# Designed for sealed or ported



## Delta Echo (Sep 3, 2011)

I am aware of many guidelines for determining enclosure suitability. As that may be often times these methods seem to contradict themselves. 

Some sources (manufacturers, professionals) suggest EBP,or compliance, or CMS, or resonance, and again some go with total Q. 

Three Examples that come to mind:
1990's Stillwater Designs designed for sealed systems had very compliant suspensions, Low Q values, and moderate EBP's. S10C FS 23Hz, Qts of .29, Vas of 95.4 liters and an EBP of 72.
(warranty disclaimer in manual if not used in a sealed cabinet)

Current DD's designed for ported systems have incredibly stiff suspensions, high Q's and relatively low EBP's. 1510A, FS 34Hz, Qts .619, Vas of 12 liters with an EBP of 50.

On the extreme side MMATS 3.0/ProCast 10 designed for sealed or ported cabinets (as stated on their current website) have moderate compliance very low Q's and an extremely high EBP. 3010 FS 30Hz, Qts .105, Vas 45 liters with an EBP of 260. 

I would like to explore this disparity.

Thanks
Rick


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## Hillbilly SQ (Jan 26, 2007)

Can't believe no one is touching this topic.


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## ChrisB (Jul 3, 2008)

It could always be worse... I had a nuthugger telling me that a certain brand of overpriced component speakers would work great in my Mustang, even though I had sealed factory pods. When I asked him to explain just how something designed for infinite baffle use would work well in my sealed pods, he quoted one of the greatest marketing bullsh*tters of all times by saying "He said..."

I'll stick to T/S parameters and modeling software to attempt to choose which ~6.5" driver will work best in ~.7 cubic feet sealed after displacement, should the need ever arise.


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## minbari (Mar 3, 2011)

honestly, some speakers do work better in a ported or sealed design and not work well in both. dont beieve it, model a few. not to say that it wont work, just that is will not be ideal on one or the other.


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## Eric Stevens (Dec 29, 2007)

For a larger listening environment it is useful to use EBP and other typical methods of determining a drivers usefulness in a particular enclosure type. 

For the automobile the transfer function is so strong that these measurements are not anywhere as meaningful. Add to that that below a certain frequency we enter a constant pressure domain where output is solely determined by pressure caused by the amount of displacement the speaker can create.

So to really know what you are going to get you need to look at large signal parameters such as klippel and combine that with the transfer function response to know the end result.


Eric


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## XtremeRevolution (Dec 3, 2010)

minbari said:


> honestly, some speakers do work better in a ported or sealed design and not work well in both. dont beieve it, model a few. not to say that it wont work, just that is will not be ideal on one or the other.


What he said. The number of subs I've modeled so far have confirmed this repeatedly.


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## captainscarlett (Mar 15, 2011)

I want to get into a bit of box building for the sake of a regaining some boot space. And as people seem to have a distinct disdain for prefab enclosures, i thought i'd start to do a bit of reading up to make sure I have at least a basic idea of what's going on. 



Delta Echo said:


> 1990's Stillwater Designs designed for sealed systems Qts of .29,
> 
> Current DD's designed for ported systems have incredibly stiff suspensions, Qts .619
> 
> On the extreme side MMATS 3.0/ProCast 10 designed for sealed or ported cabinets Qts .105


Yet on another forum you get this advice, which seems contradict some of the suggestions for sealed or ported enclosures:



> Qts of 0.4 or below indicates a transducer well suited to a vented enclosure. Qts between 0.4 and 0.7 indicates suitability for a sealed enclosure. Qts of 0.7 or above indicates suitability for free-air or infinite baffle applications. However, there are exceptions!



So who or which advice do i believe? or am i looking at this wrong?


So if I'm to take the above advice, this would be in a ported box ...



> 1990's Stillwater Designs designed for sealed systems Qts of .29



The DD, of which I have all three enclosed subs, would be the biggest contender for a sealed box .. (but having a little experience of DD I wouldn't even try it) 



> Current DD's designed for ported systems have incredibly stiff suspensions, Qts .619



.... and this would have to be the biggest contender for a ported box and a sealed box wouldn't even get a look in!



