10" TC OEM with 104sq in of port

[mobeious 10+ year member]

in SPL u want to keep the excursion down at the burp freq so the port size reflects the tunning of the enclosure and box size and Sd of the woofers being used

 

[dman4486 5,000+ posts]

O.P.

is it possible that you increased the port area and got the math wrong for the length?

maybe you are not playing a tone as close to tuning freq as you though thus creating more excursion and air volume flow through the port

 

[Rashaddd 5,000+ posts]

One draw-back is that a HUGE port has less band-width -- it is really loud at tuning but doesn't do as much around tuning as a smaller port.
I use a big port for SPL - not quite that big, though. But my box has 96 in^2 for a 15" driver.

I lose 4 dB with an equivalent 12" driver in the same box.

I missed the other thread... what exactly was the debate ?

Hmm, this is interesting

I'll keep it in mind for sure. Have you tried an equivalent 18" driver in the same box? Also, what's your port velocity like for these burps with the various sub sizes?

Because you are decreasing the enclosure pressure, thus less of an air-spring effect on the sub.
This is also why your port velocity is so high.

Not sure I follow, less of an air spring should mean less mech power handling right? So how can I throw double the power at it and have the same or less excursion?

Again, I'm not claiming my theory here is all factual and indisputable, I want to discuss it, and I may be wrong, but that's why I'm sharing it.

 

[dman4486 5,000+ posts]

in SPL u want to keep the excursion down at the burp freq so the port size reflects the tunning of the enclosure and box size and Sd of the woofers being used

^^this is why you can only burp for short times.....less excursion = less cooling

 

[mobeious 10+ year member]

^^this is why you can only burp for short times.....less excursion = less cooling

exactly but it keeps almost all the coil in the gap thos controls the sub better to handle ungodly power

 

[Rashaddd 5,000+ posts]

O.P.
is it possible that you increased the port area and got the math wrong for the length?

maybe you are not playing a tone as close to tuning freq as you though thus creating more excursion and air volume flow through the port

I figured out tuning through testing, not calculating. 33hz is the obvious tuning point given by running a sweep through it (and going back and finding that exact spot with tones) Unless there is something else decreasing excursion at 33hz, and causing a steep roll off in handling below that.

This doesn't mean it's a good idea.
Besides, it's totally impractical in every aspect, so why bother? Just trying to sound smart?

Not at all trying to sound smart...discussing my findings. Yes I realize this is very impractical in most cases...but the concept isn't. And for classes that you have an advantage in by being able to use a smaller sub or less subs and less power for the same output levels, this is obviously relevant.

 

[tommyk90 5,000+ posts]

Hmm, this is interesting
Not sure I follow, less of an air spring should mean less mech power handling right? So how can I throw double the power at it and have the same or less excursion?

Again, I'm not claiming my theory here is all factual and indisputable, I want to discuss it, and I may be wrong, but that's why I'm sharing it.

Sorry if i misworded things there.

When comparing enclosure sizes with similar tuning/port area, a larger will enclosure will make the sub move less with the same amount of power.

Reason being is that the sub is unable to pressurize the enclosure as much, thus losing some of the air-spring effect.

 

[Rashaddd 5,000+ posts]

Sorry if i misworded things there.
When comparing enclosure sizes with similar tuning/port area, a larger will enclosure will make the sub move less with the same amount of power.

Reason being is that the sub is unable to pressurize the enclosure as much, thus losing some of the air-spring effect.

Still not wording it right, or just contradicting what is common knowledge for the most part

Larger box = less excursion?

 

[audioholic 5,000+ posts]

Port excursion would be referring to the distance air moves in the port, similar to the distance the cone moves being cone excursion

When have we ever debated on the topic of distance the air moves inside the port? We were discussing port air velocity.

I think its pretty clear this doesn't just "still make noise", based on yours and a few others statements, and the general understanding of port area vs cone area that seems to be thrown around here, we should've expected port velocity/movement to be pretty minimal, shouldn't we? How do you explain the ridiculously high port velocity in comparison to the relatively small amount of cone excursion, and the ratio of port area to cone area?

I think its pretty clear you took offense to my 'make noise' comment. It was not a comment to suggest performance levels, merely that your video only shows it does in fact... make noise. Holding a bag over the port to see it move measures port air velocity? And what are we comparing the bag flapping to? What we think the bag would do with a 4" port?
Bag flapping does show air is moving. It even shows alot of air is moving (never debated), but it does not show velocity nor give any indications of what would happen to velocity were the port area to change.

You seem to be trying to suggest that greater port area does NOT equal lower port velocity. Are you then suggesting port air velocity is always constant, no matter the port area? Or, are you suggesting port air velocity INCREASES as port area goes up? The answer is... you are confusing the amount of air displaced, with how rapidly it moves within the port.

and yes it unloads below tuning like no other...that was assumed and I've always said that would happen, obviously, however, above tuning, it plays very solidly and loud, just with less air movement in the port. It can play down to about 29-30hz before bottoming out off this much power

Besides the specific numbers, all of that was predicted for you by us before you ever built this box. You seem to be trying to wage a quantitative argument while using subjecting information (your video) as your proof. That never works out well. But I do applaud you trying this, and sharing it with us.

