Suspended TTs: How much bounce is too much bounce?

[danieldust]

Yesterday I removed the foam inserts from the springs on my AR XA. Conventional wisdom is that they do more harm than good. Now I notice that my turntable has much more bounce than it ever did before. Even when cueing up a record, I get some jiggle that carries over into the first few seconds of play.

Do I need to tighten up my suspension?

I have never messed with the suspension on my turntable because a previous owner apparently glued the nuts into a specific position. I can move them, but it's not easy, and I figured he probably knew what he was doing. But now I suspect I need to re-tune.

Any thoughts from the Linn, Thorens & AR folks on here?

[bauzace50]

Hello danieldust,
First of all, I admire your owning one AR XA, which is the very first model I purchased in my life, when it cost $78.00 new! Then, I had two other new ones over the years...but not anymore.
However, your problem seems quite repetitive with XA's. Our own V.Engine member ddarch (Dave Darchambault) has LOTS of experience fixing these, and could inform you better. But I believe that the XA suspension should resonate at two Hertz, if I am not mistaken. The idea is to have it resonate at such a frequency that isolates it from footfalls, and blows on the turntable's plinth.
bauzace50
_________________
Benign is what you will be after you be eight.

[danieldust]

Thanks for the response, bauzace50. I'm hoping Dave might have something to say about this, but I asked the question here in hopes of getting some comments from the Linn & Thorens users also.

The foam inserts are supposedly only useful for reducing footfall problems, and I have done that already by placing my TT on a shelf in a closet. It also sits on a 40-pound slab of marble. Conventional wisdom seems to be that once you have done something like this, the foam inserts should be removed.

I guess I just need some guidance on how much bounce to look for.

[mosin]

Hello Daniel,

It's a springy, so I suppose it should basically behave like the other springies. I say that because I have not owned an AR. I have owned Thorens TD-150s and a Linn LP12, however. In the case of those, the most important thing is that the bounce is only vertical with no sideways movement. How much bounce with those depends a lot on the weight of the tonearm itself. Personally, I have had the best results with minimal bounce, but your mileage may vary.

Regards,
m-

[andyr]

[danieldust]

Thanks for the replies. So far I have heard 15 seconds is recommended by Thorens, 18 seconds by Linn and "minimal bounce" recommended by Mosin. Hmm.

Mine is giving me at least 15 seconds right now.

I guess I'll just have to experiment.

[tonyptony]

Hmm, how is the bounce test conducted?

[LPspinner]

Hi Guys…

Been following this thread for a bit and now I’m about to jump in with my input.

The bounce test is a curious and subjective thing full of all sorts of mystic overtones …. Yeh right !!!

The main thing to look for with the bounce test, and this goes for any suspended sub-chassis deck, is that when excited (pushed down at the centre of gravity for the sub-chassis – not the centre of the platter) the deck should continue to bounce in a vertical mode only. Any side-ways yawing is a sign of imbalance. You must also remember that the springs are not the only active member in the suspension system, there is also the dynamic element caused by the belt, the arm cable and the sub-chassis earth wire where fitted.

The belt is the most commonly over looked part of the mechanism as it will help dampen out some of the lateral or torsional components of the oscillating suspended mass. Trying to set up the deck with an old or worn-out belt is like trying to get good handling from a sports car with worn out shock absorbers, don’t skimp on an old worn out or a cheap non-genuine and ill fitting after market belt. Also, as many Linn DIYer’s will know the arm cable dressing also plays a big part in damping out lateral oscillations within the sub-chassis, get the tension just right and an will assist in dampening out lateral oscillations. Too tight and it will restrict the movement of the suspended mass, too loose and the arm cable will be ineffectual.

Also the frequency of the bounce is dependant purely on the spring rate and the mass of the sub-chassis. The only way a user can change the bounce frequency is to add more mass to the sub-chassis (this will lower the resonant frequency of the oscillations) or change the springs to a lighter rate spring (for lower frequency) or a stiffer spring (for higher frequency). Simply moving the position of the spring’s adjusting nut will only change the height at which the platter will sit relative to the main plinth / top-plate or how level the platter is relative to the plinth / top-plate. It should also be noted that the Platter should sit level with the plinth / Top-plate, or more precisely the platter / sub-chassis should be absolutely square to the springs and there for the direction of the intended sub-chassis oscillation. If this is not right the sub-chassis will have a definite yawing mode.

