Tonearm effective mass??
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hakaplan
Needs professional help
Arm mass is includes the headshell, but not the cartridge. For the rare times you see arm mass published, that's what the number represents, so that's what I use as a comparison.
The cartridge and hardware is only added in when using the formula to calculate resonant frequency. And as I've said, without reliable compliance numbers, that formula is worthless.
Cartridges do vary in mass, but the average is 6g and rarely are they more than 2g over or under. Sometimes that difference will help even out the match a little better, and sometimes it will worsen the match a bit, but rarely will a 2g variation one way or the other drastically change the arm/compliance compatibility.
I agree with Gusten about the tracking force. It is not a mass and should not be added.
Now you can significantly lower or raise the arm mass at the headshell end. If your arm is too low in mass for the cartridge you want to use you can just add weight to the headshell. If your cartridge is too high in compliance, you can use a lighter headshell. Yes, as with the cartridge a 2g difference may not be that significant, but some fancy headshells can weigh as much as 12-15g by themselves. Compare that with an 8g ehadshell, and you can see how that could be significant.
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I think we're halfway there-if You do mean that if a tonearm with an effective mass of "X", will have around 5g (cart mass) added to it by the cartridge.
Specifically, my PX-2 has a published spec of "tonearm effective mass: 16-18g, tracking force dependent.
I "get" why the effective MASS doesn't include the tracking force and therefore is 16g.
I know it doesn't include the 5-6g avg cart weight.
I think that to make sense of/decide how compliant a cart is a good match for it, I need to include cart mass in the calculus.
I get confused when you make statements like this:
" I think I'd call under 10g low mass, above perhaps 15g high mass and 10-15 middle."
Doe the low mass/10g arm have an effective mass of 5g + an (assumed) 5g cartridge?
Or does it have an eff arm mass of 10g and we assume another 5g for the typical cart for an total eff mass of 15g?
Once this is clarified, the other half of my question would be: "what ranges of tracking forces correlates to what ranges of effective tonearm masses"
signed, Weedhopper
PS: Context: the PX headshell (8g) is included in the 16g eff tonearm mass spec. But I have a headshell/cart combination based on the B&O 1.6g MMC-1 cartridge that weighs only 6.4g. The recommended tracking force for the cart is 1.0g.
The typical "total" eff mass with a typical 5g cart and the 8g headshell would be 21g.
The "total" effective mass with the modded setup is 14.4g
Where in the constellation of tonearm effective masses does this fall? (low? med? why?)
Given the recommended tracking force for this cart of 1.0g, what do you think about it?
And, please-could you respond to the general question(s) as well as the specific one?
Specifically, my PX-2 has a published spec of "tonearm effective mass: 16-18g, tracking force dependent.
I "get" why the effective MASS doesn't include the tracking force and therefore is 16g.
I know it doesn't include the 5-6g avg cart weight.
I think that to make sense of/decide how compliant a cart is a good match for it, I need to include cart mass in the calculus.
I get confused when you make statements like this:
" I think I'd call under 10g low mass, above perhaps 15g high mass and 10-15 middle."
Doe the low mass/10g arm have an effective mass of 5g + an (assumed) 5g cartridge?
Or does it have an eff arm mass of 10g and we assume another 5g for the typical cart for an total eff mass of 15g?
Once this is clarified, the other half of my question would be: "what ranges of tracking forces correlates to what ranges of effective tonearm masses"
signed, Weedhopper
PS: Context: the PX headshell (8g) is included in the 16g eff tonearm mass spec. But I have a headshell/cart combination based on the B&O 1.6g MMC-1 cartridge that weighs only 6.4g. The recommended tracking force for the cart is 1.0g.
The typical "total" eff mass with a typical 5g cart and the 8g headshell would be 21g.
The "total" effective mass with the modded setup is 14.4g
Where in the constellation of tonearm effective masses does this fall? (low? med? why?)
Given the recommended tracking force for this cart of 1.0g, what do you think about it?
And, please-could you respond to the general question(s) as well as the specific one?
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Definitely a muddle which needs sorting out. Then we can get down to business. Very relevant to me these days and I'm looking forward to some clarification.
Fred Longworth
audio fanatic
Spring-and-mass oscillator -- comparing tonearm dynamic masses
There are various ways to measure the dynamic mass of a tonearm with extreme precision. That said, there are simple ways to provide a rough, working measure of a tonearm’s effective mass when compared to another tonearm.
The only tools required are a small, light spring capable of both tension and compression, a ruler, and a stopwatch.
* * * * *
Right now, I have a small pocket novel sitting by my laptop. The front cover is popped up from the rest of the book about 30 degrees. If I press the cover with my finger so that it is against the body of the book, and then release, it will oscillate very quickly and decay exponentially to a stop. If I take the end of my highlighter pen and clip it to the thin cardboard of the cover, and displace the page the same amount with my finger, it will also decay exponentially -- but it will oscillate for a longer time, and at a noticeably lower frequency.
