box check - 2 BTL 15s at 3200w vented

[merzbow 0]

Does this look good?

[Ohjay 116]

hmm, I can't see the images

[merzbow 0]

hmm, I can't see the images

I can see them fine from multiple computers... but I will put them on a different site, perhaps that will work better:

<original second post repeated now...>

Changed my mind, I want to do a middle T-shaped port now. Here are the new specs and diagrams. 3.65cf net per driver, which is within Fi's range of 3-5. Port area is 16.41 in^2 per cf, above the 12-16 recommended by Fi because there are TWO drivers sharing the same port. Modeling with WinISD puts port velocity within the range of the 23-30 m/s I'm seeing with Fi's recommended enclosures, so I think port area OK.

Also, I'm going to be using a Sundown SAZ-3500D, so I'll be running with 3500 watts at least, not 3200 as in the thread title.

Opinions please before I potentially waste a LOT of money on materials? I cannot change the outer dimensions, that is the max I can possibly go, the only thing I can adjust now is the port.

Edited May 11, 2011 by Merzbow

[Quentin Jarrell 671]

Is your port 34 inches long. If I am reading the sketch up correctly it appears you only have about 24-27 inches of port length

[merzbow 0]

Is your port 34 inches long. If I am reading the sketch up correctly it appears you only have about 24-27 inches of port length

31 inches actually, you have to measure from the middle as it bends. From what I understand, you can consider a T port to be the same as an L port by "stacking" the two upper halves of the T on top of each other. So if we do that here, then measure down the middle, we get 0.75 + 16.75 + 2.75 + 2.75 + 8 = 31.

[merzbow 0]

Is your port 34 inches long. If I am reading the sketch up correctly it appears you only have about 24-27 inches of port length

31 inches actually, you have to measure from the middle as it bends. From what I understand, you can consider a T port to be the same as an L port by "stacking" the two upper halves of the T on top of each other. So if we do that here, then measure down the middle, we get 0.75 + 16.75 + 2.75 + 2.75 + 8 = 31.

And before anyone asks this post is where I got this technique from:

http://www.caraudio.com/forums/enclosure-design-construction-help/272321-port-tuning-question-3.html#post3656749

I don't know enough about the theory to verify if this is actually correct, but the poster seems reliable.

[merzbow 0]

Anyone at all have experience building these types of boxes (dual subs, shared center port)? I'm going to start putting it together this weekend so time is running out... as for bracing, I think the port walls will be enough, except I will also fiberglass the interior edges for added strength.

[slim2fattycake 85]

Is your port 34 inches long. If I am reading the sketch up correctly it appears you only have about 24-27 inches of port length

31 inches actually, you have to measure from the middle as it bends. From what I understand, you can consider a T port to be the same as an L port by "stacking" the two upper halves of the T on top of each other. So if we do that here, then measure down the middle, we get 0.75 + 16.75 + 2.75 + 2.75 + 8 = 31.

Its 0.75+16.75+2.75+0.75+8=29" physical length since there isn't a triangular divider at the end of the wall in the port splitting the original port. Effective length is 29+(2.75/2)= 30.375". To me, its basically two ports.

I have never built a "shared" center port so take it however you like.

[Quentin Jarrell 671]

I've got a tad bit of experience

[slim2fattycake 85]

So how did you come up with 24-27inches? Did you not count the 3/4" MDF thickness at the exit and at the turn?

[merzbow 0]

Is your port 34 inches long. If I am reading the sketch up correctly it appears you only have about 24-27 inches of port length

31 inches actually, you have to measure from the middle as it bends. From what I understand, you can consider a T port to be the same as an L port by "stacking" the two upper halves of the T on top of each other. So if we do that here, then measure down the middle, we get 0.75 + 16.75 + 2.75 + 2.75 + 8 = 31.

Its 0.75+16.75+2.75+0.75+8=29" physical length since there isn't a triangular divider at the end of the wall in the port splitting the original port. Effective length is 29+(2.75/2)= 30.375". To me, its basically two ports.

I have never built a "shared" center port so take it however you like.

The (2.75/2) you mention above is end correction, right? Hmm. (The Torres calculator actually doesn't appear to take end correction into account, seems like a bug). So I guess I'm not really that far off. I'll be happy with anything reasonably close to 32hz to be honest, what I'm trying to avoid is screwing it up REALLY badly. I suppose a triangle divider might help reduce turbulence by redirecting the air towards the mouth before it merges.

