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Is my box designed correctly?


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Hey guys, I’m completely new to this forum, so I would like to just thank everyone on here for doing what you do and offering the opinions and advice to others like me to gain knowledge about all of this. I would consider myself a newbie for the most part, as I have a lot of book knowledge but little hands on experience. So, on to my situation- I currently have 4 15s in a ported box. They are MMATS Procast line, powered by a Stetsom 3000.1d. Vehicle is 06 expedition with stock electrical. The guy that installed everything said the box is tuned to ~29hz. I listen to mostly rock and rap with the occasional hard hitters when I wanna show off. I’ve noticed that the subs get very loud around 40-50hz but the closer it gets to where it’s tuned to, it’s not near as loud. It literally just rattles everything and the actual bass is less heard. It just seems like it’s lacking with the lows. Admittedly, I’m not sure what the subs are intended to be tuned to so they may not be able to go low, therefore, the box is tuned too low for them. I was just curious if anyone could maybe let me know what could be going on? Or possibly design a box for me? I’m seriously considering getting another box built with a tune around 33hz. My current box dimensions are 46”x33”x16.5”.  I measured the outside of the box, so those measurements are including the 3/4” wood. The port itself is 15”x3” (45sq.in?) and 7.5” long. If someone could at least let me know how close these dimensions are to where they actually should be for the subs, it would be greatly appreciated. I’m not very happy with the way it is sounding and I’m pretty positive it’s the enclosure. Thanks for any advice. Like I said, I’m here to learn more so any criticism is welcome lol

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My phone app shows 11.3ft2 net tuned at 27hz after speaker and port displacement. But you need more port area for 4 15's, at least double what you have now. You are most likely suffering from port compression. You will need to make the next box larger for proper port area. Do you have any room to spare?

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Like CrackFactory said, you have way WAY too little port area.  I would suggest at LEAST 100 sq in of port area and 135 sq in would be a lot better. 

You are absolutely correct that the problem is your enclosure,  unfortunately it needs to be rebuilt.  

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

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Thank you guys for the replies. I figured the port area was too small, but I keep getting told that you don’t need a big port to get loud, HOWEVER, I’ve read a lot of topics on here and I sort of learn the opposite of what I’m being told, based on what people say about the subject. Since I’m still learning about how much port area is needed, how exactly do I figure that out using the subs I have? @Triticum Agricolam You said a minimum of 100 sq in but ideally 135 sq in- how are you getting that?  @CrackFactory I have an expedition and the current box is able to fit behind the second row of seats, so needless to say, I have the space lol I’ll try to post a pic. Also, what exactly is port compression? I’ve heard of port noise...is it the same thing, or the opposite?

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Upload pics to imgur then post the URL.

Triticum uses his spreadsheet to calculate port area (I use it too, Thanks again Triticum).

You can also use WinISD or another box program like Horn resp to determine the port area needed.

Port noise accompanies port compression. Basically your ported box starts to act like a leaky sealed box.

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at the very least i would fire the port toward the hatch. if you rebuild consider having at least the port width clearance between the port opening and the back hatch. 

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3 minutes ago, strangeduck said:

at the very least i would fire the port toward the hatch. if you rebuild consider having at least the port width clearance between the port opening and the back hatch. 

That was the way I had it installed originally. I couldn’t go a day without it sliding back towards the door, closing the space between the port opening and hatch. And that was another reason I turned the box around to the way it is now, because I was having the same issue I’m having- very harsh sound (port noise I guess?) especially when turned up or when it would go “low”. I was hoping that turning it around would sort of kill two birds with one stone but it really didn’t fix anything. The strange thing that I forgot to mention in my original post is that when I first got everything put in, it sounded great at all volumes (still rattled very bad when going low) but over the course of like two weeks it’s just been sounding terrible and my output has seemed to go out the window. I’ve read a lot about how much port area one should use and given the cubic volume each sub should have, I figured I should have around 140 sq in of port area (Triticum told me the same thing earlier). I have only about 35 sq in. That’s literally enough for one sub. So I figured the port and box in general is not designed or build correctly, which is why I made this post, to see how close, if at all, the measurements are compared to what they really should be. 

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