ported box question

[THATpurpleKUSH 5,000+ posts]

My owner's manual for my subs lists the ported box should be 2.0cu ft after driver and port displacement with a port size of 4x14" at 33hz. I want to shift the port to 28-30hz, would I just have to increase the overall airspace and change the shape of the port to get to the lower frequency? I am designing a custom ported box for my Boston G5's and I'm worried a 33hz tune won't give me the low-lows that I want. This is my first ported build. All help is greatly appreciated.

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[hamel52 10+ year member]

making the port longer will drop the frequency but it will also change the volume after displacement, another way to drop the freq is make the port smaller in width assuming your doing a slot port of some kind

 

[hamel52 10+ year member]

also 33hz will give you plenty of lows i had 2 12s at about 35hz and it hit the lows great as well as mids, making the tuning too low just will make your sub less efficient and your overall sound for different songs frequencies will probably be not as good i would recommend 33hz i think it would be perfect im doing a new box right now to 34hz i just love the output i get with the frequency.

 

[THATpurpleKUSH 5,000+ posts]

The manufacturer listed a round port in the owners manual.

 

[hamel52 10+ year member]

i haven't worked much with round ports just slot ports and ive loved how they have turned out, im sure it wouldn't matter if you used slot port over the aero port but its your choice, if you want to try out slot port and mess with size and frequencies i'd try using http://www. reaudio.com/speaker_box/LPort_Box_Calc.html

 

[RAM_Designs 5,000+ posts]

Do not use a 4" PVC port, use an aeroport. A full length(17") aeroport will give you the 30hz tuning you're wanting with a 2ft^3 box(after displacements). I'm not a fan of tuning higher either, and prefer a flat response over a big bump around 40hz, so I know where you're coming from.

 

[THATpurpleKUSH 5,000+ posts]

I will talk to my local shop about the aeroport as I won't be building the box myself. The response curve of the recommended ported enclosure peaks at 50-60hz and is at -9db attenuation at 30hz. The sealed enclosure, which I'm running now is peaking at 70-80hz and is at about -10.5db attenuation at 30hz. I just want something that will shift the curve to help out ~40hz and lower a little better.

 

[RAM_Designs 5,000+ posts]

I will talk to my local shop about the aeroport as I won't be building the box myself. The response curve of the recommended ported enclosure peaks at 50-60hz and is at -9db attenuation at 30hz. The sealed enclosure, which I'm running now is peaking at 70-80hz and is at about -10.5db attenuation at 30hz. I just want something that will shift the curve to help out ~40hz and lower a little better.

I find it very odd that the ported box would be 9db down at 30hz if it's tuned to 33hz...I can understand 4-6db, but nine is a pretty steep drop off...or it just rolls off early anyways. And it peaking at 50-60hz makes no sense(maybe in-car, but not the actual box itself). Normally the box peaks around 5hz above tuning, depending on the sub and box, but there's no way that a box tuned to 33hz is going to have an out-of-car response curve peaking in the 50's...at least I've never seen something do that before that wasn't supposed to be in a sealed box in the first place.

 

[THATpurpleKUSH 5,000+ posts]

Yea I thought it was odd too, but I was definitely looking at the enclosure response curve.

http://mobile.bostonacoustics.com/Manuals/G5_GTR_Man.pdf