Any minimum distance from driver to port?

Circlotron · 26th December 2002, 12:02 PM

At the moment I am considering building a pair of boxes approx 110cm x 50cm x 40cm with an 8 inch driver at one end of the 40 cm x 110cm face. Does it make very much difference where the port is located? The most convenient place for me would be either on the 40cm x 50cm side adjacent to the driver or on the front right next to it. The box is to be laying on it's side so it would be 110cm wide, 40cm high, 50cm deep.

Actually, seeing the driver and port output are in phase at resonance, how would it be if the driver was encircled by 4 to 6 small ports so that the two sound sources were concentric? Worthwile?

ThomasW · 26th December 2002, 03:45 PM

There is too much air resistance with multiple small ports. It's best to use a single large port

lieven · 26th December 2002, 10:09 PM

try the onken-style
1 big port is easiest, but not the only way.
IMHO, Q-factor of 1 big port is high, so one get's more spectacular result but in a much narower frequency-spectrum compared to onken or different tuned pipes with the same resulting airflow resistance than 1 big pipe.

Compare it to the sound of 1 big exhaust pipe for a car, or multiple ones.

on this site is a onken calculator

http://www.mhsoft.nl/SQL7/ViewDownloadFiles.asp

Circlotron · 27th December 2002, 10:39 PM

...so that anyone that hasn't seen it might be able to tell me about port location...

pinkmouse · 27th December 2002, 11:23 PM

It's a tweaky answer I'm afraid...

Port position is not normally a problem, because at the wavelengths involved, a port would have to be metres away from the driver to affect the response. But depending on you cabinet/driver/port/stuffing interactions, sometimes placing a port on the side or rear of a box will reduce out of band and turbulence noises, simply because they are not firing towards you.

So it's the old "build a test box and try it" answer, sorry

As for multiple ports all tuned the same, I personally have never heard any difference other than more port noise. Unless you stagger tune the ports, which I don't think is simulatable( new word?

) in normal software, and I have only done it by trial and error.

26th December 2002, 12:02 PM	#1
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	Any minimum distance from driver to port? At the moment I am considering building a pair of boxes approx 110cm x 50cm x 40cm with an 8 inch driver at one end of the 40 cm x 110cm face. Does it make very much difference where the port is located? The most convenient place for me would be either on the 40cm x 50cm side adjacent to the driver or on the front right next to it. The box is to be laying on it's side so it would be 110cm wide, 40cm high, 50cm deep. Actually, seeing the driver and port output are in phase at resonance, how would it be if the driver was encircled by 4 to 6 small ports so that the two sound sources were concentric? Worthwile? __________________ Best-ever T/S parameter spreadsheet. http://www.diyaudio.com/forums/multi...tml#post353269

26th December 2002, 03:45 PM	#2
ThomasW diyAudio Member Join Date: Oct 2001 Location: 5280'	There is too much air resistance with multiple small ports. It's best to use a single large port __________________ Cult of the Infinitely Baffled (Resource for IB sub builders)

27th December 2002, 10:39 PM	#4
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	Just pushing this post to the top of the stack again... ...so that anyone that hasn't seen it might be able to tell me about port location... __________________ Best-ever T/S parameter spreadsheet. http://www.diyaudio.com/forums/multi...tml#post353269

27th December 2002, 11:23 PM	#5
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	It's a tweaky answer I'm afraid... Port position is not normally a problem, because at the wavelengths involved, a port would have to be metres away from the driver to affect the response. But depending on you cabinet/driver/port/stuffing interactions, sometimes placing a port on the side or rear of a box will reduce out of band and turbulence noises, simply because they are not firing towards you. So it's the old "build a test box and try it" answer, sorry As for multiple ports all tuned the same, I personally have never heard any difference other than more port noise. Unless you stagger tune the ports, which I don't think is simulatable( new word? ) in normal software, and I have only done it by trial and error. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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26th December 2002, 10:09 PM	#3
lieven diyAudio Member Join Date: Aug 2002 Location: Belgium	try the onken-style 1 big port is easiest, but not the only way. IMHO, Q-factor of 1 big port is high, so one get's more spectacular result but in a much narower frequency-spectrum compared to onken or different tuned pipes with the same resulting airflow resistance than 1 big pipe. Compare it to the sound of 1 big exhaust pipe for a car, or multiple ones. on this site is a onken calculator http://www.mhsoft.nl/SQL7/ViewDownloadFiles.asp

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