Ported vs Sealed, lets open this can of worms. lol

[Killerwatt]

While i agree that a cabin does boost certain frequencies, as explioited by many spl people, there is also a steady gain in response as frequency drops. I've measured it a few times and what you see is a gain as freq drops, not exactly 12bd/oct but close. I have a graph created by andy at jbl that i can mail to you.
Im sorry work blocks those pictures above and did not get a chance to look at them. what part do you see as contradicting?
I dont know of a specific article for the delay, its just something i have learnt over the years. I will see if i can dig up something.

[Killerwatt]

audiophyle, i seem to have misunderstood you a little. I do completely agree that the sealed response will be lacking under 35hs due to the whole cabin gain thing. This is due to that hump in the response. Also i agree that the added low freq from a ported will make the sub 40 hz frequencies louder in a car. What I was trying to get at is that while that ruler flat curve from the ported enclousure will sound better that the sealed, it will sound a little boomy due to cabin gain/resonance.

[capitolj80]

all I know is that my RSdC 12's had more authority in 25-35hz range in a 1.25cu sealed than they do now ported in 1.75cu tuned at 30 hz. The ported box is somewhat louder at around 45hz and above though.

[audiophyle_247]

I've measured it a few times and what you see is a gain as freq drops, not exactly 12bd/oct but close. I have a graph created by andy at jbl that i can mail to you.

If you would that would be great, Id love to check it out.

Ive only tested a few cars for transfer response (with an Audiocontrol RTA) and each car seemed pretty fixed at 45~50hz for its main peak & tapered out slowly much like a sealed box does. Ive never seen a steady increase in response as freq drops, but I am by no means any kind of authority on this topic.
I agree the ported will have a tendency to peak around that 40~50hz range, but it is no different than what a compact sealed box would do built around a subs smallest limit.
I think most sub systems need reductions around that freq range anyway, but I just cant live without that enormous boost of low end response typical of a well tuned ported enclosure.

In theory, if a cabin gain was a steady increase equal to the sealed box's roll off, then when metered in a car the freq response should be a perfectly flat line. But, if that transfer function is applied to the already flat response of the ported design above, then it would climb 12db/oct meaning the freq response would curve upward almost mirroring the sealed box's response curve. If this was the case, then the sound would be ideal because our hearing sensitivity decreases as freq drops, so an upward curved response would be more likely to sound flat to our ears than compared to an actually flat response which would still sound like it tapered off as freq drops.
Our hearing sensitivity, per wikipedia

As found here
http://en.wikipedia.org/wiki/Equal-loudness_contour

capitolj80 we need more details from you, because opinion based claims are a dime a dozen and is what we are trying to stay away from. (as best as possible)
What you claim goes against everything already discussed in this thread, but it needs examination. What car is the system in? Where in the car is it? What direction is the sub & port firing & does that differ from the sealed boxes orientation? How much power are you running? Did anything else change besides swapping from sealed to ported?

Care to post your dimensions & calcs on the box? Your result sounds very typical of a miscalculated ported enclosure, where the actual port freq is much higher than the calculated freq, where say a 45hz tuned port would have much lower sub 30hz bass than sealed with much higher 45hz+ output. It doesnt take much at all to have the port freq climb from where it "should" be, which is part of the difficulty of a ported enclosure. The math & construction has to be perfect, because errors & flaws only compound into large variances in the end results, and rarely for the better.

[Eric D]

If you want to get rid of opinions, then you need to do something about your claim that it is "always worth doing a ported box" or what ever you exactly stated.

It might always be worth it for you to do a ported box, but that is an opinion, nothing more. For everyone else in the world, they have a choice, and they can look at the pros and cons of each to make their decision.

