Woofers Gone Wild

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.

Ralph, just curious: are your speakers a sealed design or are they ported?

Ported.

Hi Ralph, You said you have two 15" woofers per side and that they go to 20 hz, but is not subsonic noise less than 20hz? If your speakers only go to 20 hz and fall off after that would I not be correct that you dont need a filter since there is nothing to filter?

Being a manufacturer I am sure you have the ability to do an in room freq response. I am sure that is the way you know if you speakers are responding down to 20hz. What system did you use for measuring that room response?

Also you said that a 20 hz filter would affect up as high as 200hz. Why would that be so when the filter is filtering from 20 hz down not 20 hz and up?

Bob

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.