Hairtrick port area?

[audioholic 5,000+ posts]

The larger the port the more air displaced. It will also have to be longer to get to a given tuning frequency. It is a trade off with space and displacement. Also, larger ports will have less port noise.
Or to be put simply: go a big as you can while keeping the desired net volume of the enclosure.

That's not exactly true. A smaller port will have higher port velocity to compensate for less port area, not just less air movement. Its this higher port air velocity that causes the audible turbulence we call port noise.

 

[CadillacMatt 10+ year member]

no ports small ports and large ports do hairtricks
the actual hairtrick depends on the amount of woofers and power..

And don't forget about the positioning... when I turned the massive sub box to face inward instead of towards the trunk lid in my '95 Deville, and cut a slot in the rear deck, you can feel waves of air being moved over your hapless body //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

Also, it's much easier with a hatchback or SUV //content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif

 

[DDbump 10+ year member]

The larger the port the more air displaced. It will also have to be longer to get to a given tuning frequency. It is a trade off with space and displacement. Also, larger ports will have less port noise.
Or to be put simply: go a big as you can while keeping the desired net volume of the enclosure.

couldnt of said it better.

 

[Rashaddd 5,000+ posts]

That's not exactly true. A smaller port will have higher port velocity to compensate for less port area, not just less air movement. Its this higher port air velocity that causes the audible turbulence we call port noise.

What happens when you use a garden hose to try and push the same amount of water/min as you would through a fire hose? Not just increased velocity, in fact velocity eventually stays the same, and you get nothing but friction and therefore significantly less total water being displaced due to the opening being too small.

The friction caused by the higher air velocity is what really causes the turbulence, and that same friction is loss, and is present whether you can audibly hear it or not. I don't believe that whether or not we can hear it is a good indicator of whether or not we will benefit significantly enough to justify increasing port area.

 

[skmfkr 5,000+ posts]

And don't forget about the positioning... when I turned the massive sub box to face inward instead of towards the trunk lid in my '95 Deville, and cut a slot in the rear deck, you can feel waves of air being moved over your hapless body //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
Also, it's much easier with a hatchback or SUV //content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif

or pretty much anything but a a coupe or sedan, unless your frankie rio

 

[audioholic 5,000+ posts]

What happens when you use a garden hose to try and push the same amount of water/min as you would through a fire hose? Not just increased velocity, in fact velocity eventually stays the same, and you get nothing but friction and therefore significantly less total water being displaced due to the opening being too small.
The friction caused by the higher air velocity is what really causes the turbulence, and that same friction is loss, and is present whether you can audibly hear it or not. I don't believe that whether or not we can hear it is a good indicator of whether or not we will benefit significantly enough to justify increasing port area.

This is not a garden hose, and we are not talking about displacing water. We are discussing a port that displaces air. Are we on the same page now? Good. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
If friction were the only thing that caused port noise, why doesn't the larger port display more port noise? It, being the larger port, displays more surface area and hence, more friction. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif Your theory is incorrect, sorry.

Friction IS a loss, you are correct about that. But you are incorrect in thinking this is the reasoning behind different sized ports displaying different output abilities. And you can say friction causes the turbulence if you want. I said air velocity does. You seem to think you are disagreeing with me on that point, but you aren't. What happens when the amount of surface area remains constant, but air velocity moving past it increases? Friction goes up. So as you can imagine, increasing port area and thereby decreasing air velocity, will in fact reduce friction, and turbulence.

"I don't believe that whether or not we can hear it is a good indicator of whether or not we will benefit significantly enough to justify increasing port area."

What? You should explain that statement, because the way i read it now, its completely wrong. Turbulence CAN easily be audible, and increasing port area to decrease air velocity WILL decrease its audibility. To suggest otherwise is to suggest you dont understand the situation.

 

[Rashaddd 5,000+ posts]

This is not a garden hose, and we are not talking about displacing water. We are discussing a port that displaces air. Are we on the same page now? Good. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Does not each individual stroke of the sub and consequently port air resemble and behave similarly to water through a hose?

If friction were the only thing that caused port noise, why doesn't the larger port display more port noise? It, being the larger port, displays more surface area and hence, more friction. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif Your theory is incorrect, sorry.

More friction is created by the added pressure of a smaller port than by the added contact area of a larger port.

Friction IS a loss, you are correct about that. But you are incorrect in thinking this is the reasoning behind different sized ports displaying different output abilities. And you can say friction causes the turbulence if you want. I said air velocity does. You seem to think you are disagreeing with me on that point, but you aren't. What happens when the amount of surface area remains constant, but air velocity moving past it increases? Friction goes up. So as you can imagine, increasing port area and thereby decreasing air velocity, will in fact reduce friction, and turbulence.

I didn't really think I was disagreeing, just pointing out that the root of it is friction, velocity is just part of the friction force equation

If not for friction and the loss caused by it, what creates the difference in output between different sized ports? It can't be air velocity, if it is, then why isn't a smaller sub with more excursion inherently quieter than a bigger sub with less excursion (same displacement)?

