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Old 14th February 2013, 08:45 PM   #1
krafty is offline krafty  Brazil
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Join Date: Jul 2012
Default Port location on box / Multiple Ports

I have this current situation:

Enclosure (4,1 Liters)
224mm (h)
142mm (w)
142mm (d)

Driver 1
102mm or 4"

Driver 2 Piezo Tweeter
62mm or 2.5"

After calculating the right parameters for Driver 1, I found out that its EBP is around 155Hz.

WinISD suggests that I should have a port below Driver 1:

102mm wide tube (same size of the Driver 1) being 98mm long OR
a 102 x 102mm squared port with about the same length.

The issue is that I don't have any space for that on the front.
What are my options here?

a) Don't mess with it anymore and leave it as sealed design.

b) Make the same suggested dimensions port on the back of the enclosure
(if that is the case, up or downwards the enclosure).

c) Make the same suggested dimensions port on the side on symmetric sides of enclosure (outwards).
(again, upwards or downwards the enclosure)?

c) Make multiple ports with PVC on the front until the port area is satisfied.
(if that is the case, how many, say 2" tubes, should I have on the front and how long should them all be to match the suggested WinISD dimension).
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Old 14th February 2013, 10:57 PM   #2
Dissi is offline Dissi  Switzerland
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Join Date: Sep 2012
Location: Winterthur
Quote:
Originally Posted by krafty View Post
WinISD suggests that I should have a port below Driver 1:

102mm wide tube (same size of the Driver 1) being 98mm long OR
a 102 x 102mm squared port with about the same length.
Hard to believe. A round port of 35 mm diameter and 100 mm length seems more realistic to me.
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Old 14th February 2013, 11:40 PM   #3
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Location: Western Sydney
a 4" port for a 4" driver - you're joking, right??? a 4" driver simply can't pump that much air - follow Dissi's advice & use a much smaller diameter pipe...
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 15th February 2013, 12:17 AM   #4
krafty is offline krafty  Brazil
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Join Date: Jul 2012
No, I am not joking...
It seems then that the software has a bug.
Anyways I feel more relieved that I just need to make a front 35mm port 10cm long.

Please take a look at the WinISD screens.

Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
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Old 15th February 2013, 12:39 AM   #5
Dissi is offline Dissi  Switzerland
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Join Date: Sep 2012
Location: Winterthur
You have a port diameter of 10.2 cm (this seems to be the default value of WinISD) and the program calculates a length of 98.27 cm (almost 1 meter!). Simply edit the diameter to 3.5 cm and see what happens to the length...
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Old 15th February 2013, 12:58 AM   #6
krafty is offline krafty  Brazil
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Join Date: Jul 2012
I changed the diameter to 3,5cm, and I got a length of 9,89cm.
Curiously the numbers are related since 9,89 x 10 is almost the first value given.

I wonder what the software did here. Bug? Misinterpretation?
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Old 15th February 2013, 01:04 AM   #7
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Join Date: Feb 2002
Location: Western Sydney
re:'It seems then that the software has a bug' no- it's just that it calculates for the worst case scenario, e.g. a huge PA system, where port chuffing may be an issue. For most home systems it is not a problem. Like any tool, you need to learn how to use it...
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 15th February 2013, 01:10 AM   #8
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Location: MN
WinISD does not attempt to optimize the port dimensions, it just sets 10.2cm every time and calculates the length for that diameter. It doesn't try very hard to optimize much of anything automatically, really. You're intended to increase the signal level setting while watching the excursion plot, see what level you can reach for the tuning you chose, check the airspeed at your max level, adjust the port diameter, check the length, tweak the tuning or cabinet size, do it all over, etc.

Last edited by dumptruck; 15th February 2013 at 01:15 AM.
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Old 15th February 2013, 01:26 AM   #9
krafty is offline krafty  Brazil
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Join Date: Jul 2012
I don't understand much about this part... tuning part...

How am I supposed to tune this?

Isn't it just ok for me to go with the 35mm x 100mm port on the middle/side of the front face or does it have to be below the main driver?
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Old 15th February 2013, 01:56 AM   #10
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Join Date: Feb 2002
Location: Western Sydney
you can put the port wherever you like.
Re: tuning, you change the box size and frequency until you get the shape of frequency response you want/like. THEN you chose the port size, so, you've already tuned the box....
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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