Need Port Help ASAP

[ObTechAudio]

Hey guys,

I am needing some direction or reassurance in what I'm doing with my port. This is my first time working with an 18" sub and with SoundQubed equipment. According to soundqubed.com, the HDC3 18" wants a box anywhere from 5-6 cubes @ 31hz and a vent 96sq" x 18" long. To me, that port seems odd.

So I just got done designing my box. External dimensions are 25" x 25" x 26" but I'm using double sheets of .75 MDF, so each measurement take off 3". I calculate internal space at 22" x 22" x 23" = 11,132 inches = 6.44 cubes. Rough internal space after ONLY sub displacements is 6.4ish cubes. My desired tuning frequency is 31-32hz. So, I designed my port on both WinISD and CarStereo.com at 3" x 16" and 15.5" long.

Both WinISD and CarStereo said with that size of box (6.3 cubes internal), port size (3 x 16 x 15.5), and tuning frequency (31hz), I should have zero problem. After all displacements, I'll roughly have an internal space of 5.95 cubes, which is EXACTLY what I wanted. I'm asking you guys, because it's not what soundqubed suggests and that's what worries me. I want you guys to check out what I'm doing and see if it all looks good to go. I appreciate any insight or feedback.

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[ObTechAudio]

anybody?

 

[Matthewcorwin69]

In sure your good bro. Especially if you've confirmed your measurements on two reliable sources.

 

[brian84corvette 10+ year member]

did you remove the space the port will take up from your box when calculating the "net" volume ?

is that a thing ? ive always figured out my internal space with no port yet - then figured out the space the port will occupy

and subtracted that from the internal net cu

to then go back to the port calculator with those measurments and plug them in for the fine tune.

actually

dont listen to me im probably doing it wrong

lol

 

[ObTechAudio]

did you remove the space the port will take up from your box when calculating the "net" volume ?is that a thing ? ive always figured out my internal space with no port yet - then figured out the space the port will occupy

and subtracted that from the internal net cu

to then go back to the port calculator with those measurments and plug them in for the fine tune.

actually

dont listen to me im probably doing it wrong

lol

haha yes, I figured displacement before and after the port. I state that above. "I'm probably doing it wrong." Thanks for your input brian4corvette hahaha

 

[hispls 5,000+ posts]

Hey guys,
I am needing some direction or reassurance in what I'm doing with my port. This is my first time working with an 18" sub and with SoundQubed equipment. According to soundqubed.com, the HDC3 18" wants a box anywhere from 5-6 cubes @ 31hz and a vent 96sq" x 18" long. To me, that port seems odd.

So I just got done designing my box. External dimensions are 25" x 25" x 26" but I'm using double sheets of .75 MDF, so each measurement take off 3". I calculate internal space at 22" x 22" x 23" = 11,132 inches = 6.44 cubes. Rough internal space after ONLY sub displacements is 6.4ish cubes. My desired tuning frequency is 31-32hz. So, I designed my port on both WinISD and CarStereo.com at 3" x 16" and 15.5" long.

Both WinISD and CarStereo said with that size of box (6.3 cubes internal), port size (3 x 16 x 15.5), and tuning frequency (31hz), I should have zero problem. After all displacements, I'll roughly have an internal space of 5.95 cubes, which is EXACTLY what I wanted. I'm asking you guys, because it's not what soundqubed suggests and that's what worries me. I want you guys to check out what I'm doing and see if it all looks good to go. I appreciate any insight or feedback.

Where are you getting 31hz tuning? They have recommended box specs which are for much higher tuning. Not to be a wet blanket here, but why not just go with what the manufacturer recommends?

 

[ObTechAudio]

Where are you getting 31hz tuning? They have recommended box specs which are for much higher tuning. Not to be a wet blanket here, but why not just go with what the manufacturer recommends?

I get exactly what you're saying and you're not being a wet blanket. It just seems to me that their recommended port space of 96sq" x 18" long is just too big. That would roughly put my size of box in the range of 37hz, which is too high in my opinion. The original 31hz I had in mind is this particular sub's fs. I should have said that instead of "recommended," but with an fs of 31hz, their recommended port would be too big. That's why I've made this particular design to 5.95 cubes @ 32hz after all displacements.

