Woofers Gone Wild

Actusreus... Of course the sound is improved. Those pumping woofers screw up the bass and mid frequencies.

Atmasphere,
My speakers are the Totem Acoustics Hawk.

Eldartford,
That's my understanding of the filter as well. I've personally noticed absolutely no deterioration in sound since I put it in the signal path. In fact, I think it has improved the sound.

Everyone is talking as if the rumble filter were merely a high pass filter. Actually, a rumble filter mixes the two channels below a certain frequency without affecting pass band (although there is often a subsonic filter included that does that). LPs produce signals which are mono at low frequency. Stereo signals involve vertical modulation of the groove, and will result in tracking problems, so record producers mix to mono at low frequency. Therefore, any stereo signal you see at low frequency is NOISE alone, and the rumble filter gets rid of it.

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.

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, 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.

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

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.

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

Ported.

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

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.

I understand the sentiment of the purist approach to this problem, but I wonder how many of the purists actually used the filter and can offer meaningful advice. Saying it filters ergo it wrongs the signal is, in my opinion, a simplistic theoretical approach that does little to shed any light on its actual real life effect. I've been using the filter for a few months now and don't look back. I have no doubt that the woofer fluttering caused more deterioration to the sound that removing frequencies from the signal that can't even be heard. And warps often have little to do with the fluttering; the worse woofer pumping I noticed happened with a perfectly flat 200 gr record. And yes, my cartridge/tonearm matching is spot on.

whatever you do, contrary to what some people might say, though not on this thread yet, it can damage your speakers. I blew out a woofer on an Aerial 10T twice because of infrasonic info being passed to my speakers. Mike Kelly had to chastise me to use the rumble filter on the pre I had at the time

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.

I have woofer pumping too. My TT is well isolated. Although it is very near one of my speakers it is on a sandbox. I tried an experiment, bought a cheap very long cable, and put the TT in another room. It didn't help at all. The thing is that the pumping I get is different depending on the record being played. My solution was to stop worrying about it although the KAB rumble filter does look tempting - do you put it between the phono stage and the amp?

DS

Is this happening with all LPs? Cone weaving occurs at a few hz is likely caused by warped LPs. You can see the disk surface ripples whils spinning. Other cause could be grossly mismatched arm mass and cartridge compliance. If you use Rega and Sumiko it is not likely the case. Personally I would not use rumble filter to cure cone weave.

I agree with the above post. Filters are useful, but they do filter, an Hi Fi is about running it all out , or as close to the performance limit as possible. Plus this does not remove the sonic problem in the system , just removes the results of the problem. Same as painting over a garden window with a view you don't like instead of doing the yard work.

It could very well be a straight mechanical problem, a compliance mismatch with the cart and arm. If this started with a cart change, or any other change , well it doesn't take Sherlock to come by and point out a few things. If your beer is empty by now, this has already occurred to you. Acoustic problems could also be in play, and are easy to finger, but tougher for some to understand.

I would point out that the more modern resonance understandings take the limit up a little higher than the above poster recommends. If my recent reading is correct to 15hz is the new deal.

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.

The KAB filter is very high quality and extremely transparent. I've used it in the past and my current phono stage has a very high quality built-in subsonic filter. In fact, I'd argue that you should actually experience slightly improved sound quality with the KAB.

Woofers, amplifiers and ported speakers are simply not meant to be dealing with subsonic frequencies that come into play with vinyl.

Woofer pumping is an extremely common problem for those using vinyl with ported speakers and, provided the system is well set up and located and properly matched with respect to tonearm effective mass and cartridge compliance, the subsonic filter is in many cases the only solution to the problem.

Thanks to all!!!

I tried the feedback test, and all was well. So am going to give the low-pass filter a shot. The reviews of the KAB filter are pretty impressive!

Again, thanks for your help guys.

Doc

Most likely culprit is rumble. I had the same problem and got the KAB filter referenced in the first response to your post and never looked back. To be fair, you should examine a mechanical solution to your problem first (compliance, damping, etc.), but it might very likely be the pesky rumble that's so common with vinyl causing the problem. If so, get the filter; your woofers will thank you and you'll be able to sleep at night.

I used to have that problem, too. Some phono preamps don't filter out the very low frequencies, and this ends up getting transmitted to your amp and speakers.

Here is your solution:

KAB rumble filter

Michael