Question about cone excursion.

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I had always been under the impression that a sealed box would reduce the cone excursion as opposed to a vented one.

Is PE correct in saying that the vented enclosure is the one that reduces cone excursion?

If they are correct, wouldn't a driver in a ported enclosure have less distortion, be more controlled and handle more wattage than if it was in a sealed enclosure?

(I thought the cone would move more in a vented enclosure due to some of the air coming out through the port.)

I'm confused because from what i've read, the driver would be more controlled and handle more wattage in a sealed enclosure.

BTW, I'm assuming that cone excursion = the cone's movement in and out, so the less or the shorter the movement of the cone, the less distortion and the more controlled the sub will sound.

High above the tuning frequency, the equivalent driver will move about the same distance in both BR and sealed boxes. As the signal frequency approaches tuning frequency, the driver in the BR box will move less. The excursion is generally at a minimum at the tuning frequency. Below it, the excursion rises sharply. The driver in a sealed box will gradually have higher movement as frequency decreases.

This is all of the top of my head so I'm probably wrong. ;)
A very simple way to see what effects a sealed and ported box will have on excursion is to download WinISD and do some simulations.

What you will find is, A ported box reduces excursion near the resonant frequency of the enclosure, but below this excursion will skyrocket and the woofer's movement will be uncontroled(and excursion will be much higher than that of a sealed box). About an octave above tuning the port will no longer have a substantial effect and the excursion will be equivilant to that of a sealed box.

Thermal power handling might be slightly higher in a ported box due to the venthilation of the rear chamber(the voice coil will get cooler air) but this effect will be minimal and you probably wont gain more than an extra couple watts of power handling. I wouldnt believe even 3db would be possible to gain power-wise.

Excursion limited power handling will be increase in a ported enclosure near the tuning of the enclosure, but below it will be far less than that of a sealed box and an octave above tuning it will be the same.

My understanding is that dampening is more a factor of enclosure size (tuning has a some effect for a ported box) than anything else.
well its not so much as above tuning as it is near tuning. The port will contrubute a small bit slightly above and below the exact tuning, but it quickly becomes useless a bit farther below and above.

Distortion can take many forms and just saying that a one box or the other has less distortion really isnt telling much.

Sealed boxes are said to be prefered due to their better transient response and lower group delay. Ported boxs can have low group delay and sound very musical, but the tuning must be very low.

There are probably other factors that I cant think of right now.... Maybe someone else can chime in
If I tune a sub to about 20Hz, will it bottom out with a 15hz signal?

Since most bass in music is above 30Hz, wouldn't the sealed and ported enclosures perform the same with music? (given that the ported sub is tuned to about 20Hz)

Am I wrong in thinking that in order to produce the same output level, the driver in the sealed enclosure would have to move a lot more than the driver in the ported enclosure.
if you tune to 20hz, you will probably bottom out using a 15hz signal yes. But that is dependant upon the power level and how much excursion you have available. The driver will not be controlled by the enclosure at this frequency so basically it will be acting as if it had no box at all. You even wont bottom out a driver in free air if you use too low of a signal level, so you wont bottom it out in the ported enclosure either.

With 20hz tuning you will still have a change in group delay above 30hz. It may or may not be an audible difference, I cant say without doing a listening test.

For the same output level a sealed box will use more excursion than a ported one at tuning, but an octave above tuning the excursion will be the exact same, and below tuning the sealed box will have less excursion and more output

Like I said earlier. You should download WinISD. It's free software available at and it will give you graphs of excursion, SPL, power handling, group delay, and many other things. If you dont understand exactly then read the help file, it isnt incredibly technical, and it should clear a few things up for you.
An externally hosted image should be here but it was not working when we last tested it.

This is a graph showing three subs gains.

green = vented box tuned to 25.71hz.

white = vented box tuned to 21.19hz.

Yellow = sealed box.

Given this graph, will the driver in the sealed box have to move a lot more than the ported ones to produce the same output from about 50Hz to about 16Hz?
Tried the Cone Excursion tab in WinISD my friend?
First, go into signal, and enter the amplifier power you want to use.

Instead of using the Transfer Function Magnitude, scroll down to Cone Excursion. You'll see it by yourself.

But, yes, the sealed woofer will need to move alot more.
Vent diameter or cross sectional area is dependent on the amount of air the cone moves. You need a bigger vent area for a bigger cone movement. It's also dependent on frequency, qith lower frequencies creating less noise so a smaller diameter can suffice. All this has nothing to do with the box size.

The box volume will influence the vent length. A longer vent will tune to a lower frequency, so a smaller box will require a longer vent than a larger box.
The velocity of the air in the port is generally at it's top just under the tuningfrequency of the port. From the highest point to higher frequencies it will decrease fast, from the highest point to lower frequencies it will decrease slowly.

Placing the highpassfilter higher can eliminate portnoise (or applying less power off course ;))

Mvg Johan
diyAudio Moderator Emeritus
Joined 2001
If you buy flares for the 4" port, it should have the same port noise as a 6" port without flares, yet will only require the same length as a 4" port.

At the tuning frequency, the cone excursion in a ported box is only about 25% that which a sealed box woofer would have to move to put out the same output.

The ported box saves cone excursion greatest at the tuning frequency, gradually less higher up the scale. At an octave above tuning frequency, the output and excursion of the ported and sealed boxes is about the same.

If a box is tuned to 20 Hz:

At 20 Hz, the ported box woofer will have 25% the cone excursion of the sealed box woofer, (if the sealed box woofer was driven to equal SPL).

At 28 Hz, the ported box woofer will have 50% the cone excursion of the sealed box woofer, (if the sealed box woofer was driven to sequal SPL).

At 40 Hz, the cone excursion and output of the ported box ans sealed box woofers are very close.
If a box is tuned to 20 Hz:

Below 20 Hz the cone excursion will quickly increase and gain will fall with about 24 dB/octave below tuningfrequency.

A 6 to 12 dB/octave highpass filter will generally be sufficient, tho many choose not to use it at all, well...lack to use mostly ;)

To maintain high powerhandling (if wanted) it's advisable to tune around fs.

Mvg Johan
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