Why do I (not) need a subsonic filter

Hello there,

I'm looking for a new phono stage. At the moment I listen to a Lehmann Black Cube. This stage is not up to my "new" turntable combination with Benz L2. The first stage I had on a loan base was a Elektrokompaniet. I was just cleaning the house (four day job and one day housewife). My woofers did not look healty. So I decided to buy a phono stage with subsonic filter just like my Lehmann (11hz). That's really hard. You cannot get them anymore - why? You will not hear anything down to 20 Hz but you speakers will.

But Lemann is smart. They just introduced a new phono stage with a subsonic and with an on/off switch. Anybody other suggestions?

Thank you,

Carl

 

The subsonic filter is supposed to kill the rumble from warped records, what do you mean your woofers don't look healthy? How loud do you play your music? What is the rest of your system? I don't understand why you would want a filter, would better speakers not be more of an improvement if your current ones can't cope with a bit of bass

 

Hello Lord,

I do not see my woofers move/"flapper" with CD, but I see them move/flapper with LP. The rest of my system is all right and in good condition (Oracle mark V/Graham 2.1/Benz L2, Conrad Johnson 17LS and 11a and Monitor Audio 20 SE). The drivers of my Monitor Audio are exotic and I'm afraid to break them.

Why amplify sound you cannot hear? I think a subsonic filter like Lehmann (Black Cube 11Hz, Silver Cube 7 Hz) is an ideal solution. Bye the way phono stages like Chord symphonic and Oracle have subsonic filters but are really to expensive.

Carl

 

A correct implementation of the IEC playback curve implies 'subsonic' filtering. But an excess of woofer flapping may imply an arm/cart mismatch or a problem with the turntable or turntable mount. There shouldn't be much 'subsonic' signal in the first place. Fixing this by changing the phono amp is a bodge.

Paul

 

You need to find an expert on the relationship between your cart and your arm, it does sound like a problem there.

 

As has been said. It sounds very much like there may be an arm resonance issue here. What arm and cart are they?

Its easy enough to work out if the arm mass and cart compliance (accurate ones anyway) are available.

 

I thought that the woofers "going mental" was part and parcel of analogue replay. It does worry me a bit when I see them dancing in and out so vigorously, and is it does prevent me from turning it up for fear of damaging the woofers.

So are you guy saying that such cone movement isn't normal? I saw this effect with both my Rega P3 and my LP12 and with both phono stages I've had (Graham Slee 2SE and Dino)

Lefty

 

such cone movement isn't uncommon ... but it isn't normal either. Usually an arm/cart mismatch - broadly speaking a high arm plus cart mass requires a low compliance cart and a low arm mass+cart requires a high compliance cart.

If you get it wrong the result could either be

1. a combined resonance for the arm/cart which is in roughly the same region as record warps (a slowish woofer "pump" in the sub 8Hz region ... ooer that sounds rude ... for a high mass and high compliance mismatch) or

2. a resonance in the region approaching 20Hz (a faster woofer "wobble") for a low mass/low compliance mismatch - which corresponds with footfalls.

If you get the resonance figure around 10Hz to 11Hz these can be avoided.

The whole thing can sometimes be made worse if the setup is poorly isolated ... especially if you play vinyl with subterranean bass bearing rumble can exacerbate and so can noisy vinyl.

It all tends to be bit theoretical though as the specs issued for carts can be way out sometimes.

A google says the ittok has an effective mass of 11.5g ... Unfortunately from what I can see Rega don't issue specs , so unless someone here knows the mass and compiance of the SuperBias we couldn't even work out in theory whether you have a problem. Mind you from the sounds of it, you have a problem in practice so theory doesn't come into it

Interesting thing is the rega rb250/300 tonearms (for which the rega carts will be designed) have a mass 11g - ie. not a million miles from the ittok, so its surprising you have this issue.

Do any of the other LP12 owners know of any resonance issues surrounding the suspension? My experience of bouncy decks is limited to an old Thorens.

 

just to add to this:

The VdH site has some good stuff on this and a graph here

The Graham has a mass of 11g, the LP2 a mass of 9g and a published compliance of 15g (according to the Cartridge Database an excellent resource which also has a handy resonance calculator). Thing is if we assume the screws weigh a gram. That puts the theoretical resonance at 9Hz. Which is just about perfect.

 

Hello ZeroGain,

An Oracle Mark V and a Graham 2.1 is a tried and tested combination. I do not think there is a mismatch but I'm not a technician (at all) like Uncle Ants. I noticed the woofer flapping when I had an Elektrokompaniet phono amplifier on loan base. No problems with my Lehmann Black Cube with SF (11 HZ).

To be complete I had a bearing problem with my Oracle which is fixed. I could not try if the woofer flapping is still there because my Lehmann has a fixed SF.

On the otherhand a lot of amplifiers used to have a SF: Luxmann, Quad and many others. In the Netherlands they used to advise to buy only amplifiers with SF. What has changed? And why not a phono stage with switchable SF today?

By the way I think of trying the brand new new Lehmann
Black Cube Decade with switchable SF.

I agree with Lefty: there is aways more woofer flapping with turntable than with CD

Carl

 

Hi Carl, Its not the turntable/arm combination where the potential problem lies, but in the arm/cartridge combination. That said, the theoretical figures for your arm and cart combo look just fine.

I must say I think the idea of a switchable SF is a very good idea simply because these problems can be so difficult to nail and I can only imagine the absence is due to a)cost or b)the "no unnecessary switches in the signal path" argument.

That said I don't agree that there is ALWAYS this problem, as I don't have it with my setup - quite possibly more through luck than judgement. CD of course has effectively got a built in 20Hz filter, though I have got the odd track that somehow makes my woofers flap like bastards at certain points at what certainly looks like a lower frequency than 20Hz, I don't know how that happens though.

Given that the theoretical resonance of the arm and cart is not problematic, either the published tonearm mass or the published cart specs are wrong OR its something else - something else - the deck, its stand,the wall, floor, whatever - is picking up vibrations from somewhere which is at the frequency your woofers are pumping at (or a harmonic of it) and resonating at that frequency or harmonic and putting it back into the system as feedback and a feedback loop may be forming as tyhe speakers are now pumping out that frequency as well. At least that's how I understand it. There are far more knowledgable souls on this forum than I and I could well be wrong.

PS. If I had flapping woofers and couldn't isolate it ... I too would hanker for an SF on my phono amp. Worth investigating the possible source of the problem first though.

 

Thanks for the detailed reply Uncle Ants, you're a star!

My understanding of the problem is that an arm/cart mismatch should result in cones flapping all over the place in EVERY record, since the resonance would still be an issue, regardless of the record played. If this is the case, (as I hope it is), then I shouldn't have an arm/cart mismatch, as this problem only happens on some records. I guess this must mean that it's the warps in those records that is causing the flapping.

Incidentally, these records aren't all old, and one of the records which exhibits this problem is my Simply Vinyl issue of Pearl Jam's "Ten", which is a nice brand spanking 160g pressing

Lefty

 

Thank you uncle. I will come back to this discussion the moment I have another subsonic filter on a loan base.

Carl

PS (an hour later)

It's the bloody floor !

 

If it's the floor you can fix it, and your sound should improve regardless of phono stage.

Good news, I think.

Paul