Poll: Adding Extra Port Wall Better Or not in Box - Drawing Given

[ARSkemp 10+ year member]

Hi, I'm thinking about doing a box for 2 12s. The drawing is not to scale, but I'm sure you guys get the idea. Would it be a better idea to leave the extra port wall out, or add it in? Which is the better design?

Please vote if you have experience or have a reason why one would be better than the other.

Thanks in advance....

Click to read more...

 

[slam 5,000+ posts]

figure one but id have the nipple out more

 

[Toone 10+ year member]

well tuning would change

 

[soloXgt 10+ year member]

figure one but id have the nipple out more

would it be preferable to extend the nipple out to the depth of the port between the port wall and back wall?

 

[mlstrass 5,000+ posts]

I've built numerous enclosures like #1 and have never had any issues. I see no reason to divide the port like in #2.

 

[ARSkemp 10+ year member]

well tuning would change

I know i didn't really make it clear but i'm assuming that if extra wall is removed, then the box width is decreased slightly to compensate for the width of the wall, allowing the shared port area to be exactly the same as the 'port area of sub 1' + 'the port area of sub 2'. In which case the tuning should still be the same, right?

 

[ARSkemp 10+ year member]

figure one but id have the nipple out more

something more like what soloXgt said? With it having a depth of about the port width? Like this?

and i'm assuming that in the above pic that both angles are made parallel between the opposite walls and that the port width is roughly the same as the rest of the port.

 

[PV Audio 5,000+ posts]

Neither. Move the port wall all the way to the left so that the subs share the airspace. The problem with doing designs the first way is that to hold proper tuning, you need to make the port width along the back half of what it is in the middle. This causes port compression and you can end up with losses. There really aren't any flaws with the second method, so I'd just stick with either that, or just use one L port along the left or right wall.

 

[ARSkemp 10+ year member]

Neither. Move the port wall all the way to the left so that the subs share the airspace. The problem with doing designs the first way is that to hold proper tuning, you need to make the port width along the back half of what it is in the middle. This causes port compression and you can end up with losses. There really aren't any flaws with the second method, so I'd just stick with either that, or just use one L port along the left or right wall.

The only reason i'm thinking about doing it this way, is because it lets me split the port width in half. This way, the L shape that is made with the back wall gives me more space for mounting the subs, since i'm trying to make the box with as small as depth as possible (with the port opening being on the 'front' of the box). If i use one large L port, then i'll have less space to work with in terms of mounting the subs, be it sub up, or subs facing the same way as the port.

 

[PV Audio 5,000+ posts]

The only reason i'm thinking about doing it this way, is because it lets me split the port width in half. This way, the L shape that is made with the back wall gives me more space for mounting the subs, since i'm trying to make the box with as small as depth as possible (with the port opening being on the 'front' of the box). If i use one large L port, then i'll have less space to work with in terms of mounting the subs, be it sub up, or subs facing the same way as the port.

//content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif No, you definitely won't have less room. You will have the same port width regardless of which you choose. The golden rule in audio, specifically subwoofer design is that simplest is best. Your boxes are going to have losses naturally, so the fewer chances you allow a loss to come into play, the better the performance. Very rarely will doing a divided port yield better results than a single slot. This no longer applies of using a CRX style enclosure, but that isn't what this is.

 

[ARSkemp 10+ year member]

//content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif No, you definitely won't have less room. You will have the same port width regardless of which you choose. The golden rule in audio, specifically subwoofer design is that simplest is best. Your boxes are going to have losses naturally, so the fewer chances you allow a loss to come into play, the better the performance. Very rarely will doing a divided port yield better results than a single slot. This no longer applies of using a CRX style enclosure, but that isn't what this is.

Here's an example of what i meant, for a 15" deep box:

This is neglecting the wood thickness, and the tuning is probably some random hz, but should be enough to explain. Say i wanted the subs to face the same direction of the port opening, and i needed 11" of clearance for the subs. They would fit in the dual port box, but not the single L port box.

 

[PV Audio 5,000+ posts]

Ah, I misunderstood you and I see your problem. If that's the case, then let's talk about it like this: why do you need a 5" wide port when your enclosure is only 15" deep? If you're moving that much air, then your box will be rather large as it is due to you having a large speaker or numerous ones. My point is this: what is the application, because if I'm right in my thinking, then you definitely want to go with the single port idea.

 

[ARSkemp 10+ year member]

Ah, I misunderstood you and I see your problem. If that's the case, then let's talk about it like this: why do you need a 5" wide port when your enclosure is only 15" deep? If you're moving that much air, then your box will be rather large as it is due to you having a large speaker or numerous ones. My point is this: what is the application, because if I'm right in my thinking, then you definitely want to go with the single port idea.

I know the 5" port width may be a little farfetched, but if wood thickness is taken into account, then even if the port width is smaller, there's still the .75"x3 for the 3 pieces of mdf that needs to be dealt with if the subs are facing up.

Ya, I know the drawings probably aren't to scale too much at all, but I'm looking at trying to fit a box that is ~20-21" tall, 40" wide, and as shallow as possible, for 12" subs facing up. probably ~4-5 cubes or so with ~80" of port area (I like a little extra port area, have had good experience with ~18-20" per cube. Will probably be running an ab500.1 @ .5ohm to 2 12" HDCs).

I know that the port would probably not be as long as shown in the single L shaped design, but i wasn't sure how close one sub could get to the port opening vs the other, and i didnt want unloading issues. with dual ports, the subs are each the same distance from the port opening, which i thought may be better in this case.

 

[PV Audio 5,000+ posts]

I am not a fan of single port setups with separate chambers, because imagine that the box is filled with water instead of air (fluid's a fluid, right? //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif). When you build up enough water pressure to force the water out of the port, it isn't going out the front because it's being directed there, it's going out the front because the opposing pressure from the other chamber dictates that out the front is the area of low pressure. As a consequence, you are going to get turbulence right in the middle area which you don't get when using single ports along the outside or with a divider.

 

[PV Audio 5,000+ posts]

What about porting along the bottom? Or no, even better, porting out the side if you can manage that, since that way you'll definitely have plenty of height to work with and you have all the space in the world on the top baffle.