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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
dan_ed
2,451 posts
 
My bass horns roll off pretty fast down in that subsonic region. They are down 6dB at 20Hz and drop pretty fast after that. Once you get down below 16Hz or so I would think that the system would begin to pick up resonances from the arm/cart. Who wants to listen to that? :-)
fap
32 posts
 
Well, I took the subsonic filter option. I built this excellent subsonic filter, and if anything the quality of vinyl playback has improved with additional clarity and increased apparent available power. I highly recommend this subsonic filter.
http://sound.westhost.com/project99.htm Regards, Fap.
ptmconsulting OP
1,000 posts
 
Thanks for your suggestions, but I still think the problem is more inherent to the medium than my setup.

My racks are about 200 lbs each. Each shelf is it's own seismic sink with 50 lbs of sand in them. They are spiked to a cement floor. My TT itself weighs about 30 lbs (plus the motor which is about another 30 lbs). I am also using a Mark Kelly designed motor controller (think SDS), which makes the motor dead quiet. That's not the source of any vibrations either.

See here: http://cgim.audiogon.com/i/vs/i/f/1155818474.jpg

and here: http://cgim.audiogon.com/i/vs/i/f/1155818602.jpg
(note: bubble wrap is replaced by squash balls which proved much better at isolation from the shelf)

The subsonics are definitely not due to speaker interaction, since it happens on the lead in groove right away, before anything is playing. It is visible on the regular speakers too, when the sub is on or off. This is not an isolation problem due to standing waves in the room, but a rumble problem due to low signal vinyl interaction with the cartridge and phono stage.

Therefore: standard subsonic issues with vinyl. I even tried damping the tonearm, with no affect on the subsonics but a lack of air and life to the music - so that's been reversed now.

I spoke with Jim Hagerman about this and he said he purposely did not limit any extension at either end, making the Trumpet very wide bandwidth. He suggested changing out the .22uF inter-stage coupling caps to .1uF as a possible partial solution. I did this with no obvious change (however they are now upgraded to RTX's).

Please keep the ideas coming. At this point I think the answer is going to be electrical (e.g. a rumble filter), but I'm open to trying other suggestions first.

Thanks,
Bob
chadnliz
3,736 posts
 
Is the Corian material a great option to use for plinth? I only ask because I have a DIY Corian arm-board on my SOTA and question its immunity from feedback.
ptmconsulting OP
1,000 posts
 
Thanks for the link Fap. Is this filter available in a kit form, or just the schematic as provided? Where does it plug in, between the cartridge and phono stage or after the phono?

I assume the whole signal rides through it ... if so then I assume the op-amps affect the entire signal. So I would expect that different op-amps might affect the overall sound in different ways - no?

You mentioned an increase in apparent available power, so maybe it adds a bit of gain also?

What phono stage are you using with it? Did you notice any affect on transparency or soundstaging or the top end?

Thanks,
Bob
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