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If a Heresy I w. K22 were tuned w. a leaky vent to flatten its normal Z peak - would it "boom"?


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11 hours ago, RandyH said:

 making sure the cabinet is properly sealed with Foam for the rear panel and  the midrange horn and tweeter helps quite a bit

 

A 'leaky vent' is a port design, NOT what you are thinking or reading into this.

 

 

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"The Variovent consists of two grilles with some damping material stuck in between. Simple as that. The diameter, amount of damping material and the compression of the material determines the air flow properties = acoustic resistance. The late Gilbert Briggs (Wharfedale) made slits in the rear panel and added damping material over the slits. Works the same and costs nothing. But you have to be able to follow the impedance of the system to tune the amount of damping material needed.

The Variovent is a device sometimes causing much debate. What is an acoustic vent? Well, an acoustic vent allows some ventilation at low frequences and virtually none at higher frequences. So what's that supposed to be good for? Neville Thiele studied the Variovent in detail and concluded it didn't offer any advantage over a properly designed vented systems. The general advice on the use of acoustic vents is simple: Try it! Which offers little comfort to those addicted to math. But box calculation based on Thiele/Small data really only apply for speakers with a Qt = 0.35, which only counts for very few drivers. Based on experience we use speakers with high Qt in cabs too small and drivers with low Qt in cabs too large compared to strict box simulation.

Comparing the impedance peaks of a driver in free air and a perfectly closed and empty box should reveal the same peak height, so we have no loss in the closed box. Obviously the resonance frequency is higher. Adding damping material to the closed box we see a decline in peak height; now we have some loss. Adding an acoustic vent may produce a significant reduction in peak height depending on how open the vent is. So, the system Q-value is lowered (= more loss) from applying an acoustic vent although we really can't speak of a Q-value of an aperiodic system. Basically a closed box has 2nd order roll-off, a vented system a 4th order roll-off and the aperiodic system a 3rd order roll-off."

 

I messed around with this years ago. Does a Variovent work? Yes. Did it audibly change the sound? No, not in my case, perhaps because my enclosure was close to the correct size. The leaky vent concept is mainly for sealed enclosures that are smaller than optimum. 

 

 

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