Subwoofer

At AU$245 (or US$115), an Adire Audio Shiva driver unit is really not that heavy on the budget until I remember that I'm a jobless, fulltime student, which makes a DIY subwoofer all the more practical. Besides, after having read a lot about loudspeakers, I refuse to spend my savings on retail loudspeakers; much less retail subwoofers.

I had planned to make the construction significantly easier by using Formatube/Sonotube as the enclosure. But I changed my mind when I found out it would cost AU$60 to have the tube delivered. I decided the money would be better spent on a cordless drill since I haven't got one yet. So, the enclosure is of vented-box type.

1. Project Goals

a. Minimal wood cutting

- I started this project without any power tools; a jigsaw and a cordless drill was all my budget could allow for. So I had to come up with enclosure parts dimensions which would require minimal cutting of pre-cut wood panels.

b. Possibility of recycling materials

- Realizing my budget only allows for a box that is 16mm thick, I did not bother putting cross braces so that it could be recycled easier. The box itself is large enough that when torn down, it can be recycled into, say, a pair of bookshelf enclosures. In the near future, Sonotube/Formatube will be used.

c. Highest possible performance

- Of course, reasonable performance is a design goal.

2. Alignment

I decided that bass extension was important, therefore I used the EBS alignment. Adire Audio recommends a box volume of 143l tuned to 18Hz, which is rather awkward to realize when quality flared ports are not available locally.

3. Enclosure

When I started this project, I knew I wouldn't have enough savings left to purchase a circular saw, so I chose box dimensions that would minimise wood cutting, which in turn minimises wobbly panel edges when only a cheap jigsaw is available. Luckily, 600mm by 900mm MDF panels are available at our local hardware store. Two of such panels made for the sides of the enclosure, while I only had to use my jigsaw four times to cut the front, back, top and bottom panels. Twelve 42mm by 42mm pine sticks make up the corner braces, which in turn were glued and screwed to the MDF panels. If you're reading this and looking for a cheap jigsaw, STAY AWAY from the NRG Jigsaw -- yes it's cheap, but the blade wobbles by as much as 2mm side to side!

4. Ports

As was already mentioned, quality flared ports are difficult to find here down under, so I had to use cardboard mailing tubes for ports. 4-inch flared ports are available at Jaycar Electronics, but I wouldn't pay more than AU$2 for their ports. To minimise port noise and resonance, I settled for two 25-inch long ports each of which are 90mm in diameter. Both ports tuned the box to 17Hz (+/- 1Hz).

5. Quick Simulation (anechoic)

6. Measurements

soon, I hope!

7. List of materials

8. Pictures

	Here is a picture with the top panel in place but not glued yet. The final box houses 3 Polyester sheets instead of the planned 4 sheets to give the ports some room to breath.
	The box can be positioned in any way so long, of course, as the speaker terminals are not visible.
	I know I should have given the screws some pine or plywood to bite on to, but this box won't last a couple of months anyway, so I didn't bother.
	I didn't have to brace the ports since they were light and strong enough to be mounted just like so.
	Port noise is inaudible, although I haven't really tried pushing the Shiva to its mechanical limits.