First venture into ported box

[chawski 10+ year member]

Hey guys, looking to build my first ported box and have a few questions. Sub in mind is a 10" Kenwood kfc-something model sub. Manufacturer recommends 1.6cuft with a 5"L x 3.5"Dia port for 35hz tuning. Running off a kenwood amp, i think around 800ish watt. I mainly listen to rock, country, a little rap here and there. Not looking for any competition type building, just filling in the low end. Box is going in a civic trunk. I plan on just making a simple rectangle box, as shallow as possible while using as much width as needed bw the wheel wells (I think I have approx 30ish inches)

Few questions:

1) is it safe going for a slightly lower tuning, say 32ish or should I stick with the 35 as suggested by kenwood.

2) is there any appreciable difference bw slot port and a cylinder, other than less wood? I only have a few days over thanksgiving break so looking to keep it simple

Thanks for any input!

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[hispls 5,000+ posts]

Stick with 35hz tuning. Round port is accoustically supperior, though you'll likely not notice any difference provided no width is way too thin. DO make sure you don't crowd the port opening into anything.

 

[chawski 10+ year member]

awesome, I was thinking sub back, port up. should work ok?

edit:

Was looking online at ports and found some for pretty cheap from precision sound products. Only question I have is the retailer I found only has 3" and 4", no 3.5 as kenwood recommends. Is this a problem at all or just as long as its the correct volume it doesnt matter? Am I better off with the 3 or the 4?

 

[Moble Enclosurs 10+ year member]

If you are limited on the length of the port and the area, you have the ability to correct it with chamber volume, but again, this is only if you have no other options. SO, if you get the closest to the recommended one (my recommendations may be different so Ill leave it simple for now), then you can adjust the chamber volume to get the sound you want as long as it does not cause issues by making it too small or large. -just trying to keep it simple as requested...I would not actually recommend this if you do not know the effect it will cause.

 

[CAT MAN 5,000+ posts]

Stick with 35hz tuning. Round port is accoustically supperior, though you'll likely not notice any difference provided no width is way too thin. DO make sure you don't crowd the port opening into anything.

i would not say this. i find slots a bit more efficient spl wise in what ive done

 

[Moble Enclosurs 10+ year member]

i would not say this. i find slots a bit more efficient spl wise in what ive done

It's relative. Depending on the application, situation, and preference and also position of the port. I would like to possibly do a comparison for this as well for you guys. Maybe soon. That way, it can be determined more easily for each individual. But generally, slot ports are what I use if that means anything. So, again....relative at this point. it is when the slot ports have a greater ratio than 8:1 or say 9:1 that it is really less efficient. Round ports can be good for SQ systems because of vortex propagation, much like a gun barrel that guides a bullet. Slot ports are pressure related and may have more resonances, therefore, tuning is more concentrated than overall response. If you want to have the slot port work better for SQ and not SPL, make it as square as possible. Hope that helps.

So, to the OP, maybe this will help you determine what you want to do with the port before purchasing anything.

 

[chawski 10+ year member]

port length will not be an issue, just questioning width.

So if I used a 3.5" aeroport x 5" long, thats approx 74sqin of port area. Would it be correct to say that if I used a 4" aeroport, going 4inches long, again giving me approx 74sqin of port area, it would work, or do I really need to find a 3.5" as per manufacturer?

edit - I think the best way to phrase my question is if my box has an internal volume of 1.6cubes, how long does my 3" or 4" aero port need to be to keep my 35hz tuning frequency, given that 3.5" diameter doesnt seem to be an option

 

[Moble Enclosurs 10+ year member]

port length will not be an issue, just questioning width. So if I used a 3.5" aeroport x 5" long, thats approx 74sqin of port area. Would it be correct to say that if I used a 4" aeroport, going 4inches long, again giving me approx 74sqin of port area, it would work, or do I really need to find a 3.5" as per manufacturer?

Actually, a 3.5" is only roughly 9.6in^2 of area. It would be 62.16cm^2. 74in^2 port is about 9.7 inches round. Now, square inches is area, and cubic is volume(when you include length). I wouldn't concentrate on length right now until you get area down. If you use a 4" instead of a 3.5", that is not a big deal at all. Length will just need to be adjusted from the 3.5" aero tuning just a bit longer is all.

A 4" aero is about 12.59in^2.

 

[chawski 10+ year member]

sorry, not sure if I edited before you posted a response. If I run the 4" what length do I need. Im just not sure how to calculate given the flares? Is only the actual cylinder length calculated or does the area of the flares matter as well?

 

[Moble Enclosurs 10+ year member]

Well, if the flare is exponential, then it is generally around half the length of each flare added to the length of the port, but a good number to use is about 1.5". The nominal factor is just under 3/4" but for aero, best to use 1.5 as a simple flange is not used. So, this is added 1.5" to each length for each flare. SO, a port that is 32", should be about 29" plus the flares if the flares are on both sides of the port. Or about 30.5 plus flare for single flare port. This can vary, and you may get other answers as well, or even corrections to this, but this is based on an exponential flare rate and is very generic. For more of a hyperbolic flare, it may be shorter, or you can use the diysubwoofer page for that as well.

 

[chawski 10+ year member]

so for calculating how long of a port I need, as long as I retain the internal volume of the 3.5dia x 5long, its golden?

 

[DukeNut 10+ year member]

try using this precision sound port calculator link Products Menu

 

[chawski 10+ year member]

yea I gave that a shot. Im getting 15.5 for the straight section and 16.5 for the flared. What unit is that though

 

[DukeNut 10+ year member]

that is inches

 

[chawski 10+ year member]

thats almost 30 inches of port length... seems a bit on the long side, no? Manufacturer states a 3.5dia x 5" Long...kinda confused how I went from 5 inches long to 30 inches long

After re-looking my math, the 3.5"x5" port gives me 48cuin of volume. If using a 4" dia port, to retain the 48 cuin of volume, Im calculating 3.84 inches long. Sorry for so many questions, but Im just confused as to how psp's calculator is giving me 30inches long, yet my 3.14r^2 x H gives me just under 4 if using a 4inch dia port?