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Subsonic Rumble Solutions

I know many of you have tried to address this issue. Short of buying or building a subsonic filter (that will/may negatively affect your transparency) - what methods reduce subsonics (meaning the pumping of woofers and subs when a record is playing)?

My system:
I have a DIY VPI Aries clone with a 1" thick Corian plinth, a Moerch DP6 tonearm and Dynavector 20X-H cartridge. This sits on a maple shelf. The shelf sits on squash balls. The balls sit on another maple board floating in a 3" deep sand box. All this on a rack spiked to a cement floor. The phono stage is a Hagerman Trumpet (no built in subsonic filter and very wide bandwidth). I use the 1 piece Delrin clamp on the TT. Yes, I clean records thoroughly and there are no obvious warps, especially after being clamped.

So my isolation is very good - no thumps or thwacks on the rack coming through the speakers. But if I turn the sub on I get that extra low end pumping on some records that hurts my ears. Mostly I leave the sub off when playing vinyl, but I would like to use it if possible.

There was some brief discussion of this on Albert Porter's system thread. I'm hoping to get more answers here.

So ... what methods have you tried to reduce subsonics that you have found effective?

Thanks,
Bob
ptmconsulting
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islandmandan
1,260 posts
 
The solution I just got around to using is a good, and easy one, though somewhat expensive. I just a day or so ago changed the equalization from standard RIAA to IEC in my Simaudio LP 5.3 phono pre, which has the filter built in. What a difference! Needless to say, I recommend getting and using a subsonic filter.

Dan
ptmconsulting OP
1,000 posts
 
Here's an update. I bumped into Michael fremer. he suggested adding some Bluetac or Moretite to the headshell, effectively increasin the mass of the tonearm and changing the compliance. unfortunately this didn't change anything.

another suggestion was to take the TT off the rack and put it right on the floor, to see if there was some rack related issues. No dice.

Another friend, Wes Bender, has a VERY high end system (Hanson's, Redpoint TT, etc.) said he sees the pumping also, but figures it's just part of the medium and so ignores it. I'm afraid he's right and that some kind of subsonic filter would be the only real solution.

So, live with it or build a filter. Lets see what the New Year brings. There may be a project in my future.

Bob
mapman's avatar
mapman
22,308 posts
 
FWIW, some speaker manufacturers build subsonic filters into their speaks as a way of tightening up the low end by filtering out low end frequencies that the speaks are not designed to reproduce accurately. That is another possible reason why some do not observe this phenomena on their system. It is a true statement though that it is inherent to the medium. For example, I believe Ohm does this with newer design speakers that employ their "sub bass activator" circuit internally.
eldartford
4,262 posts
 
Mapman...A passive rumble filter would require large and expensive inductors and capacitors. And lots of them to yield the minimal 18 dB slope. Rumble filters are only practical for line level signals.
mapman's avatar
mapman
22,308 posts
 
Eldartford,

I've seen the Ohm sub bass activator device. It is a rectangular circuit board just a few inches in dimension that connects between crossover and woofer internally as I recall. I ordered a pair and installed them into my Ohm L's as an upgrade. The cost was nominal as I recall, less than $100.

My understanding is that it acts as a subsonic high pass filter to some extent. It definitely helped clean up and tighten the low end on these moderate sized bookshelf speakers.

Here;s the description of the SBA upgrade on the Ohm site:

"Tighter and deeper bass is heard with the addition of a SubBass Activator (SBA) and vent adapter. The SBA eliminates the drive below the speaker's natural response to reduce distortion and clean up the deep bass. The vent adapter tunes the cabinet to work with the SBA and new woofers for deeper bass response. "
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