> On the extreme side MMATS 3.0/ProCast 10 designed for sealed or ported cabinets Qts .105


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## 14642 (May 19, 2008)

captainscarlett said:


> I want to get into a bit of box building for the sake of a regaining some boot space. And as people seem to have a distinct disdain for prefab enclosures, i thought i'd start to do a bit of reading up to make sure I have at least a basic idea of what's going on.
> 
> 
> 
> ...


they're both right and they're both wrong. 

Here's the deal...go get a cup of coffee...

The Qts of the speaker indicates the shape of the roll-off. A Qts of .707 is considered ideal for infinite baffle because provides the best compromise between low frequency extension and transient response. So, let's say you have a woofer and you want to build a sealed box. Let's also say you have a TARGET Qtc (total Q of the box and woofer) of .707 and your woofer has a Qts of .5

The box volume will be calculated to provide an "aid" to the speaker's suspension (makes the suspension stiffer) so that the Qtc will be raised to the target of .707. If the woofer has a very compliant suspension (low Q) then the box will have to contribute more restoring force, so it will have to be small. If the woofer has a stiff suspension (higher Q) then the box will have to contribute less restoring force, so it will have to be bigger. If the Qts of your woofer is higher than the target Qtc, then the target isn't achievable.

So, the Q of the woofer determines the volume of the box for a given target Qtc. The low frequency extension is determined by the woofer's resonance frequency, Fs. The Fs is also raised in the sealed box iin the same proportion as the increase in Qts to Qtc.

So, a woofer with a really low Qts and a low Fs is well suited to a small sealed box SO LONG AS THE VOICE COIL IS LONG. Sealed boxes require much more excursion from the speaker than vented boxes do. A woofer with a short coil is not well suited to a sealed box unless it will be driven with very low power.

A vented box is more complicated. It's a combination of a sealed box and an additional resonance. A low Q woofer designed for a sealed box will work just fine in a vented box, but the additional coil necessary for the sealed box will be wasted in the vented box and its mass makes for a less efficient system than a woofer with the same Q and less mass.

Anyway, the box volume for a vented box is calculated to provide a target response similar to the sealed box. Usually the volume is a bit bigger because we want a lower Qtc (which doesn't really exist in the vented arrangement, but we'll use it as an example). 

The port is basically a speaker that's designed to play loudly at one note. Its response is a peak. We design the port to have a response that compliments the response of the woofer. We hear the sum of the output of the woofer and the output of the port. If we increase the tuning frequency, we have an area where the port's response and the woofer's response have a small gap--that creates a peak in the response in those frequencies. If we move the port to a lower frequency, we have a dip in the frequencies in between. Usually, the resonance frequency is chosen to extend the low frequency response as low as possible while maintaining flat response. For small bookshelf-style home speakers, a little bump is often helpful in providing some additional bass. 

At the frequency where the box is tuned, the port plays, but the woofer hardly moves. This is because the acoustic impedance (pressure) inside the box is much higher. Yes, the pressure inside a ported box is HIGHER (at the tuned frequency) than in a sealed box. Below the frequency where the box is tuned, there is much LESS pressure than in a sealed box--hence the need for a subsonic filter. So, at the low frequencies where the box is tuned, the woofer doesn't move much, so we don't need a heavy long coil. That makes it easier to make a more efficient woofer, since we don't need so much moving mass.

OK, so what does all of this mean? 

1. If you're going to use lots of power and a sealed box, then you need a woofer with a long coil.

2. If you're going to use a vented box, a woofer with a shorter coil will be fine.

3. If you use a woofer designed for a small sealed box (low Q) in a vented box, the box volume requirement will be small and the port frequency requirement will be low. That means the port will be very long and the box will be difficult to build because the port will be difficult to fit in the box. 

4. If you use a woofer with a short coil, designed for a vented box, in a sealed box with high power, the woofer will run out of coil and you'll hear distortion. Because the condition that produces the distortion is symmetrical (coil leaves the gap in both directions), the distortion will be mostly odd-order, which sounds nasty. "Brap Brap Brap". 

