Can a port be too short!!????problem

[vehementSPL 10+ year member]

At first I figured this would be an obvious answer of no. But here is my delima .. I have a 4th order with 9 12s. The 12s are in a sealed chamber firing up into the ported chamber and that fires into the cab. NOW. Here is something interesting. The port is 12x41 by 4 inches deep. I use the top of the box as the port. Now here is where it got ODD metering today. Typically the port will be way louder than the internal of the box. My truck metered on the dash outlaw style, then taken at the head. then IN the port ALL scored within .2 db of each other. In the box up 3 db. I was wondering if the port could be too short in ratio to its height. It honestly to me seems it is just treating the front chamber as a reflective chamber with no tuning. To also support my theory is from looking at when ISD where my imp spikes and dips should be. Testing power and ohms today. In my 4th order 35hz should have a HIGH ohm and 50hz a LOW ohm. Now in just a sealed enclosure taking the size of my sealed chamber if it wasn't in the ported chamber(sealed box)... Shows LOW ohm at 35hz and peak ohm at 50hz... TOday noticed the peak ohm was at 50hz and low ohm was at 35hz. EXACTLY following the sealed box curve from winisd and not the 4th order at all! Seems from memory somebody had mentioned there is a min. port length you can go.. But the memory is VERY vague and not sure where I read it or what truth it holds. But PLEASE somebody respond because something obviously is off here.

Click to read more...

 

[vehementSPL 10+ year member]

Oh and this is daily tuned. not for spl .. if that matters on the min length. Also the scores were done on a termlab so not meter fluctuation. But to meter the EXACT same outlaw style on the dash and in the port...... Really makes me think port isn't doing any work

 

[helotaxi 5,000+ posts]

Length wouldn't be the issue. The issue would be too much port area which would then fail to load correctly leaving you with basically a sealed box.

 

[Audio Master 10+ year member]

yes

 

[vehementSPL 10+ year member]

I get two different answers lol. It is 9 12's though. only like 55 inches per sub. I guess Right now the power is kinda low though. I guess as I would up the power it would create more resistance on the port . keep giving ideas though please want to find this out because makes no **** sense to me. And I have seen people use massive ports before. What is difference. easier to do with high tunings .

 

[vehementSPL 10+ year member]

ttt

 

[vehementSPL 10+ year member]

Thanks for the responses. I shrunk the port by like 20 to 25 percent. so you would think 20 to 25 percent more air velocity ... Wrong. like 1000 percent more. Before there was NO air in the port I could put my hand in it felt nothing and inside the box felt louder as well as metered louder. I didn't have a chance to throw it on the meter again today so I just used my hand. Now instead of putting my hand in the cab and feel the same and in the port the same and in the box a hair louder. now cab normal. port tons more. and in box hardly anything. I am honestly shocked that little reduction makes that big of a difference. I guess when you start to go over on port it is a VERY weighted scale. a little over makes a big difference. thanks again

 

[savagebee 10+ year member]

just fyi, port size is determined by enclosure volume, not the amount of subs

 

[Hintzyboy 5,000+ posts]

I think you should shrink the port area considerably. I don't know if BP boxes work differently from regular ported boxes as far as port size, but you definitely don't need 60 sq.in. of port per sub for a normal ported enclosure. About half that would be enough for a regular porte box. I would assume that the same principles would hold true here.

Talk to 80INCHES on here. He's the resident BP guru.

 

[mlstrass 5,000+ posts]

492^2 of port area seems a tad excessive. That's enough port area for a 30-40^3 box. Unless a BP box is different, but it still seems like WAY too much...