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| Build-Your-Own | Main Panel | Dipole Woofer | Crossover/EQ | Supplies |
| System Test | Design Models | Prototypes | Active Filters | Surround | FAQ |

 

Dipole Woofer - 1

All dimensions are in inch units unless otherwise stated. (1" = 25.4 mm)
For construction use 0.75" and 0.5" thick Baltic plywood for structural solidity.

A - Side panel (2x), 19" x 13" x 0.5"
An acoustically transparent, opaque cloth might be wrapped around the cabinet sides.

B - Top, 19" x 16" x 0.5"
The panel might be finished around its edges and top surface for cosmetics.

C - Bottom, 19" x 16" x 0.5", with screw holes if made removable. 
The visible edges of the panel might be finished.

D - Baffle (2x), 14.5" x 13" x 0.75", one 11.25" diameter hole with 12.5" diameter recess of 0.25" depth, 8 screw holes.

E - Spacer, 13" x 3" x 0.75". 
All spacers to be glued and screwed to the mating surfaces.

F - Spacer, 13" x 5.75" x 0.75"

G - Spacer, 13" x 4.75" x 0.75"

H - 12" Driver, Madisound 1252 DVC - 12" Dual Voice Coil Woofer. 

April 2002 note: 
The 1252DVC and X6100 drivers are no longer available. Select either Woofer2 or Woofer3 as alternatives. They require a cabinet width of more than 16 inch, because of larger magnet structures. 

The driver is mounted to its baffle with metal screws and self locking nuts. This is a tedious operation when the cabinet is completely assembled. Consider to leave the cabinet bottom C removable or to have the drivers attached to their baffles when assembling the cabinet. Use compressed weather stripping foam tape between metal basket and wood. 
Some drivers may buzz due to marginal attachment of the magnet assembly to the basket. This is difficult to determine before the dipole woofer is completed. To avoid this, apply a heavy bead of Silicone II Sealer & Glue to the gap between magnet and basket. 
    A drop-in replacement woofer of higher quality construction and without the potential buzz problem is the Gefco X6100 single voice coil woofer. It is built with a stronger basket and a non-foam surround. The driver is no longer available from Madisound. Before selecting different drivers see FAQ4 and Woofer2. I have since found a real alternative if you want to built a stacked woofer for larger output, which would normally take four 1252DVC, see Woofer3.
    The 16" cabinet width is the result of the driver dimensions and an effort to minimize the overall size of the dipole woofer. I consider the slight assembly difficulties a worthwhile trade-off. There is an added benefit to the chosen driver arrangement. The direction of cone movement is such that mechanical forces cancel and only a minimum of vibration is transferred to the cabinet's outside surfaces for possible re-radiation. Force cancellation is important because of the large cone excursions necessary for dipole operation and the associated large reaction forces. - Ref.4theory.gifspl_max1.xls
    The two drivers are wired in parallel. On each 1252DVC connect the two voice coil windings in series (red to black), then wire the two drivers in parallel, accounting for their push-pull operation (red to black, black to red). Check with a D-Cell, 1.5 V battery, that both cones move towards each other when seen from the front of the cabinet, when the positive terminal of the battery is connected to the positive terminal of your wiring. One cone moves out of the magnet, while the other cone moves into it.

The woofer is directional with a cos(angle) or figure-of-eight polar pattern. The response is 3 dB down at 450 off-axis. When placed near the side walls the woofer may need to be angled towards the listening position.

The woofer requires electronic equalization of the 6 dB/oct frequency response roll-off which is due to front-to-rear sound cancellation. | Crossover/EQ |
You will find measured frequency response data on the | System Test | page
and answers to a number of woofer related questions on the | FAQ | page. Acoustic theory of open-baffle woofers is on the | Design Models | page.

 

| Build-Your-Own | Main Panel | Dipole Woofer | Crossover/EQ | Supplies |
| System Test | Design Models | Prototypes | Active Filters | Surround | FAQ |

 
What you hear is not the air pressure variation in itself 
but what has drawn your attention
in the two streams of superimposed air pressure variations at your eardrums

An acoustic event has dimensions of Time, Tone, Loudness and Space
Have they been recorded and rendered sensibly?

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Last revised: 06/28/2014   -  1999-2014 LINKWITZ LAB, All Rights Reserved