[capitolj80]

Ported 2 sub box external dimensions...H-16.5" W-32.1875" D-20"....single square port is 3.5"x15" with a length of 38.75". No poly fill or center divide. Don't have sealed box dimensions in front of me, but it's a basic homemade 1.25cu ft gross (per side) rectangle. Both were ran in a 2006 hyundai sonata. both had subs facing rear....ported had port facing rear also. both ran on around 1200rms. nothing changed but the box itself. i'm very familiar with how most of my music sounded with the sealed box and the stuff that goes the lowest just seems weaker now in comparison to tones that are a bit higher..but hey, it's just what it seems like to me.

[audiophyle_247]

Ported 2 sub box external dimensions...H-16.5" W-32.1875" D-20"....single square port is 3.5"x15" with a length of 38.75". No poly fill or center divide. Don't have sealed box dimensions in front of me, but it's a basic homemade 1.25cu ft gross (per side) rectangle. Both were ran in a 2006 hyundai sonata. both had subs facing rear....ported had port facing rear also. both ran on around 1200rms. nothing changed but the box itself. i'm very familiar with how most of my music sounded with the sealed box and the stuff that goes the lowest just seems weaker now in comparison to tones that are a bit higher..but hey, it's just what it seems like to me.

I sketched it out & it looks like your math is spot on, so that's good right?
I modeled the RSDc12 in a sealed enclosure like you had, a ported enclosure like you have, and what it would take to get a flat response with the pair of RSDc12" subs.

Yellow = Dual 12" 2.5cuft sealed
Green = Dual 12" 3.2cuft @30hz (yours is actually 30.8hz, but close enough)
Blue = Dual 12" 7.9cuft @ 21hz
That green line tells me exactly what you are experiencing, look at where that peak is and how sharply the response falls off. You have a great ear for picking up exactly where the response bumped and dropped, because its response difference is identical to what you experienced.
Part of why modeling a box is an important practice is to see this ahead of time, and know that 3.2cuft is not enough airspace for a pair of these.
I also noted that PG recommends a 2.5cuft box for their SQ vented enclosure (for a single 12" )
I think while the 2 subs you have are probably hella loud, one sub in that same box would shift that curve a little closer to the blue graph at the cost of a little overall output for a bit more low end. Otherwise a much lower port tuning could have really helped bring up the low end and smooth out that hump.

If you want to get rid of opinions, then you need to do something about your claim that it is "always worth doing a ported box" or what ever you exactly stated.

It might always be worth it for you to do a ported box, but that is an opinion, nothing more. For everyone else in the world, they have a choice, and they can look at the pros and cons of each to make their decision.

I did say "as best as possible" because the entire subject of whats best is entirely opinion oriented, but everyone has to be a wise guy around here.
So while there is still a decent amount of opinion involved in this topic, not all of it has evidence standing behind it.
Turns out capitolj80's opinion was correct, and look, there is now evidence to support it.

[Eric D]

Wouldn't "as best as possible" be whats "bestest"...

[capitolj80]

lol thanks audiophyle...i was hoping i wasn't crazy seems where I may be mistaken (based on the graph) is in feeling that the sealed box was actually louder between around 20-35hz than the ported, whereas the reality is that it may just seem that way because it's output doesn't drop off from crazy loud to just kinda loud in such a short span of frequencies like the ported box does even thought the ported box is still at least slightly louder all the way down to around 20hz. It's funny how the smoother transition really does make the sealed box come across as beefier in that lower register. I guess these subs really are naturally suited for a sealed box.

[audiophyle_247]

I don't think it's a matter of them being more suited for sealed, I think it's that sealed boxes have a much higher margin of error. Had your box been tuned a little lower that roll off would be lower and really reinforce that bottom octave.

The difference between 50hz and 30hz on the ported is much greater than the difference with the sealed, so even if the output is louder on the ported at 30hz it's reference makes it seem lower due to the larger difference.

[shawn k]

Love plotting subs

Love WinISD

Love this thread

[ttocs]

sealed has a higher margin of err? Not sure how you can build a box with in the recomended specs given and get a simple sealed box wrong compaired to all the problems you can get from little things with ports(sharp edges on the ports, not supported well enough and rattling even before you include port noise).

