SEALED vs PORTED (basic info.)

BASS OUTLAW

Single sub fan
Apr 18, 2004
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Now we will start with :

Sealed enclosures : A SEALED enclosure will be the smallest,and is the simplest of enclosures and will have good low frequency extension, but might not have the best low frequency extension. If space is limited.

and its a good choice for SQ fans (Sound Quality).

PORTED enclosures (Bass Reflex) : A PORTED enclosure will generally have a better low frequency extension for a given response shape,but would require a larger enclosure. If you made the enclosure as small as the sealed enclosure, but ported it to gain the low frequency response, the output would deviate from the desired flat response.

Ported enclosures are slightly more difficult to design than a sealed enclosure. When using a sealed enclosure, it is difficult to be so far off as to risk damaging the woofers. In any type of enclosure, the woofer relies on the enclosure for damping. If there is insufficient damping, the woofer's cone will move significantly more than it should. The ported box will provide virtually no damping below the port frequency, all of the control will be provided by the woofer's suspension. Below the tuning (port) frequency, it is possible to cause damage to the woofer well before power levels approach the maximum power ratings of the woofer.

common tunning frequencies :

Sound Quality : 20 up to 28 Hz.

Sound Quality Loudness : 30 up to 35 Hz

Sound Pressure LeveL SPL : 40 up to 80 Hz (test tones are played rather than normal music, to avoid Low frequencies, which damages the speaker).

Its commonly used for competition propose. and not everyday driving.(unless you like listening to test tones for everyday driving).

BandPass enclosures (Single Reflex): Bandpass enclosure can sound good and give you a flat response,but most of the bandpass enclosures(in the market), are not designed for a flat response, this means that they are built to produce a large peak at some frequency from 50 to 60 Hz, these enclosures will work well with Rap, but generally they dont sound good with other types of music.

if u use a banpass enclosure. it should be designed specificaly for your speaker.

P.S : its not always recommended.



hope that this info will help many to understand the different types of enclosures.and which type will perform better for their propose.

-zAK

 

BASS OUTLAW

Single sub fan
Apr 18, 2004
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CALCULATIONS/ FORMULAS

dV = is the required diameter of port in inches.

Fb = is the tunning frequency of the enclosure in hertz.

Vd = is the volume displaced by the driver (woofer)

Lv = is the LENGHT of port in inches.

R = is the internal radius of vent tube

Vb = is the internal volume of the enclosure cubic inches.

PS : to convert cuft into cubic inches

# cuft *1728 = value in cubic inches
Vd = Sd x Xmax
dV>/= 39.37*(Fb*Vd)^0.5
Lv = [(1.463*10^7R^2)/(Fb^2*Vb)] - 1.463
value of R
R = square root (a/3.142)
and "a" is the area of square vent = Width*Hight
changing Round vent to Square vent

A= Pi* (4/2)^2
and Pi =3.142
 

geolemon

Senior VIP Member
Mar 31, 2003
383
2
Buffalo, NY
Awesome info, BASS OUTLAW!

If you don't mind, let me take a step backwards...

You explained what the benefits/tradeoffs commonly are.... I want to touch on the fundamentals just a tad, and that might bridge the gap as to "why do certain enclosures offer certain benefits/tradeoffs?" //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

Why do you need an enclosure at all?

Picture a sub moving. The cone moves in and out, rapidly - and it's that simple.

Picture the cone moving out, in slow motion. It compresses the air in front of the cone, and rarefies the air behind the cone.

IF the sub were just sitting there, the compressed air would largely simply bleed into the rarefied vacuum behind the cone, and most of the sound would simply cancel out as a result... leaving you with not much sound at all, if any.

Sealed box:

The sealed box simply contains the rear-of-cone energy, so that it can't escape, to cause the cancellations with the front-of-cone energy. The front-of-cone energy is what you ultimately end up hearing.

The sealed box also, inherently, ends up affecting cone motion - because the trapped air inside the box acts as a spring, essentially. It's more difficult for the cone to move in and out in an enclosure, because the air is preventing the cone from moving in and out, it's resisting being squished and stretched.

As a result, if you put a sub in a tiny enclosure, it inherently will always be inefficient - requiring lots and lots of power to even get moderately loud - because you are trying to brute-force your cone motion... a large enclosure is much more efficient, requiring less power to get as loud.

But maybe you don't want to waste that rear-of-cone energy anyways?

Ported box:

In this case, a vent is installed in the enclosure. Might be round, might be rectangular, might be any shape... ultimately it doesn't matter - what does matter, is that the port opening area and length of the port have to be sized such that they provide just a little resistance against air passing through it. The amount of resistance is critical to the performance of the enclosure.

