Hairtrick port area?

[audioholic 5,000+ posts]

Im suppose to guess why your system moves more air and sounded better with smaller ports? Uhm, lol?

Look, all I have to say to you is, go to an SPL competition some time and ask the guys why they dont run smaller ports, since they move more air. //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

The sub is the air pump, it determines how much air moves through the port. The diameter of the port simply defines how much velocity will be required to displace that much air through that sized port.

 

[murderedtahoe 10+ year member]

Im suppose to guess why your system moves more air and sounded better with smaller ports? Uhm, lol?
Look, all I have to say to you is, go to an SPL competition some time and ask the guys why they dont run smaller ports, since they move more air. //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

The sub is the air pump, it determines how much air moves through the port. The diameter of the port simply defines how much velocity will be required to displace that much air through that sized port.

can u explain that a bit more i mean im kinda a noob here

 

[murderedtahoe 10+ year member]

or anyone who know what he is talking about break it down for an noob

 

[Rashaddd 5,000+ posts]

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.

Indeed, but it actually has the opposite effect at tuning. A bigger port = less excursion at tuning, why? Because more air is being moved through the port, and it is more efficient. Why can I put a 10" sub with a VAS of less than .5 cubes, in 3 cubes net, feed it it's full power and not bottom it out even at 27hz? Because the port is big enough (bigger than cone area), and 27hz is the tuning frequency, creating much more backpressure than a sealed box, or a box with less port area could. That little 10 in that box creates almost as much if not more port air movement as my MJ's do with the same amount of port area and more than double the power.

air is compressable, water is not.

This is a valid point

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

Higher velocity is how you equalize higher pressure. The port makes up for the added pressure by having higher air velocity, therefore higher pressure does create higher friction, resulting in more loss of output. This is also one reason (along with power compression) why a sub has to work exponentially harder for an equal increase in output as it gets closer to it's maximum potential for displacement.

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.

again, it's the friction caused by air velocity, caused by pressure, which creates port noise and a loss of output

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.

Does this not imply that inherently two sealed subs will outperform one ported one? Experience tells us this isn't at all inherently true. How does a bandpass work if displacement (and therefore output) is strictly dictated by woofer displacement? Does a bandpass increase the movement of the woofer? I don't think so.

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

Who's to say that our hearing sensitivity has anything to do with how much of an impact the 'choking off' of a sub's performance makes?

Dont mean to sound argumentative Rashaddd, just trying to make sure everyone understands.

As am I

 

[Rashaddd 5,000+ posts]

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?

You sure about that? I've done tests exhibiting the exact opposite. Are you confusing an increase in air velocity from the port with an increase in the amount of air being moved? If not, did the net volume of the box, tuning, or any other factor change?

 

[audioholic 5,000+ posts]

Indeed, but it actually has the opposite effect at tuning. A bigger port = less excursion at tuning, why? Because more air is being moved through the port, and it is more efficient. Why can I put a 10" sub with a VAS of less than .5 cubes, in 3 cubes net, feed it it's full power and not bottom it out even at 27hz? Because the port is big enough (bigger than cone area), and 27hz is the tuning frequency, creating much more backpressure than a sealed box, or a box with less port area could. That little 10 in that box creates almost as much if not more port air movement as my MJ's do with the same amount of port area and more than double the power.


This is a valid point

Higher velocity is how you equalize higher pressure. The port makes up for the added pressure by having higher air velocity, therefore higher pressure does create higher friction, resulting in more loss of output. This is also one reason (along with power compression) why a sub has to work exponentially harder for an equal increase in output as it gets closer to it's maximum potential for displacement.

again, it's the friction caused by air velocity, caused by pressure, which creates port noise and a loss of output

Does this not imply that inherently two sealed subs will outperform one ported one? Experience tells us this isn't at all inherently true. How does a bandpass work if displacement (and therefore output) is strictly dictated by woofer displacement? Does a bandpass increase the movement of the woofer? I don't think so.

Who's to say that our hearing sensitivity has anything to do with how much of an impact the 'choking off' of a sub's performance makes?

As am I

You are going way off topic here. What EXACTLY is your point Rashaddd? That a larger port always means more air movement? Again, not true. A smaller port will display higher air velocity due to moving THE SAME AMOUNT OF AIR through a smaller port diameter. The sub's movement dictates how much air is displaced, not the port size. I dont know any more basic way to put it to you.

 

[Rashaddd 5,000+ posts]

You are going way off topic here. What EXACTLY is your point Rashaddd? That a larger port always means more air movement? Again, not true. A smaller port will display higher air velocity due to moving THE SAME AMOUNT OF AIR through a smaller port diameter. The sub's movement dictates how much air is displaced, not the port size. I dont know any more basic way to put it to you.

True I did go a little off topic...however, my main point was that yes, a larger port ALWAYS will result in more air being moved, and almost always measurably more output, if not audibly more. Often this will be a large increase, and in some cases it may only be a very small increase.

