Woofers Gone Wild

Before you add a rumble filter, I would take a look at the specs of the cartridge and the effective mass of the arm. They should combine to create a mechanical resonance between 7 and 12 Hz. If you get outside that window (for example if your cartridge is high compliance in combination with a high effective mass) you can get woofer pumping. Its worth looking into this issue because it can result in better tracking (better sound) also.

Davidsss, my suggestion is the same for you; if you can, try a cartridge that has a lower compliance figure. That will reduce the woofer 'wobble' and actually improve the bass at the same time.

Actusreus, I'll put it to you this way- the phono preamp I use is good to 2Hz and the amp is good to 1 Hz. I have 2 15" woofers in each channel, and they go to 20Hz. They really don't move much unless there is a bass drum whack or the like. The trick was simply to get the relationship right between the arm and the cartridge.

If you install a rumble filter, you add phase shift components that rob the signal of impact, as a 20Hz cutoff will have audible artifacts up to 200Hz- lower midrange! That's why keeping filters out is so important if you can do it.

Ported.

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.

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.

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.