"I don't believe that whether or not we can hear it is a good indicator of whether or not we will benefit significantly enough to justify increasing port area."
What? You should explain that statement, because the way i read it now, its completely wrong. Turbulence CAN easily be audible, and increasing port area to decrease air velocity WILL decrease its audibility. To suggest otherwise is to suggest you dont understand the situation.

You read it wrong, I wasn't implying that turbulence/friction/port noise can't or isn't easily audible, and I wasn't implying that increasing port area and thereby decreasing air velocity wouldn't decrease its audibility. I was pointing out that the idea that "if i can't hear port noise there's no reason to increase port area" is invalid, unless port noise is your only concern regarding the system, obviously.

 

[MisterGrubbs 5,000+ posts]

//content.invisioncic.com/y282845/emoticons/popcorn.gif.32dd9e22fd77e77bc3c907062768fcd2.gif and reading glasses. Taking notes, anyone?

 

[Rashaddd 5,000+ posts]

This is not all to say that there's no reason not to increase port area. As with everything, there is a trade off. The most significant, imo, part of that trade-off is the poorer response below tuning. The bigger the port is, the more the sub will act like it's in free-air below tuning. A smaller port will cause the sub to act more like it is sealed below tuning. I'm honestly not entirely sure how this affects it above tuning, as I've never measured or seen a definite loss above tuning caused by increased port area, but it would be logical that it would happen, unless there is something else I'm forgetting that prevents it.

The other part of the trade off which can be an obvious problem is the need for a longer port, exponentially taking up more and more room.

 

[murderedtahoe 10+ year member]

KEEP this up guys im really learning something here

 

[audioholic 5,000+ posts]

Does not each individual stroke of the sub and consequently port air resemble and behave similarly to water through a hose?

Only to an extent. people love to use the water hose parallel, but air is compressable, water is not.

More friction is created by the added pressure of a smaller port than by the added contact area of a larger port.

Im sorry, but that's simply not true. Higher pressure does not equal greater friction, greater velocity across the surface DOES.

I didn't really think I was disagreeing, just pointing out that the root of it is friction, velocity is just part of the friction force equation

My point was you are arguing the opposite side of the same coin. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif Friction does increase as velocity goes up. I said higher velocity causes the turbulence, you said it was friction. Answer is, its both. But within the context of this discussion, its more relevant to discuss air velocity, not simply friction. The topic was about port diameter, not necessarily how smooth or rounded the edges are.[
QUOTE=Rashaddd;5596095]If not for friction and the loss caused by it, what creates the difference in output between different sized ports? It can't be air velocity, if it is, then why isn't a smaller sub with more excursion inherently quieter than a bigger sub with less excursion (same displacement)?that's where you are misunderstanding, you assume a different sized port will automatically mean different output levels. Again, you can have a smaller port with increased air velocity inside it that will display the same over all air displacement as would a larger port that would inherently have lower air velogity within it. Now a port CAN become so small as to choke off the woofer and decrease its displacement capability, but that's not what Im referring to here. Assuming the port is within an acceptable size range, the woofer itselt will dictate the amount of air displaced through the port, not the port itself.

You read it wrong, I wasn't implying that turbulence/friction/port noise can't or isn't easily audible, and I wasn't implying that increasing port area and thereby decreasing air velocity wouldn't decrease its audibility. I was pointing out that the idea that "if i can't hear port noise there's no reason to increase port area" is invalid, unless port noise is your only concern regarding the system, obviously.

I understand your comment better now. I still dont fully agree however. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif If the port is of sufficient size that the amount of air displacing through it creates no audible port noise, turbulence is likely low enough that increasing port diameter wont help much. that may not be true for an SPL competitor trying to inch every tenth out of his system as he can, but for most of us, if it doesn't have audible port noise, you have plenty of port area. If you think your port is too small that it is choking off your sub's performance, it would have audible port noise. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
Dont mean to sound argumentative Rashaddd, just trying to make sure everyone understands.

 

[audioholic 5,000+ posts]

This is not all to say that there's no reason not to increase port area. As with everything, there is a trade off. The most significant, imo, part of that trade-off is the poorer response below tuning. The bigger the port is, the more the sub will act like it's in free-air below tuning. A smaller port will cause the sub to act more like it is sealed below tuning. I'm honestly not entirely sure how this affects it above tuning, as I've never measured or seen a definite loss above tuning caused by increased port area, but it would be logical that it would happen, unless there is something else I'm forgetting that prevents it.
The other part of the trade off which can be an obvious problem is the need for a longer port, exponentially taking up more and more room.

The reason a larger portt allows the sub to 'unload' quicker below tuning is because the smaller port actually WOULD choke off the sub while its trying to over-excurt, thus 'helping' it.

 

[murderedtahoe 10+ year member]

so audio why does it seems guys who are using small port area moving lot of air? i even had an experience with 4 15" memphis pr 15's in the same size box i had a ton of port area first and switched to an much smaller port it seemed like the stup moved wayyyy more air?

 

[murderedtahoe 10+ year member]

not to mention the smaller port sounded better/ both ports were tuned to the same thing

 

[murderedtahoe 10+ year member]

ahhh wheres audioholic when u need him?