The point often missed about those Gyrator equalizers is the Q is *not* constant. The Q and the amount of boost/cut are linked. At low boost/cut the Q is very low. You only get the design Q at full boost. The Q is roughly proportional to the boost.

As the circuit stands it's not so easy to see. However, imagine designing a boost only equalizer except you make the boost variable by adjusting the series resistor. To first order approximation that's what is going on. Now look at the design equations. The Q depends on the total series resistance.

Suppose you design an equalizer with 12dB boost and Q=3 then design another with 15dB boost and Q=3. When you set each equalizer to say 6dB boost the actual Q produced on the 12dB design will be about 1 but the Q on the 15dB design is 0.65. To get 6dB boost the 15dB design need to backed-off the boost more relative to 15dB that means the Q gets backed-off more than the 12dB design.

When set to 6dB the *total series resistance* must be set to the same resistance in both designs. The L and C values (and minimum series R value) for the 12dB and 15dB cases are not the same so the final Q is different for any given resistance.

My advice for these things is to tweak the Q by ear *at the settings you are going to use*. Typically you might only use 6 to 10dB and a Q of around 1.0 usually sounds pretty good. That just happens to match-up with a Q=3 design for 12dB or 15dB equalizer.

One more point is calculator only calculates maximum Q. The series R value is linked to the L in the gyrator design. When you add a boost pot there is a second series R which adds to the gyrator series R, it doesn't affect the L but it does affect the amount of boost and the Q. So what I'm saying is you won't be able to use the calculator to see the Q variations at different boosts because the calculator only has one series R, the one that affects L.

I was expecting them to be an octave wide, no? Half an octave to the left, half an octave to the right. Instead they are around 0.4 octaves wide according to Jack's calculator.

When you have a numbers of band those equalizers perform much differently to a single band. The centre frequency is about as expected but the Q's and maximum boost get screwed up because the bands interact.

The best way to convince yourself is to compare spice with the design equations. You will see it's almost pointless using a calculator for the graphic equalizer case. For widely split bands the calculator is OK but you will still find it doesn't agree with what you expected from the design equations.

Something I forgot to mention is the value of the boost/cut pot affects things as well.

You have to use graphic equalizer pot tapers for those equalizers otherwise all the boost/cut is bunched-up in the last 10% of the pot sweep. You can reduce that effect by using lower value pots but you then have to watch out for the increase in noise.

Single-band circuit vs multi-band circuit with same gyrator:

Here the Q's are close because the Q is high but it doesn't always work out like that.