[capitolj80]

I don't think it's a matter of them being more suited for sealed, I think it's that sealed boxes have a much higher margin of error. Had your box been tuned a little lower that roll off would be lower and really reinforce that bottom octave.

The difference between 50hz and 30hz on the ported is much greater than the difference with the sealed, so even if the output is louder on the ported at 30hz it's reference makes it seem lower due to the larger difference.

true, it is the difference in roll off that makes the sealed seem louder in the lower register...also true that a bigger ported box tuned lower would remedy that, but I've been lead to believe before that the RSDc's are better suited for a sealed box and I just figured this might be evidence of that in some way. BTW, I've always wondered, what qualified a sub to be better suited for a sealed or ported enclosure? I know it's based primarily on the T/S parameters, but I would think that ANY sub can sound it's best in EITHER type if it's designed and built correctly...hmmm.

[shawn k]

sealed has a higher margin of err? Not sure how you can build a box with in the recomended specs given and get a simple sealed box wrong compaired to all the problems you can get from little things with ports(sharp edges on the ports, not supported well enough and rattling even before you include port noise).

That's exactly the point though.

Let's say that you need to do some funky molded fiberglass "sealed" enclosure. It's much more difficult to determine (precisely anyway) how much volume you have in the enclosure once it is built compared to building a simple box. In the end, you can be a good 10-20 even 30% off of the "recommended" volume and still have good performance/results.

Now take that 10-20% margin over to a vented design and in many cases you will see poor results compared to the "ideal" enclosure.

So yes. When designing an enclosure a sealed enclosure has a higher margin of error or "tolerance" compared to the vented.

[ttocs]

That is the funniest stuff I have read on this post now. Ah, wouldn't your ported box in the same place suffer from the same err in measuring, only now compounded by the fact all the #'s entered into the program are not correct now? Saying someone might mis-measure the sealed enclosure, my argument there is that they will not be smart enough to then get all the measurements on the port correct either....

[shawn k]

but I've been lead to believe before that the RSDc's are better suited for a sealed box and I just figured this might be evidence of that in some way. BTW, I've always wondered, what qualified a sub to be better suited for a sealed or ported enclosure? I know it's based primarily on the T/S parameters, but I would think that ANY sub can sound it's best in EITHER type if it's designed and built correctly...hmmm.

There are many factors withing the TS parameters that determine which type of enclosure would be best suited for a given driver. To simplify things, you would want to look at the EBP (Efficiency Bandwidth Product) of the driver to determine which enclosure. EBP is determined by Fs/Qes. Typically, an EBP of less than 50 is good for sealed and an EBP of greater than 50 is good for vented.

So, the RSD has an EBP of 48.1 which actually makes it well suited for either enclsure (although the .707 alignment vented enclosure is relatively large). Keep in mind however, that this does account for transfer function (as mentioned earlier)

WinISD is a fantastic tool. Espesially considering it's free!!

TTOCS asked earlier: "do any of those programs give #'s on port noise or accuracy"

Well yes, in fact it does. It also does so much more. You can even predetermine how the driver itself is going to actand perform within a given enclosure. As said earlier, Group delay is one of the factory, but you can also "virtually" apply power to the system and see if the driver is working within it's mechanical limits and or xmax! Now how cool is that!!??

[shawn k]

That is the funniest stuff I have read on this post now. Ah, wouldn't your ported box in the same place suffer from the same err in measuring, only now compounded by the fact all the #'s entered into the program are not correct now? Saying someone might mis-measure the sealed enclosure, my argument there is that they will not be smart enough to then get all the measurements on the port correct either....

You apparently didn't understand what I was getting at there.

To put it in laymens terms.... a sealed enclosure that is 20% off from its "recomended" volume will "most likely" still provide good performance.

Where a vented enclosure that is 20% off from its "recommended" volume will "most likey" provide poor performance.

