Do you lengthen or shorten the length of port to lower the db?

[eb2phkingood 10+ year member]

 

I MEANT HZ SORRY! not db! if the box design is say 31hz and you wanted to make it 30 hz would you lengthen or shorten the port?

 

is there a standard equation for lenghtening/shortening ports for a 1hz change?

 

port is 3" wide

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[cd6551 10+ year member]

Dont't really have a direct answer other than I think you need the box volume to work it out, but you wont really hear a difference by lowering the tuning by 1 hz.

 

[Buck 5,000+ posts]

You'd lengthen it. Try downloaded windisd, and you'll figure out how ports work.

 

[chillin 10+ year member]

Lengthening the port lowers HZ, not db. It will have a higher output at the tuning freq.

You should download winisd. You can play with box sizes and port lengths and see a graph of how changing things affects the sound

 

[power-fanatic07 5,000+ posts]

Dont't really have a direct answer other than I think you need the box volume to work it out, but you wont really hear a difference by lowering the tuning by 1 hz.

Please explain further. No matter if the box is 100 cubic feet or 1 cubic feet, lengthening the port will ALWAYS lower tuning.

Edit...haha you are correct. The OP is obviously confused and I didn't read it right. The length of a port determines the tuning, the size of the port determines how loud it can get, so to speak.

 

[chillin 10+ year member]

Buck beat me to it

 

[cd6551 10+ year member]

Please explain further. No matter if the box is 100 cubic feet or 1 cubic feet, lengthening the port will ALWAYS lower tuning.

I wasn't trying to say that, I just meant that people would to need to know the volume to tell him exactly how much to lengthen it by. Worded it wrong, I apologize

 

[iLL Ridge 10+ year member]

1-3" round port don't seem like enough port area.

 

[tommyk90 5,000+ posts]

Guys, you are forgetting one MAJOR factor here.

When you lengthen the port, you are going to take up airspace (given that the port is internal, which I'm assuming it is).

If you make the box smaller and keep the port area the same, the port needs to be longer to maintain the SAME tuning as the larger box.

Thus, you are counteracting the work you've done.

If you want to make the tuning lower while using the same box, you're going to have to cut down on the port area if you want to make a noticeable difference. You can add an inch or two and drop the tuning 1-2hz without really affecting the airspace, but I highly doubt you'll notice a difference in performance.

And to answer your question OP, no there is not one formula to figure out how to lower your tuning 1 hz. And odds are you'll never hear such a minuscule difference anyways.

 

[dbeez 5,000+ posts]

Tommyk beat me to it ****.

 

[VWBobby 10+ year member]

Say What??

Lengthening the port, lowers the tuning point.... Not necessarily the tuning freq or range, but the peak of the freq and where the slope starts. What HZ the box peaks at and how much it peaks is determined by the port length alone (WHEN no other factors are changed).

Example: Open up WinISD. Select any generic driver. Select a standard ported box. Make the port diameter 3 inches. Adjust ONLY the port length 1" at a time and observe how the slope changes and how the peak moves lower with each inch that you add to the port length.

It lowers the tuning freq approx 1 - 3 hz for every inch that you add to the port, depending on the driver and box size. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[RAM_Designs 5,000+ posts]

Say What??Lengthening the port, lowers the tuning point.

*But like Tommyk said, just adding length to an already made box design takes away box volume and requires a longer port length for the same tuning. So you have to add a good deal of length to get any real change in tuning, and by that point you've reduced box size quite a bit and probably altered the response curve(in a bad way) more than a simple 2hz drop in tuning would have(in a good way).

 

[VWBobby 10+ year member]

I understand what you guys are saying, but unless you're talking about a L-ported box or some type of box that uses 3/4 - 1" port walls - I don't see it.

If you're using standard 3" PVC/ABS plastic tube, the wall is only about 1/4", if that. The displacement for the tube, especially an Aero port wall is a lot less than using a L-Port or other port that uses 3/4 - 1" walls. Is that what you guys are referring to?//content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif

 

[rodneyv]

Lengthening the port does take away net volume but it doesn't effect the equation as much as you think. You can easily lengthen the port without changing cross sectional area and frequency will increase, yes you will lose net volume when you do this but not enough to keep the frequency from increasing.

The volume loss is not the wall thickness of your pvc, it's the entire diameter of port tube, which is pi*radius*radius*length

 

[tommyk90 5,000+ posts]

Like I said, you can increase the length a few inches and drop the tuning a little bit, but not enough to notice a difference in frequency response. In order to do that you'll most likely have to add enough length to drop it 5 hz, which can really start to affect the net enclosure volume, thus affecting the enclosures performance (and probably low-end due to the decrease in airspace).

However, if the OP is using only a 3" port then I'd say he has bigger problems.