Take this circuit..
Some would call this first order with a notch filter.. however it can be used to create a steep slope if you choose the right values. Here is one time I modelled the effect of an existing crossover (link below). The measured response is in red and the model to fit it is blue.
The model is a good fit for response over a span of 40dB, which is more than we'd typically consider important, yet the phase is 2 or 3 orders behind.
https://www.diyaudio.com/community/threads/the-elsinore-project-thread.97043/post-6872695
Some would call this first order with a notch filter.. however it can be used to create a steep slope if you choose the right values. Here is one time I modelled the effect of an existing crossover (link below). The measured response is in red and the model to fit it is blue.
The model is a good fit for response over a span of 40dB, which is more than we'd typically consider important, yet the phase is 2 or 3 orders behind.
https://www.diyaudio.com/community/threads/the-elsinore-project-thread.97043/post-6872695
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Deleted member 375592
It's about current vs voltage feed.
For example, Focal's PS130, Rseries = 0/6/12/24 Ohm:
However, the details depend on the driver - heavily.
I've modelled the above circuit, and some results are presented below. If the LC leg of the circuit is disabled, we have a first-order filter with a −3dB cutoff frequency of about 4.2kHz. The circuit creates a very steep slope below about 1.8kHz due to the severe notch in the magnitude response, with a great deal of extra phase shift also added to the response.
The circuit components used in the above simulation with the LC leg active are shown below.
However, if we re-purpose capacitor C2 and place it as follows,
we get the following 3rd-order response function, with approximately the same cutoff frequency and quite similar phase response behaviour in the transition band of the filter, between 1kHz and 4.2kHz. The resulting response has much less interaction with the low-frequency response below about 700Hz. The classical 3rd-order filter also appears to have benefits by greatly reducing driver displacement below 1kHz in an ongoing continuous manner, which would be helpful for a tweeter.
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Our demonstrations differ. Yours shows two of the same slope with a notch part way down. Mine show two different slopes with the notch bringing them to the same response for a while, then back to their own slopes.