In this case, essentially you have the same properties of the sealed enclosure, but the vent does something interesting...

Again, picture the sub in slow motion.

Picture it moving in, compressing the air behind the cone, inside the enclosure.

Naturally, this air tries to escape out the port, having suddenly been pressurized.

...and it does, but the port slows it's escape. As the air is travelling out the port, the sub has changed direction, and is now heading out again.

By now, the compressed air has travelled out the port - just in time for the cone to move out again - and now we have a situation where the front-of-cone energy is creating a pressure node in the listening space, and the rear-of-cone energy is creating a pressure node in the listening space, thanks to our friend, the port.

...and continuing the thought, the cone has moved out, rarefying the air behind the cone, creating a vacuum effect inside the enclosure, sucking air in the port... by the time the air can be sucked in through the slightly resistive port, creating a vacuum outside, the cone has again moved in, creating a vacuum node itself.

One common misconception is that since it has a hole, the pressures must be lower inside a ported box, compared to a sealed box.

The opposite is true, however!

Again, thinking about what is happening in slow motion - with the sealed box, you simply have the sub compressing and decompressing the air trapped inside the enclosure.

With a ported box, however, you have not only the sub, but the momentum of the air in the port pressurizing and depressurizing the air inside the enclosure.

As such, pressures are actually HIGHER inside a ported enclosure than a sealed one.

Things aren't perfect in "ported land" however. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

The port is a static thing, and as such, it's air resistance - and therefore it's delay, are a static value.

Wavelengths, however, are different for every frequency, increasing in length as the frequencies decrease. As a result, one wave takes more time to pass for a low frequency, than for a high frequency.

As such, you end up building a port that's "ideal" at one particular frequency - but as you move away from that frequency, you either overcompensate for the frequency being played, or undercompensate for it - but either way, the phase relationship is degraded, and you again move in the direction of being more or less like a sub that isn't even in an enclosure at all.

...In fact, if you operate a subwoofer too far below its tuning frequency, the air moving in the port is cycling too slow to increase, or even equal the pressures inside the enclosure - and it acts like a simple hole - resulting in little or no air 'spring' value inside the enclosure - making it very easy to bottom out your sub with even less than the RMS powerhandling limit of the sub being sent to it.

...well, that covers ported and sealed boxes... which is a good start anyway.

Infinite baffle is much like a sealed box, but with no "air spring" factor, since there's no trapped air involved.

Outside of that, other types of enclosures get more complicated...

...although it's fundamentally interesting to note that 4th order, or "single vented" bandpass enclosures utilize one sealed chamber (the one that defines the low end response), making it somewhat synonymous with the behaviors of a sealed box, and compatible with subs that are compatible with sealed enclosures.

Similarly, the 6th order, or "double vented" bandpass enclosure utilizes ports in both chambers, making it somewhat synonymous with the properties of a ported box, and compatible with subs that are compatible with ported enclosures.

Hopefully that helps augment what BASS OUTLAW started with. //content.invisioncic.com/y282845/emoticons/nerd.gif.c6fa51ddf7ff75f1c0371fbc648f70ae.gif

 
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squeak9798

Banned
Jun 22, 2004
26,551
96
USA
Now we will start with :
Sealed enclosures : A SEALED but might not have the best low frequency extension. If space is limited.

PORTED enclosures (Bass Reflex) : A PORTED enclosure will generally have a better low frequency extension for a given response shape
I think you may have your terminology a little off there, or I am reading it wrong. The ported will have greater low frequency output down to the tuning, but a sealed with a decent Qtc will have greater low frequency extension (i.e. sealed can play lower than a ported box, but down around the tuning frequency the ported will have greater output).

Also a good time to mention Hoffman's Iron Law:

You can only have two of the following three at any one time;

1) Small Box

2) High Efficiency

3) Low frequency extension

If you want any two of them, then you must sacrifice the third.

 

supa_c

Abministrator
Apr 5, 2004
21,705
21
In a chair
Might want to add a good one.
Ported=Vented - samething:D
slot port=slot vent- also samething:D //content.invisioncic.com/y282845/emoticons/moon.gif.9d317aec3339ffe7fde0638df52c628a.gifP.S

i found that using a graphing calculator makes finding the port size very easy.

a normal calculator just sucks

 

BASS OUTLAW

Single sub fan
Apr 18, 2004
1,084
0
next street
I think you may have your terminology a little off there, or I am reading it wrong. The ported will have greater low frequency output down to the tuning, but a sealed with a decent Qtc will have greater low frequency extension (i.e. sealed can play lower than a ported box, but down around the tuning frequency the ported will have greater output).

