i need more help with ports than GW

[asoprs]

I am trying to come up with a simple 2-way design with a ported box. Being a beginner, i was using win isd to get a box volume, port, etc. looking at several small ( 4-6in) woofers by dayton and Hi-Vi, win isd would return small boxes (good) with extremely long ports (bad). by long ports, i mean greater than a meter. What am i doing wrong?

I have used this program with single driver designs with good results.

thanks

tom

 

[69stingray]

What drivers are you looking at?

Sometimes with a really long port, you can use two (2) smaller ports. The two smaller ports are shorter but sometime not by much.

NOTE: When calculating the length for dual ports, be sure to cut the internal box volume in half.

 

[69stingray]

Here are some calculations I have for a 6.5" Dayton Classic Woofer. I used a 2" port @ approx. 8" for a Tuning of approx. 37 Hz.

 

[RJ]

Doubling the ports - lengthens them.
Increasing the box size - decreases the length.
Decreasing the diameter - shortens them. Bad! Increases the chance of chuffing.
Try square or rectangular ports. Just click on the circle in WinIsd and it changes to a square.

 

[69stingray]

Doubling the ports - lengthens them.

Please verify my math, but this is what I come up with (as an example):

Box Enclosure: 1.5 ft^3
Fb = 40 Hz
Port Diameter: 4 " (1 port)

Port Length = 11.18 "


Box Enclosure: 1.5 ft^3 (0.75 ft^3 for port calculation)
Fb = 40 Hz
Port Diameter = 2" (2 ports)

Port Length = 5.59 " each (assuming there are two)

Granted, the total length of both ports is longer, but each individual port is shorter.

JL Audio Tutorial: Ports

 

[asoprs]

those values look much better.
when i can get to my home computer i will give my values.
somehow i was getting port legths of 3 or 4 meters and box volumes of 1/2 liter. this is impossible unless you are Dr. Who.
I must be doing something very wrong, will double check tomorrow morning.

thanks for the replies

tom

 

[sreten]

Please verify my math, but this is what I come up with (as an example):

Box Enclosure: 1.5 ft^3
Fb = 40 Hz
Port Diameter: 4 " (1 port)

Port Length = 11.18 "


Box Enclosure: 1.5 ft^3 (0.75 ft^3 for port calculation)
Fb = 40 Hz
Port Diameter = 2" (2 ports)

Port Length = 5.59 " each (assuming there are two)

Granted, the total length of both ports is longer, but each individual port is shorter.

JL Audio Tutorial: Ports

Hi,

the equivalent of one 4" port is 4 2" ports.

RJ is correct, as you will find if you do calculations for 4 ports.

Or for 2 ports 0.7*4" diameter.

/sreten.

 

[69stingray]

Good point.....I guess I was assuming a small reduction in port cross-sectional area.