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Help with understanding slot ports

Old 06-14-2012, 03:14 AM
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Help with understanding slot ports

Ok I have done plenty of research and learned alot about T/S paramaters and have a basic understanding of it all. What I am wondering now is at what point is a slot port too short? I usually stick with <1.5 in for width to avoid port noise. I also use a router and round all corners of the port.

Actually lets see if I can just get some advice on current application.

I trying to build a setup for a RF T1D212. Running 1000/1 to it.

External Dimensions are as follows and the width and height have to stay.

H= 13" W= 19" D= up to 21" Tune to 36hz I to keep the port width between 1.5-2". Now I have used WinISD and bass box pro but am reluctant to build the box because the port length is on the short side. I mean at 2" it says the port length should be around 15" long and that seems off to me.

Would someone please explain to me why this is good or bad. Also I am fairly proficient in math and would like someone to explain to me how to calculate port length. Please use the T1 T/S paramaters and the external dimensions of the box I have given as the example.

All help and time donated to my insuperiority is greatly appreciated and I thank you in advance.

Last edited by DivineShot; 06-14-2012 at 03:51 AM.
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Old 06-14-2012, 10:04 AM
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Assuming the final internal (net) volume will be about 2.5 cubes, and that the slot port would run vertically along one wall of the box (so height=13") car stereo port calculator gives me a slot length of 16.5"- not far off your 15".
Seems as though you're on the right track.
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Old 06-14-2012, 10:37 AM
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13 X 19 x 21 will give you 2.27 cuft internally which is too small to build a slot ported box tuned tune 36 Hz using the manufacturer's specs and prevent port noise. You would need 2.59 cuft internally to do this correctly.

Try using a 4" round aero port.
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Old 06-14-2012, 02:54 PM
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how to calculate port length
Follow this link for guidance to both minmum area and vent length.
http://www.carstereo.com/help/Articles.cfm?id=21

If you want to just fill in fields rather than figuring out the math:
http://www.carstereo.com/help/Articles.cfm?id=31
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Old 06-15-2012, 12:32 AM
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Originally Posted by Sonic View Post
13 X 19 x 21 will give you 2.27 cuft internally which is too small to build a slot ported box tuned tune 36 Hz using the manufacturer's specs and prevent port noise. You would need 2.59 cuft internally to do this correctly.

Try using a 4" round aero port.
I'm not familiar with the xmax of the RF sub he's using, but a single 4" aero routinely makes me think I left one of my back windows open, often with the chuff you'd associate with an open window at highway speed.
If he's going to push it hard, I'd say a 6" aero or slot port would avoid doing just so a month after installing the 4" aero.
My $.02
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Old 06-15-2012, 08:01 AM
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Oh a 6" would work, but it would reduce the recommended Vb far more than a 4" and be quite long, on the other hand a smaller slot port would work with port noise at full tilt just as the 4'' aero, but the 4" aero would take up much less space than the smaller slot port, hence the value of the Vb would be much closer to recommended and simpler that's why I said to try it. Its a case of give and take.
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Old 06-15-2012, 03:09 PM
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I am curious to the method you are using to determine why the 6" port is going to significantly alter the net enclosure volume compared to the 4" and why a 4" aeroport is suitable but not a slot vent of the same effective area.

This isn't a bait for argument or a confrontation - just looking for some insight.
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Old 06-17-2012, 10:48 AM
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Originally Posted by Dukk View Post
I am curious to the method you are using to determine why the 6" port is going to significantly alter the net enclosure volume compared to the 4"
@ 36 Hz with Vb = 1.75 cuft (manufacturer recommended spec.)

These below are calculated for straight pipe with out flairs.
4" dia. port >> length = 12" , Volume = 0.1 cuft

6'' dia port >> length = 29" , Volume = 0.52 cuft


Originally Posted by Dukk View Post
why a 4" aeroport is suitable but not a slot vent of the same effective area.
The theory is just not the same, the flow dynamics vastly differs, hence, the end result.


Actually, a 6'' would definitely work, I just recheck and found that the Vb given from r/f does include woofer displacement, hence, the Gross volume would be exactly on target Only problem the port would have to include a bend because of the dimension of the box.
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Old 06-17-2012, 10:54 AM
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Originally Posted by Dukk View Post
This isn't a bait for argument or a confrontation - just looking for some insight.
I understand !

I am not a Guru by any means lol... I like to help with as much as I know...and learn too
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Old 06-17-2012, 04:19 PM
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Well I have done some more checking and bought a few more things as well.

New equipment is putting me at 2 Rockford Fosgate T1D212 / T1 12's / 2ohm
and 2 1000/1 amps, or a 1000/1 to each sub however you want it worded.

I am adjusting some things now and want to know if I can make this any smaller without screwing with the tuning. I will only use slot ports.

My external dimensions that I came up with are as follows.

H=13" this cannot change space limitation.

W=38" this also cannot change space limitation that is for both subs combined.

D=up to 30" however I would like to keep this as short as possible.

I will be putting in a divider / making it 2 seperate boxes.
Port dimensions. Tuned to 36hz

H=11.5 cannot change

W=2.5 cannot change

L=Unknown

My port area is around 11" per cu/ft will this cause any problems?

I came up with D=28 and L=17.32 inches per port I would like to know how accurate that is? That is at 2.6 cubes per sub. Also is 2.6 cubes per sub enough? Or is it possible for me to shrink that down without losing much.

My port area is around 11" per cu/ft will this cause any problems?

Please give details on answers I really am trying to find the answers to all this for future applications. From the previous posts I have read on this site and others people here tend to give sound advice and seem to explain things well enough. Thanks in advance again. Sorry for the change up already
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