle driver cutouts and rear baffle terminal/binding post cutout. Cut holes for the ports. Install the ports. If veneering, don't cut driver flush-mount rabbets until after veneer is attached.

 

 

 

Note: you can use the plastic ports sold by Parts Express -- 1 1/2" I.D. -- part number 260-402. They will need to be lengthened to 5 3/4" by adding a piece of 1 1/2" PVC. The plastic ports should work well, especially if you're veneering the front of the speaker.

 

 

Cut holes in braces.

 

 

Attach top, bottom, and braces to sides.

 

 

Attach front and back.

 

 

Trim edges to remove excess 1/8".

 

 

1/2" roundover port holes.

 

 

 

 

 

 

 

 

Tools needed:

 

 

 

 

 

 

Radial-arm or table saw. A hand-held Skil Saw can be used if appropriate guides are used.

 

 

Router with these bits:

 

 

 

1. Straight cutting bit with bearing

2. 3/8" rabbetting bit with bearing for woofer flush mount recess

3. 1/2" rabbeting bit with bearing for tweeter flush mount recess

4. If rounded corners are desired, a 1/2" roundover bit

 

 

 

 

 

3 1/2" hole saw for tweeter cutout.

 

 

Scroll saw for making templates. Templates are used for cutting the driver and port holes. Alternatively, a circle cutting jig with a straight bit can be used for the driver cutouts.

 

 

 

 

 

(Click on the drawing for a MS Word document with the drawing which can be enlarged)

 

 

 

 

Crossover

 

 

 

I measured the woofer and tweeter SPL response in the enclosure using Speaker Workshop. Then I measured impedance of each driver using Woofer Tester and converting the plot into a .zma file using SPL Tracer. After that, I plugged the data into Speaker Workshop and developed the crossover.

 
 

 

 

 

 

 

 

 

After listening to the speakers, you might find a need to lower the tweeter's output. This may be due to your personal taste or your ears, or it may be due to the listening room. Use the resistors in the table below to replace Rs and Rp.

 
 

 

 

Additional tweeter attenuation desired

Rs, ohms

Rp, ohms

1

3

8

2

3.5

6

3

4

5

4

4

4

5

4

3

 

 

 
 

The SpeakerWorkshop crossover simulation.

 

 

 

Here's the SPL response measured on-axis at 20".

 

 

 

 

 

 

 

And here's the impedance plot.

 

 

 

 

 

 

 

 

 
 

The impedance response is smooth. Overall, the dB61s sound musical and have extended bass and excellent imaging.

 
 
 

 

 

 

 

 

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