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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
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?
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
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