Disadvantages of using Zobel and Series notch filter ?

[percy]

In the effort of flatening out the impedance curve of a speaker to make it as tube-friendly as possible for a typical pentode push-pull amplifier, does the use of a Zobel and a resonance trap (for the Fs hump) at the speaker pose any problems ? Any thing that I should watch out for ? Any disadvantages of using a Zobel and resonance trap on a speaker to be used with such a vacuum tube amp ?

I am also wondering if it causes any phase problems and how it would interact with the amp's feedback system ?

[Tweeker]

I am also wondering if it causes any phase problems and how it would interact with the amp's feedback system ?

Could not the same be said of the speakers reactances your trying to correct?

[Johan Potgieter]

To my limited experience this depends largely on the particular amplifier and loudspeaker. Generally, if well done at both components (meaning an at least moderate tolerance of load at the amplifier) there is no more effect than that of loading the amp with a corresponding dummy load, i.e. it can be simulated. Seeing as how some loudspeakers present quite horrible loads (peaks in Z, sharp phase shifts), amplifiers seem to be by and large tolerant.

BUT: Outside the audio band (usually h.f.) there can be trouble especially with semiconductor designs (just in the interest of completeness) if not checked. Tube amplifiers should certainly not present a problem - if they do, there is a serious design problem that should not be difficult to solve.

[Klimon]

The zobel will most likely rob a bit of the woofers output near it's (high) roll-off (actually countering the rising response that makes for a somewhat shrill sound). This is the case with both unfiltered and filtered woofers. To me this is the primary benefit of a zobel filter and in practice has no downside.

Simon