[ttocs]

That is the funniest stuff I have read on this post now. Ah, wouldn't your ported box in the same place suffer from the same err in measuring, only now compounded by the fact all the #'s entered into the program are not correct now? Saying someone might mis-measure the sealed enclosure, my argument there is that they will not be smart enough to then get all the measurements on the port correct either....

You apparently didn't understand what I was getting at there.

To put it in laymens terms.... a sealed enclosure that is 20% off from its "recomended" volume will "most likely" still provide good performance.

Where a vented enclosure that is 20% off from its "recommended" volume will "most likey" provide poor performance.

ok, thanks for the "laymens terms", not sure you understand what your saying though.

the original comment audiophyl said was "I think it's that sealed boxes have a much higher margin of error"

I then asked how that worked and then you said because people do not bet the measurements correct when making sealed boxes - You then tried to change the subj to how the program will tell you the port noise - but you failed to realized that with out accurate numbers put into that program its plotted output would be for a different box.

Now again when I bring up the point that if they can't measure a sealed box correctly, they will not do a ported one either. Now you change the subj and go completely aginst your original point that started my responce that "sealed suffer from a higher marging of err" by saying a sealed box off of its volume will sound better then a ported box that is off in its volume.

your going in circles.... if it has a higher margin off err then how come when they are both off by %20 the sealed will sound better?

[shawn k]

Alright... first and foremost I'm not "going in circles" nor am I trying to change the subject!

ok, thanks for the "laymens terms", not sure you understand what your saying though.

the original comment audiophyl said was "I think it's that sealed boxes have a much higher margin of error"

I then asked how that worked and then you said because people do not bet the measurements correct when making sealed boxes -

Yes that was the point I was making. Especially considering when making molded/fiberglass enclosures. And, or trying to fit an enclosure into a tight spot and perhaps sacrificing a little internal volume because of it.

You then tried to change the subj to how the program will tell you the port noise - but you failed to realized that with out accurate numbers put into that program its plotted output would be for a different box.

I wasn't changing the subject at all man! I had no intention of that post coinsiding with the other post. It was a completely different subject and I was just trying to explain some of the other abilities that WinISD provides other than simple volume calculations. Those two posts are of different topics. I'm sorry if you thought otherwise, but don't blame me for that!

Now again when I bring up the point that if they can't measure a sealed box correctly, they will not do a ported one either.

This goes back to what I was saying earlier. This isn't about the "competence" of the box builder. Rather it's about the "compromises" that the installer may have to make when designing/building and enclosure. And from time to time, the higher "margin for errror" of the sealed enclosure may be the more feasible design.

Now you change the subj and go completely aginst your original point that started my responce that "sealed suffer from a higher marging of err" by saying a sealed box off of its volume will sound better then a ported box that is off in its volume.

I still fail to see how I'm "changing the subject" (is this really your way of dabating??? geese man) Furthermore, I have not once gone against my own point! Again, I'm not seeing where you're getting all of this!

So all in all... and this has been my point this whole time (as well as audiophyle 247) that a sealed enclosure does indeed have a higher margin for error compared to a vented one. To be completely honest with you bro... this is pretty much fundemental information, and pretty much has been common knowledge within the enclosure design field for decades.

You're doing an aweful lot of debating for someone who has never used any of these programs before. I'd highly suggest that you download it and start ploting sone drivers for yourself. You'll soon see what we're all talking about!

Here, I'll even make it easy for you:
http://www.linearteam.dk/default.aspx?pageid=winisdpro

your going in circles.... if it has a higher margin off err then how come when they are both off by %20 the sealed will sound better?

Download the program... plot some drivers... and you will see for yourself!

[ttocs]

sounds like all your "margins of err" have to do with the possibility of the box builder taking shortcuts or the idea that most sealed boxes are made of FG and and guestimated. I fail too see why these would not effect someone building a ported box? I say the competence of the box builder is directly related to the comprimises he takes and what he ends up with. This is true for the sealed box builder, as well as the ported one....

are you defining "margin of err" as how far off from the original design(optimum specs) or how far off the sound is from the expected output. I looked up "margin of err" but the only definitions I found has to do with sampling rates in surveys.........