 

[hispls 5,000+ posts]

I get exactly what you're saying and you're not being a wet blanket. It just seems to me that their recommended port space of 96sq" x 18" long is just too big. That would roughly put my size of box in the range of 37hz, which is too high in my opinion. The original 31hz I had in mind is this particular sub's fs. I should have said that instead of "recommended," but with an fs of 31hz, their recommended port would be too big. That's why I've made this particular design to 5.95 cubes @ 32hz after all displacements.

I'm going to say that the company who designs and sells them probably has a good idea of optimum application, but suit yourself.

 

[ObTechAudio]

I'm going to say that the company who designs and sells them probably has a good idea of optimum application, but suit yourself.

I get what you're saying, but do that math. Doesn't something seem off? Another Soundqubed forum I'm part of seems to agree that the port recommendations on SQ website is off.

 

[hispls 5,000+ posts]

I get what you're saying, but do that math. Doesn't something seem off? Another Soundqubed forum I'm part of seems to agree that the port recommendations on SQ website is off.

SQ recommends a box but their recommended boxes are NOT 31hz for anything they make. They're essentially an older DD 95XX knockoff and use the same "DD box". I'm very confident that if they intended you to tune at 30hz they'd put those specs on their site.

Use the box they recommend for best results, if you really need to listen to whale songs or pipe organ music you should probably invest in a woofer that's designed for that application.

 

[T3mpest 10+ year member]

I get what you're saying, but do that math. Doesn't something seem off? Another Soundqubed forum I'm part of seems to agree that the port recommendations on SQ website is off.

Couple things.. First off a 3x16 inch port is TOO SMALL for an 18inch subwoofer.. Go graph your airspeed in winisd, without a computer in front of me I can tell you your well above 20m/s at full tilt.. Second, the lower you tune a box, the lower airspeed you actually need to avoid port compression, winisd will NOT show you this, it'll just show lower airspeed with lower tuning which is great, but it NEEDS to be lower to be adequate. A port tuned at 20hz with 25m/s airspeed is too high a port tuned at 40hz with a 35m/s airspeed will actually suffer LESS compression effects. The port airflow switches directions more often, which stops turbulence from forming.

Your doing 2 bad by switching this design up.. First your lowering tuning, which means you need a bigger port and lower airspeed for your port to be effective.. Then to keep your keep your port length managable, your shrinking your port size way down so the port fits easily and doesn't eat up all your airspace.. However, all the airspace makes your woofer nice and effecient at driving that port. In this case driving it right into compression where it's not doing it's job.

A large 5 or 6inch port tuned at 37hz will outperform a 3inch port when you start throwing 2kw at it, even below tuning. A 3x16inch port is more a long the lines of a high powered 12inch woofer or a mid level 15, not a high powered 18. These subs use very stiff suspensions so going below tuning isn't a problem, but if you want the output in the mid 30's and up that your paying for, you need to use a nice big port. Also when designing a port it is always preferred to use as few bends in the port is possible, air doesn't like to make turns lol. You also want to keep at least a port widths distance away from the back wall of the enclosure for the same reason, if not it acts as a bottle neck.. If you look at your enclosure depth of 25 inches, a 17 or 18 inch port accomodates this VERY well, again, something a box program won't show you, that holds up in real life.

Box programs like winisd won't show you everything although they DO have their place in making a good design. Anyway if you can fit a 30hz tuning with an adequate sized port and proper airspace, go for it. However I think you'll find a 6inch 30hz tuned port is going to be a little to long to fit your design without at least 1 bend and will probably take away from your airspace quite a bit which lowers low end output regardless of tuning.

