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How narrow can a slotted port be? pics of box, any tips are appreciated


CorNut

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I have minimal space to work with, I'm attaching some photos so you can get an idea of what I'm hoping to do.

 

It's a down firing box for under my truck's rear seat. It's an RE Audio SL-12 D4 shallow mount and its minimum ported box size is 1.25, The only way I can maintain that is if I do an external/slotted port. The port will be going on the longer side of the box which will have 1.75" clearance from the floor. Since I can't do the port on the inside of the box, would a 10"x.75" be enough? using an online calculator, it says 6.75" long would be 34hz. Would that create too much port noise? Also, which way should I face it, towards or away from the sub? I initially planned to do it on the inside and have it face down like the sub but that's not an option. If I got some 1/2" plywood (I assume MDF is more likely to split) I could do a 10"x1" port, the calculator says it'd have to be 11" long which there's plenty of room for. 

 

All help/ideas are appreciated

1.jpg

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So its a 1.25 cu ft box, is that correct?  How much power are you going to be running?

 

 

"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."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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56 minutes ago, Triticum Agricolam said:

So its a 1.25 cu ft box, is that correct?  How much power are you going to be running?

 

 

It'll be right around 1.25, I don't have exact measurements yet but it'll be roughly that. I'll line it with plastic and see how many cups of water it holds. I was doing 3/4" MDF where I'm mounting the sub but I'm going to do 5/8" instead. I'll get the 5/8" sometime next week to redo it. I'll get slightly more airspace and the sub is light/not very powerful anyway. 

 

The amp is a Soundstream TN5.950D 5 channel amp. The sub is 350W RMS, the amp's sub channel is 430W RMS @ 2 ohm

 

Between the amp, DSP and box, I won't have room for my jack, chains, tool kit or trailer hitch if I go any bigger. I'm just trying to make the most out of what I have to work with.

 

If you're good at figuring out exact port lengths etc for 34-35hz, I'll have exact measurements most likely next weekend. In all honesty, this box is way above my skill level. I'll be using a bit of resin/fiberglass to fix some mistakes I made. When it comes to tuning, that's something I can definitely use some help with. The sub's displacement is .1, so in reality, this box will provide slightly less air space than the recommended minimum. I actually bought a 10 and a 12. Both are RE Audio slims and both are 350W. Do you think that would be a better idea? The minimum ported box size for the 10 is only .65. Also, if I use the 10, I can just use the 3/4" I already have since airspace isn't at such a premium

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So there are a couple issues with what you want to do.  The first is you really should have more port area than 10 (or 7.5) square inches.  14 would be the minimum in my opinion and 18 sq in would be a lot better.  The other issue is the port aspect ratio, which is the relationship between the width and the height.  A port 10" wide and 1" high has a 10:1 aspect ratio.  Lower is better, I don't like to use anything over 8:1 if possible.  

One thing you could do would be to run the port along the back of the box and then have it fire out the side.  I've done that before with good results.  

Or you could just leave it sealed. 

"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."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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12 minutes ago, Triticum Agricolam said:

So there are a couple issues with what you want to do.  The first is you really should have more port area than 10 (or 7.5) square inches.  14 would be the minimum in my opinion and 18 sq in would be a lot better.  The other issue is the port aspect ratio, which is the relationship between the width and the height.  A port 10" wide and 1" high has a 10:1 aspect ratio.  Lower is better, I don't like to use anything over 8:1 if possible.  

One thing you could do would be to run the port along the back of the box and then have it fire out the side.  I've done that before with good results.  

Or you could just leave it sealed. 

thank you for that info. Next week when I mess with it more, I'll try to figure out a way to meet those minimums. If I can't then I'll leave it sealed. 

 

Is the minimum 14" port area a rule of thumb regardless if I run the 10 or 12? Thanks again for the tips, that's exactly the type of info I needed.

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The 14" recommendation is based on the size of the box, tuning frequency, and how much power you are going to be running.  It would be the same for a 10 or a 12, as long as everything else stayed the same. 

"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."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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I'm happy to hear you're willing to leave it sealed if the specs don't come out right. You wouldn't believe how many people refuse to go sealed when they can't feasibly fit a ported box in their space with their requirements. A proper sealed box will likely do better than an improper ported box. Hopefully it all works out for you. 

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It's hard to tell in the pic, but the way it'll sit in there I won't be able to run a port out of the back. My only options are run the 12 sealed or run the 10 ported with an internal port. 

 

The DSP is going behind the seat when I install the amp. I'm using the DSP's internal amp right now and I left the wires that long so I have more options when I mount it. Ignore the clutter

 

I'm leaning towards the 10. I originally planned to do the 10 until I realized the 12 would fit so I ordered it as well. It looks like I should've saved my $. 

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