when porting a speaker

  could i use diffrent sized ports in the same box would there be an advantage to tuning freq " 6x1 3x2"

How much theory and practical knowledge do you want to learn? There's quite a bit...

Ports on a bass reflex speaker are meant to enhance the low frequencies near the bass driver's F3, or resonant frequency. Each port is calculated to resonate in a narrow band near that F3, as close as the box and driver characteristics will allow. In the case of what you are hypothesizing, 6x1 (6Dia.x1L) and 3x2 (3Dia.x2L), the lengths are backward. Almost always, the smaller port is shorter. This is because the mass of air is smaller and needs less room to resonate at the particular frequency. If you elongate the smaller port, the resonant frequency will rise or cause turbulence which will destroy any advantage the port may have had.

Also, you need to be aware of making a port too small as you can introduce "wind" noise at certain freqencies. This happens when the woofer is trying to push large amounts of air through a poorly sized port. The air at the frequencies involved should flow freely, not be restricted to the point of causing turbulence. Think 4" pvc pipe vs. garden hose vs. drinking straw. Try to push the same amount of air through them and see which one makes the most "air" noise.

With multiple ports, you are dividing the acoustic energy available to be harnessed by each individual port. Add to the fact that you are using different cross-sectional areas and you get an imbalance in pressures inside the cabinet. The smaller port represents a greater impedance and hence produces less output. Of course, if you open up the port areas enough, there won't be any resonance from them and they will make the box act as if it is an infinite baffle.

My suggestion is that if you want to use multiple ports, make sure your driver has the energy to utilize them (look for larger Xmax ratings) and make the ports the same diameter. Changing the length of one of them will allow you to tune the box to multpile different frequencies without creating much of an imbalance inside.

Qa
andybuda (author)  Quercus austrina6 years ago
thank for that. the port iv used was 1 dia x 3L maybe 4"L of an older set of speakers they have a small fin that runs through the dia at the front i dont know if this is to cut down wind noise or just decorative, iv have seen ports with a inverted golf ball affect on them b+w speakers i think this was to cut down the port noise.
im going to test the speakers later they are very sold and have used a fooring as a vaneer on them. bit disapointed with the mitered corners alot of time and effort went in to sanding them so they were just right only to have the corners flare with the wood glue. so iv filled with wood filler and now im stuck trying to find a touch up crayon of the same colour.
iv put a concret slag inside them both and carpet and braced the insides and some l e d s on a terminal at the back "well y not"