Vented Enclosures

[philwsailz]

I do not want to write a book, but we can start a thread... I copied and pasted from a post in General Discussion...
If anyone wants to chat / visit about ported boxes, this might be a good place.

Some quick thoughts of my own to start the dialogue...

Most of the time ported boxes only get a bad reputation as a result of the ones that were not designed and/or built right. Crappy ported boxes sound, well, crappy...


* A properly designed ported box will usually be larger than a sealed box for the same woofer.
* A properly designed ported box will usually be noticeably louder than a sealed box for the same woofer.
* A properly designed and properly tuned ported box can have an extremely broad frequency response and can sound as good or better than a sealed box. Every concert PA you have ever heard uses ported boxes.
* Sealed boxes are easy to build; ported boxes are hard by comparison.



A properly built ported box will withstand the boat environment. It should not be made from MDF or particle board though:
Here are a few options:
* Use a 13-ply void-free plywood built with an exterior rated glue in the layup, (most 13-ply sheets are bonded with epoxy / resin type adhesive anyway, so don't worry too much) Use a waterproof glue like Franklin Tite-Bond II or that foamy, yet bad-a$$ stuff called Gorilla Glue with screws for your construction joints.
* Use a synthetic material like King Star-Board. Use 3M 5200 sealant/adhesive in the joints combined with pre-drilled screw holes to make for a box that will last forever. Just know that this is a very costly alternative to the 13-ply above.



If you want the ported box go for it. Just understand that you need to consider a properly designed enclosure:

* If you cheat on size and go too small, the enclosure can tune too high, resulting in one-note sound and poor power handling.
* If you shrink the port area and make the port really long to get the tuning right for that small box, the air velocity in the port will be too high, and it will sound BAD!!!
* As a result, if you have room and can build a great big box, you can get good low tuning and quiet airflow with a reasonably sized, (i.e. not too large) simple port.

A ported box will make your boat sound like a million bucks, but it requires planning and thought. If you and/or your stereo guys are not up for all the work and planning it takes to do it right, go sealed. If you end up just slapping something together and shoving a tube in it, you will be disappointed.

[Timmy!]

Phil, do you have a design for the factory Kicker 10" sub as it sits in the wall under the drivers dashboard? I've built a lot of speaker boxes in my day (used to have some software to design them) but thought if there's already a proven ported box for the factory location that I could just throw that together. I had a sealed design all spec'd up and ready to go but decided that I wanted a ported enclosure so I never built it.

[philwsailz]

I do not have a design as far as actual part dimensions, cut list, hole locations etc.

Sorry...

I bet we could come up with one fairly quickly, using the instruction manual and the vented enclosure recommendations that it has in it.

Hmmm.... Might need to go look to see what would make sense...

[philwsailz]

After a quick check on the specs for that woofer...

We can use a vented enclosure that has a gross volume of between 2 and 2.25 cubic feet. With gross volume specified here, I have already compensated for an approximate volume displacement for the woofer and the port, (which is usually inside the box). So if you care to actually calculate now much the woofer and the port displace, you will find that nets us to around 1.75 cubic feet for an effective box volume.

There are a couple of ways to do the port. a 6" diameter, (inside diameter) port at 20" length will work quite well. If you cannot find 20" in length for the port, we can go a little smaller on the diameter and shorten the port to compensate. We just do not want to get the port diameter too small or it will start to get way too noisy..

If you want to construct a slot port, you can use one that is made of wood with inside dimensions at 2.5 x 10.5, (10.5 is convenient as it is about the same as the OD of the woofer so it will look nice), or at some other combination of dimensons that gives a similar araea, roughly 262.5 sq. in. A slot port will sound the same as a round port; don't let anyone sway you otherwise....

Howzat?

[Timmy!]

That sounds good! I like it! I like the slot port since I don't think there would be 20" of depth in that box. Is that vent made of out the same 3/4" material and taken into consideration of the 2 - 2.25 cu feet?

Now I just need to find the dimensions that I had before and see it will clear my heater...oh and then figure out the best way to attach the box to the existing panel (or maybe that comes out?). I guess I could just pull the carpet, cut the vent, attach it, screw the box to the backside and then re-carpet.

[chpthril]

The RZ's have an incredible amount of room for a box. With the way the seat back opens and the bench seats come out, it leaves a huge opening for a box to be mounted on the back side of the driver's bulk-head wall. Once you kinda decide on your gross dimensions, do a mock up in cardboard to make sure it fits before cutting any wood.

