We will begin our analysis with Subwoofers.

How does a subwoofer work? When a current travels through a driver it creates a magnetic field, the magnetic field created by this current as it passes through the voice coil interacts with the drivers' static magnetic field (magnet/s). Put a direct current through the voice coil and it will move from the rest point to another stationary position, usually where the resistance from the suspension (spider and surround) are equal to the force of the magnetic interaction. When an alternating current (such as a sine wave) is put through a driver the voice coil and hence cone move in and out many times a second. How many times the voice moves in and out a second is referred to as the frequency. Say the VC is in its rest position and a current that alternates (crosses from negative to positive) 20 times a second is put through the VC, the magnetic field created by the AC current will alternate 20 times in one second thus the direction the VC travels will also change 20 times in one second. The VC and hence the cone has moved in and out at 20 times a seconds so the subwoofer has just reproduced a 20Hz frequency.

God aren't speakers simple put the same power through them and they will all do exactly the same thing?

Unfortunately no, there are so many variables when it comes to analysing how a driver works that it is not funny. The most important differences where highlighted back in the 70's by a dedicated pair of Australians! Yes that's right A.N. Thiele and R.H. Small

They produced what are now known as the Thiele Small Parameters.

These parameters describe the electrical and mechanical characteristics of loudspeakers operating in their linear (stable) region. These parameters are crucial for designing quality sealed, ported, SQ and SPL enclosures. This is possible because they show how the parameters define the relationship between a speaker and a particular enclosure. They are absolutely invaluable in making choices because they tell SO MUCH MORE about the drivers' real performance than the basic HYPE of size, maximum power rating or peak sensitivity.

A complete list and explanation of T/S parameters can be found here

Probably the most important T/S parameters to look at when buying subwoofers are:

Fs - Generally gives a good idea of low end response, ultimately it is a combination of parameters but for the sake of simplicity this is the main one to look at.

Le - This is important for people concerned with quick response. Inductance "is a measure of the amount of magnetic flux produced for a given electric current". In reality the VC is an inductor which means that it resists any change of electric current through the coil, the change in current induces a back EMF that opposes the change. The result is that changes in current are smoothed out. How smoothed out they are is the inductance. Now if our AC is smoothed out when it gets to the VC then the cone will not move as far and it will do so a bit later than it should. Thus transient response is reduced. The lower the Le the better, for a more in depth and ultimately better explanation see here

Pe - Shows the woofers rms power handling, more is not always better; I threw it in here because it is important to try and get a woofer that is a good match to your amps.

Qts - function of Qes and Qms. Can give a rough idea of what enclosure the sub is suited to. Qts of below 0.45 is suited to ported enclosures, 0.45-0.7 means the speaker is suited to sealed enclosure and above .07 the speker can be used in an infinite baffle setup. This is not a hard and fast rule only a loose guide, for example my type x with a Qts of 0.64 performs admirably in a ported enclosure both output and SQ wise.

SD - Once again so you can match it to you application just as easily look at parameter D here.

Xmax - Linear excursion of the sub, more looks cooler, more also means longer coil = more weight = lower sensitivity = more power. Technology is really coming along here just look at xbl^2 Adire found away around this very nicely, here and here

Znom - Ensure a good match to you amplifiers.

Ok now we have a rough idea of what to look at when purchasing our sub for our application. Please note as I have already indicated these are not hard and fast, set in concrete rules they are a GUIDE to help narrow the field and give you an indication of what you're getting yourself into

To help with our analysis it is essential to have a box designing program a good site is http://www.linearteam.dk/ or you can use the CAA box calculator. In case my house burns down and I loose my copy of bass box pro it would be good if some one could hold a copy for me, if you want to hold a copy for me then pme me.

Learn the ins and outs of your program, love it for it is your guide

For actual box building Blackice has many excellent tutorials but I digress.

To continue our analysis lets now look at sealed and ported boxes.

When a sub moves it produces a front wave and a back wave. These waves will cancel each other out if they are not separated or manipulated in a certain way.

Sealed enclosures completely isolate the rear wave from the front wave by trapping the wave in a box thus reducing the total non directional output by a theoretical 3 db.

