Port area

[cubdenno 0]

I was reading a port area article on here.

Port Area - SSA Car Audio Forum

Utilizing the recommendations from other in that article and going back and looking at white papers from various manufacturers from the likes of JL, JBL, and Boston Acoustics etc,,, I notice that their port size recommendations are in the 3-4" area. Even on woofs that are known to be seeing 500+ watts. Why? After looking at those enclosure recommendations it is very apparent that the port noise is going to be horrendous let alone compression.

Also utilizing the port area calculators in the above listed topic, I noticed that port resonance frequencies drop in frequency the larger the port diameter. What affect does that have on enclosure performance?

[Huricaine 0]

Those other subs like jbl probly have smaller xmax, and on a little bit of wattage seems like they won't produce much compression. I have actually read a thread where a guy said that the power you are running is also vital to calculation.

[Duran 387]

Power is not going to be as important as the displacement the woofer is capable of.

[Huricaine 0]

Really? That helps me to know.

[Duran 387]

That thread he quoted, while there is a LOT of flaming, has good information about ports.

[s_carter 5]

Most likely due to the fact that the subs are mass marketed, they simply cant tell the consumers that they need a port that has 36 inches of area, and needs to be 3 feet long to achieve a decent tune. Besides, most people dont even realize what port compression and air velocity means. 99% of people buying the drivers will not realize what a properly tuned enclosure should sound like, because they are used to shitty prefab designs with next to no port area and decent airspace...

[RAM_Designs 25]

The amount of air that the woofer is going to displace, along with your desired tuning frequency, is what you need to worry about when trying to get enough port area for a given setup. Box size doesn't matter, power being applied doesn't matter. The woofer is simply pushing a given amount of air in and out of the port at a given rate(frequency). The lower the tuning, the smaller the port area that you can get away with.

Edited January 21, 2011 by RAM_Designs

[Adrian_D 520]

Box size doesn't matter, power being applied doesn't matter. The woofer is simply pushing a given amount of air in and out of the port at a given rate(frequency). The lower the tuning, the smaller the port area that you can get away with.

That is incorrect. And I have done tests to prove that for an ideal port area (maximum output/area) box volume and power applied will be the main factors.

For a given power and box (including tuning) the woofer will move a certain amount. That amount will dictate your port area.

[RAM_Designs 25]

That is incorrect. And I have done tests to prove that for an ideal port area (maximum output/area) box volume and power applied will be the main factors.

For a given power and box (including tuning) the woofer will move a certain amount. That amount will dictate your port area.

You must have missed the first sentence of my post. Air being displaced is what matters most. How much power or how big of a box it takes to get that displacement is irrelevant. Tuning frequency is the next important factor as a lower tuning means a lower port velocity, which means you can get away with less port area.

Maybe you thought I meant the physical sub displacement inside the box, not the air the cone will be displacing?

Edited January 22, 2011 by RAM_Designs

[Adrian_D 520]

That is incorrect. And I have done tests to prove that for an ideal port area (maximum output/area) box volume and power applied will be the main factors.

For a given power and box (including tuning) the woofer will move a certain amount. That amount will dictate your port area.

You must have missed the first sentence of my post. Air being displaced is what matters most. How much power or how big of a box it takes to get that displacement is irrelevant. Tuning frequency is the next important factor as a lower tuning means a lower port velocity, which means you can get away with less port area.

Maybe you thought I meant the physical sub displacement inside the box, not the air the cone will be displacing?

Box volume and power DO matter in how much cone displacement you are going to have.

If you look only at cone displacement simulated for a given box / volume combo, ok, roll with that but don't say box volume and power don't matter.

I'm not stupid, I understand what displacement means in this discussion.

[RAM_Designs 25]

That is incorrect. And I have done tests to prove that for an ideal port area (maximum output/area) box volume and power applied will be the main factors.

For a given power and box (including tuning) the woofer will move a certain amount. That amount will dictate your port area.

You must have missed the first sentence of my post. Air being displaced is what matters most. How much power or how big of a box it takes to get that displacement is irrelevant. Tuning frequency is the next important factor as a lower tuning means a lower port velocity, which means you can get away with less port area.

Maybe you thought I meant the physical sub displacement inside the box, not the air the cone will be displacing?

Saying that power applied and box volume is not relevant to the cone displacement is false. There's a big freaking difference between putting 500w on a speaker of putting 2000w on the same speaker when it comes to displacement. And there's a big difference in displacement when you switch a woofer from a 1.5cf box to a 2.5cf box.

No, I'm not stupid, I understand what you are saying and it is incorrect.

You're completely misunderstanding what I am saying. Obviously box size and power will affect how much a sub moves in a given application, that is obvious. What I'm saying is that 2" of excursion is 2" of excursion, regardless if it's in a 1.5ft^3 box requiring 1kw or a 2.5ft^3 box requiring 500 watts. Required port volume is 99% dependent on sub displacement in the given box and what frequency you're tuning to.