* * * * *
You can see that if you have two tonearms and a small spring, you can run a very similar test. Glue the bottom of the spring to a square of wood heavy enough so that -- for the purposes of the experiment -- its mass can be considered infinite. Loop the other end of the spring over the little handle on the right side of the arm that is used for cuing-by-hand.
Remove the stylus to keep it from being damaged.
Now, press the tonearm down somewhere between half and inch and an inch -- and then release. (When comparing arms, it’s important to displace the arm by the same amount every time.)
Assuming both tonearms have good bearings, so that only the mass of the arm and the spring constant of the spring are operative, the tonearm with the lower frequency of oscillation is the one with the greater effective dynamic mass.
How do you compare the frequencies of oscillation? Simple. Click the stopwatch at the instant you release the arm, and click it again when the arm has oscillated five times. Run the test a few times, and strike an average. The arm that takes longer to oscillate five times has the greater dynamic mass, and the arm that takes less time has the lesser effective mass.
* * * * *
Fred
repairing audio gear since 1972
* * * * *
There are various ways to measure the dynamic mass of a tonearm with extreme precision. That said, there are simple ways to provide a rough, working measure of a tonearm’s effective mass when compared to another tonearm.
The only tools required are a small, light spring capable of both tension and compression, a ruler, and a stopwatch.
* * * * *
Right now, I have a small pocket novel sitting by my laptop. The front cover is popped up from the rest of the book about 30 degrees. If I press the cover with my finger so that it is against the body of the book, and then release, it will oscillate very quickly and decay exponentially to a stop. If I take the end of my highlighter pen and clip it to the thin cardboard of the cover, and displace the page the same amount with my finger, it will also decay exponentially -- but it will oscillate for a longer time, and at a noticeably lower frequency.
* * * * *
You can see that if you have two tonearms and a small spring, you can run a very similar test. Glue the bottom of the spring to a square of wood heavy enough so that -- for the purposes of the experiment -- its mass can be considered infinite. Loop the other end of the spring over the little handle on the right side of the arm that is used for cuing-by-hand.
Remove the stylus to keep it from being damaged.
Now, press the tonearm down somewhere between half and inch and an inch -- and then release. (When comparing arms, it’s important to displace the arm by the same amount every time.)
Assuming both tonearms have good bearings, so that only the mass of the arm and the spring constant of the spring are operative, the tonearm with the lower frequency of oscillation is the one with the greater effective dynamic mass.
How do you compare the frequencies of oscillation? Simple. Click the stopwatch at the instant you release the arm, and click it again when the arm has oscillated five times. Run the test a few times, and strike an average. The arm that takes longer to oscillate five times has the greater dynamic mass, and the arm that takes less time has the lesser effective mass.
* * * * *
Fred
repairing audio gear since 1972
* * * * *
gusten
Addicted Member
Hi
It is the total effective mass that is relevant when playing. That will include all masses added to the arm when playing. Cartridge weight must be added to get the whole effective mass.
As there is no standard what is low, medium or high tonearm effective mass, this thinking is rather imprecise, but if consider this thinking, it is always only the tonearm including original headshell that is mentioned.
There is no corrolation between eff. mass and VTF. The VTF needed is only corrolated with suspension compliance. The VTF You choose to set, is totally independent of the eff. mass, and must not be thought off as related. HTH
gusten
Edit: My opinion is that the resonance freq. should be rather high and the tracking force should also be high. If one can achieve a freq. of 12-15Hz it´s very beneficial in my book.
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Where's Howard when we need him??
"Hi
It is the total effective mass that is relevant when playing. That will include all masses added to the arm when playing. Cartridge weight must be added to get the whole effective mass.
As there is no standard what is low, medium or high tonearm effective mass, this thinking is rather imprecise, but if consider this thinking, it is always only the tonearm including original headshell that is mentioned."
I totally agree and am waiting for God to put his (their) caveat imprinteur on that statement.
THEN-give His enlightened opinion of what constitutes (by TOTAL eff mass) in grams, the categories/classes of tonearm masses......................
THEN-correlate them with cartridges by their VTFs.
"There is no corrolation between eff. mass and VTF. The VTF needed is only corrolated with suspension compliance. The VTF You choose to set, is totally independent of the eff. mass, and must not be thought off as related."
I would expect vertical and lateral compliance to be closely related/equal in a stereo cartridge or there would be inherent signal distortions induced.
Vertical tracking force is a direct function of (vertical) compliance (i.e: spring rate) in a resonant system and, acting against the tot eff mass determines vertical resonance peak (except as affected by any dampening in the system)
That is surely true/physical law.
[When I have tried to check vert and horiz resonances by graphing output voltage, vertical resonance always is higher freq than lateral, implying higher spring rate/less compliance in that axis (excepting damping). However, the resonances are relatively close I.E: 13 lat/18 vert]
"Hi
It is the total effective mass that is relevant when playing. That will include all masses added to the arm when playing. Cartridge weight must be added to get the whole effective mass.