So, what's the conclusion? 
Your power requirement and choice of box type determines whether a long coil (woofer with high Xmax) is necessary. Almost all woofers will work in a sealed or vented box, so long as the woofer's Qts is lower than your target Qtc. A woofer with a Qts higher than .707 will have a peak in its response NO MATTER WHAT KIND OF BOX YOU USE. The rest is a matter of compromising between box size, power required to hit a target SPL and required low frequency extension.

When you put the box in the car, the transfer function (car's frequency response) will be added to the response of the woofer. this will produce roughly a 12dB per octave increase in level as frequency is reduced starting at about 50 or 60 Hz, depending on the size of the car. A vented box will give you a big peak and a sealed box will not. If you have an EQ, then you can reduce the peak by reducing the power the amp has to provide at those frequencies. I think a vented box and EQ is always the best way to go, so long as you can afford the space and the EQ.


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## minbari (Mar 3, 2011)

excellent write up. someone should sticky that!


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## captainscarlett (Mar 15, 2011)

Andy Wehmeyer said:


> they're both right and they're both wrong.
> 
> Here's the deal...go get a cup of coffee...
> 
> ...


I cannot believe the great help and advice I'm getting from this forum. I've tried on a few others and have gotten a mouth full of sarcastic comments about how thick i am. I'm asking so i can learn!

So first things first .. Thank You very much .. all of you!

OK, so there's a lot of info in there for my slow mind to digest, but i get the idea. But i will study your anwswer again and again 'til i get it right. 

Next question i have is: What's considered to be a good xmax number?


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## subwoofery (Nov 9, 2008)

captainscarlett said:


> I cannot believe the great help and advice I'm getting from this forum. I've tried on a few others and have gotten a mouth full of sarcastic comments about how thick i am. I'm asking so i can learn!
> 
> So first things first .. Thank You very much .. all of you!
> 
> ...


Depends on your application... 5mm of Xmax can be enough for ported alignments... 
Sealed? As much as possible 

Kelvin


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## fish (Jun 30, 2007)

Great post Andy!

Question though...

At what point (lengthwise) do you decide if the coil is better designed for sealed or ported?


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## 14642 (May 19, 2008)

fish said:


> Great post Andy!
> 
> Question though...
> 
> At what point (lengthwise) do you decide if the coil is better designed for sealed or ported?


That depends on the amount of power that you'll use. If the woofer has a Qts of .4 or lower and a linear Xmax of 10mm or longer, it's designed for a sealed box. If it has a Qts of .4 or lower and has a coil length less than about 10mm, then it's a sealed box woofer that's designed for low power. Does that help?


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## wheelieking71 (Dec 20, 2006)

im not going to quote your response Andy (because its huge! LOL). but i would like to thank you for laying the info out there for the "avarage Joe" in terms that we can understand, and reference! that is awsome stuff! thank you!


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## fish (Jun 30, 2007)

Andy Wehmeyer said:


> That depends on the amount of power that you'll use. If the woofer has a Qts of .4 or lower and a linear Xmax of 10mm or longer, it's designed for a sealed box. If it has a Qts of .4 or lower and has a coil length less than about 10mm, then it's a sealed box woofer that's designed for low power. Does that help?



Yes, that's the answer I was looking for. Thanks!


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## fetoma (Jul 12, 2011)

This is great info. I'm thinking of building a box for my F250 and this helped. Thanks!


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## adrenalinejunkie (Oct 17, 2010)

Great info in this thread. I'm thinking of making a new enclosure for the 18" W6 now...


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## BuickGN (May 29, 2009)

Brought back from the dead but I would like to say thanks as well. I probably would never have seen this thread if someone didn't revive it.

Interestingly my IB subs have a pretty low Qts, low Mms, and very compliant suspension. They feel like the spider is detatched they're so "loose" when you push on them. I'm guessing to get a low Fs with a low Mms you have to have a very compliant suspension?? Maybe this is why efficiency is pretty good? Does this also explain why they need a very large box? I hope this isn't going off topic, just trying to tie some of the T/S parameters together in my head for a sealed arrangement.

