Woofers Gone Wild

Bob, Yes, I don't need a filter- the electronics are flat to 2 Hz from the phono input and the speakers begin to roll at about 23 Hz and are 3 db down at 20Hz.

Anytime you have a cutoff frequency, such as one introduced by a filter, phase anomalies will be seen in the signal usually to about 10X or 1/10th the f3, depending on what type of filter, high or low pass. This is how a filter can make itself audible, even when it is operating out-of band.

In fact, this is why you want your electronics to go down to at least 2 Hz, so that there will be no artifact at 20Hz. The old MFA Magus had an error in the RIAA curve (I know, the RIAA does not spec that high) that made the preamp go from -6db per octave to flat at 50KHz. It manifested as a brightness in the phono. Once fixed, the phono got very relaxed.

I've used pink noise systems to analyze the room. I have a peak at 26 Hz that some speakers exacerbate, and I have found that certain designs minimize that node. My current speakers have one woofer down-firing, and are pretty successful at that.

Atmasphere,
So what do you suggest for those whose cart and tonearm matching looks correct, at least on paper, but still experience woofer fluttering?

Actusreus, I guess I would really challenge whether or not that cartridge and arm combo is really correct. I'm a big fan of Occam's Razor, so I'm always looking for the simplest explanation. So when I hear that, the simplest explanation to me is that maybe someone made a mistake. Its a lot more complex explanation to have two properly set up arm/cartridge combos, where one causes wild woofers and the other doesn't, despite the electronics having the bandwidth.

The test record and my calculations both put the resonant frequency of my tonearm and cartridge combination above 9 Hz, which I understand is considered correct. My phono stage is from the same manufacturer as my cart, and matches the recommended capacitive and resistive load of the cartridge. I realize it's a complex issue, but reasonably can anything else be done, I wonder?

Actusreus, what kind of speakers do you have? One area where there is not much you can do is if you have smaller woofers in a smaller cabinet. Once you get out-of-band there is nothing keeping the woofers from flopping around. In a case like this I would recommend the filter.