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Discussion Starter · #1 · (Edited)
I was reading up on trying to build a diy sub. I was looking for a low budget option and came across the infinity 1260. The only box I was able to find was one with a slot port. What I was wondering is there any way to build this with round ports? I'm not sure how to use the calculators so any help on this would be greatly appreciated. It will be used for home theater, and tuned as low as possible with the 300 watt bash plate amp. I think I've got everything in there.:D
 

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short answer: yes - it can use round ports.



Short..ish... answer: Box size and port area x length determines tuning, not the shape of the port.



If you're really interested in learning how ^ kind of numbers get produced there is some good software (free) that works well. WinISD is the most common and it will let you input all the T/S parameters (details about the subwoofer) and it will show you what a box size / port size will do to the sound coming from the speaker. It can also be used to get an idea of how much cone excursion you'll get (or warn you if you're going to throw the speaker way past it's safe range).
 

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Discussion Starter · #4 · (Edited)
Thanks for the help guys. I will check out that program. I also thought I saw that the bash amp has a built in high pass filter at 18 Hz. Is this correct? Also would it have any effect if the speaker was down firing? Sorry for all the questions just trying to gain some knowledge.
 

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I've read in different places they have a high pass filter somewhere between 17.7 and 20 depending where I read it. Regardless it should work.

There is a figure for calculating if the port opens up near a wall or floor that can simulate the port being a bit longer. Likely not a big deal as long as you have the port farther away from the floor (if it's downfiring too) than it's diameter.
 

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I have 4 of these subs. All down fire. I would shoot for a 4.0 internal box an a single 4 x23-24 inch PVC port. Mine are getting 500w rms and they so great. Like said before as long as your internal volume is the same you can make it any denentions. I get no port noise. Please ask any ? You have. I will try to help. You can't beat these subs for even twice the money. Also if you use the bash amps I would still tune 16-17hz so you will have even less concern of of port noise. I had these running. Off of a 200 w plate amp and now a epx2000 each now gets 500w and it is a huge improvement. They no longer sound like they are running out of steam
 

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Those boxes above at a little over 2 cube would be way to small ported. You would have a big hump at 50-50hz and will sound more like a cheaper store bought sub. Just my 2 cents but if your gonna make your own you might as well make them the best you can. Are you limited on the size of box?
 

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Discussion Starter · #8 ·
Ok so i messed with Winisd tonight. still not sure how to read everything on there. I put in a 4 cubic foot box tuned to 19hz. and it looked pretty good. I think. I'm not sure how to post a screenshot of winisd though.
 

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I know what that looks like my front subs are the same I just uses a longer port so I could get the 17hz tune. I'm sure you would be happy with a 19hz tune. Especially if you have never had a sub capable of that before.
 

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Discussion Starter · #10 ·
It seems to me that when I try a single four inch port that I get a very high port velocity. What should I be aiming for in that department.
 

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Discussion Starter · #11 ·
Almost forgot I was modeling it with a 101 litre box. That's before sub and port displacement. I even tried going up to 170 litres. Maybe I will have to stick with an l port.
 

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I had the same problem. I was I think in the 30s. I ended up fairing the port and I have no trouble with port noise. You could also buy the precision ports from PE they are great. I just didn't want to spend that much for 4 of them. My rears even have a bend and I can't hear any port noise.
 

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Sorry my liters to cube conversions are not so good. Also not sure what you mean by l port. The trouble with two ports is the box has to be bigger to make up for the space it takes up. Also most 300-500 watt subs from svs and such have a single 4 inch port.
 

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Discussion Starter · #14 ·
The box I was thinking of building is 21 tall x 21 wide x 20.5 long. It comes out to 4.18 cubic ft I figured about 3.6 with port sub and braces. With a single 4 inch port tuned to 29 hertz was like 30 inches long. Not exactly sure on the port length but I know it was long. I tried a 6 cubic foot enclosure which flattened out freq. Response more and made the port a little shorter.
 

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Discussion Starter · #15 ·
Sorry I should have checked my post. I meant L shaped or slot port. I haven't modeled it yet but I'm sure it would get better results.
 

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I would roll with this
a 4 inch PVC is 3.75 internal. So they would be tuned closer to high 16s. If you could make then longer and less wide tall. But still keep the same internal volume you could keep the port straight.


Wood Thickness - .75 inches

Displacements - .18 cubic feet


Frequency - 17.88 hz

Box Length - 21 inches
Box Width - 21 inches
Box Height - 20.5 inches

Port Length - 25 inches
Port Diameter - 4 inches
# of ports - 1

Gross Volume(Feet) - 4.18 ft³
Gross Volume(Litres) - 118.36 L
Net Volume(Feet) - 3.79 ft³
Net Volume(Litres) - 107.27 L
Port Displacement(Feet) - 0.21 ft³Prt Displacement(Litres) - 5.97 L

Port Area - 12.57 in²
Port Area(Metric) - 81.1 cm²
Port Area Per Foot - 3.32in²
Port Area Per Litre - 21.42cm²
 

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Or try this. A square sonotube downfire with some 3 inch feet. Port on the top



Wood Thickness - .75 inches

Displacements - .18 cubic feet



Frequency - 17.74 hz

Box Length - 32 inches
Box Width - 17 inches
Box Height - 17 inches

Port Length - 25 inches
Port Diameter - 4 inches
# of ports - 1

Gross Volume(Feet) - 4.24 ft³
Gross Volume(Litres) - 120.06 L
Net Volume(Feet) - 3.85 ft³
Net Volume(Litres) - 108.97 L
Port Displacement(Feet) - 0.21 ft³
Port Displacement(Litres) - 5.97 L

Port Area - 12.57 in²
Port Area(Metric) - 81.1 cm²
Port Area Per Foot - 3.26in²
Port Area Per Litre - 21.03cm²
 

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Discussion Starter · #18 ·
Ok I had to do it the hard way, but these are some measurments I got. I don't even know if I can get a 5 inch port. One is with a 4 inch 23 inches long. The other is a 5 inch 37 inches long.


 

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You also have to remember that if your amp has a HPF at or around 19. It will suck down that low end you show. Witch inturn will also lower your port turbulance in the area you are concerned about. I honestly have no trouble with a flaired 4 inch port. And I have even taken the hpf out of the mix to see and it still does ok. But I now run it at at about 10 Hz. With 500w rms I never hear port noise especially at any of my seating locations.
 

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Discussion Starter · #20 ·
Yeah I'm just gonna roll with that plan. It should be ok because I will rarely feed it full power. Did you buy a flange for your port. If not how did you attach it? Glue obviously, but did you rounter or sand the hole you cut in the box?
 
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