Vented enclosures use a port to manipulate the back wave, thus bringing it back inline with the front wave, the result being constructive interference (theoretical 3 db output gain over sealed).

There are downfalls for each design, these however are easily overcome if they are designed correctly.

Group Delay:

Quite often the so called "lag" that many refer to when using vented enclosures is actually the result of poor box design.

A characteristic of a vented design is a higher group delay than a sealed enclosure, the effect however can be completley overcome. The issue to control is that ported boxes tend to display a large increase in group delay as they approach the tuning frequency.

In theory this should make the subs sound laggy. In reality though if the enclosure is well designed, these peaks can be tamed and tend to lie under 40hz. At these frequencies human ears are very very insensitive and the lag is completley inaudible (also barely any commercial music is recorded this low anyway). In practice a poorly designed vented enclosure might have a noticeable group delay and thus sound a bit laggy. At frequencies higher than 45Hz the group delay is exactly the same as a sealed box. Lag in a ported box can sometimes be cured by phase adjustments.

Sealed enclosures are characterised by a lower group delay which does not present any problems (if there is a problem it can be cured by box orientation or phase).

Frequency Response:

Ported boxes simply play lower and louder. Most subs in a sealed enclosure would be lucky to play down to 40hz at -3dB. Yet the same sub in a purpose built ported box could play down to 20hz at -3dB.

Vented enclosures also provide the opportunity to adjust volumes and the tuning frequency to achieve a desired response, you can fine tune the size of your peak and where it occurs. With vented you can achieve a flat response down to a lower frequency after the tuning frequency it roles off more quickly that a sealed enclosure (24db/oct).

Sealed enclosures tend to have a much higher f3 (-3dB point) but roll off more slowly (12db/oct). Some find the slow roll off a positive however it doesn't compensate for being able to play very low. One shortfall of sealed enclosures is that the only tuning variable is the volume of the enclosure. Here the effect of polyfill is very debatable.

Increasing the size of a sealed enclosure reduces the Qtc, which lowers its F3 point however this will also increase group delay. Reducing the enclosure size reduces the Qtc which raises the F3 point so the sub won't play as deep but will be more responsive. The idea is of course to get a good balance of the two, while maintaining a nice flat response.

The only thing that limits the range of frequencies the sub can play in a ported box is the sub itself and the frequency the box is tuned to. If the box is tuned to 50 Hz it will not play below this well. They are tuned to a certain frequency and this is where they have their max output i.e. a peak in the response curve. Below the port tuning frequency (Fb) the subs front wave is cancelled out by its rear wave due to phase shift (or lack of as frequency decreases) this usually happens at an octave below the tuning frequency. So the actual output is quieter even though the sub is moving quite a lot of air, known as unloading. A well designed ported box will play lower than a sealed box and will maintain it's loudness to a lower frequency before it rolls off (again due to unloading/cancellation).

Construction and Installation:

Sealed boxes are very easy to make and have a high tolerance for error volume wise, usually up to 20% difference in volume will not result in an audible change.

When designing a ported box all the measurement must be spot on in order to achieve optimum results.

The shape of either box generally does not matter; so long as the internal volume is correct.

Small boxes are easier to install than larger ones.

When you are designing a ported box you can make your life much easier by keeping the sub/s on the same plane as the port/s. It is not critical but it greatly reduces any chance of phase issues (read constructive and destructive interference) at higher frequencies.

Vehicles Acoustics:

All cars have cabin gain. Cabin gains occur because in reality a sub, in a box, in a car is really a sub, in a box, in a larger box! This results in the boosting of lower frequencies at ~18db/oct from ~50Hz downwards. A small sealed box usually has a more natural roll off as its inherent 12db/oct roll off is compensated for by the cars acoustic boost. The 24dB/oct roll off experienced by a ported box is not fully compensated for by the cars acoustic boost. This however doesn't matter if the ported box is tuned lowish ~40Hz.

The advantage of a vented box is that you can contour the response of the enclosure to suit the vehicle's acoustics. A ported box gives more flexability so that the desired response can be accurately achieved.

It's however possible that in a car, with in car gain, a poorly designed ported box can have slightly exaggerated low bass however with the right sub, and the right box specifications, a ported box can be designed to give a very similar curve to a sealed box with a downwards shift of the F3 point, louder and with much lower distortion.

