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Discussion in 'Archived Threads 2001-2004' started by Sebastian, Aug 3, 2002.
I was wondering why some subs have two ports instead of one. Anyone know the reasons
Some have three. Port design is a function of port number, diameter, length, as well as flaring.
Thanks for the reply, I was looking more for what effect does it have on sound quality and freq response of the sub. Is there a sound difference between one and two ported designs?
"I was looking more for what effect does it have on sound quality and freq response of the sub. Is there a sound difference between one and two ported designs?" No, this is a design consideration. Normally the designer will opt between one large port or two smaller ones for the same tunning goal. A lot of times the physical location of the driver(s) as well as the cabinet factors in the choice.
The differences between subwoofers with one, two, three or even four ports are not distinguishable from the differences they express due to other design factors. I don't think there are subwoofers that are so similar, that you would choose one over the other because of the number of ports alone. Choosing to buy one subwoofer over another will not be restricted to the number of ports it has. There is a difference between a subwoofer with one large port and two small ports, but someone else here will need to step in and clarify. As I've said, don't base your decision on the number of ports, rather, base it on the overall subwoofer design and function. My front speakers have three ports each because they have 3 6.5" woofers each. My subwoofer, on the other hand, is sealed. I like my subwoofer
I'd suggest reading this to learn what a port does:
The number of ports, the diameter of the ports, the length of the ports and the size of the enclosure all have to be considered in order to determine what the enclosure is tuned to. What an enclosure is tuned to is very important.
There are two problems with a port that need to be avoided. Compression and port noise. I understand the later reasonably well, but not the former.
Basically as a subs output increases more air is pumped in and out of the port. If too much air is pumped in and out you get audible port noise and compression that prevents the sub from going as loud as it could. The larger the port, or the greater the number of ports the larger the amount of air being moved can be before it starts to make noise. The thing is, lots of 1" ports would not be as good as a single much larger port. As lots of 1" ports will have lots of surface area (in comparison to their crossectional area) to cause frictional loses. Using more smaller ports also doesn't result in needing shorter ports, they each need to be just as long as a larger port with equivalent cross sectional area. Which can create another problem, long narrow ports will have resonances that will color the sound.
Flared ends on the ports make it so more air has to be pumped through the ports before it becomes a problem.
But the bottom line is you end up in a catch 22. The more air you want to move through the port, the larger it's diameter needs to be. The larger it's diamter the longer it has to be to tune to the same frequency. And the smaller you make the enclosure the longer the port has to be. So it becomes impossible to fit adequit porting tuned low enough into small enclosures. So if you see a small ported sub you can be confident it won't be a big performer.
In the case of the Hsu VTF-2 and VTF-3, you can adjust the sub for either max output or extension by plugging one port and flipping a switch on the rear. Dr. Hsu's design using 2 ports allows more flexibility in optimizing a sub for either music or HT use.