Sealed Sub VS. Ported, questions about room gain...

[wigginjs]

I'm designing a sub around the Dayton 12" Titanic MKII driver (pretty popular it seems) and after modeling a few enclosures with WinISD I immediately decided on a vented enclosure because of the higher SPLs at low (~20Hz) frequencies. I've been thinking about the design more and realized I wasn't taking into account the room gain (which apparently is pretty substantial with subwoofers). If the room gain is high enough at the lower frequencies I may be able to use a sealed enclosure to get pretty flat response all the way to 20Hz. Here are my 2 questions:

1) How do I calculate room gain for my particular room?

and

2) I've heard that a sealed enclosure provides better (read cleaner?) bass than a vented enclosure. How does the sound that a sealed enclosure produces differ from a vented enclosure?

[BillFitzmaurice]

Room gain is more due to boundary effects than room dimensions, which means that placement near a wall or in a corner can get you an additional 6 to 8dB on average irrespective of room size. Larger rooms can result in stronger positive nodes but also require higher SPL to achieve room compression, so the two tend to be a wash.

There are two reasons for the difference in sound. First, below the F3 a sealed box rolls off at 12dB/octave, a vented box at 24dB/octave, so the sealed has a potential advantage for the lowest frequency extension. However, if the F3 is at, say, 20 Hz, the 12dB difference between the two at 10Hz won't matter much anyway. From the same driver you can get to the same F3 in a sealed or VB, but the sealed box will have to be larger.

The other factor is restorative force, which the compressed air mass within a sealed box is more effective at controlling cone motion than a vented box. This generally makes for a cleaner sound.

Bottom line is that you can take advantage of the vented box properties to get a smaller box or get a somewhat cleaner sound from a sealed box but it will have to be larger to match the F3 of a VB.

[sreten]

Well BF doesn't mention you can get an F3 in a larger box than
sealed way below the possibiliities of any sealed alignment.

And generally for a particular driver reflex needs a bigger
box than sealed, you can't choose reflex for a smaller box.
(you can choose a different driver for this to be true)

Using an overdamped reflex alignment you can approximate
a 6dB/ octave roll-off which matches with rooms well and the
necessarily low port tuning will play cleaner than the sealed
box as it has 12dB more low bass SPL capability.

But this is general stuff, the titanic2 driver seems well suited
a sealed box of ~ 2cuft, with possibly some low bass boost.

Reflex alignments that suit room gain seem quite difficult.
An overdamped reflex is heading towards 5cuft.

sreten.

[wigginjs]

thanks for the response, but I'm still pretty confused. Is it ok to just ignore room gain?

[Dave Jones]

Originally posted by m0tion
thanks for the response, but I'm still pretty confused. Is it ok to just ignore room gain?

That's the ticket. Ask only one question at a time. Or if you ask more than one question, number them! (Works for me.) Asking about sealed vs. vented and room gain both is too much.

Here's a question: If I assume the sub will go near a wall (and perhaps in a corner), what will the room gain chart look like? I've seen one on the net, but someone here said it was unrealistic. I still do not know what is realistic.

[wigginjs]

I did number them =)

[Dave Jones]

Originally posted by m0tion
I did number them =)

So you did. Well, just keep trying.

[Vikash]

Originally posted by m0tion
thanks for the response, but I'm still pretty confused. Is it ok to just ignore room gain?

I think most people ignore room gain as there are so many other variables involved. Start by going through this thread: Room gain

[baggystevo82]

Here's a question: If I assume the sub will go near a wall (and perhaps in a corner), what will the room gain chart look like? I've seen one on the net, but someone here said it was unrealistic. I still do not know what is realistic

Try this
I haven't been able to verify its validity in a real life situation, but I guess it's better than nothing
Steve

[goobz]

This is somewhat tangential to your question, but you could just ignore room gain, and then if you have too much low bass cut those frequencies. This is better than assuming there will be heaps of room gain and finding out there isn't and having to boost the lows, hence putting more strain on your amp and driver. Especially with ported you need to watch out for boost below tuning frequency.