[audiophyle_247]

Thank you Shawn.


Ttocs, higher margin of error = larger acceptable tolerances.
Model a sealed box for a specific volume, say 1cuft gross.
Now model another sealed box at 1.3cuft & 0.7cuft (+/- 30%), and you will see the difference in response will be tiny, and most likely in audible. A difference of 0.3cuft is large, and makes minimal difference to the sealed performance when compared to what was modeled (at the intended but missed volume). If you can't hit within .6cuft of your target, you have no business building things.

Now model a ported box, and see that a difference of even 10% can greatly effect the performance. This is because internal volume & port volume must be exact in order to get what has been modeled on the computer. A difference of 5% in volume or 5% difference in actual port length can shift the tuned freq quite a bit, which will significantly alter it's performance vs what it should have been (& was modeled at). That is only a difference of .05cuft when dealing with the same 1cuft goal. That is a much smaller target you have to hit or risk serious disappointment.

The margin of error lies in the construction process, not the program. If you build an enclosure to exactly the same specs as you modeled you will get the same results. If your enclosure is not exact to spec as modeled, then you will not get the same results.
Sealed box is pretty hard to f**k up, while ported on the other hand requires much tighter tolerances & measurements to be as exact as possible.

Simple thing like omitting the woofer displacement is enough to throw off a ported box, or the most common error of counting the port space as internal volume (& that's a big error). You forget woofer displacement on a sealed box and the difference will be in audible, even with sloppy construction or imprecise measurements.

[shawn k]

sounds like all your "margins of err" have to do with the possibility of the box builder taking shortcuts or the idea that most sealed boxes are made of FG and and guestimated.

It's rediculously easy to build a simple "box" with a specific internal volume. However, in the real world, not all vehicles allow a box builder to build & fit a nice square box into said vehicle. This is where the higher tolerance to "margin of error" or "play room" is nice with the sealed enclosure. In other words, you don't have to be spot on the recommended volume in order to still have good performance. The ported enclosure design is not so forgiving and requires more precision in the execution of the build. I don't like using "shortcut" to describe this. As an installer who has built literally hundreds of enclosures I can tell you first hand that many times designing and building enclosures it's all about compromises. The use of fiberglass enclosures is just a good example of where a little "give" might be needed.

I fail too see why these would not effect someone building a ported box? I say the competence of the box builder is directly related to the comprimises he takes and what he ends up with. This is true for the sealed box builder, as well as the ported one....

They would effect ported enclosures even more so than sealed... this has been our point this whole time!

are you defining "margin of err" as how far off from the original design(optimum specs)

Exactly! I'm not sure why that was so hard to comprehend.

[ttocs]

its hard to comprehend because from what I can tell you are taking a technical term that has nothing to do with this situation and then trying to beat me over the head with it. Mix in some very polite "poking"(for lack of a better term) with comments like "lay mans terms" mixed in with a condescending attitude with the way you explain things and its no wonder you get into so many heated debates with people here.

Now that you were able to explain what YOU define as "margin of err" I realize its just a useless term to explain why a person building a sealed box would take a shortcut, to you. I find this laughable as if a sealed box builder was not able to get the space he needed then the ported builder sure as hell will not fit. not sure why ported builders are exempt from this "margin of err" but now that I understand its useless it doesn't matter.

[shawn k]

its hard to comprehend because from what I can tell you are taking a technical term that has nothing to do with this situation and then trying to beat me over the head with it. Mix in some very polite "poking"(for lack of a better term) with comments like "lay mans terms" mixed in with a condescending attitude with the way you explain things and its no wonder you get into so many heated debates with people here.

Now that you were able to explain what YOU define as "margin of err" I realize its just a useless term to explain why a person building a sealed box would take a shortcut, to you. I find this laughable as if a sealed box builder was not able to get the space he needed then the ported builder sure as hell will not fit.