Subsonic Filters:

Below the port tunning frequency the woofer can unload as we have seen. The result is the woofer can theoretically bottom out, damaging the coil resulting in the destruction of the woofer. A subsonic filters is a high pass filter, it cuts out all the frequencies below a certain point (eg 20Hz). Since these lower "harmful" frequencies have been cut out the sub will no longer reach its mechanical limits (Xmech). In theory the subsonic filter should be set slightly higher than the point where the woofer starts to unload.

The above is all in theory I personal (as well as many others) have found it quite impossible to bottom out our woofers. This "bottomless" aspect is all to do with the design of the box. Barley any commercial music dips below where a port should be tuned to anyways (below 40Hz).

Sub sonic filters are still helpful though maybe just not in respect to driver excursion. They can help the amplifiers' power supply. The result is the amplifier running cooler and also provides the opportunity to increase levels. This goes for both ported and sealed enclosures.

Distortion and Power Handling:

An inherent characteristic of ported boxes is reduced excursion! This means lower distortion! The vent is not subject to the mechanical suspension limitations of the speaker. The excursion-controlling aspect of a good vented design is of fundamental importance, particularly in high-performance systems where high acoustic output and low distortion are desirable.

Do to the subwoofer never realising its mechanical limits often its power handling is increased. The only limit you have to worry about is the woofers thermal limit, which becomes very obvious due to power compression.

The more a cone moves the more cone break-up/flex, harmonics and non-linearities it experiences.

Don't need much power to hit x-max with a sealed design.

Sealed has better impedance control.

SQ and SPL:

If SQ is your goal then the ability to tailor the acoustic response of your sub and car then ported is the way to go.

If you want to win SPL comps then measure your cars acoustic response find the cars resonant frequency, out put should be considerably higher at this point. Then build yourself a big F.O. vented sub enclosure that is tuned to this frequency. You will own.

If you want to compromise/don't have much time/not too worried about results then theoretically a sealed enclosure is fair middle ground.

Musicality and Tonality:

You here many people say ported is laggy, sloppy not as tight. Well it can be but with a properly designed box it will be on par with a sealed box just louder and lower and less distroted, which gives a fuller more natural sound.

I am not of the opinion that every sub will sound better in a ported box! I do however believe that about 5% of car sub matches don't suit ported designs without massive amounts of EQ.

Some people have found that a sealed box is not very exciting to listen to and seems to be quite monotone.

"We opened the vent in the Audio Enhancers enclosure and slid in the port to tune it to 33Hz. This made a magical difference. Whereas we found the WOOFER to be as tight and solid as a sealed system, the vented system was powerful and had a very satisfying weight at the bottom end of the scale. Technically slightly exaggerated, this response was -3dB at 48Hz, but had more energy just above the roll-off, and was just fabulous to listen to. A couple of musicians visiting the lab while this was going on had the opportunity to listen to the WOOFER in sealed and vented modes, and the verdict was unanimous in favour of the vented set-up"

Speaker Construction:

Woofers that are designed to be used in small sealed boxes tend to have weak suspension and high moving mass, so they are inherently not very efficient and do not have the best cone control often moving in each direction more than they should, this is of course to help combat the extra resistance (due to the air compression/decompression) in a sealed box, the resistance versus over throw due to extra weight will be equal at a certain output level but not at all output levels so the design is of compromises.

Woofers built for ported boxes have stronger suspension and lower moving mass, the result is higher efficiency and more control and less distrotion.

Port Noise:

If a port is not very strong then at some frequencies it can suffer from port resonances, this is very uncommon especially with slot ported enclosures.

Port noise (chuffing) occurs when there is too much air being forced through a port that is too small, it happens when the air velocity in the port exceeds about 5% of the speed of sound. Ports with a great opening area reduce air turbulence through them and therefore reduces the risk of port noise, wider ports do end up needing to be longer though so it is somewhat of a trade off in this respect (flared ports also help reduce port noise).

Choosing the right box is all pretty well summed up by Iron Hofmann's law.

Efficient
Low end
Small box

You can have any two of those box characteristics that you want its always going to be a compromise.

