Test Ports and Boxes
This page provides details on the test ports
and test boxes used in the flared ports turbulence tests.
The WinISD project files for the alignments are provided at the end of the page
For round one of the testing , seven test ports were built
The ports are made from PVC pipe, with a 270mm flange at each end. One or more smaller supporting rings are utilised, depending on the construction of the actual flare.
The MDF pieces were glued together with PVA glue, and the PVC pipe was glued into the MDF with epoxy resin.
The mounting end of the flare has a bolt pattern the same as a 10 inch driver, and is stepped so that the flare lines up with the inside face of the box.
Round one ports
The ports have a stepped mounting flange so that they line up flush with the inside face of the box, as shown in this picture.
Inside view of flush mounting
For round two of the testing, another eight ports were built.
The same construction method was employed for the round two ports, except that a larger 360mm mounting flange was required
The eight 86mm ports - flare radii of 0 10 25 35 50 63 & 71mm
The remaining round two ports 100/13 100/52 100/64 152/13 152/25 & 100/75
Several different test boxes were built to test the range of flared ports
To achieve a high enough velocity to test the larger ports, the size of the test box was increased as the port size increased, but there were several conflicting principles:
- The port had to flow enough air to generate turbulence with the largest flare fitted
- The tuning frequency for the port should be in the normal operating range of a subwoofer - 30hz was chosen
- The port shouldn't be too short, which might lead to an "all flare and no port" situation. To have a reasonable length straight section when testing large flares, a small box is desirable
- To have a high enough airspeed to test larger flares, a large box is desirable
The solution was to use several different sized boxes.
Round one tests used a 50litre box and had a pair of 10inch drivers driven by the Jaycar 350w amplifier. Into the 7ohm load presented by the two drivers in series, it delivers up to 240w.
The test port is mounted externally and is forward firing, whilst the drivers are located on each side.
Foam gaskets were used under the drivers and the port. The port was mounted with eight roofing screws, which, along with a cordless drill, made changeover time much easier.
Round one test box sitting on top of "Blast Furnace" sub, utilising its amplifier
Round two tests used a 100litre box which started life as the very first subwoofer I built. Four 10 inch drivers mount to the sides and a 255mm opening for the port is at the front. An identical opening at the top allows fitting of a plain plate, a 50 litre add-on box, or a 30 litre reducing cylinder. Both openings have foam gaskets and eight studs - this proved much more durable than the roofing screws used with the round one tests
100 litre test box with 30 litre cylinder fitted, reducing volume to 70 litres
Test box with add-on box to give 160 litres