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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
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
acoustat6
357 posts
 
Hi Bob#1, Keep us informed. Many times, people report a increased clarity to the music, as a result of removing unwanted cone movement (equals noise, wasted power from you amp and loss of control of the driver). And your amp will be happier.

You appear to have only one sub, so you are in mono at your crossover point. That would be your "rumble filter".
You now need to try a 20hz filter for the subsonics.

Albert had kindly offered to speak to me over the phone regarding this issue, but I think we should keep it in this thread so everyone can benefit. Albert if you have any suggestions or comments please post them here.

Bob#1, you are probably limiting your system if this is a problem in your system. It needs to be eliminated for your system to shine (if it is disturbing/loud enough). How you do it is up to you. Whether you can find a mechanical solution, adding a filter or roll off of your speakers low freq extension. All of these have benefit in not hearing rumble or subsonics. If you can live with a little "rumble" that is an option that is up to you.
My guess is it is not rumble (since you have a mono sub, OR it may be rumble that is above your crossover point!) so it is probably subsonics ie: below 20hz. And filters work very well for this.

You never did mention when you have this problem, is it at certain volume levels, LPs with low bass, certain records that otherwise appear quiet?

Of course there is one other problem that is not system related which I mentiond above, which is rumble pressed into the record. Some of this rumble can even be above 100hz. This you just have to live with, knowing that it is in the lp and not your system. But even this can be eliminated, with a filter. The problem with this is that you want to keep it stereo down to as low as you can. I think this means stereo down to at least 50hz or better yet 40hz. And these freq will do a very good job of elimininating most rumble.

Bob#2
We are not men , we are Devo

ptmconsulting OP
1,000 posts
 
Hey Buddy-Bob 2,

I can say with some certainty that the woofer pumping is there on most LP's to one extent of the other. But my ears feel like they are popping on some, but not all, LP's. If I turn the sub off on these I don't get that annoyance (my regular speakers probably drop down to about 30hZ). It is most noticeable on the lead-in groove and 1st song or two, and less at the end of the record, but still there.

You are correct about the amp - less low frequency need means a more efficient presentation overall, helping both speakers and amp.

I don't have time for a new project right now, but I will probably get itchy after New Years and look at this possibility again. It also means adding another interconnect into the mix, since there's no room to incorporate this into an existing box.

Bob #1
mapman's avatar
mapman
22,915 posts
 
I've seen or been able to feel (to the touch) unwanted low end woofer excursions in smaller bookshelf/monitor speaks I've owned in the past during record playback that on paper could not produce subsonic frequencies.

This tells me that the unwanted signal was not subsonic, yet still undesirable in terms of reproducing unwanted low frequency noise often associated with record playback that one would ideally prefer to not exist.

Despite having access to low in addition to subsonic filters available, my choice was most always to not apply low (high pass) filters that would also negatively impact the real music signal in that range of the audio spectrum.

Effective isolation, clamps, etc. are probably more effective ways of dealing with low end noise introduced during playback of warped records, etc. without impacting the music.
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