The long version...links to part suppliers at the bottom
I was skeptical when I first saw the Dayton 8" Quatro but very impressed when I heard it. This sub is a good match for my small tube speakers. The box fits under my computer desk in front of my chair but it plays loud enough to fill a much larger space.
Dayton claims a 9.5mm xmax excursion and output down to 36 Hz in a ported box. A quick test with my old signal generator produced a lot of output in this region for such a small speaker. I was happy to hear some deep bass notes on the Enya "Watermark" CD that are often lost on home stereos and ear buds.
The driver itself has a fast rolloff above 100Hz and you might be able to get away without a crossover if you have to. Driving it hard with a big amp produced some port turbulence noise around the tuning frequency. A larger diameter tube would probably help but that would have to be longer and use a bend in my box. I don't notice the port noise with a small amp.
The speaker impedance is 4 ohms and works well with the Keiga 2.1 plate amp which has a 50w mono sub amp. You don't need the optional boost switch at 40 Hz. You can use a much larger amp but watch for over excursion. I would recommend an electronic high pass filter to cut off the signal below 30 Hz.
I use 16 guage stranded zip cord for speaker wire most of the time. It comes in black, white and brown with a raised ridge on one side to indicate polarity. For longer runs I use 14 guage. I'd rather spend my money on better audio components than designer speaker cables. I get a better return.
Construction
I expect to drag this box around with me so I built it out of 3/4" baltic birch plywood and applied a polyeurethane finish. This plywood is very dense and free of voids. It's imported from Russia and carried by a local lumber store where I live. I have used something called "Finland Birch" in the past and that was very good too.
I used yellow wood glue, dado joints and giant rubber bands made from old bicycle innertubes to hold the pieces tight while drying. I cut and tied the tubes to get bands that produced enough tension. Polyeurothane glue works very well too but expands as it cures. That may require pipe clamps to hold all the joints so the glue doesn't push them apart as it expands.
I used an adjustable dado blade to cut 3/8"x3/4" dados on the sides. Refer to the diagram above to see where they were located. These are stronger than simple butt joints and align the pieces while the glue dries. I put blue tape at the glue boundaries to keep the wood clean and then laid out the pieces on the floor and put glue on the joint edges. I assembled the box and used the rubber bands to hold it together. I put weight on the top and shims under the bottom to keep them pressed into the dados on the sides.
The next day I removed the rubber bands and protective tape, used various sanders and then a router to round the edges. I applied polyeurethane before doing anything else to protect the freshly sanded surface. Extra coats can be applied any time after that. I like the look and durability of oil based polyeurethane but I recommend using a resperator with a chemical cartridge while applying it. I would like to try the new polyacrylic finishes sometime. For a fine furniture look you may want to use a Danish oil instead.
The speaker is fastened by 10x32 machine screws that are threaded into T-nuts inside the cabinet. I used aluminum window brackets to hold the grill onto the speaker frame with separate screws and T-nuts. The box panels are small and the plywood is very stiff so I didn't bother to add interior braces. I put a single piece of carpet pad on the inside of the back panel to stop some cabinet resonance I was hearing leak out the port. I screwed small rubber feet on the bottom panel to keep it off the floor.
It makes sense to cut a hole for the speaker before assembling the box so you can drive in T-nuts on the inside with a hammer. Once the box is assembled you have to use a different method. I used a grade 5 hex cap screw and a large fender washer on the outside to screw in the T-nut on the inside. My hand drill has torque settings and plenty of power.
Trial and error...
Dayton recommends a 0.75 cu-ft box. I built a slightly larger box to allow space for things I might want to add later. The net volume is currently about 0.85 cu-ft but will be reduced when I use a larger dia port or add an internal amp. I may have to adjust the port length when I do that.
Dayton recommends a 2.5" dia port, 13.9" long. In my box that would require a long tube with a 90 deg bend to keep it away from the back panel. A 90 deg pvc bend has sharp internal edges that will add to port noise. A long tube also takes up a lot of volume. If I find a 2.5" bend that is smooth internally I'll try it.
I decided to use a 2" dia flared port that would not require a bend due to it's smaller surface area. Smaller diameter ports have more port noise but flared ports are supposed to reduce that. This is a commercial product made up of 3 parts: external flare; center tube; internal flare. You cut the center tube to get the desired length. This works fine in most situations but if you drive it hard near the tuning frequencey you can hear a little bit of whistle. If I build another 8" sub I'll compare it with a 2.5" dia port.
Links
Last update: March 15, 2006