Regardless, if you want to get into the 'law' side of it, it is not even physically possible to move the same amount of air through a smaller port in the same time interval, than a bigger port, because of the added friction, no matter how small of a decrease in port area it is. In a frictionless world, yes, there would be no loss, and you could even just make the port small enough that the velocity of air in it breaks speed of sound, but when there is friction, there is loss. More friction = more loss. No matter how it's worded, a bigger port inherently means more air will be moved.

Tbh I dont even remember what we started arguing about to begin with:crazy:

Edit:

also, the actual movement of the sub doesn't necessarily directly reflect the air movement in the port. For example, with that single 10 I mentioned, Even when the sub looks like it's maybe moving 1-2mm each way, the port is moving pretty violently, despite the fact that tehre is more port area than cone area. Why? Because there's more to it when you have a port radiating and energy being stored and released as pressure many times per second.

 

[audioholic 5,000+ posts]

True I did go a little off topic...however, my main point was that yes, a larger port ALWAYS will result in more air being moved, and almost always measurably more output, if not audibly more. Often this will be a large increase, and in some cases it may only be a very small increase.
Regardless, if you want to get into the 'law' side of it, it is not even physically possible to move the same amount of air through a smaller port in the same time interval, than a bigger port, because of the added friction, no matter how small of a decrease in port area it is. In a frictionless world, yes, there would be no loss, and you could even just make the port small enough that the velocity of air in it breaks speed of sound, but when there is friction, there is loss. More friction = more loss. No matter how it's worded, a bigger port inherently means more air will be moved.

Tbh I dont even remember what we started arguing about to begin with:crazy:

Edit:

also, the actual movement of the sub doesn't necessarily directly reflect the air movement in the port. For example, with that single 10 I mentioned, Even when the sub looks like it's maybe moving 1-2mm each way, the port is moving pretty violently, despite the fact that tehre is more port area than cone area. Why? Because there's more to it when you have a port radiating and energy being stored and released as pressure many times per second.

If a larger port area always yields more output, why do SPL setups generally go with smaller round aeroports rather than the more port area of a slot loaded setup?
I believe you are over exaggerating the affect of port wall friction on actual output. Larger ports do not always display more air movement. Even logic tells us at some point the port would become so large that the sub would unload immediately and work as if mounted free-air. Would this mean we've reached our maximum air movement possible? Running free-air?

 

[Rashaddd 5,000+ posts]

If a larger port area always yields more output, why do SPL setups generally go with smaller round aeroports rather than the more port area of a slot loaded setup?
I believe you are over exaggerating the affect of port wall friction on actual output. Larger ports do not always display more air movement. Even logic tells us at some point the port would become so large that the sub would unload immediately and work as if mounted free-air. Would this mean we've reached our maximum air movement possible? Running free-air?

I did mention that it can be TOO big (i've never seen it, but like you said, logically its hard to believe that there's no such thing as too big) and I also did imply in my last post that the gain can be very small at times, depending on circumstances and not worth it, especially because of the added space required to be used. And remember that the port, at tuning, doesn't act like a hole in the box, it acts the opposite. When the sub moves in, the port pushes the sub out (by moving in as well), and vice versa.

 

[chunky cumz 10+ year member]

too many words in this thread.... ouch

 

[Supergumby5000 5,000+ posts]

the port has to be tthhhiiiiiiisssss big

*holds arms straight out*

*sigh* so full of noob and fial i dont even wanna start.

 

[audioholic 5,000+ posts]

I did mention that it can be TOO big (i've never seen it, but like you said, logically its hard to believe that there's no such thing as too big) and I also did imply in my last post that the gain can be very small at times, depending on circumstances and not worth it, especially because of the added space required to be used. And remember that the port, at tuning, doesn't act like a hole in the box, it acts the opposite. When the sub moves in, the port pushes the sub out (by moving in as well), and vice versa.

So we agree bigger isn't always better/more output. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif And that port wall friction is pretty much a non-factor? We haven't even discussed that most of the air inside the port actually passes thru the center of the port, not along the outside or uniformly as many think. This is why we can get away with square cornered slot ports, most of the air passes thru the center, not down near the corners.
I understand how the air in the port reacts with woofer movement.

 

[Rashaddd 5,000+ posts]

So we agree bigger isn't always better/more output. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif And that port wall friction is pretty much a non-factor? We haven't even discussed that most of the air inside the port actually passes thru the center of the port, not along the outside or uniformly as many think. This is why we can get away with square cornered slot ports, most of the air passes thru the center, not down near the corners.
I understand how the air in the port reacts with woofer movement.

//content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif i wasn't talking about port friction on the inside walls lol, I hope that's not what you thought I was and was causing all the confusion:crap:

I do believe that (until you get to that 'too big' point) bigger port is always better in terms of output, just it can get to the point where the gain is insignificant and negligible (diminishing return obviously applies), I think this is what you were really trying to say?

I think in applicable terms we agree //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif, we're just arguing technicalities

 

[audioholic 5,000+ posts]

What friction were you talking about?

I agree that bigger is always better, until its too big, then its no longer better. lol //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

Yeah we pretty much agree. I think we are just trying to figure out why exactly.