To be fair, in closing I would like you to note that I am biased towards ported enclosures. I have done much research on the issue and have tried my best to interpret the data and show my findings in a non biased way, but if you feel that I have not represented something accurately or left some information out I would appreciate if you would make a post so as to help my understanding of the topic as well as others

Cheers for reading and hope the analysis helped your understanding.

Lindsay

Great thread mate!

The more I read, the more I learn

very good info there....

after reading that, imn damn keen to go ported haha

a good program is only the starting point, it may take a bit of incar listening and then tuning to get it to sound they way you want it to, it will be worth it though.

great tut

good thread and some great info in there, but as you said, the bias towards ported is quite apparent .

maybe ported in general is just better though, i mean if you can think of any advantages of sealed or disadvantages of ported that i haven't mentioned then please let me know and i will add them

ill just list the ones that i can think of, and if they have been mentioned, ignore them.

*sealed only needs a small box, ported needs large.
*can get shocking group delay in a bad designed ported.
*^^as above with port noise
*mostly ported will be louder, but at the expense of sound quality (read:MOSTLY)
*is easy to stuff up a ported box..

yeh man all been covered, note though that all of the disadvantages you mentioned about ported (excpet the size factor) are the result of a badly designed box or and extreme case where the sub just won't work in a ported aplication (about 10% of the time i'm lead to believe)

Defiantely some good points made there, 20Hurtz. I've gone sealed so far, but I think it's important to open up people's minds to the potential advantages of different enclosures. Sometimes, the most limiting factor of a persons installation can be their own narrow-mindedness, and there are alot of people out there who refuse to go with anything other then sealed, based purely on word of mouth



In general, I disagree.

If you take 80% of subs designed for sealed boxes, put them into a ported box of exactly the same volume, and tune the box to 25hz, you will be amazed at how similar it will perform to the sealed box (interms of group delay, frequency response, etc).

Basically the lower then tuning frequency gets, the closer a ported box gets to a sealed box. At least this is my understanding.

A sealed enclosure of the right size will (hopefully) offset cabin gain to present a nice flat curve, but the extra bottom end provided by the ported box will often combine with the cars cabin gain to provide an unnatural low frequency peak. Some people may consider this 'playing deeper', wheras i simply consider it 'playing unnaturally'.

This is not such an issue in a house setup, because the room gain is nowhere near as dramatic as that of a car. In a house, most subs will sounds feeble when put inside a sealed enclosure, and require the use of a port to bring their low end performance up to respectable levels.

Assuming a sub plays fairly flat in a sealed box (given the right volume), then I fail to see how a ported box could reduce the -3dB point significantly without sacrificing the flatness of the curve.

As I said earler, youc an just tune it very low and use a similar volume, in which case it will look much like it's sealed equivalent, but in this case your -3dB point would be at the same place (more or less) and so to me woludn't justify the extra effort required.

That said, i've no doubts some subs will definately work better in ported boxes.

P.s. I defiantely don't think I know all, so please do feel free to correct me if i've gotten anything wrong here

But with increased power handling and reduced distortion!

Seeing as not much music is recorded below 40Hz by tuning ~ 30Hz the peak in the response is usually finished by 40Hz so the peak isn't really noticable at all.

A fair enough idea, but I'm still not particularly happy with the idea of intentionally sacrificing accuracy if it can be avoided. That said, many subs will also present a peak of some degree around 40hz - 50hz in sealed enclosures once put in a car, so this is a factor in both cases. Reducing the frequency at which this peak takes place would be nice, but i'd still prefer to avoid having that peak in the first place

It seems to me that with ported, you are heavilly reducing power handing BELOW the tuning frequency in order to imcrease power handling ABOVE the tuning frequency - hence swapping one weakness for another. This is understandable because it seems that the power handling of the ported enclosure is at no point actually worse then that of the sealed.

Excursion is another factor though, and imo related to power handling because it can limit how much power your sub han realistically take before shatting itself. This is where one major weakness of the ported design comes into play. Excursion in a ported box actually seems to reduce significantly approaching the tuning frequency... however as it passes below the tuning frequency excursion balloons out to epic high levels (200% - 300% higher then the sealed enclosure).

