Excellence Two – Mini Monitor Construction Update6!

December 11, 2011 Posted by gornir


Notch filter and distortion measurements:

I’ve built the first prototype (see my last post) of the cross-over and made some distortion and mid-woofer near-field frequency measurements with the focus on the cone break-up behavior.

The mid-woofer cross-over section is made of a simple 2nd order electrical filter in order to achieve a 4th order LR cross-over slope with a cross-over point at 2000Hz. For the notch filter section a cap shunt over the series coil is used to reduce the cone break-up at 10kHz.

In order to simplify the cross-over and to get a more accurate notch filter, I choose the cap shunt instead of the LCR notch filter type. A cap shunt connected across the coil and in series with signal path, requires a high quality component in order not to degrade the sound quality.

Thanks to the relatively low cross-over frequency, the odd-order distortions are low, even at higher listening levels. There isn’t a huge difference in the distortion measurements between using a notch filter or not for the mid-woofer cone break-up.

Don’t be fooled by the distortion measurements alone, the cone break-up is very audible and a notch filter is a must. The notch filter reduces the break-up with an additional 15dB and the effect is clearly visible in the frequency measurements.

A brief listening test to the prototype cross-over suggests that some work needs to be done at the tweeter section in order to find the proper balance between the mid and highs and the tweeter level.

For the mid-woofer cross-over section I want to use a coil with as low internal resistance as possible. I will test and listen to both iron-core and copper-foil coils to determine the best choice for the design.



Left picture: Cross-over version 1.0 with mid-woofer notch filter – 85dB level.

Right picture: Cross-over version 1.0 without mid-woofer notch filter – 85dB level.



Blue = 10cm near-field measurement without notch filter.

Red = 10cm near-field measurement with notch filter.

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