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Friday, March 31, 2017
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    Importance of the Impedance Curve

and what can you do with it...



Bass Refelx Alignment

Impedancecurves are essential for the vote of BassReflex enclosures.


The BassRelex alignment is through the impendance minimum between the two impedance peaks defined and therefore accurately determined only with a impedance measurement.

The formular:

fb = 48.4 * d / Sqrt(V * (L + 0.8 * d))

  • fb = tuning frequency [ Hz ]
  • d = Port diameter [ mm ]
  • V = Enclosure volume [ liters ]
  • L = Portlength [ mm]


The measured Reflexport alignement is 34.6 Hz


The Reflexport frequency is measured at 0 degrees Phase.
  • d = 50 mm
  • L = 110 mm
  • V = 28 liters
fb = 48.4 * 50 / Sqrt(28 * (110 + 0.8 * 110)) = 37.34 Hz

The difference to the measured Portfrequency is 2.73 Hz

Calculate fb
Port diameter   [ mm ]
Port length   [ mm ]
Enclosure volume   [ liters ]
        
Port alignment frequency  (fb)  Hz



Enclosures Errors

Impedance curves are helpful to find enclosures leaks or too little, too much or incorrectly found damping material arranged.


Improperly damping: Enclosure resonance at 220Hz


Too much or improperly arranged damping material is recognized by flattened impedancepeaks without rizing the impedance minimum inbetween


Leaks in vented systems make themselves felt through a less than optimal pronounced minimum between the impedance peaks.


Leaky enclosure

Here we have by not properly tightened the chassis screws a leaky enclosure produced.
The impedance peaks becomes flatter, the minimum between them increases.



Circuit Errors

A circuit error in the crossover is clearly show in the impedance curve of the loudspeaker.


Defect capacitor in the midrange section



A shorted capacitor in the impedance correction of the midrange driver.





Impedance measurements are an important systems tools for every loudspeaker builder

All measurement are done with ARTA