Vent question

[gwilliams20]

I have an 8 Cuft. net cabinet. I would like to tune it to 20Hz. A 6" port at 20 Hz is 19.42" according to one of the online vent calculators. With the bracing in place, this 6" vent just won't fit.

My question is; Is there a formular or rule of thumb for multiple vents? I would like to install 2 or more smaller and shorter vents if possible.

Yes, I have searched for hours for a method. I have seen multiple vents mentioned, but no real info.

I would greatly appreciate it if someone would take the time to point me in the right direction.

[mbar]

If I remember correctly, WinISD can be used to calculate dual BR vent sizes.

Sent from my Milestone using Tapatalk

[Ron E]

Originally Posted by gwilliams20

I have an 8 Cuft. net cabinet. I would like to tune it to 20Hz. A 6" port at 20 Hz is 19.42" according to one of the online vent calculators. With the bracing in place, this 6" vent just won't fit.

My question is; Is there a formular or rule of thumb for multiple vents? I would like to install 2 or more smaller and shorter vents if possible. I would greatly appreciate it if someone would take the time to point me in the right direction.

You can put in an elbow to make the port fit. You could also use a PR
What are the woofer parameters and how much power are you going to throw at it?

Lv=2350*Dv^2/(Fb^2*Vb)-0.73*Dv
dimensions in mm, volume in liters
8 ft^3= 226.5L
6" port ~19.3"
4" port ~7.6"

Multiple vents are not magic, they act like an equivalent area round port. In order to tune to 20Hz, 2-4" ports would need to be 17" long, and 4-3" would be the same area and thus the same length as a 6" port.

[infinia]

Hi Ron
While yer on the subject, are there any empirical formulas for rectangular slot loaded using the full width of bottom and part of the back? Solving for Fb or Lv with magic correction factors for angles and end effects?

[hawkei67]

This might be a stupid question for some but for others like myself do have stupid questions here and there.

Here is my question:

I use BassBox Pro the latest version (6.0.22) with all current driver database drivers up to date also. I have tried to design a good vented box cube or prism and my port lengths come up pretty long to. I instead went from using round no flush ports to rectangular ports, can I use those dimensions that it spits out and do one of those ports like you see in a lot of custom box's that have only 1 side and 1 top and for the other side and bottom will be the wall of the box itself?

Also, a friend of mine who is still into the scene and built a box for my oldest nephew about 5 years back (a single 12 in a prisim with 2 round ports coming outta the low frequency end and a plexiglass face on the front so you could watch the speaker excursions, no amplifier playing Metallica and about half way up on volume I had to get out cause my heart heart) in a 1994 Ford Ranger Extend Cab and it would hit hard with no amp at all, just radio/cd-player. So he must know what he is talking about. Anyway he told me to build a 2x2x2 (sounds like a bandpass) box and divide it dead center in half to place the baffle at then place 2 round vents at 3in o.d. and 9in long and place them on the high frequency end of the box not the low frequency of the box and the front of the speaker box could have plexiglass to see the front of the sub if you want. Aren't the ports suppose to always be mounted in the low frequency side of the sub which would be the back of the sub and not in the front of the sub to get desired bass response?

The woofer I told him I would be using is a Polk Audio db104, 10in 4ohm. BassBox Pro has the TS/Parameters in it's database.

Sorry for so lengthy but wanted to familiarize you to the knowledge he has but did not want to dis-respect him by questioning him in person, that is why I am asking here. Thank you for such a great site and keep up the great work.

[gwilliams20]

The woofer is an Exodus Audio Tempest X-2.
Dual 2 Ohm voice coils
Qts .42
Vas 255 liters
X max 26 mm
P max 1000 watts
Spl 87.9
Bl 15.3
Re 3.8 Ohms

I have a Face Audio amp and will have 700 watts @ 4 Ohms from one channel.

In this particular enclosure there is something blocking anything you try to do.

There is a brace made of MDF parallel to the front baffle and about midway from front to back. It is the same size as the interior of the enclosure (20" x 35 1/2") with eight 6" holes routed in it.

There are three horizontal braces (20" x 21 3/4") with four 7 1/2 holes evenly spaced on the center brace.

This thing has been a nightmare.

I finally wound up with a slot vent 18.5"x 2.25 x 29.7". Had to make a turn at the back of the box.

To turn a slot vent measure along the centerline of the vent to determine the cuts you need to make. I hope. That's what I've been told.

[gwilliams20]

Google slot port calculator and the top site was the one I used. It also has the formula they use.

[infinia]

Originally Posted by gwilliams20

Google slot port calculator and the top site was the one I used. It also has the formula they use.

how close was target Fb to measured impedance minima. accuracy of the given formula>

[gwilliams20]

infinia,I don't have any test equipment. I also have a Mac. No software.

The only thing I can tell you is that the area of the slot vent was about 25% larger than the area of a 6" round vent. This coincides with the info I picked up off the web. I have a lot to learn about this business.

Guess I'll just have to take what I get.

[weltersys]

Originally Posted by gwilliams20

infinia,I don't have any test equipment. I also have a Mac. No software.

The only thing I can tell you is that the area of the slot vent was about 25% larger than the area of a 6" round vent. This coincides with the info I picked up off the web. I have a lot to learn about this business.

Guess I'll just have to take what I get.

You don't need any test equipment other than your eyes and free test tones downloaded from the net to determine if your port tuning has come out as predicted.

Port proximity to walls and braces will affect tuning. Port shape also has an affect, round vs square vs triangular will all tune slightly different even with the same area and length.

The speaker movement will be at minimum at Fb. If Fb is too low, shorten the port. Too long, add on.

It is generally easier to shorten ports rather than lengthen, best to err on the side of too long and cut down.

Art