Since we've covered sealed vs ported, what about T/S parameters in relation to an AP vent enclosure? Would this be the same as a large sealed box?


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## BuickGN (May 29, 2009)

adrenalinejunkie said:


> Great info in this thread. I'm thinking of making a new enclosure for the 18" W6 now...


What kind of enclosure? I only ask because of the problems with those in vented enclosures.


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## adrenalinejunkie (Oct 17, 2010)

BuickGN said:


> What kind of enclosure? I only ask because of the problems with those in vented enclosures.


I was thinking of going with lil volume with a low port tune, but i'm probably better off staying with my current enclosure. I don't want the woofers VC to get damaged.


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## Bayboy (Dec 29, 2010)

BuickGN said:


> Since we've covered sealed vs ported, what about T/S parameters in relation to an AP vent enclosure? Would this be the same as a large sealed box?




Aperiodic vents or assisted enclosures are very hard to determine what woofer is suited best. Basically you will have to make the enclosure to suit whatever driver you choose by measuring the impedance changes after the box is built. You could very well wind up in a tedious task of changing box size, adding more or less resistance, etc. To model one would be too complex and guessing at best unless you knew ahead of time the exact amount of impedance peak reduction will be presented. Scan Speak makes/made a unit called the Vario vent. I had one, but can't recall if it even suggested how much reduction it would make.

Of course it would seem that higher Q drivers would benefit most if you were trying to avoid excessively large enclosures, but it depends on what you're trying to achieve. Low Q drivers would seem to be sort of a mess with a resistively leaky box, yet can be useful depending on the box size. Almost no need unless you wanted a super tiny box. Once a driver is over a certain level of Qts, then the vent or whatever will not make much use so you can see it's not as cut & dry as it comes across. The very low end response of a AP box isn't all that great if you're used to tightly sealed enclosures anyways so I abandoned it. I'm not even sure if I still have the vent. It may be tucked away somewhere, but it's definitely going to keep collecting dust if it is.


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## captainscarlett (Mar 15, 2011)

Bayboy said:


> Aperiodic vents or assisted enclosures are very hard to determine what woofer is suited best. Basically you will have to make the enclosure to suit whatever driver you choose by measuring the impedance changes after the box is built. You could very well wind up in a tedious task of changing box size, adding more or less resistance, etc. To model one would be too complex and guessing at best unless you knew ahead of time the exact amount of impedance peak reduction will be presented.


From the little i've read and understood, an Aperiodic is .... almost as hit and miss as adding stuffing to a quarter wave line design. I can't see how one could accurately model before hand. Isn't the response dependnat on he material used?


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## Bayboy (Dec 29, 2010)

I would think source material is definitely a factor, but at the same time it's common to opt for a system design that suits such anyway. I'm no expert, so take my input with a grain of salt. I did later stumble upon an older thread where Lycan gave some good info on the subject. You will have to search that one as I failed to post a link.

Sent from my SCH-I500 using Tapatalk


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## amalmer71 (Feb 29, 2012)

Andy Wehmeyer said:


> they're both right and they're both wrong.
> 
> Here's the deal...go get a cup of coffee...


I'm also resurrecting this from the dead just to say... 

Forget a cup of coffee. I need a cigarette after reading that. :smoking:

That was better than free sex with no commitment. Beautifully written and explained a lot of stuff without sounding like "Hear now, peasants!"

I was recently trained at a new job, but the trainer I had sucked. I told my supervisor, "There are people that write music, people that teach music and people that play music. Jason (the guy who was training me) is a someone who plays music. He's very good at his job, but he's not a teacher by any means."

You, Andy, are a teacher. Kudos to you, and thanks.

Now, where'd I put my lighter?


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## sundownz (Apr 13, 2007)

Good post Andy; too many people hang on HARD to the Qts = ALL rule when designing enclosures.

What is really fun is when people are still driving woofers to x-max even at port tuning with all this cheap power any more *laughs* I've been working on alot of new parts to handle that for my Bass Boxing guys.


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