Need help with enclosures and ports, better understanding?

[scooter99]

I'm trying to design an enclosure for my center console sub. I understand airspace, well how to get it anyway. But I'm trying to figure out port size based off of airspace. I don't want to have to build the thing in Torres just to get the number, I want simpiler. So I did some Google seaching.

Found this site:http://www.carstereo.com/help/Articles.cfm?id=31

But now I'm more confused. So I'may trying to figure it out and hoping someone can help answer my questions.

Starting at the top of the page is the "Minimum usable vent diameter". It explains how to enter the info and that we have to figure this out so we don't get port noise. Ok.

I enter my driver, a 10" sub, the Xmax 26, desired tuning 47 hz, and click calculate. Says minimum area is 47 inches. The below that says Length of a side for a square vent - 6.86". Ok so 6.86 x 6.86 = 47.06 Sq in. Ok then.

So I go to the next section where it calculates the vent length. I enter my numbers. Select Square vent, select slot port, 1 port quantity, enclosure volume of .80 cu ft, desired tuning of 45hz. Then enter the 6.86 width and 6.86 height. I hit calculate, and it suggests 69.19 inches of port length. Wtf?!?!

So then I entered in what I thought might be a decent sized area, 10.5" wide by 1.5" tall, and got a 17.68 long port. But it's only 15.75 as the area. So does that mean that I would have bad port noise?

I'm confused, I need help.

This is what I need. I need an enclosure of about 1.05 cu ft which would give me about .80 cu ft of air space after sub displacement. Then attach a slot port to the outside of it, and have my tuning at around 45hz.

[Triticum Agricolam]

How much power are you going to be running?

The problem with the port area calculator you linked is xmax isn't a good way to determine how much port area you need. You are never going to push a sub to Xmax at your port tuning frequency, which is usually (but not always) where port velocity is the highest. That calculator is almost always going to give you a really high port area number. This wouldn't be a problem except it makes for unreasonably long ports, as you discovered. Also that calculator doesn't consider box size, which also has a big impact on port velocity.

A better way (IMHO) to determine how much port area you need is using a system that takes into account box volume, input power, tuning frequency, and the specs of the sub. Most of the box simulation software (BassBoxPro, TermPro, WinISD, etc) will do this.

[Esgedi]

The issue with that calculator is that there's no way that driver will sweep 26mm one way in that box unless you throw BIG power on it.
For comparison, here's my 10" dayton audio ultimax's projected displacement curve in .8ft^3 tuned to 45hz on 1000w RMS.

[scooter99]

I'm running anow Ampere Audio 2000.1 to it, but it's overpowering. I'm going to be gaining down on it quite a bit.

I thought that sounded crazy, thanks for confirming it isn't me.

Right now in my temporary enclosure I have it at about .75 cu ft with a port that's about 28" long by 10.5" wide and 2" tall. I was aiming for a mid 40's tune because I'll be using it as a mid bass type of application in the center console sole. It's an Ampere Audio v3 2.0 10.

I started out real large on the enclosure and ran into some issues. I went from 1.05 cu ft after displacement to between .75-.80 cu ft and it sounds much better, but I didn't touch the port so I think it tuned lower by shrinking the enclosure.

[scooter99]

The issue with that calculator is that there's no way that driver will sweep 26mm one way in that box unless you throw BIG power on it.

For comparison, here's my 10" dayton audio ultimax's projected displacement curve in .8ft^3 tuned to 45hz on 1000w RMS.

Thanks I appreciate the info. Problem is, I have no clue what I'm looking at. How do I read that graph?

[scooter99]

A better way (IMHO) to determine how much port area you need is using a system that takes into account box volume, input power, tuning frequency, and the specs of the sub. Most of the box simulation software (BassBoxPro, TermPro, WinISD, etc) will do this.

Sorry forgot to answer this. I have messed around with WinISD, but I have never really gotten the grasp of it. I have to walk away sometimes because I get frustrated.

I can get the parameters in, and get everything set up, but when it comes to filters and stuff like that it's way over my head. I'm going to sit down and play with it again. I think I found a video a while back that will help me to understand it a little better.

[Triticum Agricolam]

If you need any help with WinISD just let me know.

[buff_n3rd]

I could use some help with WinISD.

I have no idea what the charts are doing or what kind of curve we should be trying to achieve.
Not trying to hijack his thread but hoping you wouldn't mind elaborating to help us all learn.

[Joe X]

The issue with that calculator is that there's no way that driver will sweep 26mm one way in that box unless you throw BIG power on it.

For comparison, here's my 10" dayton audio ultimax's projected displacement curve in .8ft^3 tuned to 45hz on 1000w RMS.

Thanks I appreciate the info. Problem is, I have no clue what I'm looking at. How do I read that graph?

That's the amount of excursion over the frequency range on 1000W power, as you can see the cone tends to move more as the signal frequency is lower, at tuning you can see the effect of the loading of the port.