 

[Popwarhomie 5,000+ posts]

This^^^^

 

[ObTechAudio]

Couple things.. First off a 3x16 inch port is TOO SMALL for an 18inch subwoofer.. Go graph your airspeed in winisd, without a computer in front of me I can tell you your well above 20m/s at full tilt.. Second, the lower you tune a box, the lower airspeed you actually need to avoid port compression, winisd will NOT show you this, it'll just show lower airspeed with lower tuning which is great, but it NEEDS to be lower to be adequate. A port tuned at 20hz with 25m/s airspeed is too high a port tuned at 40hz with a 35m/s airspeed will actually suffer LESS compression effects. The port airflow switches directions more often, which stops turbulence from forming.
Your doing 2 bad by switching this design up.. First your lowering tuning, which means you need a bigger port and lower airspeed for your port to be effective.. Then to keep your keep your port length managable, your shrinking your port size way down so the port fits easily and doesn't eat up all your airspace.. However, all the airspace makes your woofer nice and effecient at driving that port. In this case driving it right into compression where it's not doing it's job.

A large 5 or 6inch port tuned at 37hz will outperform a 3inch port when you start throwing 2kw at it, even below tuning. A 3x16inch port is more a long the lines of a high powered 12inch woofer or a mid level 15, not a high powered 18. These subs use very stiff suspensions so going below tuning isn't a problem, but if you want the output in the mid 30's and up that your paying for, you need to use a nice big port. Also when designing a port it is always preferred to use as few bends in the port is possible, air doesn't like to make turns lol. You also want to keep at least a port widths distance away from the back wall of the enclosure for the same reason, if not it acts as a bottle neck.. If you look at your enclosure depth of 25 inches, a 17 or 18 inch port accomodates this VERY well, again, something a box program won't show you, that holds up in real life.

Box programs like winisd won't show you everything although they DO have their place in making a good design. Anyway if you can fit a 30hz tuning with an adequate sized port and proper airspace, go for it. However I think you'll find a 6inch 30hz tuned port is going to be a little to long to fit your design without at least 1 bend and will probably take away from your airspace quite a bit which lowers low end output regardless of tuning.

Awesome... My box is now a nightmare hahaha... I wish you would have said this earlier! Well, there goes hours and money down the drain.

 

[ObTechAudio]

Just ran some quick numbers... 3" x 16" = 48in^2, 2000watts, 32hz, vent mach: 36 m/s or 0.10 (36/340). Do I need to be concerned about port noise that's in a vehicle if the port speed is 36 m/s?

 

[T3mpest 10+ year member]

Just ran some quick numbers... 3" x 16" = 48in^2, 2000watts, 32hz, vent mach: 36 m/s or 0.10 (36/340). Do I need to be concerned about port noise that's in a vehicle if the port speed is 36 m/s?

It's not all about port noise.. If it was JUST noise, big ******* deal, 140db of bass and the trunk muffle that anyways. The MAIN issue is that even before a port chuffs it "compresses" and when it's chuffing its REALLY compressing. Basically realize what you see in WINISD is a 1w/1m response. It's the acoustic combination of your port and your woofer. Woofer does the higher notes, port plays notes near tuning, they both play stuff just above tuning, and below tuning they play stuff together as well, but out of phase.. However, a smaller port has a lower potential for moving air than a bigger one.. So when the port compresses all your notes near tuning will stop getting louder while the woofer keeps going.. So once you turn up the volume knob that nice low end the program shows you goes away as the port compresses.. Imagine a response much closer to sealed box, but even higher distortion due to the air noises and turbulence. So yes, it's a mess.. Will it sound terible, hard to say, turn it up and see what you think.. Generall speaking I try to keep port velocity below 20m/s for a box tuned at 30hz or below.. As I tune closer to 35hz I can do as high as 25m/s without worrying at all about port noise. These are just my main goals a little higher than this won't be a problem. When you get the sub in play something like White Girl" by Young Jeezy. It has a 32hz tone and 58hz tone.. Play it at low to medium volume and listen to the difference in SPL between the high and low note.. Then do it again at full tilt and see if the higher note isn't abit more overbearing than it was compared to at low volume.. If it is, that's port compression

I would still strongly suggest finishing it for now, run it for the time being, but build a new box with the guidance I and SQ have given you.. I think you'll find the A/B comparison enlightening.