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Re: Horns below driver Fs

Posted by tomservo (M) on February 27, 2007 at 13:26:03

In Reply to: Horns below driver Fs posted by dsm on February 26, 2007 at 08:31:52:

Hi

The Fs is set by how much moving mass you have and how stiff the suspension spring is, you can picture the relationship.
In a horn, the suspension spring part is in parallel with the spring force produced by the air trapped in the sealed box, acting on the piston area. This new stiffer spring produces a new resonant frequency, Fb.
To get the most bass out of a given horn, both the driver properties and the rear air volume have optimum values.
In this case, all things being equal, if one lowered the Fs, the ideal rear volume would have to be made smaller to off set that. The up side is the air spring is typically more linear than driver suspension.
Fb, resonance “in box” with no horn attached is normally above the low corner when horn loaded.
When you approach the low cutoff of a proper horn, one has some acoustic reactance, the horn appears to have an increasing mass reactance as the frequency falls.
By choosing the right flare “t” for the driver, the rear volume is sized to off set this reactance, extending the low corner f (reactance annulling). It is entirely possible on many horns to end with more bass by making this volume smaller than intuition might suggest.
Where to go now?
Look into Marshal Leach’s paper on matching moving coil drivers to horn parameters.
Some one here will likely have a link to it handy.
Look in to the McBean horn simulator and the other free or near free modeling programs for horns, nothing saves sawdust and sweat like a good computer model.
Best,

Tom Danley

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