I am buiding an 18" sub to add to my PA system for live music. I
purchased the driver from an online vendor. Parts Express sells the
same driver and has a recomended design produced by anonymous
software. I'm assuming that the design is adequate.

My question is regarding the port size. The suggested port diameter
is 4.5" @ 2.7" long. The closest manufactured port I can find is 4"
dia by 4" long (I can cut it to length). Standard PVC pipe steps up
from 4" to 6".

Would a 4" dia tube work OK or would it seriously affect performance?

If I can use the 4" dia tube, would I need to shorten the length?

Should I use a 6" diameter tube and alter the length?

Am I concerned about something I shouldn't be concerned about?

I've included some of the design and speaker parameters below. I
would appreciated any insights.



---Box---
Vb = 9.029 cu.ft
V(total) = 9.141 cu.ft
Fb = 35 Hz
F3 = 36.34 Hz
Fill = minimal

--Vents--
No. of Vents = 2
Vent shape = round
Vent ends = one flush
Dv = 4.5 in (port diameter)
Lv = 2.71 in (port length)

--Driver Parameters--
Fs = 27.4 Hz
Qms = 5.59
Vas = 14.9 cu.ft
Xmax = 5.5 mm
Qes = 0.3
Re = 5.55 ohms
Le = 1.57 mH
Z = 8 ohms
Pe = 600 watts

"Joel Ramsey" wrote in message
m...
I am buiding an 18" sub to add to my PA system for live music. I
purchased the driver from an online vendor. Parts Express sells the
same driver and has a recomended design produced by anonymous
software. I'm assuming that the design is adequate.

My question is regarding the port size. The suggested port diameter
is 4.5" @ 2.7" long. The closest manufactured port I can find is 4"
dia by 4" long (I can cut it to length). Standard PVC pipe steps up
from 4" to 6".

Would a 4" dia tube work OK or would it seriously affect performance?

2 x 4 inch ports should be OK for a single 18" driver.

If I can use the 4" dia tube, would I need to shorten the length?

You would need to make them about an inch shorter. Just off the top of my
head.

Stephen

Parts Express. They are near me and I visit their warehouse often.

The port length depends on a few variables. They sell speaker design books
and software that can be of great use. Be careful on such large speakers
moving such large amount of air. The velocity in a smaller port will be
higher and can cause turbulence noise. Check the Web, someone may have the
size you needed or flared ports for less noise.
John

"Joel Ramsey" wrote in message
m...
I am buiding an 18" sub to add to my PA system for live music. I
purchased the driver from an online vendor. Parts Express sells the
same driver and has a recomended design produced by anonymous
software. I'm assuming that the design is adequate.

My question is regarding the port size. The suggested port diameter
is 4.5" @ 2.7" long. The closest manufactured port I can find is 4"
dia by 4" long (I can cut it to length). Standard PVC pipe steps up
from 4" to 6".

Would a 4" dia tube work OK or would it seriously affect performance?

If I can use the 4" dia tube, would I need to shorten the length?

Should I use a 6" diameter tube and alter the length?

Am I concerned about something I shouldn't be concerned about?

I've included some of the design and speaker parameters below. I
would appreciated any insights.



---Box---
Vb = 9.029 cu.ft
V(total) = 9.141 cu.ft
Fb = 35 Hz
F3 = 36.34 Hz
Fill = minimal

--Vents--
No. of Vents = 2
Vent shape = round
Vent ends = one flush
Dv = 4.5 in (port diameter)
Lv = 2.71 in (port length)

--Driver Parameters--
Fs = 27.4 Hz
Qms = 5.59
Vas = 14.9 cu.ft
Xmax = 5.5 mm
Qes = 0.3
Re = 5.55 ohms
Le = 1.57 mH
Z = 8 ohms
Pe = 600 watts

(Joel Ramsey) wrote in message om...
I am buiding an 18" sub to add to my PA system for live music. I
purchased the driver from an online vendor. Parts Express sells the
same driver and has a recomended design produced by anonymous
software. I'm assuming that the design is adequate.

My question is regarding the port size. The suggested port diameter
is 4.5" @ 2.7" long. The closest manufactured port I can find is 4"
dia by 4" long (I can cut it to length). Standard PVC pipe steps up
from 4" to 6".

Would a 4" dia tube work OK or would it seriously affect performance?

A 4" tube would work just fine. The difference in effective area
is only 20%.

If I can use the 4" dia tube, would I need to shorten the length?

Yes, you'd have to shorten it by roughly 20%

Should I use a 6" diameter tube and alter the length?

If you did, you'd have to make it over twice as long. If
you have the room for that, go for it.

Thank you for responding. The info helps.

Parts Express sells tapered tubes as well.

"Joel Ramsey" wrote in message
m...
I am buiding an 18" sub to add to my PA system for live music. I
purchased the driver from an online vendor. Parts Express sells the
same driver and has a recomended design produced by anonymous
software. I'm assuming that the design is adequate.

My question is regarding the port size. The suggested port diameter
is 4.5" @ 2.7" long. The closest manufactured port I can find is 4"
dia by 4" long (I can cut it to length). Standard PVC pipe steps up
from 4" to 6".

Would a 4" dia tube work OK or would it seriously affect performance?

If I can use the 4" dia tube, would I need to shorten the length?

Should I use a 6" diameter tube and alter the length?

Am I concerned about something I shouldn't be concerned about?

I've included some of the design and speaker parameters below. I
would appreciated any insights.



---Box---
Vb = 9.029 cu.ft
V(total) = 9.141 cu.ft
Fb = 35 Hz
F3 = 36.34 Hz
Fill = minimal

--Vents--
No. of Vents = 2
Vent shape = round
Vent ends = one flush
Dv = 4.5 in (port diameter)
Lv = 2.71 in (port length)

--Driver Parameters--
Fs = 27.4 Hz
Qms = 5.59
Vas = 14.9 cu.ft
Xmax = 5.5 mm
Qes = 0.3
Re = 5.55 ohms
Le = 1.57 mH
Z = 8 ohms
Pe = 600 watts