Subwoofer starts fluttering when playing LP's

I just added a REL sub to my system and when I tried to play a record the Sub starts to make a fluttering sound as soon as the stylus contacts the LP surface. No problem with CD or SACD's. Does anyone have an explanation for this? I just realized could it be because I leave the dust-cover up when I play records? Would removing or closing the dust-cover solve this or is it something else? Perhaps more damping of the arm (JMW arm / Helicon)

 

Hmm, sounds like turntable rumble. Table level? Anti-skate set? More stylus pressure maybe? Phono-amp too close to subwoofer? Subwoofer too close to turntable?

 

Tommy: Using your preamp's subsonic filter will eliminate or at least minimise this effect. If this happens at high volume levels it could damage the woofer.

[T]

 

Another source for turntable rumble is the platter spindle bearing. I'm not familiar with VPI tables, but perhaps it needs a lube job?

 

The fact that your turntable has rumble could mean that something may be wrong, but probably means that you need a better turntable. Since most people do not have a music system that reproduces the bottom octave rumble isn't usually a problem. Having an excellent subwoofer that can reproduce the "bottom" has unfortunately brought to life an existing problem.

 

I have seen this at my dealer's for the first time (I have no turntable). He had a very good tt playing (so it's not a defect!) and played the "Elegant Punk" bass solo album by Jonas Hellborg. Between the tracks there was no sound but the woofers of those little Monitor Audio speakers moved like crazy! My dealer's comment: this is normal; if you have one, use the subsonic filter...

 

Is it always turtable rumble, or is some of this subsonic noise due to very low frequency gyrations in the groove? I've noticed that different pressings often either lend more or less of this effect..

If it is strictly TT rumble, I suppose a really good mat might help dampen some vibration.

 

SOunds like rumble but at worse, feedback. So what everyone says...

 

It's more likely that this is a result of the resonant frequency of the tonearm cartridge combination. Usually you can see that the woofer jumping is intermittent and coincides with a pinch warp in the vinyl. Rumble should be a relatively consistent purring. This also explains why some pressings do this more than others.
It can't be avoided, but tonearm judicious damping can reduce the amplitude of the resonant peak (see SME tonearms and many others - Townshend's Rock had a damping trough that allowed damping at the headshell(!!) instead of the tonearm pivot end).
Unfortunately, a large amount of amplfier power is wasted here and may explain why some amplifiers perform better when reproducing CDs - less bandwidth at both high and low ends is required (ie no warps, rolled off high end).

 

If you can experiment with your table's placement, try moving it/placing on a different shelf or rack; a good set of isolation feet could help; a subsonic filter is probably the ticket - when I built a 5 cu. ft. subwoofer in college I HAD to also build a subsonic filter - zapped the nasty cone jumping an inch and flopping uncontrollably with the dropping of the needle into the groove...

 

I spoke with Sumiko REL's distributor and they said it's not that unusual with LP playback because the sub goes down to about 10hz. If have the Table on a Wall mount Target shelf with a Bright Star Air Mass 19 under it. Right now I simply have to turn the sub down a notch while I play an LP and it seems to cure it. I fined tuned the sub intergration with the panels using CD's.

 

Think I solved the problem. The Sub and TT shelf share a common wall by moving the Sub to the side wall away from the TT wall the rumble was eliminated.

 

I had this same problem. Fixed it by ditching the turntable

 

Better to have ditched the subwoofer.

 

This is a much more likely scenario - vpis simply don't do rumble!

While isolating the table may have alleviated some of the problem, it is not a case of feedback per se. It doesn't take much to excite a less than perfect tonearm/cartridge combination (which most are to some degree) even if the source isn't from external vibrations. You will probably still see the fluttering more often at the beginning of an lp and/or on a less than flat lp.

The air mass could also be contributing to the probelm. IF it is too springy - it wobbles a lot, the tonearm/cartridge could be reacting to that - you might try letting some air out to steady it.

You could always use a shure v15 w/the damper or get a turntable that that uses a vacuum seal to adhere the record to the platter. I believe vpi also now offers a peripheral platter clamp.

 

I once had a similar problem. For the most part, it was the dustcover's fault. When I left the dustcover on, either up or down, and cranked up the volume the subwoofer cone would vibrate viciously. In fact, if I just sat the stylus in the groove with the platter stationary and lightly tapped once or twice on the side of the turntable I could start some tremendous feedback.

I solved the problem by simply removing the dustcover and using sorbothane feet under the turntable. After that I could blast an LP as loud as I wanted to! Note that although I've since changed my room configuration, back then I had the subwoofer sitting *next to the turntable stand* but even so, with the dustcover off and the sorbothane feet in use...nothing, no feedback or resonance.

 

That's for sure.

John Buchanan mentioned an important point - there is a relationship between the effective mass of the arm and the compliance of the catilever. One needs to get this right or the resonance frequency of the combination will fall in the common range for pinch warps.

But it seems as if you have fixed your problem.

 

I experienced the same thing with my Rega P9 when I added a Revel Sub. Sorbothene feet under the TT solved the problem - it was not due to rumble but an acoustic/vibration feedback loop.

 

Good comments posted above. Turntable produced rumble and flutter can sometimes be heard or waste power.

The low frequency resonance between the stylus and a high mass arm can adversely effect tracking and perhaps introduce very low frequency output that may waste power. (Shure V-15 series have a brush to eliminate this).

But as we have seen, the interaction between the environment and the turntable and the stylus can be a real source for feedback at very low frequencies.
My good old AR turntable could be hit with a hammer and it just played on. Physical vibration conducted through its base and through the air did not phase it one bit.

Then I "upgraded" to a very very highly rated (by Hi-Fidelity), all electronic turntable from JVC. Full electronic control over speed, arm dampening, arm movement, record size, etc. But it would pick up even the slightest vibration and induce feedback through the stylus. No leg dampening would help, and I tried it all. Sometimes less is more. (Still wish I did not give away that AR midified with simple anti-skate feature.)

Richard.