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Port calculations - 90 degree bend
Port calculations - 90 degree bend
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Old 22nd February 2012, 04:10 PM   #1
Shatronics is offline Shatronics  Denmark
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Default Port calculations - 90 degree bend

Hi DIY'ers,

I'm making a subwoofer box and due to my square ports are a bit too long for the box dimensions intended, I'm considering making a 90 degree bend, but does that effect the tuning of the box?
If so, how do I calculate the dimensions for the new port?

Regards,

Simon H.A.
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Old 22nd February 2012, 05:07 PM   #2
TheBaronGroog is offline TheBaronGroog  United Kingdom
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I'll probably go down in a blaze for this-just measure down the centre of the port and the bend shouldn't make any real difference-but I only have basic modeling software, so can't get any different tuning that might occur to model..
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Old 22nd February 2012, 05:12 PM   #3
Shatronics is offline Shatronics  Denmark
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Okay, I have a box right now with normal straight ports, so I can compare it to the new box when I've made it. Guess I'll just will go for the try.

Regards,

Simon H.A.
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Old 22nd February 2012, 08:49 PM   #4
OscarS is offline OscarS  United States
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So long as your port area is adequate enough, the center length measurement should be accurate. If port velocity is too high, you'll get chuffing and a corresponding loss of SPL.
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Old 22nd February 2012, 08:56 PM   #5
ODougbo is offline ODougbo  United States
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I would check the tuning with a resistor load - generator - voltmeter. Adjust the port length as necessary.
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Old 23rd February 2012, 03:46 PM   #6
Shatronics is offline Shatronics  Denmark
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My port velocity is not too high (according to WinISD), so it shouldn't be a problem. I think I will test the enclosure in a sound dead room that we have at my high school.
Thanks for your responses.

Regards,

Simon H.A.
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Old 23rd February 2012, 06:04 PM   #7
weltersys is offline weltersys  United States
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Quote:
Originally Posted by Shatronics View Post
My port velocity is not too high (according to WinISD), so it shouldn't be a problem.
Port velocity is a separate issue from tuning (Fb).
You can easily check the port tuning by eye, put a dot on the cone and play sine wave tones through the cabinet, the cone will have least movement at Fb.

Always best to go a little long on the port length, you can cut it down if Fb is lower than you want.

The 90 degree bend will probably lower the tuning a bit from what it would be if it were straight.
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Old 23rd February 2012, 07:46 PM   #8
ODougbo is offline ODougbo  United States
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Never heard of the dot method.

Agree with the bend lowering the tuning, but the size and lenght of the "L" would also.
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Old 23rd February 2012, 10:35 PM   #9
grecon is offline grecon  United States
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this page has helped me with a bent slot vent
Port Design
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Old 24th February 2012, 09:28 AM   #10
Shatronics is offline Shatronics  Denmark
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Great info on the link, thanks!
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