Are subsonic filters important?

Nor should you necessarily have to have an "arm damper" permanently in the the solution.

A high pass filter can be taken in and out of the system with a push of a button.

It is not necessary to have in the system all of the time if someone has an objection to it.

 

The noise is warp velocities, mainly. These are normally from 2-15 Hz with a common max at 4Hz. These are triggering the suspension/arm resonance, not as much as can normally be seen, but they are there. This 'noise' is what´s important to deal with as it´s frequency modulating normal tones, besides other problems. It´s so wonderfully arranged that this is exactly what a fluid damping does. It reduces arm amplitudes at these low freq.

 

I don’t see a reason I would want to remove the arm damper, though. It’s never making anything sound worse. Also, the paddle can be removed from the arm pretty quickly to disable the damper, if you would ever want to do that. Not as easy as a switch, but to be fair, the filter doesn’t actually have a switch, so you’d need a switchable loop somewhere to make it that easy to remove.

I do think having both solutions in place, with the filter switchable, would be ideal. KAB makes and sells both, so I would assume he agrees (in a case where woofer pumping is observed, as even his product description for the filter says it won’t solve anything if you don’t see woofer pumping).

I don’t really like the idea of summing everything below 140 Hz, but, to be fair, I haven’t heard it in my system. 140 Hz just seems high, but I’m sure he has a reason for putting it there and not at, say, 80 Hz.

Specific to the OP’s MoFi, though, virtually every user’s comments I have read about the subsonic filter indicate it doesn’t have any audible effect, and the filter seems to be truly subsonic, so I think I would probably leave it switched in all the time (as long as the OP observes the same, that nothing sounds different with it switched in).

 

Because he believes recordings intended to be pressed on LPs are mastered so that all bass is mono below 150Hz. I think that's the case for some LPs, not all.

From KAB:
Unique to vinyl records:
1. When records are made, frequencies below about 150Hz are combined to mono. This is done to avoid large out of phase groove excursions.
2. When the stereo stylus moves vertically, the two signals produced are equal and 180 degrees out of phase.
Therefore, below 140Hz, the music is in phase in the lateral stylus motion, and only out of phase noise is found in the vertical stylus motion.
The KAB RF-1 takes advantage of this by electronically combining the left and right channels together below 140Hz.

But be advised, this guy has no clue about such things.

 

When I had the MOFI SP as my main phono pre I couldn't tell the difference with it on or off either. I will say the instructions that came with the unit were wrong w/r/t how to use the filter though. Corrected instructions were available online. IIRC the unit was later revised. If you do a set of button up/button down needledrops and analyze both in Audacity it is very obvious where the on/off position is, no matter what iteration of the SP you have.

 

Ah, yes, now that you quote it, I recall having read that assertion. This makes sense, assuming the assertion that LPs are mastered in mono below 150Hz is true (or at least most of the time). Not doubting KAB, I just haven’t seen other sources for that fact.

Surely using the KAB filter or not is a “try it and see for yourself” proposition, but it’s a bridge I’ll likely only approach if I ever actually observe woofer pumping.

 

Douglas Self's Devinyliser cross feed cuts at 60Hz at -3dB, falls at -18dB per octave, and has a deep -50dB notch at 8.5Hz. For out of phase vertical signals, AKA warps. In-phase true bass signal pass through unchanged (in mono below 60Hz)

So much lower frequency that KAB's 140Hz. And he puts a 20Hz 3rd order filter in there too, which Self's design does not need.

http://www.douglas-self.com/ampins/Paris 2016 devinyliser.ppt

 

But is this actually a product for sale, or just an engineering brief? I cannot find anywhere on that page, or through a Google search, a link to buy one.

 

I get it first hit on google using devinyliser as the search term The Signal Transfer Company: The Devinyliser

 

I don't agree with this. Now, keep in mind, I use a modified Rega arm which has not ability to add fluid damping, and I think it's a big flaw and I can't believe, with all the Rega add-ons and tweeks out there that no one is marketing a commercial fluid damping kit.

There's always a subsonic resonance in a turntable because the mass-compliance spring of the arm and cart will ring at some 7, 8, 9, 10 Hz center frequency, as we know.

These resonances are easy to set into motion because vinyl surfaces aren't smooth (these aren't polished surfaces) and records aren't perfectly flat or perfectly centered. So that subsonic ringing is going on pretty much even under the best of conditions (ie, no problems with acoustic breakthrough or isolation from air or structure borne vibrations like from footfalls). I highly recommend Poul Ladegaard's famous 1977 AES paper "The Audible Effects of Mechanical Resonances in Turntables" for clear explanations and tests showing all this (and more).

