2nd Order Filters Cause 180 Phase Shift


Am sure most folks know about Hlabs Fmods. Plug in filters straight into your amp if you use a pre. People use them as high or low pass filter “plug ins” on subs in cars and home audio. Since I have been considering Passive Horizontal Bi Amping and need some filters to protect the load on my tube amp I’ve sought out this inexpensive solution. Anyway from the only comment I can find out about what order this plug in filter is someone stated they are considered 2nd Order with a 12db slope. So I probably read to much as stereo buff but at the site Audioholics.com they have a 2004 article on filters/crossovers. When they get to 2nd order filters they make mention that they cause 180 phase shift in the tweeters and suggest reversing the polarity of them to correct it. See the quote below. Question is if I go with this filter route and use the Fmod should I in fact reverse my tweets? Thanks for reading and commenting.

“2nd-order Filters

Advantages: Can produce a maximally flat amplitude response. Requires relatively few components. Has a 180 degree phase shift which can often be accommodated by reversing the polarity of the tweeter and which produces minimal or no lobing or tilt in the coverage pattern. Is less sensitive to driver misalignment than 1st-order filters.

Disadvantages: Although the 12 dB/octave slope is better than a 1st-order filter, it may still be too shallow to minimize the modulation distortion of many drivers.”
rob_1958
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No worries, you won't have to change polarity on your tweets - that's only required when designing dedicated crossovers for a given speaker system, but since you're only filtering out the lows from your amp, your speaker crossovers will continue to operate as originally designed, so you'd just be (correctly) removing the lows going into your amp, is all.
^^ This. The phase will be correct in the passband.