Many fix this via use of a subsonic filter, and defend it based on the fact that you dont really hear music below that frequency anyway. Again, i'm so-so on the concept of intentionally cutting a portion of soud out of your response inorder to patch up a weakness that could have been avoided by simply not using a ported enclosure.

To illustrate my ideas, here are a couple of screen dumps taken from BassBox Pro. I moddeled an Image Dynamics IDQ10 D4 (without factoring cabin gain). The Red line indicates the 14L sealed enclosure, while the blue line indicates a ported enclosure of identical proportions, tuned to 20hz.

I make note of a couple of things:

1) How near identical the two response curves look: contrary to the beliefs of most, this shows you can make a ported box play just as flat as a sealed sub in car.

2) That the group delay of the ported box looks almost identical to that of the sealed box until you get down to the tuning frequency, below which it increased dramatically. The lower the box is tuned, the less this is a factor. This strongly defies the idea people have that a ported box will always have significantly higher group delay then sealed. and shows that this is dependant on the enclosures design.

3) Phase response is very close, again only worsening slightly as it goes below the tuning frequency

4) Impedance is clearly more controlled in the sealed encloure, with a single peak from the driver. In the ported enclosure, the port itself seems to add a second peak at the tuning frequency.

5) Maximum power handling in fact DOES seem to improve with the ported box. Power handing is reduced heavilly below 50hz in the sealed box. but in the ported box it doesn't seem to drop off significantly until around 20hz. This result suprised me, as i expected the reverse.

6) Cone displacement (i.e. excursion) clearly is smoother in the sealed box. In the ported box there is a significant reduction in excursion from 50hz - 20hz, after which it goes through the roof. Given this was graphed with only 200w of input, this suggests a definate need for a subsonic filter below 20hz in order to prevent over-excursion and prevent the sub from bottoming.

My view for the time being is that ported does seem to have an advantage of two over sealed, those being:
* Increased power handling up to the tuning frequency
* Improved tunability to the situation at hand
* Far greater achievable output in SPL applications
* Improved control of excursion up to the tuning frequency

That said, they also seem to posess the following weaknesses:
* Dramatic increase of excursion below the tuning frequency
* Heavy and rapid reduction in power handling below the tuning frequency (although no worse then sealed if tuned low enough)
* More complex to design, and more expensive to build
* Tighter margin for error in design and construction
* Do not work well at all for some (not many) subs

At the end of the day, many people recommend larger ported boxes then sealed for SQ applications, however it seems to me that a successful ported enclosure would require to be close in size to a suitable sealed enclosure, or else risk large peaks in the bottem end response. This can of course be bandaided with EQ, but I personally prefer to use as little 'band aiding' as is necessary.

I'm gonna have a think about using a ported box for my Vanadium when I get it, and see how I like it.. may go off and play around a little to see what I can come up with. If I can get it to work out nicely, then I may get someone with an RTA to design me a properly build ported box. If i'm not all that impressed I'll go back to sealed.

I'm not impressed with the thought of using a subsonic filter though, as I have used these before and did definately notice a difference in the overall weight of the sound (or feel).

I would also like to note that all of these measurements were attained from software based estimations, and real world results may differ slightly to those I have concluded upon here.

thats a champ post pete.

tho that huge cone displacement blow 20Hz isnt gunna be that of much of a concern, seeing as how not much music is down there...

right or not??

I'd image it would be. Even though you dont actually hear the music (this is because of how our ear works, not the nature of the sound necessarilly) doesn't necessarilly mean it isn't there.

I wouldn't want to risk destroying a nice sub based on the assumption that it wont play anything below 20hz.

Likewise, this is at the lower extreme with a tuning frequency at 20hz, which is considerably below where most people would tune.

Take one look at the same graphs with the tuning frequency increased to say, 40hz, and things start to get nasty. You get a nice chunky peak around 40hz - 50hz of probably 5dB - 6dB, the group delay starts to dramatically increase as soon as you get below 40hz (rather then 20), power handling starts to drop off avery sharply round 40hz (again, instead of 20hz), and cone displacement goes through the roof around 30hz - 40hz where there is still plenty of sound to be played. Suddenly things ain't so peachy, and a sealed enclosure starts to attract some appeal.

