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  The Silverado, a small d'Appolito loudspeaker 
  Sep 28, 2005, 07:30am EDT 

Bass-reflex enclosure

By: Sander Sassen

I already mentioned I wanted the loudspeaker to extend down to about 60Hz, hence the -3dB point should be centered around that. Given the fact that the H1207 Seas driver has a resonance frequency of 48Hz Iíve opted to use a bass-reflex enclosure to keep the dimensions small enough. With two drivers I can use an enclosure of about 10-liters and achieve that, which will make the loudspeaker relatively compact. If Iíd opted for a closed box I would need nearly double the volume to achieve the same effect, which would make the loudspeaker look rather bulky and out of shape.

As you can see in the drawing above the loudspeaker is small and constructed from 22-mm MDF, hence it is very stiff and strong. A PDF with a large version of the drawing is also available here. The additional bracing further increases its stiffness and also divides the enclosure into three separate compartments. The holes in these braces obviously are there to acoustically couple the compartments and hence the edges of the holes should be routed with a rounding bit to minimize chuffing noise or reflections. The same applies to the cutouts for the H1207 drivers, they should be rounded on the inside, to allow the drivers to breathe more easily. All outer panels in the drawing are cut at a 45-degree angle so the end result will be a loudspeaker enclosure void of visible seams where the panels are glued together.

Bass-reflex port Time-aligned tweeter

A look at the finished loudspeaker, note the sunken, time-aligned, tweeter and flared bass-reflex port.

The interior of the enclosure is lined with a layer of self-adhesive felt with a thickness of 5-mm. This will effectively dampen reflections and aid in absorbing mid-range and higher frequencies. The whole enclosure will also need to be loosely filled with BAF-wadding, also in the tweeter compartment, leaving the opening for the bass-reflex port free of course. The bass-reflex port, 19-cm in length with a 5-cm diameter, needs to be flared on the end thatís mated with the back-panel, any rounding bit will do really. The pictures here illustrate how things have been implemented in the loudspeakers Iíve built. Also take notice of the rounded corners at the front to reduce baffle reflections. I actually made a total of five of these, to use in a 5.1-channel surround sound setup, accompanied by a subwoofer.

1. Introduction
2. Selecting drivers
3. Bass-reflex enclosure
4. Cross-over
5. Measurements
6. Conclusion
7. References and credits

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