Rumble Filter on Phono Amp - when should it be used?

When I saw my woofers oscillating like crazy from the acoustic feedback through my turntable caused by the lightest of footsteps, I wished I'd had one.

 

But couldn't it be actually useful in many situations? Like tone controls and balance controls would be?

I wonder more and more if those things have disappeared from all our so-called minimalist designs because they really do degrade performance, or rather because there's some irrationally perceived "magic" in not having them. I have no doubt that such controls can get in the way of performance. But I have a strong suspicion that with today's technology, talented designers could find a way to give us the useful flexibility those controls afford without degrading performance. They just choose not to, out of fear that their products will be perceived as "mid-fi" if they do.

 

Oh, I agree with that. I wouldn't use a balance control, either, if I never heard anything but pinpoint center-focused imaging. I was just going off on a tangent--but an interesting and provocative one, I feel--about the way we audiophiles (and the designers who cater to us) look down our noses at potentially useful controls that can do no harm, and by doing so shoot ourselves in the collective foot!

 

Use a rumble filter if you're doing needle drops to the computer. It can give you close 10db of reduced volume "for free" (very little impact on the sound quality). This makes normalization easier, so that the tracks can be better integrated into your CD tracks. Also, if you don't do some sort of rumble filter and put a needle drop on a playlist, you'll get a loud pop.

 

Sure. Think about it - it's just like the pop you get when plugging in a cable. You're throwing a large low-frequency signal onto the wire very quickly, which means lots of high frequency energy.

Try it for yourself, or just play a needle drop in Audacity and play/stop it. You should hear a significant pop on quiet passages on every start/stop unless you filter the rumble out.

 

... which is a high-pass filter applied to L-R. The removed signal from which can just as likely cause a pop.

 

I rather doubt anyone here on the forum has ever heard rumble, as it is far too low in frequency for the human ear. We can detect it by watching our woofers moving in and out with rather large excursions.
In the past I've had a rumble filter and when turned on or off I've never heard a difference. However, I was able to see the woofer stop and start the large movements.
On the down side, filters can effect the phase of sounds in its operating range.
On the upside, they could provide peace of mind and eliminate the power draw on the power amp during those wild dance parties forum members are known to have.

Brian

 

A rumble filter cuts out 20-16Hz and below. This is not musical info (unless it's a bad filter) but warp-induced signal.
So, look at the woofs -- if they are moving woldly use it.
There's no reason to waste the gobs of power it takes to amplify this noise -- plus it can damage the woofs.

 

If there is no net filtering in that bandwidth, how can that be a filter? Either it removes low frequency signals, or it doesn't. If it does, it's a highpass filter. If it isn't, it cannot be a rumble filter.

There are obviously a bunch of different ways of implementing a rumble filter or a highpass filter, and not all of them are particularly suited for the other.

 

Minimising rumble physically is much better than using a filter in the amp! Isolate the turntable as much as is humanly possible.

JG

 

And again, this is going to take the form of a highpass filter. It doesn't matter if the filter isn't applied directly to the original signal - you're still highpassing. You can have a flat frequency response down to DC for the mono signal, and yet still have a highpass filter for the stereo info.

In terms of implementation, the most direct way to actually do this is to compose sum and difference signals, run a highpass filter operation on the difference, and reform the left and right channels from there.

Actually, I'd argue that that's the only way to implement what you describe. There's no magical basic electrical device that sums to mono at low frequencies and preserves stereo information at high frequencies. At some stage, you need a difference signal, and you need a highpass.

I suspect this is mostly a semantic argument though.

 

No doubt. But many of us have situations in which that simply isn't possible--or isn't sufficiently possible. Just as many of us have rooms that cause unevenness in the frequency spectrum and in dispersion. Which is leading me more and more to appreciate the rumble filters and tone controls that our current audio fashion has done away with.