Choosing port diameter.

Jeb-D. · 30th July 2006, 06:20 AM

Any rules of thumb for choosing a port diameter? I know too narrow will cause whistling. Is there any disadvantage of going too wide? Other than port length increasing.

sreten · 30th July 2006, 12:03 PM

http://www.users.bigpond.com/bcolliso/index.htm

/sreten.

69stingray · 30th July 2006, 01:00 PM

http://www.ajdesigner.com/phpvent/su...m_diameter.php

richie00boy · 30th July 2006, 01:10 PM

Required diameter will depend on tuning frequency, and driver excursion and surface area. As frequency goes lower the required vent diameter does also.

You can never have too big a diameter really.

Jeb-D. · 30th July 2006, 04:04 PM

Quote:

Required diameter will depend on tuning frequency, and driver excursion and surface area. As frequency goes lower the required vent diameter does also.

So, as long as it is tuned to the proper frequency. Going with a wider/long port, has no audible disadvantage as opposed to a skinner/shorter port?

richie00boy · 30th July 2006, 04:07 PM

Well if you went insane with the size you would experience more midrange leakage through the open vent, but other than that, the bigger the vent area the smaller the wind noise and compression effects, distortion etc.

Notax · 18th August 2006, 02:18 PM

I got some equations for port diameter. Or simple, my correction of Xmax to Xe.

First, I calculate Xe (real excursion, depend od SPL, Sd etc.)
Looks simple, but was long time to get it. Mixed from many formulas.

Xe=k1*Sd*sqr(Re)/(BL) where k1=0.68/(0.68+Qts)+0.28

Fb=(0.383/Qts+0.142*Qts)*Fs

Dt=a*sqr(Fb*Sd*Xe) where a=(Qts/0.28)^0.8

Last is well known formula, but in original its Xmax, which is wrong, because Xmax is physical dimension, not real excursion. Xe is real excurion at some usual max. RMS power and around frequency of max. excursion (above Fb) which is 1.4-1.45*Fb. And correction factor a.

Svante · 18th August 2006, 05:16 PM

Quote:

Originally posted by richie00boy
Required diameter will depend on tuning frequency, and driver excursion and surface area. As frequency goes lower the required vent diameter does also.

You can never have too big a diameter really.

Well, if it leads to a too long port, you can.

Notax · 18th August 2006, 06:34 PM

Quote:

Originally posted by Svante

Well, if it leads to a too long port, you can.

Like this case. Peerless XLS 12" in BR enclosure.

XLS 12"

Netto volume is 38-41 L, Dt=75-95 mm, and Fb=26-28 Hz. So, in that little box you must make a tunnel as long as 450-600 mm. Ouch!

Maybe:

30th July 2006, 06:20 AM	#1
Jeb-D. diyAudio Member Join Date: Nov 2005 Location: SoCal	Choosing port diameter. Any rules of thumb for choosing a port diameter? I know too narrow will cause whistling. Is there any disadvantage of going too wide? Other than port length increasing.

30th July 2006, 01:00 PM	#3
69stingray diyAudio Member Join Date: Apr 2005 Location: NH	http://www.ajdesigner.com/phpvent/su...m_diameter.php __________________ Audio DIY Page FOLLOWMY529.COM - Subscribe and follow the performance of my daughter's 529 College Saving Account.

30th July 2006, 01:10 PM	#4
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Required diameter will depend on tuning frequency, and driver excursion and surface area. As frequency goes lower the required vent diameter does also. You can never have too big a diameter really. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

30th July 2006, 04:07 PM	#6
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Well if you went insane with the size you would experience more midrange leakage through the open vent, but other than that, the bigger the vent area the smaller the wind noise and compression effects, distortion etc. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

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30th July 2006, 12:03 PM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	http://www.users.bigpond.com/bcolliso/index.htm /sreten.

18th August 2006, 02:18 PM	#7
Notax diyAudio Member Join Date: Jun 2004 Location: Belgrade	I got some equations for port diameter. Or simple, my correction of Xmax to Xe. First, I calculate Xe (real excursion, depend od SPL, Sd etc.) Looks simple, but was long time to get it. Mixed from many formulas. Xe=k1Sdsqr(Re)/(BL) where k1=0.68/(0.68+Qts)+0.28 Fb=(0.383/Qts+0.142Qts)Fs Dt=asqr(FbSdXe) where a=(Qts/0.28)^0.8 Last is well known formula, but in original its Xmax, which is wrong, because Xmax is physical dimension, not real excursion. Xe is real excurion at some usual max. RMS power and around frequency of max. excursion (above Fb) which is 1.4-1.45Fb. And correction factor a.

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