Sub box design question

[jnorion]

I have been told that a ported box makes for louder bass and a sealed box makes for cleaner sound. Is it possible to make a box that you can open and close the port on so you can switch between the two? Is it as simple as just covering the hole or is it more complicated?

BTW, I am aware this is a very noobish question.

[Kevin]

ported boxes offer deeper, louder bass hits, and in my opionion, sound just as nice as a sealed enclosure (when the bass drops.. it's definately MORE pronounced, but properly tuned, it should not be sloppy by any means). also, your sub will do more work with less power, so in other words, your sub in a ported enclosure getting the same amount of wattage will be louder. a simple visual of this is if you seal your hand over the port of a ported enclosure as the sub is pumping, you'll definately notice the cone moving more. i don't know the specific dynamics of it, but q-logic prefab ported boxes come with easy to remove port plugs and port tubes, all you really need is a screwdriver for most of their applications. someone can elaborate more, but i personally prefer ported enclosures

[jnorion]

So, in your opinion at least, there's no point in having the port with a plug, just get a regular ported box? Also, how do you tune the port? As I said, I'm very new to subs and their boxes.

[blue LEDz]

IMO the reason why sealed boxes are associated with cleaner sound is because the average joe off the street has never heard a properly tuned enclosure for todays higher excursion subs. back 10 years ago subs were not capable of the linear movement they have today. that translates into less low end bass. since the subs of today can and will move a lot further, you can tune the box lower, so the old prefab design of tuning the box above 35 hz is no longer necessary. 35 hz is the highest i would tune a box if i want good SQ out of it. if it's all about SPL, then i'll tune it a lot higher but typically i prefer to tune boxes lower, so the response is flatter. i've even built ported boxes that have a flatter response than sealed. above the tuned frequency the sub will perform as if it were in a sealed enclosure. so the lower you tune it, the more it sounds like sealed, until you get to the low bass. i will warn you, ported boxes cause for a TON more rattles, just ask misterT about it but that becuase it's the low bass that really causes rattles. from 30-40 hz i've noticed the most rattles.

port plugs are only useful if you want to tune the box higher for SPL purposes, or make it sealed for SQ competition.

https://www.linearteam.org

download winISD pro. it will show you how changing the tuning affects the frequency response. it will also show you how too small of a port causes higher wind speeds, which cause whistling/port noise. each sub has to be matched properly with a well designed box. not all subs are going to sound good in a ported box tuned to 27 hz. some need to be tuned higher, since they aren't as capable of playing the lower freq's. the type of music listened to also needs to be taken into account. i've found very few songs that play below 30 hz, and trust me, my 18 would pick those freq's up just fine

[jnorion]

I wish I understood all that stuff... half those numbers mean absolutely nothing to me. Is there a more graphical program for stuff like this?

I think I'm going to have to head down to the local audio shop and make the guy explain stuff to me... it's a lot easier when I can actually sit down and have a conversation with someone than try and get everything over the internet.

[blue LEDz]

I wish I understood all that stuff... half those numbers mean absolutely nothing to me. Is there a more graphical program for stuff like this?

I think I'm going to have to head down to the local audio shop and make the guy explain stuff to me... it's a lot easier when I can actually sit down and have a conversation with someone than try and get everything over the internet.

more graphical program? nope. winISD is the most easy to understand and use program i have found. click help, then getting started. it's a tutorial for it.

i just hope that you can find an audio shop that has someone knowledgeable enough to explain it to you. i'm suprised at how few really know how to properly tune a ported box, and how it really effects the sound.

[jnorion]

OK, so the first time around I downloaded just the basic program... I just tried the pro version and it makes a LOT more sense, although I'm still sketchy on a lot of the parameters for the sub itself.

The guy at the shop here seems to know his **** pretty well, although not being an expert myself I can't say how much he knows. He's always willing to talk things over with me though, and at least answer my basic questions.

Another quick question: when I'm building a basic ported box (not bandpass), as long as the volume and port size are correct does it matter what the shape of the box is?

[blue LEDz]

shape does not matter, except in extreme cases. i've had enough people argue that shape has no effect on the subs or the sound. to prove them wrong, i built a sealed box with two 15's in it. i built it so that one sub would be 45 degrees off from the other sub. this resulted in the back wave of one sub coming back and hitting it, as well as the back wave of the other sub reflecting and hitting the first sub. it caused audible distortion as well as destroyed the sub that both waves were hitting. in general shape has no effect, so don't worry about it

[jnorion]

Would it be worth trying to build boxes for my 6x9's in the rear? They're good down to 25hz... just for the hell of it, would it make for louder bass?

[jnorion]

Oh, and yet another question, I need some clarification on stuff from the help file. I've been reading all the technical articles in there. I'm at the part that talks about port dimensions, and it says "Rectangular ports consume a lot of internal space, and so the entire design must be re-done to allow for the area displaced by the ports."

This makes sense so far, but what I'm wondering is if I calculate the internal volume of the box, do I include the volume inside the port? I mean, is it just the wall of the port that is considered taking up internal space, or is it the entire port assembly?

I hope this question makes sense.

[blue LEDz]

Would it be worth trying to build boxes for my 6x9's in the rear? They're good down to 25hz... just for the hell of it, would it make for louder bass?

don't bother. it's not worth it.


as for the port displacement, it's the total volume of the port, ie the air space and walls of the port. so if it's round and the pipe is 4" outer diameter, then it's 2 x pi x radius, or as i like to do diameter x pi. so the cross sectional area is about 12.56 and you have to multiply that by the length to get the volume. say it's 12" long. the volume would be 150.72 cu inches, or .087 cu ft.