Why the woofer moves badly when playing certain LPs

I used to get a lot of woofer pumping when I had a suspended deck (Manticore Mantra) but not when I went for one with a bit more mass ( Townshend Rock 2). At the time of the Mantra I had a pretty basic Sansui amp (AU217) and mission 700s and with those the pumping didn’t seem to effect the sound.

A certain amount of very low frequency woofer excursion with records is perfectly normal.

Just to be clear, my signal chain has 2Hz response from the cartridge input all the way to the loudspeakers, which employ dual 15" drivers. I run them without grill cloth covers and I only see excursions on things like big bass drum whacks. It takes a pretty warped record to set them off. But I was careful to make sure that my cartridge and arm work well together.


The cartridge in the arm has something called 'effective mass'. The cartridge also has a compliance figure; that in tandem with the effective mass creates a thing called 'mechanical resonance'. These things can be calculated by the way... anyway, the mechanical resonance should fall between about 8-12Hz; if it does than minor record warp won't be bottoming out your woofers. When the mechanical resonance is not in the right window, Bad Things happen- like mistracking, even to the point of the stylus jumping out of the groove, woofers pumping, breakup during complex passages and so on.

@yeti42, a Townshend Rock 2? Congratulations on your good taste! ;-)  Another of those superior designs ignored by the majority of audiophiles, @slaw (Rock Mk.7) and myself (Rock Elite Mk.2) the rare exception.

Ralph you need to come to my house and I will demonstrate. Most of the bad records are coming from the likes of Warner. The lathe is the only mechanical step in the process now. So it is the lathe by default. When I first got one of these records I thought my turntable was shot. I put another record on, quiet as a mouse. Since then I must have returned at least 20 records for this problem. I may be a bit more sensitive to it because my bass goes ruler flat down to 18 Hz then rolls off at 80 dB/Oct (digital filter). You will notice that Starbusters only notices this with NEW records. Not old ones. It therefore could not be a cartridge tonearm miss match. Until about 10 years ago I had never had this problem. So I am waiting for anyone else to give me a more logical explanation. 

Other than both Starbusters and myself being head cases. Geoffkait, keep your mouth shut.