What's more this subsonic ringing has side bands, some in the audible range. Electronically filtering the effects of this mechanical ringing doesn't stop the ringing. And the ringing has sidebands outside the resonant frequency. Fluid damping of fast tonearm movement in the vertical and horizontal planes will significantly control this ringing, helping knock down it's sidebands and lower it's amplitude and duration. (Ladegaard also recommends a mass-compliance arrangement that sets the mechanical resonant frequency much higher than we typically do -- something on the order of 15 Hz, which is hard do to with typical available tonearms and carts.)

There is also occasionally cutter head rumble that's in a recording. But that's not that common compared to unsmooth surfaces and eccentric pressing, which are ubiquitous. I'd love it if I could add fluid damping to my arm. It seems to me like it's just a good design idea, like isolation from structure borne vibrations.

 

Strangely enough I don't see airborne vibrations discussed much which can also cause rumble-feedback problems.

 

Thanks, that link worked. I wonder if American Google just assumes I don’t want to bother with the ordering process from the UK (which, honestly, I probably don’t in light of my lack of woofer pumping, but I do appreciate having the option!).

 

Google used to have a helpful top bar menu that allowed you to easily tick which territory you wanted to search in. Now they have got too clever by half with their "expert" search system, and pre-filter depending on the sending URL.

 

I am not a turntable engineer and have no direct experience in the matter.

But if "arm dampers" were necessarily a good thing to have on a tonearm in the real world, then wouldn't every manufacturer of tonearms have dampers built into every arm that they manufacture?

My point is that while they might be good ideas in theory, they might not necessarily be the best idea in the real world and may present some audio disadvantages or unnecessarily raise the price. I have no idea?

Going back to your example of a Rega arm, Rega is famous for not having all of the "audiophile" adjustments that other high end tonearms have, like an VTA adjustment. On the surface, that would seem to rule out using a Rega arm on a high end turntable, but it doesn't (Both my modern RP6 and vintage restored and upgraded TT's had Rega arms).

You had the opportunity to purchase an arm with a damper, but you choose not to.

I'm assuming that it was because all of the other positive attributes going to your modified Rega arm outweighed no having an "arm damper"?

If Rega thought that having arm dampening as an important feature (as opposed to just a "selling point"), wouldn't they have one?

I have no doubt that you have quite a bit more knowledge and experience in turntable design as I do, having almost none.

I had just noticed the woofer pumping issue on some, which is a very few, records, because of the exposed driver's on the Zu, Omen Definitions. If they driver's were covered with grills, I doubt if it would have ever come to may attention as I can't say that it made any audible difference in the sound that I was aware of.

Still, seeing the dual 10" drivers really "pumping" back and forth, when they shouldn't really be doing anything on a quiet passage, gave rise to the fact that there was a signal that was present causing this action and that signal really should not be there. It seemed to be just common sense, that having an extra energy routed to the speaker would have to prevent and interfere with the primary audio signal.

In practice, you should never observe a speaker vibrating at all. I can play an album like the Grand Funk R.R.'s "Red" album, which has prodigious amounts of bass (not sub-bass) through the Altec A7's, with their exposed 15" bass driver's with powerful SS amplifier's at very loud SPL's and even observing the driver's up close, you can't see them moving at all. You have to actually touch them in order to feel their vibration, yet the bass is pounding.

To me, the only thing that I concern myself with is how something sounds. I don't look at frequency graphs and concern myself with things of that nature.

I only use tube amplification of the legacy Altec's and use exclusively SS amplification on all of my other systems.

To me, the Altec's with single ended tube amplification sounds the best and the most realistic. How much distortion is present? Don't know and don't care, I really don't.

I'm sure than any of the stacks of SS amps that I have, produce "ruler flat" frequency response and have their place. These amps have all different power levels from a couple of 30-Watt Nelson Pass, First Watt designs, to a 475-Watt Crown amp, but my overall preference lies with the single ended tube amps.

I don't doubt that my turntable arm is producing sidebands in the audible region but this is the first I have been aware that they may be present.

In another thread, you made me aware of "chugging" for the first time.

The thing is, I put together an exceptional downstream system that I listen to both digital and analog music on. I had two different quality turntables on the system, both modern and vintage, with quality carts and phono preamps, and I can not hear or identify any of these artifacts in either of the turntables.

What I hear, is pretty much what I expect to hear, except much better with the gear that I now own.

I have always looked to what gives me the best audible value, as far as performance goes, for the dollar, and that is what I go with.

There are many aspects of audio that seem to be of importance to the audiophile community, that mean very little to me and I don't give them much thought.

But, that's just me...