Edit: and once more...perhaps you know better, but I know the majority of the people here including audioholic would have guessed that this would bottom out with its thermal rating going to it, and/or port velocity would have been extremely low...its really the exact opposite.

I would have guessed it would 'bottom out' with rated power going to it? Why would I do that? You seem to be forgetting that as you increase port area, you also increase port length. What does this mean to the subwoofer? The same over all resistance seen to air movement/pressurization/cone movement. Also, seeing as cone motion in a vented situation is so drastically controlled by frequency, I dont see the point in making such an argument about bottoming out unless we are talking about deviating far from tuning (mostly down). And that is what I DID say in the previous thread. You've already admitted it unloads faster than normal below tuning, got you to admit half my argument.... now tell us, how's its upper frequency performance? //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[tommyk90 5,000+ posts]

Still not wording it right, or just contradicting what is common knowledge for the most part
Larger box = less excursion?

Given the same application, port area, and power, a sub will move less in a larger box. Though it GREATLY depends on the sub and port alignment, and the box dimensions themselves.

I've experienced such an event in my own testing. This may not hold true for all applications though.

 

[tommyk90 5,000+ posts]

When have we ever debated on the topic of distance the air moves inside the port? We were discussing port air velocity.
I think its pretty clear you took offense to my 'make noise' comment. It was not a comment to suggest performance levels, merely that your video only shows it does in fact... make noise. Holding a bag over the port to see it move measures port air velocity? And what are we comparing the bag flapping to? What we think the bag would do with a 4" port?

Bag flapping does show air is moving. It even shows alot of air is moving (never debated), but it does not show velocity nor give any indications of what would happen to velocity were the port area to change.

You seem to be trying to suggest that greater port area does NOT equal lower port velocity. Are you then suggesting port air velocity is always constant, no matter the port area? Or, are you suggesting port air velocity INCREASES as port area goes up? The answer is... you are confusing the amount of air displaced, with how rapidly it moves within the port.

Besides the specific numbers, all of that was predicted for you by us before you ever built this box. You seem to be trying to wage a quantitative argument while using subjecting information (your video) as your proof. That never works out well. But I do applaud you trying this, and sharing it with us.

I would have guessed it would 'bottom out' with rated power going to it? Why would I do that? You seem to be forgetting that as you increase port area, you also increase port length. What does this mean to the subwoofer? The same over resistance seen to air movement/pressurization/cone movement. Also, seeing as cone motion in a vented situation is so drastically controlled by frequency, I dont see the point in making such an argument about bottoming out unless we are talking about deviating far from tuning (mostly down). And that is what I DID say in the previous thread. You've already admitted it unloads faster than normal below tuning, got you to admit half my argument.... now tell us, how's its upper frequency performance? //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

Thank you for wording that so eloquently.

Putting a bag in front of the port proves absolutely nothing. I could do the same trick with an 8" sub with a 3" port (and probably do better scores than that ridiculous thing, also with a wider frequency range).

Sure, the air moves back and forth very quickly (as it should), but your test proves absolutely nothing as to the AMOUNT of air being displaced.

 

[RAM_Designs 5,000+ posts]

FYI, I'll put $10 on that thing not metering worth a damn.

x2

 

[tommyk90 5,000+ posts]

x2

Sure this was a cool little experiment, but I could have done similar tests on a much more manageable and realistic scale. A 10 foot long port somehow seems a bit excessive. //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif

 

[Rashaddd 5,000+ posts]

now tell us, how's its upper frequency performance? //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

Not bad at all. At least in the normal range of a subwoofer, I didn't play it very extensively on music, but with the last port (= to cone area) it was very loud in the upper frequencies as well. Not much falloff at all, and it doesn't reach mechanical limits or anything close, even with this port.

Keep in mind...I have always acknowledged the steeper drop off below tuning, I said that right from the beginning of the whole argument for bigger ports, that that was a drawback.

Also, no, I don't believe that increasing port area increases velocity, or keeps it constant. It decreases it, even if very slightly.

Thank you for wording that so eloquently.
Putting a bag in front of the port proves absolutely nothing. I could do the same trick with an 8" sub with a 3" port (and probably do better scores than that ridiculous thing, also with a wider frequency range).

Sure, the air moves back and forth very quickly (as it should), but your test proves absolutely nothing as to the AMOUNT of air being displaced.

How? If it's tearing a bag up on my fingers, and clearly quite violent, port velocity is high. I would assume high port velocity + high port area = lots of air, no? Smaller port + high port velocity = less air, right? Speed x area = amount of air displaced in a given time frame. If you have the same velocity going through a 3" port, how the hell are you going to move more air (at a given frequency)?

Please correct me.

 

[tcguy85 10+ year member]

got to be one of the dumbest car audio related things i have seen. why use a 12" port with a 10" sub?

a 4 inch port is fine on a ten, and even a 6 is overkill. hell, i use a 3" port with my 10 and it's fine.

i'm no port-ologist, but doesn't it turn into more of an "IB" or "free air" than a ported box after that much port?