I know it is not noble nor fashionable, and that ABS piping tube is the preferred method (although newer ABS pipes- called "Coextruded ABS Cellular Core"- are lower quality with "air bubbles" inside, like the famous chocolate bar, to reduce material costs). But in a pinch (where the only thing available with the correct diameter/length is a paper roll core) and with some "modifications" to it, then it may save a small satellite 2-way vented box project. I've built numerous speaker enclosures of various sizes and complexity since 1981, all of which I still own, and using components from: JBL, E-V, Audax, Vifa, Peerless, Fane, Pioneer, Motorola, Dayton Audio, SB Acoustics, and the list goes on... Yes, its an addiction, a real challenge for the mind !, and it can't be cured...
One of the the challenges in small-size boxes (VB < 5 L.) is to fit woofer/tweeter/vent on a small front panel. I prefer front firing vents and try to use as large vent diameter as possible to minimize vent noise. This is where a paper roll or other such core may be handy if it has the required specs of diameter/length, but most probably not the strength. Once in a while such core is a bit thicker and better made than usual for no specific reason. This is the one to keep (I have about half a dozen of those in stock just in case...), but still not sturdy enough. Many paper, alu. or plastic wrap roll cores can make great ducted ports as long as they are reasonably well made and have proper dimensions. I see a lot of them here and there, some of which I keep in stock for present and future projects. As an added bonus they make nearly free ducted ports. Here's how I reinforce them when required.
Use a small brush to "paint" white glue all over the tube, inside and out, even on both ends. Let it dry for the night. Repeat same once ot twice. Now that tube is stronger, and ready to be cut slowly with a sharp Swiss or utility knife to the proper length if need be. Next, time to wrap the exterior of the tube from end to end with three + layers of utility masking tape (I use 3M's cheap brand "Tartan" for that purpose because it is more sticky and will stay on almost forever, contrary to the Blue or Green painter's tape that is made to be removed). While taping the tube make sure you're not pulling too hard on the tape to prevent changing the tube's round aspect. When done It is good enough to act as a vent in a small low-power vented box. Drill the hole in the front panel to accomodate the tube's larger outside diameter considering the layers of tape and install from inside the box just a bit tight in the hole. If the latter is a little too big you can even add layers of tape as required on the end meant to be inserted in the front panel hole. Don't forget to use caulking also on the inside of the boxe's front panel around the drilled hole/tube junction to make things air tight.
For the finishing touch to cover the appearance (from outside the box) of the masking tape in the hole holding the tube in place, here's how I proceed: when I install the tube in the front panel I don't bring the tube in perfectly flush with the outside of the front panel, instead I leave a tiny gap of about 1/16" (2mm) in order to put a fine line of white silicone (all my boxes are painted white) that will hide the masking tape and make a nice looking junction between panel hole and tube (no silicone in the vent). Moreover, the silicone on the inside and outside of the box also acts as a fastener keeping the tube well in place. In case you wonder, even if the vent tube is now a tiny bit longer inside the box because of this 1/16" (2mm) "gap", don't lose sleep over this since it will not materially affect box tuning. If you're having nightmares cut the tube 2mm shorter.
By the way, for long, thick and heavy cardboard vent tubes you may additionally nail the vent tube to front panel using small finishing nails, a punch and a small hammer. I've done that a few times: place the tube in its final location making sure it fits tightly, grab a 1" finishing nail and hammer, install nail from inside the tube to middle of front panel hole thickness, intially just enough for the nail to hold in place, then take the punch and hammer to finish the job (4 nails: top, bottom, left and right).
As a last note, in order for the ducted port to do its job properly and avoid turbulence, give it some space to "breathe" inside the box , i.e. the end of the port should be at a distance from absorption material on back panel, side panels, etc., even away from braces.
P.S. I made three pairs of these small satellite speakers and use them as stand alone units, or some in a bi-amp setup with a pair of JBL 12" 2214H bass cabinets I've also made. Have fun, I do !
Richard
Reply With Quote
Originally Posted by JeffW
