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From: rutgers!sales.stern.nyu.edu!sbhattac@cmcl2.NYU.EDU (Shankar Bhattacharyya)
Newsgroups: rec.audio.high-end
Subject: Re: Subwoffer Driver Rec's Wanted...
Message-ID: <13211@uwm.edu>
Date: 18 Jun 91 13:00:17 GMT
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In article <13174@uwm.edu> miker@polari.UUCP (Mike Ranta) writes:

>>On the other hand, what drivers are good for vented subs?
>
>In my opinion, there are very few drivers that work well in vented
>subwoofers.  On the computer, several look great, but in practice,
>nearly all of them distort and/or bottom badly at frequencies well
>above and below the tuning frequency of the enclosure when driven
>hard.  You are also correct about having to second guess box losses
>and other factors.  As you're probably aware, ported designs also
>roll off at 12db per octave versus 6 for sealed systems.  For this
>reason and the first one above, they do not respond to "EQ" well
>if they require it (or the owner likes it).  There are exceptions
>to all this, but you'll likely be happier with a good sealed system.

I agree that closed boxes have the merit that they are almost impossible to
mess up entirely, and so they make a most desirable way to enter the world
of low bass. But good vented boxes are possible. I don't know much about
vented boxes, so I will refrain from making too many specific
recommendations, but many of Madisound's drivers look as if they were
designed for vented boxes. Audio Concepts seems to lean towards sealed
boxes, if their selection of drivers is any indication.

The Eton drivers are designed for vented boxes (thanks, Seth), and the
Dynaudio 30W54 works in one, although it requires rather large internal
volume.

For what it is worth, the 30W54 cannot produce F3 below 40 hz in a sealed
box without bass boost. In a B4 alignment, without any equalization at all,
the F3 would be in the neighbourhood of 25 hz, depending on the sample.

The reason vented systems bottom is that they are wildly unprotected below
resonance. This suggests the need for some subsonic filtering. Sixth order
alignments provide this "for free", and may solve many of the complaints
people have about vented boxes. Seth Bradley and Len Moskowitz have posted
information on building such systems using the Precision TA305, and its
successors, which achieve serious bass at serious spl.

Also, the question of whether vented boxes or sealed ones have lower bass
is open to discussion. While sealed boxes roll off with shallower slope
below their F3, their F3 is significantly higher than driver Fs. For a
vented box, in a B4 alignment, F3 is about the same as Fs. I am not making
any cosmic inferences based on this, but it is something to think about.

I have stuck with sealed boxes, and the related aperiodic designs,
basically because they are easy. I confess to some prejudice against vented
systems, but I know that my prejudice is not well-founded. If you are
prepared to biamp (and most woofer users are eventually likely to), adding
the low frequency filtering is not a pain.

- Shankar