Question on Port placement ...Again!

[jwc]

Ok...let me start over with this one.

Gonna put two 4 inch diameter ports on this cabinet I've got here. 33 inch tall bass bin and only 19 1/2 inches wide. Internal volume is 6.5 cu ft. The woofer is 15 inches.

Now I had a recent thread going that mutated into port placement and I seem to have gotten confused a little. A couple of gurus suggested placing the ports in a vertical alignment if I understand it correctly. Please verify what I have here and make suggections please

jc.

[D-MAN]

Jim, I would do option "B". Arrange to suit the eye (and keep out the mice!). The ears won't be able to tell!

DM

[jwc]

Ohh too funny. Didn't think about critter proof. It will have grill.

I think I will put the woofer driver high...close to the mids and tweets and then put the ports towards the floor. Somewhat Like the Cornwall 3....except...skinnier.

[D-MAN]

It's closer to the truth than you might think!

When I was a kid (lived on a farm), had a mouse set up shop inside the Klones that I had at the time.

I opened it up one day to check the woofer, etc., and the front of the cone between the baffle slot was full of newspaper shreds.

Dang little vermin! You have to watch out for them! No kidding!

DM

[DrWho]

Is your picture to scale? And are you taking into account the extra mouth size of the flare? (are you even go with flared ports?)

Anyways, you want the ports as close to each other as possible and as far away from any internal boundaries as possible (at least one port diameter away). What I usually do is draw a box of allowed port position and then manipulate the ports to fit. Since you've got 4" ports, draw a box that is 4" in from all the edges (including the rear).

And since you're front ported, you'll want some form of absorbtion on the rear panel to minimize rear wave reflections from making their way out through the ports.

[jwc]

Doc. I am aware of everything you just posted.

However, I don't know the dimensions of the "flares". This isn't published on partsexpress.com.

Here is more specifics on the cabinets. They are already made! I just haven't cutout the baffle/motorboard and mounted.

I can only assume you like "B" setup vs "A". What do you think?

jc

[DrWho]

Well I'd wait until you get the ports before you start cutting...they

even come with a cutout paper for you to follow. As far as the flares,

I can imagine that they are 8-9" total outer diameter. I've not used

the 4" versions so I'm not sure. But if I remember correctly it was

twice the inner diameter.

I was originally thinking your cabinet was much taller and so was

thinking of Option-A. Here is a scale drawing for you assuming 8" flare

of the ports...Option-A barely fits altogether and results in 25% of

the total port area being outside the target zone. Option-B has the

same problem (25% outside too), except the overlap is the same for both

ports and the closest it gets is further away with B than A. Option-C

fits in perfectly satisfying all the design goals...but is probably the

least aesthetically pleasing option. But you did mention grills and

it'd probably still look cool to have stereo symmetry (ie, put the

right port high on the right speaker and the left port high on the left

speaker).

[jwc]

The cabinet overall will be taller as the mid and tweeter drivers will be in a seperate cabinet. The bass bin total height internally is 31.5.

Called Parts Express

That dual flared 4 inch diameter ports has a total flare dimension of 7.25 inches. Therefore option "B" of your diagram may work if you move each port "inside" 3/8 inch.

jc

[DrWho]

Well that's good to know - nice legwork.

B still hangs over a bit but it's no big deal. (It really wasn't a big

deal at the beginning either). The ports are adjustable so if you run

into any problems you will have plenty of lead way for making

corrections.

[jwc]

Ok. Here is what it looks like on the motorboard/baffle.

Would the first choice be the far left?

[DizRotus]

I vote for the center one.

[DrWho]

Left is the best option of the three...I would move the ports closer together and I would move the port down a bit too (so that the port mouth is 4" from the bottom). If it's already 4" then that's where it should go.

[jwc]

Well. This is a tough issue for me. If you think the ports ought to be 4" from the bottom, then that is more like the middle one. The flare is pretty big on these things.

I was thinking that I wanted to get the drivers as close together as possible. Therefore I wanted the woofer at the very top of the cabinet. It is interesting that on the Cornwall 3 that the woofer is moved up very close to the midhorn and the ports remained close to the floor.

The other concern of mine is testing these ports at differnet lengths. Since there is a flare at both ends, I will have to remove the motorboard or woofer to get access to the back flares. I will then have to remove the back flare from the inside and the unscrew the outside flare to pull the thing out. Then I will be able to cut it shorter.

I was thinking of maybe doing the testing w/o the inside flare but the problem is that the flare attachment itself is almost 3 inches long. What a pain.

[DrWho]

Well. This is a tough issue for me. If you think the ports ought to be 4" from the bottom, then that is more like the middle one. The flare is pretty big on these things.

4" from the edge of the flare, not the tube. Think of it this way: you don't want any obstruction of air flow happening around the port. The point of the flare is to spread out the airflow (which reduces its velocity) - which means air is flowing down the sides of the flare too.

As far as changing the tuning after the fact...I usually just leave the bottom panel of the enclosure unglued so that I can unscrew it and gain access to the insides. Other times you can get by with removing the active driver. You can also just pressure fit the port on the front and remove things that way too. The size of the hole will be more than big enough to fit your hand inside to reconnect everything.

[Rotorhead09]

Just wondering, I am using the same ports(4") on my LS project...

So, would you make the holes the same size as the flair? or pipe size?

This speaker building is all new to me...

Thanks,

S Lee

[Jay481985]

I believe you need to cut the ports a little smaller than the flar but larger than the internal diameter (i.e. 4 inches)

Also I vote for number 2 or b or whatever I am not hitting the back

button since it takes 5 minutes for thios page to load. As with slot

loaded ports you would want them next to the wall to get better

bracing/stiffness. With round ports you should space them atleast 1

diameter of the port away, but there are designs that go against this

but no one really notices.

[DrWho]

The ports come with a cutout diagram...the hole will be smaller than the flare, but bigger than the port tube. There is a 3/4" deep lip on the rear of the mouth flare designed for pressure fitting into the hole you cut.

[jwc]

Hmm. I didn't notice a cutout template. Will check again when I get home.

If I were to get the ports 4 inches from the floor, then I would have them fairly close to the woofer. I didn't think about slot ports and there need to be against a sidewall or floor of a cabinet for bracing purposes. That makes good sense. Never thought of it that way.

[Rotorhead09]

I don't recall seeing cutout plans with mine either.

Jwcullison, I believe these plans on the LS project that I am doing was your Idea.

Have you ever ported LS through the to section? or just an Idea?

[DrWho]

Hmmm...maybe the cutout diagram only came with the smaller versions??? I see the 2" cutout diagram on their website:

http://www.psp-inc.com/