[kana12]

hey phil i would love for you to help me out on a slotted enclosure for my 06 22v to mount my xxx wet sounds sub in. i just want to build it right so it sounds better than a sealed box

[Timmy!]

The RZ's have an incredible amount of room for a box. With the way the seat back opens and the bench seats come out, it leaves a huge opening for a box to be mounted on the back side of the driver's bulk-head wall. Once you kinda decide on your gross dimensions, do a mock up in cardboard to make sure it fits before cutting any wood.

My main problem is that the heater hoses come in through the floor right under the woofer, I may need to move them closer to the wall. Unfortunately my boat is in storage 10 miles away. I made a mockup with cardboard the first time for the sealed box but I knew I wouldn't be happy with the sound of a sealed box.

[philwsailz]

That sounds good! I like it! I like the slot port since I don't think there would be 20" of depth in that box. Is that vent made of out the same 3/4" material and taken into consideration of the 2 - 2.25 cu feet?

Now I just need to find the dimensions that I had before and see it will clear my heater...oh and then figure out the best way to attach the box to the existing panel (or maybe that comes out?). I guess I could just pull the carpet, cut the vent, attach it, screw the box to the backside and then re-carpet.

With regards to the slot port; I should have clarified. Regardless whether you use the 6" diameter tube, or the slot with the dimensions described, both have a bout the same area and still need to have the 20" of length to work properly. Sorry, but a simple opening will not work. If we go smaller on the vent area dimensions, we can shorten the port a little, but trust me, there is a place wehre you can go too small.
From experience, I once tried a ported box design for one of our 06KM10 marine woofers for a location that only had about 1.5 cubic feet to even build a box in. The port had about 15 square inches of area and about 12" length; it had a proper tuning but it was too small, and it huffed and chuffed and whistled and made all sorts of horrible noises... I ended up squrting the port full of expanding insulation foam and painting it black so at least the box still looked ported...

Yes, the volume I quoted should take care of your slot port displacement, assumine you use the exterior walls fo the box to help define it. If not, we need to consider adding some more gross volume.


As far as attaching to the existing panel, there are lots of options. I have seen people build the entire box with the woofer mounting board, and then slide it up snug sandwiching the toe-board between the woofer and the box. I have also seen some where the to-board wall IS the wall of the box, and the thing is assembled by shoving the open-ended enclosure up on the wall, squirt lots of some sort of adhesive/sealent, and then install several screws to pull the whole thing together.

If you do it right either way works well, so I haven't a solid preference. The key is getting a good seal, regardless which way you choose.

I know, I know, some might say something like: "Why seal a ported box?"

The answer is: "You don't want it to leak."

If you have a leak, it changes tuning, (the air has another way out) and the leak can have very high air velocities making noises like I shared above, the huffing and chuffing and whistling...

[Timmy!]

Why can't the port be 20" wide x 2.5" opening by 10.5" deep or are you tuning it with the "depth"?

[noworries]

Does the port have to be one straight shot, or can it go down and back, so to speak?

[philwsailz]

Why can't the port be 20" wide x 2.5" opening by 10.5" deep or are you tuning it with the "depth"?

Yes, Depth is key, and yet it is is dependent upon the port area. Simply trying to use an equivalent volume by switching around numbers will not work.

I dont want to even try to go into the math, but in general for a given box tuning frequency:

Large diameter ports need to be long, but they make very little excess noise due to air velocities.

Small diameter / small area ports can have relatively short lengths, but they are noisier than large ports, and can be too noisy!

[philwsailz]

Does the port have to be one straight shot, or can it go down and back, so to speak?

It can bend and turn. In fact lots of designs take advantage of this to get the lenth.

Say for example you have a box that is 15" deep, but you need a 20" long port. If you were using PVC as a port tube for example, you can use a 90 deg. elbow and turn the corner in the box to get the additional length. That does work, yes.

In a slot-vent box, you can do the same thing with your box design such that the side AND the back wall help define the port.

Go for it!

[Timmy!]

Hmmm - interesting with the vent doing a 90, that gives me some ideas.

[noworries]

I'm curious. What's it like to have a subwoofer thumping right in front of you? I get to drive the boat and while I'm willing to play along with the "need" to have tunes while riding, I don't want to be beaten to death by a speaker. I swore off of that idea after being stage left in front of the speaker stand at a Robin Trower concert ("Bridge of Sighs") in San Bernadino. There are still some Stratocaster notes that in my right ear just make my head ring.