Changed port for SA15, what did I do???

[One_crazy_dude]

I started out with a 4 cubed box and ported it with 2 4" pvc tuned to 37htz. It's all I had at the time and could not go get any more. I've been recovering from a 3rd nasty shoulder surgery so god bless my 15 year old for helping me with a great install.

So the other day we decide to change the port. I pick up an 8" concrete tube not knowing it's real size is 7 3/4". Ok a few adjustments to the port and we tune it to 35 htz. Not a good idea. Before the large port man this sub hit hard. Like you can feel the air in the car pass your face and the windshield flex wipers vibrated off the glass so on and so on.

Now I had to raise the subwoofer out put on the stereo way up and still can't get the air to move like it did with the smaller ports. Barely get any flex wipers don't jump any more and although it sounds ok. It does not sound as good as before. Why would puting one large port instead of 2 smaller ports that equals the same circumference sound soo different?

I'm ready to go back to the 2 4" ports.

Click to read more...

 

[The_Quiet_One 10+ year member]

2 4" ports and 1 8" port don't have the same surface area. How did you calculate box tuning?

 

[One_crazy_dude]

Done here Car Audio - PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

Been using this sight for years and never let me down.

 

[Umbra]

Area of a circle is pi * radius squared.

2x 4" ports gives you 25.14 sq inches of area total

1x 7 3/4" port gives you 47.17 sq inches.

Without the length, I don't know your tuning, but it's much, much higher than you want. That's the problem.

 

[The_Quiet_One 10+ year member]

Done here Car Audio - PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES
Been using this sight for years and never let me down.

Just double checking it wasn't something simple. What subs are they?

 

[One_crazy_dude]

It is a sundown sa 15 d2 @1ohms. The 7 3/4 tube's length is 20 1/4". That should be 35 htz according to car stereo.com formulas.

 

[The_Quiet_One 10+ year member]

It is a sundown sa 15 d2 @1ohms. The 7 3/4 tube's length is 20 1/4". That should be 35 htz according to car stereo.com formulas.

Duh sorry about that, completely slipped my mind the title had the sub in it. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Did you change the port orientation as well?

 

[One_crazy_dude]

For information it only 1 sundown sa 15.

 

[One_crazy_dude]

Duh sorry about that, completely slipped my mind the title had the sub in it. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Did you change the port orientation as well?

No. I went from this



To this

 

[Umbra]

Well I'm stumped. Everything looks good. The only thing I can think of is maybe it's too close to the roof now, or maybe the tube isn't sturdy enough (no experience with using those).

If the PVC works for you, go back to it. I'm honestly surprised the 2 4" hit harder because that only gives you 5.61 square inches of area per foot. If I were doing it I'd double that.

 

[Papermaker85 5,000+ posts]

the transfer function of the car and phasing has changed. turn the sub up and port back. and tell me what you think money.. EDIT your in a bind now. **** this is tricky.

 

[Papermaker85 5,000+ posts]

i suggest going with e slot port. the depth of the box. you don't need more than about 40-50in^2 money..

 

[Boomin_tahoe 5,000+ posts]

Look...a chimney for the sub lol


Joking aside, lets call upon an expert @CSCStang see if we can figure this out.

 

[One_crazy_dude]

Ok. I figured out what the problem was. Like I said my son has been helping/learning how to work with tools. When he cut his first hole with the jig saw it wasn't perfect. The first time sub was installed it fit perfect. This last time it was removed it was not flat with the box.

I played some test tones and heard farting coming from all around the sub. So I took a rasp and went to work. I also put a small bead of silicone around the hole and that awesome sound is back. Thanks to you all.

 

[tc300 10+ year member]

that must have been a huge gap to effect the out put that much!!!