The Last Loudspeaker System

By Stig Erik Tangen
15 Dec 1997

Equalizer and measurements

The passive equalizer that must be input in the signal chain somewhere looks like this Fig. 6. The passive equalizer.

For this filter to work properly, a source with an output impedance less than 100 ohm is required. The load impedance should not be less than 10 kohm. However, variations in load impedance above 10 kohm does not make any significant changes in the filter function. If your source has a high output impedance, you can subtract it's value from 1,3 kohm, and replace the 1,3 kohm resistor with this value. A 600 ohm output impedance would require a 700 ohm resistor (680 ohm is the nearest E24 standard value).

This is what CALSOD tells us about the frequency response without the required equalizer Fig. 7. Frequency response without equalizer.

A good check on proper filter symmetry is to invert one of the drivers. There should now be a large symmetric dip at the crossover point. This is how it should be Fig. 8. Frequency response without equalizer, reverse phase.

When we put in the required equalizer, we get a frequency response that is very good Fig. 9. Frequency response with equalizer.

The tweeter peaks a little at the top end, but no adult person can hear it anyway, so why then bother? As we can see, the low end rolls off smoth, which works well in an ordinary room. The speaker will not become bass-heavy even with a corner placement. When judged from listening only, the speaker plays «flat» to about 40 Hz. If you want more bass, the cure is called subwoofers.

The speaker lobes upwards when placed with the woofer above the tweeter. The crossover is also designed to have its on-axis direction 5 degrees upwards. This means you should be at the same height as the woofer's centre when listening at 2 meters distance.

The impedance stays flat at 5 ohms over a wide frequency range, and the phase angle is within +/- 20 degrees Fig. 10. The impedance curve.

The finished speaker
The speaker looks very good, just take a look Fig. 11. The finished speaker.

And here's a full view Fig. 12. The owners hardware collection of the entire hardware collection (well, at least the part he wants to show us...) of Karl Anders Ellingsen, who owns the speakers. Check that grin!

Does it sound good? Build it and find out!

Stig Erik Tangen

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