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Old 16th May 2013, 05:53 PM   #41
satx is offline satx  United States
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What is an acceptable rear port air velocity to shoot for?

Another option for port could be two triangle corner vents. Any thoughts on this style of port?

Evan
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Old 16th May 2013, 05:54 PM   #42
satx is offline satx  United States
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What is an acceptable rear port air velocity to shoot for?

Another option for port could be two triangle corner vents. Any thoughts on this style of port?

Evan
55 feet per sec. or less. Is this correct?
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Old 16th May 2013, 06:46 PM   #43
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What is an acceptable rear port air velocity to shoot for?

Another option for port could be two triangle corner vents. Any thoughts on this style of port?

Evan
This is a great resource, study and understand how it applies to your models...

Porting at Subwoofer-Builder.com

I would recommend (as a VERY rough figure) 20 m/s at max output once your high pass filter is taken into account, with flares.
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Old 17th May 2013, 12:53 AM   #44
satx is offline satx  United States
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Thanks for the link, I'll take a look. That's something I'm really not too confident about. The effects of porting and enclosures, resonances, flares, etc.
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Old 17th May 2013, 03:36 PM   #45
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Thanks for the link, I'll take a look. That's something I'm really not too confident about. The effects of porting and enclosures, resonances, flares, etc.
Doouble checked my model and see that I have a predicted peak of about 25 m/s around tuning, powered to xmax, with the highpass filter. Consider that it's a port equivalent to a 7" diameter pipe and it's at 35 hz, that's quite a bit of output. I'm sure there's some port compression and port noise at max output, but with the system going at 110db in room it's not noticeable. I've run tone sweeps at about 6-8mm one way max displacement an noticed no real noise from the port at tuning, that would figure at about 12-15 m/s.
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Old 17th May 2013, 03:41 PM   #46
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Another option for port could be two triangle corner vents. Any thoughts on this style of port?
I have not seen a compeling reason to use triangle ports in most designs, the area to parimeter ratio is poor. They are used mainly in PA subs where they have a big box and the port is fairly short, extending only about half the length of one wall. I prefer a slot port of you are going to bring the port the entire length of the wall, since it's easier to make a 90 deg transition on the internal end. Or a large round port if you have tons of space.
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Old 17th May 2013, 04:44 PM   #47
satx is offline satx  United States
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So I should figure air velocity at max power? That's what I figured, but then someone on I think Hometheatershack said that people don't use more than i think 168 watts with subwoofers so you should get port vel. with this power input.

Evan
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Old 17th May 2013, 09:36 PM   #48
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Calculate the velocity at X-Max as this is really as high as you want to operate the speaker.
Some would push way beyond that, towards X-Lim.
But X-Lim(it) is where something hits and often it is destructive, plus the THD goes way up beyond X-Max or even a little before it.

Dave
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Old 18th May 2013, 01:43 AM   #49
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Thanks dave
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Old 18th May 2013, 04:14 AM   #50
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Calculate the velocity at X-Max as this is really as high as you want to operate the speaker.
Some would push way beyond that, towards X-Lim.
But X-Lim(it) is where something hits and often it is destructive, plus the THD goes way up beyond X-Max or even a little before it.

Dave
Dave,

Should I calculate velocity at x-max even if I don't plan to use that much power? The Dayton HO-15 reaches x-max with 800W input; I only plan on using 300-500 watts. Of course that's RMS not peak.

Thanks,
Evan
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