[jackman]

I just found out what was causing my woofers to "pump" or warble when I played records.  Actually, I don't know exactly what was causing it but I suspect it was incompatibility between my arm and Longhorn cartridge.  I engaged the "Filter" on my Fetvalve preamp and the woofer pumping totally went away.  Bass is slightly better and dynamics also seem to be better.  It didn't seem to create any audible sound because (according to some guys on Audioasylum) the sound was probably sub-sonic.  

Thanks to Frank for his offer to check out my cartridge, but I don't think it will be necessary.  Also, the filter doesn't seem to filter out any of the good stuff.  Aside from the improvements, there doesn't seem to be any deadening or filtering of the sound.  Is that what the filter button is for?

Thanks,
Jack

[MaxCast]

I think on receivers form the old days a subsonic filter was used to remove unwanted low frequencies.  I remember thumping coming from my TT in college and placing foam under it helped reduce the thump greatly.

[jackman]

Hi,

This wasn't "thumping" as much as pumping woofers.  Nothing to do with isolation.  I have a very heavy rack that is well isolated and sits on a cement floor.  The woofers would pump and move even when nothing was being played (at the begining of records).  It wasn't a case of lack of isolation and I tried tons of stuff to make it stop.  Since the subsonic filter eliminated the problem, I have to assume it was caused by subsonic noise coming through the speakers.  Led me to say "hmmm, that's what that button is for!"

J

[mgalusha]

Jman,

It can also be caused by low frequency rumble from the table itself and from records having many small warps in them. The filters were often labeled "Rumble Filter" on vintage gear.

Mike

[jcoat007]

About 20 years ago I had the same problem.  I didn't have a filter button then.  The woofers would just flap in the wind.  It was really wierd to see.

I never figured out what it was.  Then CD's came along and I boxed the TT.  Problem solved.  

Here I am 20 years later putting a TT back into use.  I can't remove the grills on my speakers, bit when I first set up my TT, I felt through the grill cloth for the "Woofer Flap".  No flap, so I was happy.  Until now I have never heard of anyone else having that same problem.  

Glad you found a way to get rid of it.

[John Casler]

Hi,

This wasn't "thumping" as much as pumping woofers.  Nothing to do with isolation.  I have a very heavy rack that is well isolated and sits on a cement floor.  The woofers would pump and move even when nothing was being played (at the begining of records).  It wasn't a case of lack of isolation and I tried tons of stuff to make it stop.  Since the subsonic filter eliminated the problem, I have to assume it was caused by subsonic noise coming through the speakers.  Led me to say "hmmm, that's what that button is for!"

J

Jman,

Was it only when the cartridge was in contact with the record?  Or did it happen when the arm was "up"?

The Warp thing is possible, as is the fact that the tracking might be too much for the suspension and the tone arm sets up a bounce (kinda like the guy in first gear who gives the car a little gas, and the car rises up, he lets off the gas, and the car lowers and slows, but this causes him to push on the gas again and it rises up, and the cycle repeats itself)

These types of things can cause some rather large excursions, and the SUBSONIC filters just simply remove (filter) them so they don't affect the sound.

Cartridge suspension, tracking and tone arm matching, can sometimes be very tricky, especially if you have a stiff suspension (no jokes, I've been playing the straight man too much lately ) and a light tone arm.

Also check your VTA to make sure it is correct as it can affect the suspension, if it is way off.

[jackman]

Jman,

Was it only when the cartridge was in contact with the record? Or did it happen when the arm was "up"?

The Warp thing is possible, as is the fact that the tracking might be too much for the suspension and the tone arm sets up a bounce (kinda like the guy in first gear who gives the car a little gas, and the car rises up, he lets off the gas, and the car lowers and slows, but this causes him to push on the gas again and it rises up, and the cycle repeats itself)

These types of things can cause some rather large excursions, and the SUBSONIC filters just simply remove (filter) them so they don't affect the sound.

Cartridge suspension, tracking and tone arm matching, can sometimes be very tricky, especially if you have a stiff suspension (no jokes, I've been playing the straight man too much lately  ) and a light tone arm.

Also check your VTA to make sure it is correct as it can affect the suspension, if it is way off.

John,

Thanks for the feedback.  It only happened when a record was on, even brand new records.  The filter totally fixes the problem.   I have a medium weight tonearm and a suspension-less turntable.  It pretty much happened no matter what type of material was on...bass heavy music, acoustic stuff, etc.  I had the TT professionally set up and haven't messed with the VTA.  It now works perfectly and only seems to have woofer flutter when playing warped or scratchy records.  I think it's okay for now.

Thanks,

J

[John Casler]

I have a medium weight tonearm and a suspension-less turntable.

Just to clarify, I was refering to the supspension of the stylus within the cartridge, and not the suspension on the table itself.

That suspension strength and pliability, has to match the tracking force, VTA, and ultimate mass of the tone arm to keep everything from developing any extra movement of its own, and or be able to absorb and dampen the warps and abnormal or uneven surfaces of some albums.  

But in any event your problem is solved and that's the good news.