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Old 11th October 2004, 08:12 AM   #1
ALFIrE is offline ALFIrE  Belgium
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Default winisd and air velocity calc

when designing a vented box in winisd, how can you tell when a vent is too small?

I'm modelling the seas L12 RCY/P in a 5 liter cabinet, wit a vent of 11.6 by 0.8 cm.

when going to the air velocity modus, I get a straight line of zero m/s... doesn't seem right to me!
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Old 11th October 2004, 10:06 AM   #2
m4dm4n is offline m4dm4n  Sweden
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how many watt's are you sending in?
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Old 11th October 2004, 10:20 AM   #3
REDSKIN is offline REDSKIN  England
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Just a thought but you are looking at the rear port-air velocity screen?
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Old 11th October 2004, 10:38 AM   #4
ALFIrE is offline ALFIrE  Belgium
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i've changes input to 100 watts, but it's all the same

yep, looking at rear port, but front is also at 0!

I entered another driver, where the graph was visible. maybe this doesn't work with self entered drivers?

my main concers was that 8 mm was a bit small for a port > any comments on this?
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Old 11th October 2004, 10:59 AM   #5
REDSKIN is offline REDSKIN  England
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I just tried it and I have no problems getting an air velocity curve.
here are the TS I'm using.
qes-.31
qms-2.69
qts-.278
fs-48
vas-6L
mms-6.5
bl-5.89659
sd-50cm^2
xmax-6mm
vd-30cm^3
pe-70w
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Old 11th October 2004, 11:44 AM   #6
ALFIrE is offline ALFIrE  Belgium
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it seems that my saved projects won't work, but wen doing a new one it is fine

when using 1 Watt input, I'm getting a bump between 50 and 60 Hz towards 7 m/s. With 70 watts, the number goes up towards 57! This seems a bit high ... If I remeber right, 17 m/s is still safe..
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Old 11th October 2004, 03:08 PM   #7
m4dm4n is offline m4dm4n  Sweden
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I've been using max 42m/s for flared ports and 30m/s for standard ports, at maximum power. But that is in subwoofer designs.
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Old 11th October 2004, 05:23 PM   #8
Ron E is offline Ron E  United States
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The standard answer is to keep it under 5% of the speed of sound - 17 meters/sec. You may be able to double this with flared ports.

This results in rather long ports in some circumstances. 1/4 the driver (frame) diameter seems to work with relatively low excursion drivers. For longer excursion drivers, you will want to use 1/3 to 1/2 of the frame diameter for best results.
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Old 11th October 2004, 09:34 PM   #9
owdi is offline owdi  United States
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7 m/s at 1watt? wow, that is a small port. I've had port noise using a 3" diameter piece of PVC with the edges sanded round at 20 m/s.

57 m/s is far too high. If you double the vent area, and double the length of the port, that will come down to 28.5m/s. Still too high unless you have some serious flares.

Have you checked the xmax graphs to see if this driver will actually move far enough to create an air velocity of 57 m/s? You may be suprised to find that you don't have 70 watts of power handling at low frequencies (especially with only 6mm of xmax).

Dan
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Old 12th October 2004, 09:34 AM   #10
ALFIrE is offline ALFIrE  Belgium
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just did a simulation with the original design of the HATT III by Tony Gee.

using a 5 liter cabinet, the seas L12RCY/P and a vent of 3.36 cm by 13,8 cm long at 57 Hz

result by 1watt is 7,14 m/s and at 50 watts 50,4 m/s

when doing a rectangular port of 11,6 by 1 cm, I get 5,46 and 38,6 m/s

since the original design by Tony has been built several times, and because I'm getting "better" values, I presume I'm overlooking sth. Still a noob here!
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