Finding resonant frequency when you don't know the mass of your tonearm

[Thomas_AA]

The best way is to use a test record and make som measurements. Here is vertical and horizontal resonance of the Shure V15Vx/SAS using a 10 g Linn Akito tonearm. This is the Hifi News test record, filtering out frequencies above 50 Hz and then measuring the level 4-20 Hz, with and without the brush. The effective mass of the Akito is 10 g. Combined with the mass of the cartridge and mounting, the mass is around 17 g. The compliance of the JICO SAS is around 20, giving a theoretical resonance of 159/SQR(17x20) = 8.6 Hz which fits with the vertical resonance.

The horizontal resonance is lower, about 6,5 Hz. I initially thought this was due to difference compliance, but since the resonance of my 4 g Moerch UP-4 is measured 10,5 Hz in both vertical and horizontal plane, the different result of the Akito is due to a different horizontal effective mass. There are more moving parts at the tonearm base for the horizontal movement. In theory the horizontal moving mass of the Akito arm should be approximately 23 g.

 

[onwardjames]

As am I but Im not sure why. ...The "why" is why is it important to know the RF? Not being snarky -just curious. Bob

It's quite alright. I have trouble understanding all the crazy math and wacky reasons a turntable either sounds like butt, or fantastic.

It almost seems like black magic is involved, lol.

 

[doctor fuse]

OK, so how do I adjust my suspension on my Marc Morin modified AR XA so I can use it in my main living area without getting foot fall skips? That's really all I need to know how to do. For now, the XA is in the basement system on a concrete and tile floor and SOUNDS FANTASTIC. Bring it upstairs and put it in the mix with my Audible Illusions and Pass Labs gear and it sounds OK, and I can't walk by it without it skipping.

My Thorens TD-160 used to be very susceptible to footfalls. I did the usual mods - heavy birch plywood base, stuffed Blutac and plasticine on various parts of the underside of the chassis, and at corners of the plinth, lots of Blutac between the Thorens base and the stereo rack it sits on (feet bypassed). Now it is almost immune to footfall. Have you tried these kinds of remedies?

 

[restorer-john]

Difficult to say from the above graphs. Usually there is a dip between the music signal and the tonearm resonance:

This is typical of what I've seen from various 'needle drop' recordings people post around here. The problem being, this is the spectral content and relative energy of the resultant signal in their system, i.e. they are wasting a huge amount of power amplifying system-resonant caused frequencies, that are undesirable and not remotely musically derived. All sorts of problems occur, IMD, cone over excursion etc.

Use the subsonic filters and confirm they are removing the resonant peaks sitting 6 or 7dB below your average level.

 

[onwardjames]

@restorer-john, THANK YOU for posting that. I feel that you should ALWAYS engage the subsonic filter. Never know when you'll see your woofers doing the boogaloo.

 

[trinhsman]

My Thorens TD-160 used to be very susceptible to footfalls. I did the usual mods - heavy birch plywood base, stuffed Blutac and plasticine on various parts of the underside of the chassis, and at corners of the plinth, lots of Blutac between the Thorens base and the stereo rack it sits on (feet bypassed). Now it is almost immune to footfall. Have you tried these kinds of remedies?

Did a marble base on rubber feet, with turntable plinth having sorbethane feet. Everything in the table was modded by Marc Morin, the AR guru. I’m not messing with any of that, with the exception of tweaking the Linn springs he installed. My upstairs table should actually be the better table, but the AR sounds so amazing in the basement system. I feel lucky just to be able to have a choice on what to listen to.

 

[Son-of-Vere]

Did a marble base on rubber feet, with turntable plinth having sorbethane feet. Everything in the table was modded by Marc Morin, the AR guru. I’m not messing with any of that, with the exception of tweaking the Linn springs he installed. My upstairs table should actually be the better table, but the AR sounds so amazing in the basement system. I feel lucky just to be able to have a choice on what to listen to.

Good choice. AR's can be 'damped to death'. I'd go with the wall mount shelf option. My AR is on a concrete slab. As much as I hate living on one, it does help with many audio related issues.

 

[Thomas_AA]

This is typical of what I've seen from various 'needle drop' recordings people post around here. The problem being, this is the spectral content and relative energy of the resultant signal in their system, i.e. they are wasting a huge amount of power amplifying system-resonant caused frequencies, that are undesirable and not remotely musically derived. All sorts of problems occur, IMD, cone over excursion etc.

Use the subsonic filters and confirm they are removing the resonant peaks sitting 6 or 7dB below your average level.

Agree that subsonic filter is very good. I do not have a subsonic filter at the moment but the signal below 100 Hz is mono coupled from pre-amp to amp to two separate subwoofers. So I do not have any significant problems with wasted power or woofer pumping.

Also this is why a resonance of 10-15 Hz is desirable since most energy that excites the resonance is around 4-6 Hz (warp frequencies). Many systems have the resonance between 6-10 Hz which is too close to the warp frequencies. Also when I engage the Shure brush, problems also decreases.

 

[restorer-john]

My AR is on a concrete slab. As much as I hate living on one, it does help with many audio related issues.

Why is it that humans don't like concrete floors? Is it because we descended from the trees?

I am in a pole home, with timber floors, high above the forest floor in the tree's canopy and I will never go back to a solid slab floor. As much as a concrete slab is awesome for audio, it isn't so good for my well being (all my previous homes bar one, were slab-on-ground). I sleep much better in a timber floored home.

 

[rothwellaudio]

Weird, not much difference going through the phonostage of a NAD 3020.

If the NAD has a rumble or subsonic filter if might be attenuating the resonance enough to obscure it from the graph.

You could try placing the stylus on a stationary record and then tapping the record with a pencil or suchlike. The recording will show a horrible thud corresponding to the impact but might then show a resonant decay. I've never tried it myself but I think I might give it a go.

 

[doctor fuse]

I've taken the crappy JVC out of commission, and replaced it with a much better CEC BD-2000. What an improvement in sound.
Auto-shut-off was nice, as this is a bedroom system, and I was enjoying going to sleep not worrying about taking the tonearm off the record, but we've got to have some decent standards, haven't we? WE HAVE TO, RIGHT?!?!