Why does port length increase when two ports replace one?

14442 Views 14 Replies 8 Participants Last post by talunceford, Aug 19, 2010

Parts

Discussion Starter · Jan 28, 2010

As per title,

Just wondering why two ports are required to be longer than a single port?

For instance if I tune a cab with a single 10" port, but the port velocity is too high and I add another port, these ports are then required to be 22.5" long each?

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Moonfly

· #7 · Aug 17, 2010

The driver and cabinet size both factor into the design, and they design and built their own driver, so they dictate a lot of what the final design will be like.

We have to use off the shelf drivers, and depending on what tune you want, and what size cabinet you use, this will determine the port dimensions. Companies like SVS have a little more input in how the ports will eventually be, than you or I do. Still, it would be possible to build something similar to the the SVS Ultras using say a 12" driver. With a good 15 your going to need a huge cabinet.

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Moonfly

· #10 · Aug 18, 2010

spasticteapot said:
Not necessarily - some 15" drivers work quite well in a relatively small (~2 cubic feet) box. However, the efficiency is pretty horrible - expect to use a 1kW+ amp to get the most out of 'em.

Mike P. said:
I'm sure Moonfly was referring to ported, it would be a challenge to port a high excursion 15" driver in 2 cu.ft.

Yeah I was talking about ported. Even something like the AV15-H, which is directly targeted at small enclosures with its design, still requires in the order of 150 litres volume to become an EBS sub, more for a true LLT. Considering the same driver can work in only 40 litres sealed, then 15" LLT's or -3/-6EBS subs (like the SVS Ultras) are very very hard to get into tiny cabs, even external porting wont make the cabs tiny.

I should clear up though, US huge and UK huge do differ a little. In the UK, a 600mm cube is considered pretty large, and anything even approaching an 800mm cube would be considered huge. So while 50 litres might be considered smaller in the US than where I live, its still not that small considering.

In respect of BKnights comments, I had a play with WinISD last night, and managed to get port lengths to around a meter each with a 15" driver, its still a lot for a box though, and I think a Sonotube would be the only realistic way to build an SVS Ultra type sub with a 15" driver.

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Moonfly

· #12 · Aug 18, 2010

Ill try take a look at the model(s) tomorrow and see if I can come up with anything of use, if no one beats me to the punch.

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