Just amazing

It's sort of funny actually. It seems like everytime I try to legitimately explain something on this site, certain people get all defensive and say that I am the one who's condescending! Listen ttocs, YOU were the one who started in with "That is the funniest stuff I have read on this post now". I was simply making a vilid point just trying to help you comprehend what audiophyle was talking about. I was only tryinig to help...YOU were the one who was being condescending

I'm a big boy, and comments like that only make me chuckle for a minute. But if that's the mood that YOU want to set, then why is it somehow unfair for me to throw it right back at you??? Seems silly to me. And to be honest, in this particular situation, I really don't think I was condescending towards you. You are the one who is getting all defensive over this. To me, it just seems like you're insecure with the subject and now you have to throw out the "well your an ass" card to somehow justify the debate.

I like this forum, but man o man there are a couple members on here who really just can't "handle the truth"!!! It baffles me why people would prefer to debate... even argue over certain things when they have no profound knowledge of the subject at hand. As apposed to just sitting back, observing, and perhaps actually learning something!!!

"lalymans terms" is just a way to simplify facts. Apparently your insecurities lead you to believe that I was personally attacking you with that statement... again..not my fault.

Finally, the fact that you claim that "margin of error" is "useless" only portrays ignorance. "Margin of Error" is not some profound terminology. It's really quite simple man. I'm not sure why I need define the term.

not sure why ported builders are exempt from this "margin of err" but now that I understand its useless it doesn't matter.

Holy Christ man!!! Do you even read my posts!!?? For the third time and I'll put it in bold in hopes you won't miss it again.... the vented enclosure design is NOT exempt from "margin of error"!!! in fact it is more of a problem compared to sealed!!! JESUS... PLEASE READ AND COMPREHEND THE PREVIOUS POSTS BEFORE DEBATING!!!

[audiophyle_247]

its hard to comprehend because from what I can tell you are taking a technical term that has nothing to do with this situation and then trying to beat me over the head with it. Mix in some very polite "poking"(for lack of a better term) with comments like "lay mans terms" mixed in with a condescending attitude with the way you explain things and its no wonder you get into so many heated debates with people here.

Now that you were able to explain what YOU define as "margin of err" I realize its just a useless term to explain why a person building a sealed box would take a shortcut, to you. I find this laughable as if a sealed box builder was not able to get the space he needed then the ported builder sure as hell will not fit. not sure why ported builders are exempt from this "margin of err" but now that I understand its useless it doesn't matter.

Dude, your ignorance is showing. "Margin of error" is a pretty standard explaination of an "acceptable degree of variance", 2 seconds on gogle would have given you that answer. Not to mention it is a huge significance to anything in the built environment. It is just as important to sealed boxes as it is to ported boxes, the ONLY difference is the ported must be closer to spec to operate as designed, thus LESS margin for error, where as the sealed has a little wiggle room and still have very similar results to as designed, thus more margin for error.
Shortcut is not the right term here, if anything shortcuts are not modeling a box & just building it based off recommendations or size available. You want to know what you'll get? Don't take a shortcut & model the damn thing.
You design a custom fit FG box for a car and estimate that internal volume before hand to within 10% of the actual. Few if anyone can do that, thus why most boxes like this end up sealed, because it's much easier to estimate to within 30% of actual. It isn't a matter of shortcuts, or even lack of ability, it's just how shit is.

I'm building a mostly fiberglass truck box that will be ported, for 6 8's and the shape is way to complex to calculate or even estimate what the volume will be. I've had to measure as I go, and the only option I have is to plan for less volume and try to tune the port for whe I want. At least this way when the volume is wrong from designed it will be larger than planned, so if any variances occur the tuning will shift downward a hair vs upward. This is also a judgement call, and because my tuned freq is kinda on the high side, I'd much prefer it to shift down than up. No shortcuts taken by me, and I'm more than capable of building enclosures, but this shit applies to everyone.