 

I can refer to the small article I wrote up about tonearm mass/compliance/resonance to reduce warp-related noise

Dropbox - Tonearm mass and noise LP playback.pdf - Simplify your life

The Moerch DP-8 tonearm has a much higher resonance in the vertical direction with typical cartridges (15-20 Hz) due to its construction, further reducing the warp-related noise. If money were no object I would probably get it, but no, money can be better spent...

Also, if you use subs like I do below 80 Hz, I use two of them both in mono from the HT amp. This has some advantages like better power but also it will reduce woofer pumping due to vertical warps and also less stress at the amp stage.

 

As with everything in this hobby it's a matter of where you want to compromise. Dampers arguably introduce friction into the mechanism of a tonearm, but the unfortunate reality is that dragging the stylus through a bumpy trough can cause resonance in the arm that it is attached to. Fluid damping is just one of the concepts that was devised to address this by absorbing and dissipating unwanted resonance. So many different approaches to tonearm design. It's a bit silly to cherry pick damping and state "if this is so great why doesn't everyone use it?". Wilson Benesch for exmaple uses strong armtubes (Nanotube One) and is one of a handful of commercially available items to use carbon nanotubes in its construction yielding stiffness an order of magnitude greater than any metal equivalent. If this was so great why doesn't everyone use it? Clearaudio is focused on bearing noise and come up with magnetic bearings that ‘float’ the arm over the record with no point of contact at all. If this was great why doesn't everyone use magnets? My table is a Kuzma Stabi S with a unipivot tonearm. The damping cup around the bearing works fantastic in that design. The 4Point has damping troughs as well and it's one of the best arms available at it's price point.

 

You don´t have to be a turntable designer to understand mechanics. Because there is one mtrl used in a certain application, not all uses just that, I belive we can up with endless examples on that theme. What a fluid damper does sonically you will have to listen to it, not being negative on something you havent heard.

 

I don't believe that I have said something negative about something that I have not heard.

My standpoint is maybe they are a good thing and maybe not.

I don't know.

I have simply pointed out, that there are plenty of major tonearm manufactures, such as Rega who are more informed and experienced that I am who have obviously made a deliberate and informed decision not to damp their tonearms.

Maybe you, being the expert, should contact them and enlighten them of their errors?

 

agree 100%
fluid damping is a band aid at best to compensate for some less than ideal variable(s) whether that be room or the arm itself
with the right stylus profile and arm it can also cause extreme groove wall damage and mistracking
Michael

 

And other informed, experienced tonearm manufacturers, such as VPI, makes many tonearms in both Gimbal AND Unipivot (damped) versions (including the $4K JMW Fatboy below). Why wouldn't they make just one version if one was clearly superior???? I really don't understand your point.

 

Many tonearms used to have damping and many top arms still do -- off the top of my head I think SME, Graham arms, Brinkman, Townshend had a modified Rega with damping, Well Tempered, Kuzma, I think pretty much all unipivots . Other times carts like the old Shure with the dust bug had that acted as a subsonic mechanical resonance damper. Honestly this isn't one of those radical or oddball tweaks. It's just good design (like a lot of things, btw, Regas do without like azimuth and VTA adjustment, or motor/plinth isolation, or turntables with isolation from structure borne vibration). It's also a pretty well understood element of design. A subsonic filter is really just an after-the-fact Band-Aid. It's much better to reduce the issue mass-compliance subsonic resonance mechanically. It's better to do a lot of things mechanically that a lot of tonearms and turntables don't do as a financial/design compromise -- like it's better not to just use a cap to split the phase to a turntable motor, but most turntables compromise there too, with the result of more motor vibration and noise.

I don't really buy a lot of audio gear because I don't have the means. I bought my tonearm 30 years ago and have tweaked it out to the best of my ability with arm tube and counter weight damping, adding VTA adjustment via the Origin Live set screw mounting, etc. I've done workarounds with shims if I've had to try to adjust azimuth. Never really satisfactory that solution. If I were to buy a new tonearm today, or to design one, I'd look for fluid damping for sure. And, in fact, if someone sold an aftermarket damping set up for the Rega, I'd add it.

I recommend reading the B&K paper from '77, which helped touch off a lot of ideas in turntable design when it comes to dealing with mechanical resonances. It wasn't some kind of tweaky audiophile paper, it was a presentation to the Audio Engineering Society, not exactly the bastion of odd ball audiophile ideas.

 

+1 Exactly!

 

because they are not just in the tonearm manufacturing business but they are also in the tonearm selling business
when you want to sell stuff the more choices you offer the more stuff you sell
like 2 door 4 door hatchback suv and pick up truck
Michael

 

How a fluid damper works has of course nothing to do if You think it's good or not.

 

the shure stabilizer - goop troughs - and uni-pivots are comparing apples to oranges to rib eyes