This is why it is heavilly stressed that ported boxes are less forgiving of error. a pretty small miscalculation in port dimensions can turn a planned tuning frequency of 30hz into an actual tuning frequency of 45hz or greater - and this small change can throw your plans completely out of proportion.

In comparison, a small miscalculation of volume in a sealed box will likely only bring a change in around 5K of volume. This will affect the sound, but the group delay, power handling, cone displacement, and general frequency response will generally remain within very exceptable levels.

All the more reason why I would never recommend a ported box to any person who doesn't know quite alot about audio and enclosure designing.

has been a very worth while read...nice tutorial dude...some really intellectual facts here...a man who knows his crap

Sorry its been a bit but i've been a bit lazy and preoccupied.



Is this net volume your talking about if so I agree but if your takling about gross then i disagree, tuning @ 25Hz will require a decent amount of port.



True but it does depend on application ie street beating or SQ for SQ I would tune below 30Hz but for street beating 35-40Hz is fine (sub dependent of course).



Car audio is a trade off full stop! haha

Excusrion can somewhat be controlled with vent design i'm pretty sure (will have to play with BB when i get home to be sure). So if you don't want to lessen the power handling too much below the tuneing freq you should be able to incoporate this into the design. The trade off again is with power handling above the tuning freq, by reducing excursion through vent design the thermal power handling is lowered (less air through the VC). So if i am right about the whole power handling vs vent design the tradeoff that you speak of can be tailored to the users needs. To addto this i am running my pioneer sub with and adjustable port (33Hz for a bit of SQ and 45 for just getting loud) and even at 45Hz it doesn't bottom out when playing the bass drop right at the start of Bassment Jax Good Luck when the volume is at above average listening levels (i would put the bass drop at a bit under 30Hz) i will do some tests with tones to be sure.



Agreed. There are two aspects to power handling, Thermal (at which the VC will blow) and Mechanical (at which the sub will bottom out/spider/surround will tear etc). An inherent fault of the ported design is its reduced thermal power handling around the tuning freq (i'd say give or take 3Hz) with SPL comps this could be a problem but with music the sub is producing many freq at once so the reduce power handling is minimised. From memory there is also an impdiance rise around the tuning freq which greatly decreases the chances of the woofer reaching its thermal limit. This impideance rise is also couteracted to a degree (talking about output now) by the peak expericed at the tuning frequency. So many aspects come into play all of which are directly related and to an extent couteract the negatives.



once again it does all depend where the box is tuned to and what sort of music you play. If you play stuff with low organs etc then you must account for this in your design and tune low. Like i said i listen to some pretty bassy stuff and have honestly never hurt any of my subs by exceeding thier xmech.



Very nice but as you note this sub is quite heavily suited to a sealed box. To be fair imagine what it would be like modeling a sub that is suite to both sealed and vented and then one that is suited to vented.



Agreed 100% nothing can properly compare to the real world. I do however also believe that software especially decent programs like bass box and especially LEAP give a very good indication and starting point to the box design, real life tweaking is esential to get the sound that you want.

Good discussion, this is what i wanted this tut to turn into Cheers Muzzy66

hey dude,
great discussion, got me thinkin and added somes q's to those ive encountered while playin with box pgm's tryin to make a box one that suits me and my car..

vehicle acoustics, does where the box is loading/facing/blowing/porting, dunno what to really call it, effect this??
my thought is if the sub is entirely in the boot its a box in a medium box(boot) venting to a large box(cabin), hence diff to porting/facing the sub into the cabin and being only a box in a large box. thus effectively changing like from a sealed to a 4th order in respect adding another tunning cavity.
does this change the acoustic gain?? or is this looking to deep into it making it better to just assume approx 18db per oct and correct rest with ear and eq??

group delay, what is considered acceptable/unnoticable??

boomy ported boxes, what can be done to overcome this trait?? you say with a properly designed box, ported can be on par with sealed with concern to tightness??
my thoughts are that the tight sound is to do with the Q of a system. thinking that the suspention of a ported designed driver is heavyer/tighter to compensate for the relative lack of dampening from the enclosure and vice verser, the only way i can think of increasing punch is to opt for a smaller box and or smaller diameter port and thus making the Q of the enclosure higher, increasing the port air speed and the potential for chuff??

my goals are sq oriented. i have two focal 27h's in a sealed box facing/enclosed in the boot and it sounds better, including more punch, when the boot is open. lookin at other enclosure options to solve this, as asked in another post of mine(as yet unresponded to ) http://www.caraudioaustralia.com/forums/in...showtopic=75905

Regards, Clint

I'm only just getting into "proper" car audio building and I was seeing if ported or sealed would be best. This thread, along with the many other tute's on here have bee worth their weight in gold!