Edited May 13, 2011 by Merzbow

[Notorious97200 339]

triangle divider : that may be a good idea. I see that often in that kind of boxes.

[Quentin Jarrell 671]

I was two inches off by eye balling it. Officially I see the port as 29.89" long. Each top of the "T" still needs to be almost 4 inches longer. leaving it as is will tune it to about 33.75 hertz

[suicideking602 8]

Skip to the end of the vid to see how my port is. It worked great for me, i believe i got that design from Digital Designs.

Good luck on your build...

[merzbow 0]

Audibel, that also looks like a logical way to analyze the air flow, assuming the air streams are taking the "nearest" route outwards (which I could encourage with a center divider).

So ignoring the Torres calculator for a moment, WinISD (set to 7.3cf at 32hz with this port area) wants a vent length of 32..46" if I set "two flanged ends" as the correction, which means 32.46" - 29.89" = 2.57" extra on each side of the "T". You appear to be setting WinISD as "one flanged end", which produces 33.91", and 33.91 - 22.89" = 4.02", which is where you must be getting the 4 inches from. I think the "two flanged ends" is more accurate for a slot port, so right now I'm leaning towards adding the 2.5".

Edited May 13, 2011 by Merzbow

[Quentin Jarrell 671]

I don't use winlsd because it doesn't account for parallel wiring. I use leap. I don't see any flanged ends on your design. The only reason you would consider 2 flanges is if you were using a port such ad an aero that had flanges on each end.

The reason you add half the radius of the port to the port length is because you have your port against the enclosure wall.

Don't add any flanges to winlsd because you aren't using any in your box

[merzbow 0]

I think you're mixing up "flare" with "flange". WinISD help file defines a "flanged end" as a port that terminates in a baffle, their diagram makes that clear. So I'd put the outer opening of this port in that category. As for the inner port opening, yes, that requires adding end correction also. WinISD's "flanged end" correction factor is to add 0.4 times effective diameter, which also corresponds closely to what we need for the inner port correction. So hence why I set it to "two flanged ends".

Edited May 13, 2011 by Merzbow

[Quentin Jarrell 671]

A flare is like on an aero port. A flanged port is like when spl guys cut PVC in half and put it on the baffle to help transition airflow. If you are flanging both sides of the port then you need to go by your measurements measuring from inside the flanges As winlsd states

Edited May 13, 2011 by Audibel Customs

[merzbow 0]

Decided to split the difference, a little bit, and went with 10.75" on each of the "side Ts". By any account this should be pretty close to 32hz, with proper net volume to each sub:

I can't put the top on this beeatch until the subs arrive, which is taking Fi a lot longer than they said they would originally. Anyways I can do electrical work in the car in the meantime, and also it's 45 pucking degrees in California in late May so I can't fiberglass the interior edges of the box yet until it warms up.

I'm still debating whether a V brace is necessary at the back of the port. My inclination is "no" at the moment, unless someone tells me they didn't do it and it sounded like ass.

Edited May 17, 2011 by Merzbow

[merzbow 0]

Oh happy day my subs are shipped. This is going to be a SILLY weekend...

[bakedboy08@yahoo.com 6]

So what kind of subs are going in that box. looks like a well built enclosure, very nice, I think a V brace would help alot to direct the air flow out.

[merzbow 0]

So what kind of subs are going in that box. looks like a well built enclosure, very nice, I think a V brace would help alot to direct the air flow out.

2 BTL 15s (per the thread title .

The port is wide enough I can put a V brace in the back after it's built, so that's something I can experiment with later if I need to.

[merzbow 0]

Alright I'm tired of fighting my car and am getting an SUV. Will be getting two more BTLs 15s (I accidentally ordered two more 12s today, lol, hopefully I can get that fixed on Monday over email). If anyone in the CA Bay Area wants the half-built box pictured above for free (plus two MDF sheets for the top, that I haven't cut circles in yet), let me know...

Edited May 23, 2011 by Merzbow

[bakedboy08@yahoo.com 6]

whoa for free id be willing to take that off your hands, where at in the bay area are you. im about 2 hours south of L.A in bakersfield id be willing to take the drive haha.

[merzbow 0]

whoa for free id be willing to take that off your hands, where at in the bay area are you. im about 2 hours south of L.A in bakersfield id be willing to take the drive haha.

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