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In the Forum: Audio Discussions
In the Thread: First Order on Bass channels: Designed for Sound
Post Subject: Bass from a vented box...Posted by morricab on: 11/7/2007
Hi all,
In my experience it is VERY hard to get anything resembling realistic bass from a vented box, particularly with a Q of around 0.9 or 1.  There is too much stored energy in the system and too much overhang. 

The best bass I have heard in descending order is:
Horn bass
dipole bass
Sealed box (around 0.6-0.7 Q)

The other problem in discussion, namely using first order crossovers, requires some examination of the two drivers at the crossover point.  If the drivers are two different materials, eg. aluminum and kevlar, to use a high order crossover results in a sonic disaster.  Why?  First you have a mismatch between the inherent sound of the drivers.  ALL drivers (except perhaps an ion flame or a diamond cone) have a characteristic sound from the flexing and breakup that occurs from the material not being infinitely stiff.  Then you are making an abrupt transition (with a high order filter) between one driver to the next and this makes a discontinuity in the coloration of an instrument that spans those two drivers.  The worst I have heard in this regard were some B&W speakers which had carbon fiber woofers, kevlar mid, and aluminum tweeter with 6th order filters.  No coherence to the sound whatsoever.  This is complicated by phase shift, which while perhaps inaudible in a short demo becomes obvious when listening for longer.  One hears softened transients that blunt any attempt at a lifelike sound.  A low phase shift with a 1st order filter makes it easier to get good transient response.  Any distortion increase will be more than offset by the benefits as long as a suitably robust driver is chosen.  Especially in the bass a little bit of extra harmonic distortion will largely be inaudible but a better integrated bass will give a much more coherent and upbeat sound (or PRaT).  To me higher order vented systems often sound quite sluggish.

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