Kudos!

HI, i have just finished building a sealed box for an alpine type r 12" subwoofer, it is in a large 4x4 wagon... space was important as i need as much extra room possible to pack things away when i head off on trips

so far the sub sounds great!, i am in no way worried about how loud it sounds etc.. i just want good quality sound wich is what i now have

Before i made this sealed box i used to run a ported box with a 15" soundstream sub in it and i guess the box wasent built (tuned) as good as it could have been but i do no that my new 12" alpine sounds much better.. the ported had nothing compared to the sealed as far as responsivness sound goes

The ported was very loud if you wanted it to be but as i said before im not worried about sound competitions... and it was bloody huge compared to my new sealed


So i guess for mine the sealed was a better choice as i dont want sub boxes to take up the rear of my 4x4.. and im not sayn that a propery tuned ported box would not or could not sound as good as my new sealed, but belive me the sealed sounds absolutly awsome!!


Dave

type r 12

try about 1.4 cubes tuned to 34Hz

My last half dozen low tuned vented enclosures (QWEV) had more box volume taken up by the port (some twice the volume) than in the chamber it's self I never really liked vented enclosures untill I started to use ports large and long enough to get some quarter wave action happening

Though for my own personal listening I prefer a heavily damped sealed enclosure* with drivers suited for that application.


*subject to change depending on how my front bass horn turns out

Great thread with LOTS of very good info. I have just built a sealed box for my 2 MTX 12s, I would have liked to go with a slot-port set-up but there just wasn't the space. Ported is great if it's done well and you can fit it in........

you could probably use your current box and just port it as long as the port was the right length and width for the volume of the box you are currently using
I found a port formula you can use to calculate the length required for certain volume/box type/tuning frequency not sure how good it is though
http://www.diysubwoofers.org/misc/portcal.htm
anyone more experienced have any feedback on if this formula is worth using or not

Excellent read with good facts.
Most of you know that I am extremely bias towards vented enclosures.
One thing about them that I'd like to add.
1. Group Delay-other factors
The number of drivers sharing the internal volume increses with the number of drivers and the manufacturers ability to make drivers the same. If you were the test your drivers I will put money on the fact that no two drivers are exactly the same. This difference will increase the "laggy" sound.
2. Tuning
Two way to approuch this and I like the second the best.
1. Design the tuning port to give the best response and power handling.
2. Get the box in the car and listen to the thing. Alter tuning to overcome any acoustic issues your vehilce may have. Yes you give up a little power handling and perhaps even a few cycles of the bttom end but the resulting sound is worth the effort.

Cheers

Hi all,

Sorry to bring an older topic back up - but really love this thread, lots of great info, but I just wanted help with a couple of things as I've just recently started building/installing car audio more frequently, and I would just like to know more about finding the cars frequency/acoustic response, as mentioned in the first post.

Just wondering how exactly you would go about finding these figures out?

Thanks for the great thread too!

generally by testing.

ive heard of ppl putting subs in a small ish sealed box seeing where it peaks. then building a ported one around that freq... for max cabin gain.

Well In general I disagree with your disagreement

can you get the port specks for a enclosure with 12L?? while keeping the port contained within the enclosure
it's possible but it will sound like crap at higher volumes
why?
because the port will be too small, air will move to fast, making the port large enough to avoid this problem would result in the port taking up most of the space in the enclosure not to mention alot of complex corners to fit it in

so short on space, go sealed

12 L lol

as long as the port tuning frequency is below Fs then it will act similar to sealed. - so a sub small enough to fit in 12 L - say 6 or 8 inch, Fs is high, like 60 or 80Hz or something, so the port will be smaller

I'm making a home speaker at the moment, 12L with tuning 53Hz. port fits fine.