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Port length on multiple ports [message #33904]

Mon, 24 September 2001 06:28

AP
Messages: 11
Registered: May 2009

Chancellor

What happens to port length when 2 or more ports are used in the same box??

Scott

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Re: Port length on multiple ports [message #33905 is a reply to message #33904]

Mon, 24 September 2001 10:08

Wayne Parham
Messages: 18787
Registered: January 2001

Illuminati (33rd Degree)

Grab a copy of BoxPlot because it will calculate multiple ports.

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Re: Port length on multiple ports [message #33946 is a reply to message #33905]

Thu, 27 September 2001 09:52

AP
Messages: 11
Registered: May 2009

Chancellor

Thinking about a home project related to this.

Vas-151L
Qts-.39

Coffee table size box (yes, it would me my coffee table). Internal dimensions 13"x22.5"x34.5" (assuming 3/4" wood). I figure I'd end up around 155L with internal bracing. 4"x12" port. Tuned to 21 Hz. Driver and port on one end. As near as I can tell, it'll stay flat and 3db down would be around 20Hz. What do you think?

Thanks man!
Scott

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Re: BTW, it's a 12..... [message #33947 is a reply to message #33946]

Thu, 27 September 2001 09:53

AP
Messages: 11
Registered: May 2009

Chancellor

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Box tuning [message #33948 is a reply to message #33947]

Thu, 27 September 2001 11:05

Wayne Parham
Messages: 18787
Registered: January 2001

Illuminati (33rd Degree)

To calculate box tuning, you'll need to know a little more. What is the resonant frequency in free air?

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Re: Box tuning-Fs=21Hz [message #33957 is a reply to message #33948]

Fri, 28 September 2001 05:58

AP
Messages: 11
Registered: May 2009

Chancellor

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PiAlign'ed at 2 cu ft tuned to 20Hz [message #33958 is a reply to message #33957]

Fri, 28 September 2001 06:27

Wayne Parham
Messages: 18787
Registered: January 2001

Illuminati (33rd Degree)

You have a motor with these specs:

Vas=5.33 cu ft
Fts=21Hz
Qts=0.39

So PiAlign equivalents are:

Vad=5.33
Frd=21Hz
Qd=2.56

PiAlign recommends a 2 cubic foot cabinet tuned to 20Hz using either a cylindrical 5" long, 1 5/8" diameter port or a rectangular 1" x 2" x 5" long port.

You can grab a copy of BoxPlot on the Pi Speakers website to show the response of this cabinet using Thiele/Small analysis. The box you've proposed is about 5 cubic feet, and I suspect that will work just fine. The driver will probably work very well in cabinets from 1.5 cubic feet to 6 cubic feet or so, tuned to 20Hz. You can use BoxPlot to find an alignment that will give acceptable response in this size cabinet.

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