Edited January 22, 2011 by RAM_Designs

[Adrian_D 520]

I edited silly, re-read it and got the idea. We're on the same page

[RAM_Designs 25]

I edited silly, re-read it and got the idea. We're on the same page

Yay, can we hug now?

[Adrian_D 520]

Sort of...

[95Honda 486]

Tuning frequency is the next important factor as a lower tuning means a lower port velocity, which means you can get away with less port area.

This is an incorrect assumption when you only use modeling software.

The reason is, when you get closer to the infrasonic region, which for some of us is above 20Hz, the system starts leaving the audible realm and moving into a tactile one. The problem this poses is, most of us have very insesitive hearing down there. But what we can still hear well are all of the vent attributes other than the intended output. Basically, the ratio of port introduced distortions to intended output are much greater than at higher frequencies.

This why, in practice, you really don't want to start rolling back on your vent area because you are dealing with lower frequencies...

Edited January 22, 2011 by 95Honda

[RAM_Designs 25]

Tuning frequency is the next important factor as a lower tuning means a lower port velocity, which means you can get away with less port area.

This is an incorrect assumption when you only use modeling software.

The reason is, when you get closer to the infrasonic region, which for some of us is above 20Hz, the system starts leaving the audible realm and moving into a tactile one. The problem this poses is, most of us have very insesitive hearing down there. But what we can still hear well are all of the vent attributes other than the intended output. Basically, the ratio of port introduced distortions to intended output are much greater than at higher frequencies.

This why, in practice, you really don't want to start rolling back on your vent area because you are dealing with lower frequencies...

Makes sense, but even with a 28hz tuning there is still a lot more to be heard than felt, in my experience. And I don't know of a lot of people who tune lower than that(28hz box is my daily setup). I guess it'd also depend on where your enclosure is located in relation to your listening position, but you have a point, it's not the same for everyone.

[RAM_Designs 25]

I think we can agree that there's a lot to be taken into consideration when figuring out what size port you need/want. Things like musical taste, listening habits, driver excursion, the noise floor of the vehicle itself, enclosure placement, etc. all play a role.

[Dictator1992 6]

yeaaaaaahhhhhhhhhhhhhhhh....this convo is way too complicated for my brain just going to say if its loud and sounds clean its all good lol

[starvingf150 0]

I agree its a lot of back and forth. Can it be made easier to understand for say people who aren't studying fluid dynamics? Ha.

I'd really like to build a properly designed vented box myself very soon. This thread makes me think that I haven't ever experienced that type of enclosure before, which makes me excited for what could be in store. Maybe a night and day difference between proper and improper?

So any help on simplifying how to design one would be great. Maybe asking for too much here. Ha.

-----

I.E.

How do you know the right amount of port area?

What is 'the' tuning frequency that's preferred? Dependent on power, vehicle, etc?

-----

Anyone willing to put together a comprehensive guide?

Thanks.

[Duran 387]

I agree its a lot of back and forth. Can it be made easier to understand for say people who aren't studying fluid dynamics? Ha.

I'd really like to build a properly designed vented box myself very soon. This thread makes me think that I haven't ever experienced that type of enclosure before, which makes me excited for what could be in store. Maybe a night and day difference between proper and improper?

So any help on simplifying how to design one would be great. Maybe asking for too much here. Ha.

-----

I.E.

How do you know the right amount of port area?

What is 'the' tuning frequency that's preferred? Dependent on power, vehicle, etc?

-----

Anyone willing to put together a comprehensive guide?

Thanks.

To answer your port area question: http://www.carstereo.com/help/Articles.cfm?id=31

[porkchop 304]

I agree its a lot of back and forth. Can it be made easier to understand for say people who aren't studying fluid dynamics? Ha.

I'd really like to build a properly designed vented box myself very soon. This thread makes me think that I haven't ever experienced that type of enclosure before, which makes me excited for what could be in store. Maybe a night and day difference between proper and improper?

So any help on simplifying how to design one would be great. Maybe asking for too much here. Ha.

-----

I.E.

How do you know the right amount of port area?

What is 'the' tuning frequency that's preferred? Dependent on power, vehicle, etc?-----

Anyone willing to put together a comprehensive guide?

Thanks.

"preferred" seems to hold an opinionated property to it, in which i believe a "comprehensive 'guide' " would struggle to chart out the best results.

looks like you have the proper info to design the vent area on hand,(thanks to Duran), as well as the vent length.

the desired tunning frequency for your specific install will vary outside of what can be suggested. (imo)

*ie ..... your specific listening preferances alone will step outside of what a calculator can offer.

sometimes you gotta build it a couple of time to find your sweet spot.

and

be sure to take build pics!!!!