dumb question on ports and volume

mitch808 · 7th June 2004, 09:37 PM

Does the volume of the port affect the overall volume of the enclosure?

i.e. If I have a 1 cu ft ported box and the port is 2"x10". I would have to make the box volume roughly .018 cu ft larger to make up for the volume of the port? (this is all hypothetical and I'm just trying to get a understanding of what I'm doing)

Guss · 7th June 2004, 09:42 PM

Sure, you must substract the volume of the port from your total enclosure volume.

1 cubic. + your port volume (2x(3.1416) x 10) = total cab volume

Goss

mitch808 · 7th June 2004, 09:44 PM

Fantastic, thank you.

BillFitzmaurice · 7th June 2004, 10:12 PM

The driver also takes up space that must be accounted for. A good rule of thumb with a VB is to make it 10 to 20% oversize. If flat response is absolutely critical you can always put bricks inside the box to make it smaller; you can't add a dormer to the attic if you need more room later.

Also, don't go with a rectangular ducts. Go with the requisite number of round ducts of equivalent area and use those that are flared at both ends; they have been proven far superior in both higher SPL and lessened distortion than non-flared ducts.

mitch808 · 7th June 2004, 10:14 PM

I knew about the driver volume already. Although I didn't know about the slotted ports to be inferior to flared/rounded ports?

Hmm, more to think about. Thank you

Guss · 7th June 2004, 10:48 PM

Smaller ports are more accurate than bigger ones because there is more interaction between the port and the air that flows through it, regardless of the amount and the speed of the air at this moment. Slotted ports are often larger and longer than any equivalent round vent to get satifiying results.

The diam to length ratio is to be considered too if you want better results. A ratio of 3/1 is a good rule of thumb to apply to moderated values and it should yeld more than acceptable results. It doesn't mean a port with a ratio of 5/1 sounds bad, many of us may ignore it, but with a too long port you may end up with an ''Helmholtz resonator''. All those informations have been discussed in earlier threads about port ratios/placement so a little search might be revealing for you.

Goss

7th June 2004, 09:37 PM	#1
mitch808 diyAudio Member Join Date: Apr 2004 Location: Kalifornia	dumb question on ports and volume Does the volume of the port affect the overall volume of the enclosure? i.e. If I have a 1 cu ft ported box and the port is 2"x10". I would have to make the box volume roughly .018 cu ft larger to make up for the volume of the port? (this is all hypothetical and I'm just trying to get a understanding of what I'm doing)

7th June 2004, 10:12 PM	#4
BillFitzmaurice Banned Join Date: May 2004 Location: New Hampshire	Don't forget the driver volume The driver also takes up space that must be accounted for. A good rule of thumb with a VB is to make it 10 to 20% oversize. If flat response is absolutely critical you can always put bricks inside the box to make it smaller; you can't add a dormer to the attic if you need more room later. Also, don't go with a rectangular ducts. Go with the requisite number of round ducts of equivalent area and use those that are flared at both ends; they have been proven far superior in both higher SPL and lessened distortion than non-flared ducts.

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7th June 2004, 09:42 PM	#2
Guss diyAudio Member Join Date: Jun 2003 Location: Montreal	Sure, you must substract the volume of the port from your total enclosure volume. 1 cubic. + your port volume (2x(3.1416) x 10) = total cab volume Goss

7th June 2004, 09:44 PM	#3
mitch808 diyAudio Member Join Date: Apr 2004 Location: Kalifornia	Fantastic, thank you.

7th June 2004, 10:14 PM	#5
mitch808 diyAudio Member Join Date: Apr 2004 Location: Kalifornia	I knew about the driver volume already. Although I didn't know about the slotted ports to be inferior to flared/rounded ports? Hmm, more to think about. Thank you

7th June 2004, 10:48 PM	#6
Guss diyAudio Member Join Date: Jun 2003 Location: Montreal	Smaller ports are more accurate than bigger ones because there is more interaction between the port and the air that flows through it, regardless of the amount and the speed of the air at this moment. Slotted ports are often larger and longer than any equivalent round vent to get satifiying results. The diam to length ratio is to be considered too if you want better results. A ratio of 3/1 is a good rule of thumb to apply to moderated values and it should yeld more than acceptable results. It doesn't mean a port with a ratio of 5/1 sounds bad, many of us may ignore it, but with a too long port you may end up with an ''Helmholtz resonator''. All those informations have been discussed in earlier threads about port ratios/placement so a little search might be revealing for you. Goss

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