Re-ported to larger port for sundown 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.

[ToNasty]

2 4" ports isn't enough port area in my opinion

[One_crazy_dude]

To Nasty, it sounded and felt so good for a single 15. Now I'm disappointed. The good thing is the ports are on a separate piece of mdf that can be removed and a new one can be installed. It bothers me that I thought it needed mor port also to find out it doesn't sound as well.

[Triticum Agricolam]

How long were the two 4" ports and how long is your new larger port?

[One_crazy_dude]

The new port is 20 1/4" long and the 2 4" ports are roughly 9 1/2"

[bassfreak85]

phasing changed a-bit and so did the transfer function just do a slot port money..

[ShadeTreeMechanic]

The ports are calculated by the area of the opening not the circumference. It sounds like your original tuning was closer to your cabin resonant frequency giving you a nice cabin gain. The bigger port at the same length will raise the tuning. Don't forget that port volume subtracts from box volume as does woofer displacement. This is why some people use external ports.

[Triticum Agricolam]

I think something else is going on with your box. Sounds like you have your port length properly figured out. If you are willing to experiment a little I'd suggest you verify your tuning with both sets of ports and see if there are any differences. You can check your tuning by playing sine wave tones through your sub at moderate volume. Look for the frequency where cone movement is at a minimum and that's your tuning frequency.

[One_crazy_dude]

I'm gonna play with it today and see what's going on

[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.