PORT NOISE HELP

[ZUaudio 0]

Hello

I am having problems with the JBL GTO 1514D. I have made the enclosure to the jbl specifications. It is in a 3.45 cube box with a 4 inch PVC port that is 13 inches long. However I am getting a LOT of port noise, which makes the audio very dirty. I am using this subwoofer in a home audio application.

When building the box i used liquid nails to seal the joints of mdf boards, and I also used 1 5/8 coarse thread drywall screws. After this was completed I coated the inside with fiberglass resin to fortify the interior.

The sub is recessed and down firing with a back facing port the amplifier is also on the back. These cutouts have been sealed with silicone, as well as the sub hole. I found that the sub is .115 cubes and the amp is .105 cubes which have been subtracted from the total volume of the enclosure to fully ensure that the box was the correct size. the dimensions are 22 long by 20 inches wide by 18.5 tall and its made from 3/4 mdf.

I am not an amateur box maker, however I am having trouble correcting this problem can you help me?

Also the jbl paper says that the porting is tuned to 30 Hz, however I was hoping that you could give me a new spec to tune it to 27 or 26 hertz.

Thank you,

Jason

[Duran 387]

If you have port noise, the only thing you can do to fix it is get more port. Liquid nails is not a sealant as well, use silicone to seal the edges like you did with the amplifier. Fiberglass resin makes the enclosure weaker too.

[porkchop 304]

on the inside of the enclosure, how close is the port mouth to the wall? how close is the sub to the port mouth?

do you currently hve flared ends on the pvc?

have you used this calculator before?

have you used these?

chop

[KU40 173]

You just need more port area. At LEAST two flared (aero) 4" ports, or probably at least three 4" regular ports, if not four. But you won't be able to make them each 13" long, you'll have to redo the equation to figure out the needed port lengths. The internal net volume of the enclosure will also be lowered.

Sucks that JBL published such a horrible design recommendation. If you tell us if that 3.45 cube figure is net after sub and port displacements or gross we can help you with a new design. Dimensions also help, as well as system goals.

[trevorb9 2]

You just need more port area. At LEAST two flared (aero) 4" ports, or probably at least three 4" regular ports, if not four. But you won't be able to make them each 13" long, you'll have to redo the equation to figure out the needed port lengths. The internal net volume of the enclosure will also be lowered.

Sucks that JBL published such a horrible design recommendation. If you tell us if that 3.45 cube figure is net after sub and port displacements or gross we can help you with a new design. Dimensions also help, as well as system goals.

I don't think the problem is from not enough port area.. It is most likely from not flaring the ends of the PVC for the port..

[inkfx 3]

You just need more port area. At LEAST two flared (aero) 4" ports, or probably at least three 4" regular ports, if not four. But you won't be able to make them each 13" long, you'll have to redo the equation to figure out the needed port lengths. The internal net volume of the enclosure will also be lowered.

Sucks that JBL published such a horrible design recommendation. If you tell us if that 3.45 cube figure is net after sub and port displacements or gross we can help you with a new design. Dimensions also help, as well as system goals.

I don't think the problem is from not enough port area.. It is most likely from not flaring the ends of the PVC for the port..

I've seen quite a few builds using PVC pipe that is not flared with no port noise.

[Julian 641]

It's because you don't have enough port area, that's what happens when you skimp on area.

[Tirefryr 1,742]

It's been said several times, but for your power level, you don't have enough vent. I love JBL, but they always list such ridiculously small vents. In their defense though, they designed the enclosure to sit in the trunk of a car, not in your home, so 9 out of 10 people will never hear the vent noise.

[Dictator 39]

It's been said several times, but for your power level, you don't have enough vent. I love JBL, but they always list such ridiculously small vents. In their defense though, they designed the enclosure to sit in the trunk of a car, not in your home, so 9 out of 10 people will never hear the vent noise.

So true...

[duanebrow 6]

Time to build a new box! You need to model what you have. Then design to correct the problem. If you can post the t/s specs, or a link to them. I can look into it. And how much power you are using.

Duane

Edited September 23, 2011 by Duane

[duanebrow 6]

Ok I'm not quite that lazy. I got the specs and modeled it. First try plugging your port. A nerf football will work, or you can buy a plummers test plug from a home improvement store for about $5. This models very well. And NO port noise. If you want more low stuff, you can use 2 4" ports, each 30.5" long. Or better than that, build a new box. 6 cf net, tuned to 22 Hz with a 2" by 16" slot port, 24.75" long. The port can be changed to something that works better with your design.

I can give more info (graphs, f3 points, ect.) If anyone would like.

I hope this helps,

Duane.