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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
acoustat6
357 posts
 
Hello, Bob and Dan, I believe we are of course looking at several different problems rolled into one. Turntable isolation, the turntable, system freq response, the recording/pressing, cartridge/arm compatibility etc.

Bob, most definatly it is not a "problem" with the Hagerman.

One of the things I see (and which Dan mentioned), in comparison with Dans system is that my system is 8db UP at 20hz as opposed to Dans which is down 6db at 20 hz. That is a 14db difference at 20 hz. This means my system is 4-5 times louder than Dans at 20hz! And my freq response is still climbing till 16hz (ie: 10db up at 16 hz, therefore perhaps a 20+db difference with Dans at 16hz). This is a huge difference and can certainly explain a need for a filter or for that matter not needing one.

Of course this does not address the question where does this "noise" come from. Though it may explain why some need a filter and others don't.

The other Bob,

Bob #2

dan_ed
2,451 posts
 
Bob #2 (I like that! :-)), that is the measured natural roll-off of the horns. To further complicate things there is a +6dB gain with having two subs, or so I am told. But your reasoning is still valid and does explain how different systems may need different solutions.
eldartford
4,262 posts
 
Acoustat6...What you describe is ideal. All we could quibble about is the frequencies.
ptmconsulting OP
1,000 posts
 
So I think I'm hearing what I kind of feared - that, given very good isolation, the final solution to subsonics lies in the signal path via a filter of some kind. I fear this because I would prefer to keep things as clean as possible. I fear this because I just know I will hear something missing in the top end, or the soundstage, or something like that that bothers me more than a little subsonic rumble once in a while.

I guess the only way to know is to try it myself. Well, I'm a DIY kind of guy, and the filter can probably be built for about $50 and a little time. I've got a few questions out to Elliott Sound Products about their filter and how I can implement it. I will share those on this thread when they reply.

Thanks,
The First Bob (#1 I guess, since I started the thread :-)
ptmconsulting OP
1,000 posts
 
I received a reply from Rod Elliott on my questions about his filter (see below):

My question about using a lead acid battery or a laptop power supply: "The circuit is specifically designed to operate from a split (+/-) supply. While a single 12V supply could be used, I don't recommend it."

Op-amp related questions: "All the signal runs though the opamp all the time - there's no other way to do it. You can use any dual opamp that you like - despite its age, the NE5532 is a good choice, as is the OPA2134."

Gain related question: "The circuit is unity gain."

Thanks Rod. I will have to reassess after the holidays are over. I may try a few other things in the meantime. Maybe an experiment with resonance damping in the headshell just to make sure it's not a mechanical issue I'm having.

Thanks for everyone's replies,
Bob
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