Also a good time to mention Hoffman's Iron Law:

You can only have two of the following three at any one time;

1) Small Box

2) High Efficiency

3) Low frequency extension

If you want any two of them, then you must sacrifice the third.
A SEALED enclosure will be the smallest,and is the simplest of enclosures and will have good low frequency extension. ( a good)

A PORTED enclosure will generally have a better low frequency extension for a given response shape, (notice the "Given response") u can always tune ported LOW. ( u did read it wrong). //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

BASS OUTLAW

Single sub fan
Apr 18, 2004
1,084
0
next street
geolemon, nice comments,//content.invisioncic.com/y282845/emoticons/wowflash.gif.89a61f4caede63a11dac36e97d61323e.gif

i liked the port info //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif//content.invisioncic.com/y282845/emoticons/clap.gif.178cba2c538c68e720c727fcb024b19c.gif

 

helotaxi

Kilroy was Here
A SEALED enclosure will be the smallest,and is the simplest of enclosures and will have good low frequency extension. ( a good)
A PORTED enclosure will generally have a better low frequency extension for a given response shape, (notice the "Given response") u can always tune ported LOW. ( u did read it wrong). //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
You can't get the same response shape from a sealed and ported enclosure. A sealed box rolls off more gently below resonance than a ported one. A ported box is good to basically the tuning frequecny and the output quickly becomes useless below that. A sealed box can provide usable output well into the range of inaubidility and when the transfer function of the car is factored in the response is generally pretty flat well below the range of hearing.

You can't always tune a ported enclosure low. There is an optimal combination of volume and tuning frequency for any given sub. Deviate much at all from either one and the results are anything but quality sound. The response curve will get peaky, the transient response will become poor and the group delay will become unacceptably large. If you tune an enclosure too low you lose the efficiency advantage that a ported enclosure enjoys over a sealed in the 30-50 hz range and the accuracy of the output suffers as well. You can tune a bit higher than optimal without a huge tradeoff in quality of sound (you trade efficiency for low frequency extension in this case) but go too low and you will have problems. The performance of an enclosure volume and tuning depend entirely on the sub used in the enclosure. You can't just say build a box to this volume and tuning and any sub you throw in it will work well. A larger percentage of subs will perform terribly in that enclosure than will work even marginally well. Sealed is a lot more forgiving in this respect.

To add to what geolemon said: About an octave above tuning, a ported enclosure behaves almost exactly like a sealed one. Below tuning, the pressure wave from the port not only cancels most of the output from the cone but the inertia of the air in the port acts to move the cone farther than it would in free-air. This can have rather disasterous effects on the structire of the sub. Coils jump the gap, surrounds and spiders get torn, cones get cracked/torn, fomrer strike the backplate and are cracked/deformed. None of those equate to the long life of a sub.

 

BASS OUTLAW

Single sub fan
Apr 18, 2004
1,084
0
next street
helotaxi thnx for info,

so which one helps the woofer to handle more power :

1- ported ?

2- sealed ?

a woofer that handles 300 rms in a sealed

will not perform the same as the "same" woofer in a ported enclosure.

when it comes to pushing it with 500 rms or so.

 

helotaxi

Kilroy was Here
As far as power handling, the answer as always is "It depends". It depends on the sub. It depends on the enclosure, not just sealed or ported, but tuning and volume as well. Frequency at which the power is delivered is very important as well. Below tuning, excursion increases exponentially in a vented box. Right at tuning the sub can handle a huge amount of power mechanically (in regards to excursion anyway, the stresses involved may well rip the sub apart) but just above or anywhere below tuning excursion is much higher and power handling takes a pretty big hit. A smallish sealed box will have better power handling than a larger one but will need the extra power to compensate for a drop in efficiency. Really low frequencies can damage a sub in a sealed box as well, as it takes less power to reach excursion limits when subsonic frequencies are involved.

If you really want a good idea of what the box does for power handling, get an enclosure program that does an excursion plot and play around with it a bit.

 

Folly

Junior Member
Aug 15, 2004
14
0
Los Angeles, CA
ok im making boxes for my 4 12" double stacked magnet subs......one dual box and 2 single.........which would be louder and sound better......ported or sealed they work with both......what do u all think?????

 

nweibley

this:annoyinginsomanyways
Jan 13, 2004
475
0
Tampa, FL
I tend to think that a properly designed ported box will hit lower and have flatter response than that of a sealed. I don't really like sealed boxes much except in tight spaces and ultra ultra high SQ installs like adding extension to a BMW or Mercedes.... in those cases I like to find a great SQ driver and put it in a pretty decently sized sealed box for the sake of OEM look and a non "boomy" sound no matter what.