Why are my woofers pumping?

Subsonic/rumble filters are crap! You have to use a combination of things 1. record clamp 2. Cart/tonearm compliance 3. Isolation 4.overall setup... I still get woofer pumping but not nearly to the extent it was happening before. I find that using a turntable with a great clamping system (not just a puck or weight) helps a lot to avoid these effects and having the turntable on a piece of granite will be a big plus in helping kill the pumping. Also, finding the right cart/tonearm combo makes all the difference as well. At this level things really need to be in proper order (turntable setup) because things are so sensitive double check table for level, VTF, VTA, ect... 



Matt M

Set the volume at the lowest setting at which the woofers pump with the platter spinning and the stylus in the groove. Place the arm at rest. Does the pumping stop or continue? If the woofer pumps with the arm at rest (at a volume at which you might play music), the cause would appear to be acoustic breakthrough/feed back loop: TT/arm/cartridge > amp > speakers > air > TT/arm/cartridge > etc). The solution is to minimize acoustic breakthrough via one or more of the following:

Increase TT to speaker distance

Place TT and speakers in different rooms
Increase TT mechanical isolation: if TT couples to a raised wood floor, site the TT on a shelf mounted to wall studs  
Change TT from unsuspended to suspended (I prefer unsuspended TTs).
Change to a TT that better resists acoustic breakthrough (Sota's old Saphire and Star both may have set the standard for being impervious to feedback, but Sota motors are small and low cost, and the TTs made audible W&F....I use a 68 lb TT: Empire 208 motor/platter/bearing on a 1.5” solid alloy custom plinth ala the one Atma-Sphere used to make and sell).

It appears other users reported good results with your arm/cartridge pairing.

I suspect the pumping would be visually similar in your application, even if you swapped speakers (as long as all were reflex loaded). The reason is that reflex loaded woofers (mid bass in your case) unload below the port resonance, and for all full range speakers the pumping resonance is well below the port tuning resonance frequency. (Even if the pumping looked similar between 2 different speakers, pumping likely audibly degrades one speaker more than another, based on many variables.)

But suppose 2 persons employ the exact same arm/cartridge: person A's preamp/amp cuts off very low and makes high power in the bass (your OTL amps make more power @ 16 Ohm than 8 Ohm, the opposite of typical SS....also I don't know the speaker's impedance at pumping resonance); person B's preamp/power amp cuts off much higher and has minimal bass power. Person B's results may be fine, with little to no pumping, while person A's woofer pumping may audibly degrade performance. This could explain why your pumping is worse than another system with the same arm/cartridge.

Unfortunately I lost the link, but in the 70s IIRC, a European PhD. (I think a major European company like Bruel and Kjaer employed him) did a scientific paper on the subject of the ideal resonance range. He concluded that the ideal resonance frequency range is significantly higher than usually recommended. I use a Pioneer strain gauge cartridge, high compliance and very heavy. When I lowered the Rega RB300 arm resonance with a lighter counter weight, performance audibly improved by huge margin.

Long term wise a different arm/cartridge pairing may be the best solution. My strain gauge needs a true low mass arm, so I purchased a used Audio Technica AT-1100 with two wands. I shall add mass to one wand for use with a mono cartridge.

Your SMEV is in another universe v. my AT arm. The AT arm's effective mass is only about 7g. If/when finances allow, I plan to upgrade to the Moerch DP arm, which has 4 different wands of various mass from about 4g to 12g.

I always loved the looks of the SMEV, and the pro audio reviews were effusive in their praise of its performance. I'd buy one if it fit my needs.  

IMHO, you need a filter, or (cough), an eq to filter out anything below 15 hz. Some of it could be acoustical feedback.  I thinks it’s much more simple, than a mismatch or incorrect setup of tone arm/equipment.

I am no expert but I had the same problem with a VPI Prime Signature
and a very sensitive Van den Hul cartridge. I moved the cartridge to my
other VPI Prime Signature (identical) and the problem stopped. Turned out it was a acoustic feedback loop being caused by low level sound waves bouncing off the corner of the room.  VPI turntables are well isolated but the VDH cartridge is very sensitive. So I agree with those who suggest isolating the turntable. That said, some cartridge tonearm
combinations don't work, usually low mass cartridges on high mass arms. 

Thanks, all! Great to get so much expertise input!

Cartridge is probably OK, not worn, no sign of wear, or mistracking. Like I said, it is not the Io phono stage, since when the stylus is lifted from the groove, the woofers stop pumping. I have tried a platter mat, and different weights – no difference.  Mechanical problems? Player is level, on a solid stone rack. Testing with sthetoscope and fingers: very silent. I do find that the shaft that holds the spindle could be tightened a bit, but I don’t think this relates to the pumping. Also, this is clearly not related to airborne feedback, position of speakers, damping, etc. Either, the woofers pump (stylus in the groove), or they don’t.  It happens on all kinds of records, is not dependent on warps or record problems.

My new diagnosis is this.

1) Like many of you have said, the Lyra Atlas /SME V combo can be non-optimal – the resonance is too low. Maybe, those who don’t hear problems, have a less resolving system at low Herz, or a subsonic filter. I think I have solved the numbers mystery. The Atlas specs say: “Compliance 12 x 10-6cm/dyne at 100Hz”. But the calculators I have found (e g at Vinylengine) measure compliance at 10Hz. Noone seems to know the exact conversion, but a rule of thumb is to multiply the 100Hz value with 1.5 or 2 to get the approximate 10Hz value. This means that the Atlas compliance is in the region 20 to 24 (not 12). Using this value in the calculators, I do get a too low resonance for the combo, around 7.5 Hz. This fits quite well with my Hifi News record lateral test result (6-7Hz). Since obviously people have used Lyra’s with similar compliance to the Atlas and SME V arms to great benefit, the correct term is probably “borderline low”. It can be good enough, or not, depending on the system.  

2) With this “borderline low” situation, the cart/arm picks up too much of what happens down in the subsonic region. I tested with a record at the end of the runout groove, just now. The usual situation where the LP is still going round at the end, with an audible pop for each revolution. The pop is clearly audible. The pumping is only or mainly visual. I think they interfer with each other (indicating that the pumping is no good for the sound). I also found that there is a rythm to the pumping. A pattern is repeated for each revolution, so if I change platter speed from 33 to 45 rpm, it happens faster. My conclusion: The cartridge picks up player rumble. This is not because the player is bad or poorly tuned (the Hanss T30 has received a lot of praise for its silent motors, combined magnetic/ceramic spindle system, speed stability, “inflappable” quality etc) it is just what you get when you turn on a flashlight or microphone down low, in the 5-7Hz region.  Assuming that the low resonance acts like a microphone (which fits my testing).

Agreements – or not? Am I overlooking something?

So – what to do?

Some of you say a filter works, others that it doesn’t. For me, with a great cart and arm, prone to run many years ahead, it could be worth trying. Other options (change cart, arm) are far more expensive. Suggestions welcome. There are small XLR filters, but the ones I’ve seen on the net are for microphone use, with too high cutoffs, 100 or 50Hz.