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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
eldartford
4,262 posts
 
Most rumble is from vertical groove modulation. Horizontal modulation, which is a mono signal is much cleaner. A good rumble filter will blend the LF signal to mono, which many people do anyway when they connect a single subwoofer. Also, when records are cut the LF is often blended to mono right on the LP so that less-than-audiophile cartridges can stay in the groove. If the LP has been made this way all the LF you are getting off it in stereo is rumble.

Many LPs have rumble cut into the grooves and no amount of vibration isolation will help. Particularly in older recordings the air conditioning systems of recording halls were a big cause of rumble. It went unnoticed until newer playback systems with extended LF response came into being.
stefanl
296 posts
 
In his paper on resonances in turntables,Paoul Ladegaard of the air bearing tonearm fame,theorises that cartridge/tonearm resonance is by far the most important issue to be addressed here.Therefore matching your cartridge to the effective mass of your arm,so that you have a cartridge resonance of 11-12HZ is the most optimal adjustment you can make,coupled of course with good isolation.Ladegaard was sure rumble does not exist and you corrected this parameter.
fap
32 posts
 
As I understand it, in the ESP P99 design the idea of summing the two stereo channels to mono was originally considered but later discarded because of possible frequency response anomaly considerations.

My own experience with the P99 filter is that its design is superb and it works perfectly in practice as intended. Regards, Fap.
dan_ed
2,451 posts
 
I wasn't that happy with the summing solution. Stereo subs have proven much better in my room. The bass is no longer boomy, LF details and directional clues are much better.

36 dB roll-off! That'll get the job done.

I'm curious about the phase issues mentioned on the page that Fab linked and wondered what some of you guys think. I was thinking of such a subsonic filter at the input of the sub's plate amp. My question regarding the low frequency phase variations with such a filter is this. If the mid-bass driver is feed by the line out of the sub's plate amp, would that alleviate any/most concerns about phasing?

Thanks
eldartford
4,262 posts
 
Dan_ed and Fap...I am a strong proponent of multiple subs, but when playing LPs I have found summing of LF to be essential. Of course you can make a rumble filter which simply attenuates all LF, but why throw away the mono component which is relatively rumble-free?
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