Rumble

[walpurgis]

More often than not, Wobbling cones are to do with an unloaded drive unit = Reflex. (It is the change of speakers, not the change of arm caused the observation)

The cartridge will not reproduce record warp if its compliance is correctly matched to the arm. Below arm/cart resonance the stylus suspension will act as though it is near rigid and though the arm may follow warps, the stylus cantilever suspension will not to any great degree, so there should be no significantly wobbling cones.

[Oldpinkman]

The cartridge will reproduce a record warp as well as it will a violin harmonic.

The issue about correct matching is the frequency of input which will cause the greatest movement. The point about the mechanical system resonance is it is the frequency where very little input causes lots and lots of output.

Both arms with that cartridge have the same (roughly) resonance. And we have now established both arms cause the same effect...

...when the speakers are changed to a Reflex design.

If you put a lower compliance cartridge on and get a system resonance of say 13Hz you will just watch a faster wobble. And, maybe hear it more if the harmonics are at correspondingly higher frequencies.

The problem arose when he changed speakers, not arms. He just happened to change both at the same time. A bit like , as I referred to on TAS, when I made up a new set of cables for the Pip / Benchmark as fully balanced using starquad cable, and auditioned with the speakers too close to the wall. I had changed too many variables at once.

You can't not have a mechanical resonance. You can just move it about a bit (say from 9Hz to 13Hz) but there is still going to be a frequency at which there is MUCH more output. Its the old heavy rubber on a bendy ruler stunt - change the weight of the rubber and you change the frequency at which you can keep the ruler wobbling, but you can still always find a frequency at which the ruler wobbles, with a barely perceptible movement of the hand to keep it going.

Pick your frequency - below 6Hz and you are likely to get tracking issues. Above 15Hz and you will probably hear it .

Edit: Of course - it is easier to SEE lower frequencies - so if you shift the resonance higher, you may hear it, but may not notice it visually - you would have to feel the speaker cone with your hand.

[Barry]

No - if the arm/cartridge resonance lays in the range 8 - 12Hz, the cartridge will not reproduce record warps (~ 0.55Hz), for the simple reason that below resonance, the arm and cartridge cantilever move as one: there is no differential movement, so an output cannot be generated.

An abrupt warp (a bit like a speed bump) will act like a transient and cause the stylus to 'ring' with a frequency of several hertz, which if high enough and close to the arm/cartridge resonance will be amplified by the resonance. Depending on the Q-value at resonance, this unwanted signal will be reproduce by the system. An obvious solution is to either fit a FD200 damping dashpot to the SME M9 arm and/or use a steep high-pass filter with a turnover frequency ~ 20Hz.

[dowser]

I assume it affects both bass cones? I would disconnect speaker closest to tt to see whether it is acoustic feedback related, I think it will be.

[hoopsontoast]

Upon some more testing:

The effect is worse at the start of the record, especially with more warped records although it does do it noticeably with flat records and always seems to be the same rhythm/resonance.

I have tried it with multiple albums, same effect.

It affects both speakers, I have tried with just the one furthest away playing and it still shows on that speaker.

The issue is the same with the 2M Blue on both the RB300 and M2-9.

I have not tried the old speakers yet, I may not have noticed as I have the grilles on the old speakers 99% of the time.

[struth]

i had similar problems when i used a orofon vms30 cart with my set up. I put it down to a mismatch between cart and arm/tt type. only cart ive had trouble with actually and there was nowt wrong with any of the gear or cart. I think the blue is a similar cart to the vms in many ways or so i was told.

[Macca]

is this still rumbling on.... ?

Are you sure it is actually affecting sound quality? if it is just a bit of woofer excursion at the start of the album I'd be tempted to forget about it.

[hoopsontoast]

Well some more work....

Bought an AT33PTG/II and its still doing it but seems only to show it on warped records, and near the start of the record.
It also seems to be most noticable on my 180g records, which seem more warped than most of my older normal ones.

So maybe a rumble filter may well help if the warp resonance is very low frequency?

On the plus side, very impressed with the AT33PTG so far, even new out of the box its very open and detailed without being bright.

[helma]

So maybe a rumble filter may well help if the warp resonance is very low frequency?

Yes it probably would - I'm assuming though you mean subsonic filter, which usually starts to cut off around 15-20Hz as opposed to those rumble filters present in very old vintage gear, with cut-off frequencies well in the audible range, designed to be used with crappy old TTs with all sorts of motor hum and bearing noises coming through in the bass range. Don't get one of those

Some people seem to be against subsonic filters feeling they have negative influence on the sound quality and bass response, but I've never heard this in my system and a good filter won't do much if anything to frequencies over 20Hz. Of course it might be my system is just not revealing enough or I've been very lucky with my phono stages