How does one determine sealed or ported enclosure

[oon_the_kid]

Hi,

I am trying to figure out if given the T?S parameter of a driver, how does one determine what type of enclosure is better sealed or port?

Oon

[toprepairman]

There can be lots of opinion on this one. Personally I prefer the sealed enclosure as it's easier to implement and you'll get a leaner and smoother bass. Ported is a good way of getting a bit more apparent bass from a smaller box, but difficult to get right and difficult to integrate with your room.

[oon_the_kid]

I personally prefer sealed enclosures too. I am just trying to understand the theory, something to do with the Q of the system...

On a different note do you know if it is necessary to create a groove for the speakers to be sunk into the cabinets. I've heard that it makes a difference to the sound.

Oon

[richie00boy]

Generally if Qts is higher than 0.45 sealed box is more suitable.

[speaker dave]

Most woofers can be made to work in both a sealed box or a vented box.

Here are other issues to consider: Size. A properly vented system will typically be twice as big as the same woofer in an appropriate sealed box. Power handling. A vented system will have a nice increase in available output at the excursion null of the vent frequency, but it will have more excursion below that frequency. Transient response. A vented box is higher order and will tend to have worse transient response.

David S.

[Keriwena]

Originally Posted by speaker dave

Size. A properly vented system will typically be twice as big as the same woofer in an appropriate sealed box.

Huh?!?!? Coming from you, Dave, this is a bit of a boggle. A major selling point of reflex systems has always been "reduced size".

The EVM12L, which was designed for a ported cabinet, has a Qts of .232. I suspect even lower Qs would work as well. Thing is, as the Q goes up, the bandwidth of the "bass boost" from the port gets narrower, and someplace above .7 it becomes a "Why bother?". The slight amount you can lower the bass response isn't worth the faster roll-off.


A rebate (groove) for a woofer is a nice touch, but I'd worry more about reflections from the grille frame or edge diffraction unless you're talking a very high xover.

[speaker dave]

Originally Posted by Keriwena

Huh?!?!? Coming from you, Dave, this is a bit of a boggle. A major selling point of reflex systems has always been "reduced size".

True, but you have to be careful not to be doing an "apples and oranges comparison".

Vented boxes are inherently higher performance and will give a lower cuttoff with the same efficiency, but only if you redesign the woofer to get there. (more magnet strength plus more cone mass)

If you start with a given woofer then the ideal vented box volume is typically about twice the size of the ideal sealed box.

David S.

[toprepairman]

Depends on how you qualify 'higher performance'.

[rabbitz]

Originally Posted by oon_the_kid

Hi,

I am trying to figure out if given the T?S parameter of a driver, how does one determine what type of enclosure is better sealed or port?

Oon

You can use EBP as a guide. EBP=Fs/Qes and if less than 50, then use sealed, if greater than 100, then use vented. For values between 50 - 100 it could go both ways. Excursion available is also a consideration as generally sealed may need more travel.

[speaker dave]

Originally Posted by toprepairman

Depends on how you qualify 'higher performance'.

I'm referring to the efficiency, f3, box size tradeoff. The vented box is inherently better in that regard. i.e. if you pick sensitivity and box size the vented box will go lower. If you pick f3 and box size the vented box will be more efficient, all assuming optimum woofers and enclosures.

David S.