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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, I was the original poster in Alberts thread asking him about this. I had planned for a thread but PTMCONSULTING beat me to it:)!

I told Albert that I need a 20hz (subsonic) filter and a rumble filter at 40hz. I have stereo subs, they are stereo down to 40hz, below 40hz is mono and then the 20hz filter kicks in. This eliminats most of the unwanted noise.

My system consists of a Shelter 901 on a VPI TNT 3 with a Eminent Technology ET2 arm. A pair of Bent Audio step up transformers into a Hagerman Trumpet then into my electronics/speakers. The two filters are built into my Marchand Bassis.

A simple question for everyone reading this for an informal poll. Do you or do you not need or use a 20hz filter or a rumble filter?

Myself I use (obviously, need) a 20hz filter and a rumble filter at 40hz.

Bob
ptmconsulting OP
1,000 posts
 
Bob (Acoustat6) - it seems that we both use a Hagerman Trumpet. This is a great phonostage but we both seem to suffer from a subsonic problem using this unit.

According to Jim H, he didn't limit bandwidth in any way, instead relying on the TT itself to provide the isolation.

2 questions:
- are there additional isolation solutions to eliminate this that can be implemented on the TT, like a constrained layer damped heavy sub-structure under the plinth, aka 1/4" Aluminum/lead/etc?
- is the problem inherently in the grooves where only an electronic solution would address it completely?

Bob
dan_ed
2,451 posts
 
Oh, great! Two Bob's. ;-)

Ptmconsulting, I think that at some point all you are left with is the groove thang and resonance from the table so there could be a need for an electronic solution for subsonics. I have my table sitting on two 1/4" aluminum plates that are bolted together. This plate sandwich is sitting on 3 Stillpoints. All of this is sitting on a 4" deep sandbox with granite shelf. Other than warped records I don't notice any problems.

But, as I said before, I am probably benefiting from the natural roll-off of my sub/bass horns. So maybe that answer's the other Bob's poll question. I don't think I need a sub filter at this point. Less is most always better, IMO.

However, I am open to trying it to see if I could benefit from using one. I'd probably shoot for a 16Hz cut-off.
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.
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