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Simi's Official 12" subwoofer build.

Exactly.. the three side walls and then the baffle as the 4th side..

I didn't realize that would change things even more... I figured a hole is a hole, but I guess once you start thinking about friction, turbulence and all that fun stuff...

I can make it, at least for testing, so that the front baffle is removable until I can nail the right size, then mount the baffle permanente.
 
WHEw.. OK... thanks.. I thought I messed up....

Wondering when I'm gonna get the box... .got all my other stuff, and haven't gotten any shipping info from harrison.. I trust them though. Looks to be a good legit company.

If I don't have it when I get back from Holiday, I'll give them a call.. I should have it I'd bet by then though.
 
To get acceptable airspeed on a 14" slot using 3 side walls, I'm getting that it's got to be at least 1.5"x14", which puts it at a whopping 32.25" long *edit: this is wrong*... You're going to have a pretty long port no matter what. What kind of cabinet volume are you aiming for here?
 
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My cabinet, with bracing and the driver subtracted should be right between 2.75 and 3cu ft... I just need to mess with the depth I plan to use, after I decide how I'm going to brace it. I got two bracing ideas I'm playing with, so will need to figure the lost space for each to decide the depth I'll make the box.

Ok.. so I can understand that I'd need to make the slot at 1.5" wide, but then I'm not understanding the length.. I know it will be 14" tall... but to me, length is like the tube you put in the port hole if you use a round port...

So what does length mean when using a slot?

BTW, I was aiming to tune between 25 and 27hz
 
Okay, showing my work so others can check this time. Here's what I'm getting with 2.75 ft³:

1. 14" x 1.5" port keeps airspeed good to 200W+. That's 3.80x35.60 cm.

2. Length for 27Hz with no end correction is 71.4 cm

3. effective diameter = sqrt(3.80*35.60*4 / pi) = 13.12 cm

4. estimated end correction for this type of slot = 2.227*13.12 = 29.23 cm

5. 71.3 - 29.23 = 42.07 cm = 16.56 in

So, 14"W x 1.5"H x 16.56"D... :scratch2: I think that's right.

That's 0.2 ft³ port volume to subtract, so re-check using these dimensions and 2.55 ft³ cab volume and... tuning goes up 1Hz so that's fine. (EDIT: whoops, probably should have used the effective port volume, which is 71.4*3.8*35.6cm = 0.34 ft³ ... still only moves tuning 1.8Hz)
 
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Wow.. this kinda math is way over my head... and that's why I was asking for help..

I'm still not understanding how Length plays into the equation, since you're not using anything on the back side of the slot to make it like a pipe in the port... or are you?

I am glad to see this is workable and do-able though aparently. It helps make the build easier by not having to cut holes and stick pipes into them... and helps from taking up more space in the box using pipes.
 
similost said:
I'm still not understanding how Length plays into the equation, since you're not using anything on the back side of the slot to make it like a pipe in the port... or are you?
Click to expand...
No, you do. It's a rectangular pipe you're making, one piece of wood going back into the box. Like this except hopefully without the L-bend:

175562.jpg


Tubes are easier in almost every way, but slots are neat.
 
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aaaaaahhh... OK.. well crap.. didn't know I would need to do that.. and if I did, then I would have to change my bracing ideas... and no, at 16.5" I won't have to make a bend. I got enough depth. I think I'm going to be right around 20" deep.

Soooooo... I was thinking if you made a slot, you wouldn't have to add depth. Like my Peavey SUB-118 bass bins... it's just a rectrangular hole in the front... Like a pair of altec A7's have too... just a hole.. no length.

I guess with a small box though, you have no choice and have to add length, because you wouldn't be able to fit a hole large enough?

But still.. this way would help add more brace too. Simple to add that extra wall.

I guess this was why I wasn't able to figure out the slot.. I did get 1.5" somewhere, but then that length kept throwing me, because I didn't know that's what I had to do.
 
Yeah, you kind of need to luck out on driver parameters to be able to get away with just the wall depth. It works the opposite way from what you're thinking, though. In this case, you could drill a circle a little over 1" to hit your tuning, but you can't do that because the airspeed would be insane. As you increase the port area to decrease airspeed, you have to add length to keep the same tuning.
 
hehhe.. blow out a candle at 20 paces..

Ok.. anyway, thanks so much DT... believe it or not, the numbers I had come up with were right about the same as what you got using the calculators I was, but I didn't get the length, so that's why I thought I was doing it wrong.. and now I understand. MUCH APPRECIATED!
 
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Hopefully some of the expert builders can weigh in on that length calculation. Building a non-adjustable slot port makes me nervous.
 
Yes use whatever software you are useing and figure the surface area of a pipe with PI then use the same surface area to figure your rectangle. length is the same as round.
 
I was getting right around 16.5" myself when i was figuring 14x1.5"... I played with that, and with 2"... I looked at 1" too, but those numbers weren't looking so good.

I'm just glad to hear I was on the right track, even though I had no friggin clue what I was doing :D
 
dumptruck said:
End correction is very different when you use a full side of the box - see where I used 2.227 above.
Click to expand...

If you want to add the end correction, then use the additional math to find the answer, but the basics are still the same.

I am just going for the simple explination for clarity.:yes:

But your math does seem correct. I do not mean to argue as your points are valid and understood!:thmbsp:
 
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End correction.. that's when you leave the end of the single board square correct? So would it help if I half rounded the end of it?

I read about that a bit if that's what you mean, and the more I read, the more I get confused about what I should do..
 
Spectrum77 said:
OK, you got the LAB12. Check the 3Pi (Wayne Parnham, Pi Speakers- I posted a link in other S/W thread) for box dimensions and port length using that driver.
Running two of these with Yamaha PC-2002 (250W per channel pro amp).
That X/O box thang does look good- have been using a Pyle PXLR2 car X/O with success, adjustable and cheap- although there is a hummm somewhere in the line: http://audioroundtable.com/forum/index.php?t=msg&th=1859
Click to expand...

This was my thoughts exactly when I saw the driver you were going to use. I think I recall Wayne gets response down to 20 hz, and the 4Pi and 3Pi are very very similar in efficiency to Simi's speakers. I think Wayne uses 3 of them, which would help with efficiency as well as evening out bass response around the room.

Russellc
 
similost said:
BTW... while this thread is back active again, Yesterday I was trying to figure out what size slot I would need to create in order to port these boxes.

I read, and re-read, then scratched my head a lot, and just couldn't figure out the math on how determine what size slot I need to use... is there someone here that would be able to tell me if I gave you all the measurements you'd need to figure it?

What I was thinking about doing, on the front, just create the front baffle shorter than I'd need to fill the complete space... so basically, the slot will be 14" tall on one end of the front baffle... I just couldn't figure out how wide I'd need it.. .as in, instead of cutting my board to 20" wide to fit the front of the box... cut it to like 19, or 18" or what ever..

Make sense?
Click to expand...

Again, those are the same drivers Wayne uses in his Pi subs. Why not follow his design, its proven and works with the Hi-Eff drivers.

Russellc
 
So plans take another turn here... Ended up going after the CX3400 XO for sale in bartertown.. .

Wife's gonna love me when she starts watching me stack up three amps in the livingroom... Been thinking about bi-amping my barziwaves for a while.. I bet with the subs tri-amping it all is going to be a HELL of an inprovement.

:thmbsp:

Oh. and I was looking for the cabinet sizes for Wayne's speakers, but I can't seem to find any of the design and measurement info.

You have a link to that info?
 
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