The length of the bounce is not entirely reliable as it will depend on how hard you push the sub-chassis in the first place. If it seems to move freely in an up and down mode with no obvious restrictions, this should be enough.

All this postulating makes a good argument for giving it all away and just getting a Rega 3 type “set and forget” Turntable. However I would ague that when set up correctly a good quality suspended deck can work very well and that goes for any of the suspended decks (AR, Thorens, Linn, Ariston, etc). So Danieldust, for what it is worth, I think you have done the right thing in removing the foam inner dampers as these were originally put in there to appease the lazier and less committed AR owners who didn’t want to spend the time to set up the deck properly (Thorens also did the same thing with there TD150-160 series of decks). You just have follow through with a little more setting up and choosing an appropriate location for the deck. It is common practice to sight a suspended deck on a wall mounted shelf as this will eliminate all foot fall and floor born vibrations.

I’m not sure about the large slab of marble, as the general consensus with this type of deck seems to be low mass high rigidity for the equipment supports, so you could try it without the slab. It may be that the high mass of the slab is causing the shelf to flex and move around and so messing with the AR’s internal resonant modes. Alternatively, you may want to consider a light rigid equipment rack (the lower down the better) that is spiked to the floor and is sited directly over the floor bearer where the floor is likely to be a little more rigid. If you are lucky enough to have concrete floors, a light rigid rack spiked to the floor will be the best option.

Hope this helps

LPSPinner.

[ddarch]

LP Spinner,

I finally found the time to address DD's question this morning, and I arrived here to find your excellently written comprehensive response. Well done!

I put a link to this thread on my Do-It-Yourself page. This explanation along with Tim Bailey's wonderful illustrated tutorial (Also on DIY page) should give just about anyone the courage to move forward with suspension tuning.

http://www.vinylnirvana.com/ar_diy.shtml

Dave
_________________
David Archambault, Exeter, NH

www.vinylnirvana.com

[danieldust]

Thank you, LPspinner, for your excellent and informative post! There's a lot of info to chew on there, but I am better off for having read it.

Sadly, I have suspended wooden floors and very little room for my stereo system, so the closet shelf was my best option and has so far been a huge improvement over what I was doing before. The light and rigid thing is interesting, though. I feel really good about the marble slab, but it probably wouldn't hurt to remove it and see what happens.

[BatNastard]

I'm also glad to see it explained this way, since my Thorens really only gets a few seconds of bounce and I was worried I did something wrong. However I can't go any lower or the platter will rub the safety post!

LPSpinner, your write-up sums it up nicely in a way that makes sense. Dave, there is also an article next to Tim's at TAD with more pics and video -- I actually found it to be more helpful since Tim scared me off with his safety switches and thorough cleaning rituals

[rwij]

Some spring upgrades have grommets on both ends. Does this increase isolation? Where can one get the right grommets?

[goatbreath]

I've found that the Thorens decks definitely work best on a light but rigid surface.Over the years I've had one on a pine coffee table,an old trick.About a year ago I got an Apollo wall shelf with a glass shelf.Something sounded odd for all the pronises and sales blurb you get with these items.So I tried a still record test.Put the stylus on a still record then slowly advance your volume control.The turntable was creating microphonic feed back at under 3 oclock on the volume control,not good.So I got an old board of veneered chipboard the correct size.Stuck on some sorbothane feet.Problem fixed.Turntable much better.
My own little pet theory is that you have to sit a suspended on a material a bit less dense as if not the vibration will be sent back into the turntable as you have created a closed loop.If the vibration has somewhere to drain into as long as the surface is rigid enough,at least its not in the turntable itself.
If you think about an acoustic guitar a minute.It generally uses spruce or cedar for its top.A quite open grained softwood.The back and sides are usually rosewood,mahogany,walnut or maple.Slower growing hardwood.So as the vibration travels along the soundboard,it stops at the hardwood which is more dense and is deflected back across the same soundboard.Now if you reverse the procedure and use a piece of some type of conifer.the vibration will actually travel along the grain of the wood and out of the end of the grain.How an acoustic guitar would function with no soundbox{back and sides}.
So it makes sense to me that the most logical thing to put a Thorens suspended on is a thickish piece of spruce .Thick enough to be rigid but not dense enough to send the vibration back into the turntable.
The only reason I'm using chipboard is I found it for nothing and it was the right size.I've used this trick many times and it seems to work.

Regards Goatbreath.