As there is no standard what is low, medium or high tonearm effective mass, this thinking is rather imprecise, but if consider this thinking, it is always only the tonearm including original headshell that is mentioned."
I totally agree and am waiting for God to put his (their) caveat imprinteur on that statement.
THEN-give His enlightened opinion of what constitutes (by TOTAL eff mass) in grams, the categories/classes of tonearm masses......................
THEN-correlate them with cartridges by their VTFs.
"There is no corrolation between eff. mass and VTF. The VTF needed is only corrolated with suspension compliance. The VTF You choose to set, is totally independent of the eff. mass, and must not be thought off as related."
I would expect vertical and lateral compliance to be closely related/equal in a stereo cartridge or there would be inherent signal distortions induced.
Vertical tracking force is a direct function of (vertical) compliance (i.e: spring rate) in a resonant system and, acting against the tot eff mass determines vertical resonance peak (except as affected by any dampening in the system)
That is surely true/physical law.
[When I have tried to check vert and horiz resonances by graphing output voltage, vertical resonance always is higher freq than lateral, implying higher spring rate/less compliance in that axis (excepting damping). However, the resonances are relatively close I.E: 13 lat/18 vert]
Bob_in_OKC
Addicted Member
Is there really a need to establish boundaries between low, medium and high? You'll still need to consider how close to the boundary a number is. After all, is an effective mass of 9 grams going to give you a significantly different resonant frequency in a given setup than 10 grams?
gusten
Addicted Member
"Vertical tracking force is a direct function of (vertical) compliance (i.e: spring rate) in a resonant system and, acting against the tot eff mass determines vertical resonance peak (except as affected by any dampening in the system)
That is surely true/physical law."
The resonance peak is determined by the total eff. mass and the spring constant. Instead of spring constant is normally, regarding suspensions, the reciprocal used. The VTF is not relevant.
gusten
That is surely true/physical law."
The resonance peak is determined by the total eff. mass and the spring constant. Instead of spring constant is normally, regarding suspensions, the reciprocal used. The VTF is not relevant.
gusten
As far as I know, spring constant is the same expression as spring rate,IE: displacement/force.
And because that is what keeps the arm assy in suspension against the groove, and because the tracking force then implies the relative spring rate of the combination (cartridge/arm) in question, we should be able to make reasonably accurate assumptions about what combinations of arms and carts will mate well based on recommended tracking forces/total effective masses.
And because that is what keeps the arm assy in suspension against the groove, and because the tracking force then implies the relative spring rate of the combination (cartridge/arm) in question, we should be able to make reasonably accurate assumptions about what combinations of arms and carts will mate well based on recommended tracking forces/total effective masses.
gkimeng
Forum Mod, ClassicSpeakerPages.net
If you have a copy of the HFNRR, there's a calculator on the DIY Audio site that will determine effective mass for you. You run the low frequency test bands to ID resonant frequency of your arm/cartridge combo, input the frequency, VTF and cartridge and mounting hw weight and out comes effective mass.
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gusten
Addicted Member
If You mean force/displacement they are the same.
We can make assumptions and estimations that could be good enough, how close we are will only be shown when measuring. Better a high res. figure than a low.
gusten
"We can make assumptions and estimations that could be good enough, how close we are will only be shown when measuring. Better a high res. figure than a low."
Absolutely agree! However, it would be nice to have a definitive yet generalized guide to choose matches. Something that is likely to be within 20%? (+/-10%) based on recommended TF and total effective arm&cart mass (which is easily discoverable with a $25 digital scale)
Practically speaking, I find it difficult or impossible to deal with published compliance figures and the charts people are trying to find arm resonances with. I'm fairly certain a practical "unified theory" is possible.
If you have a copy of the HFNRR, there's a calculator on the DIY Audio site that will determine effective mass for you. You run the low frequency test bands to ID resonant frequency of your arm/cartridge combo, input the frequency, VTF and cartridge and mounting hw weight and out comes effective mass."
Yes, but (see above) getting a very close mass number is easy.
What I want is an simple way/rules to match tot eff mass (easily discovered) to VTF (published by all cart mfgrs)
Absolutely agree! However, it would be nice to have a definitive yet generalized guide to choose matches. Something that is likely to be within 20%? (+/-10%) based on recommended TF and total effective arm&cart mass (which is easily discoverable with a $25 digital scale)
Practically speaking, I find it difficult or impossible to deal with published compliance figures and the charts people are trying to find arm resonances with. I'm fairly certain a practical "unified theory" is possible.
If you have a copy of the HFNRR, there's a calculator on the DIY Audio site that will determine effective mass for you. You run the low frequency test bands to ID resonant frequency of your arm/cartridge combo, input the frequency, VTF and cartridge and mounting hw weight and out comes effective mass."
Yes, but (see above) getting a very close mass number is easy.
What I want is an simple way/rules to match tot eff mass (easily discovered) to VTF (published by all cart mfgrs)
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hakaplan
Needs professional help
Well, first, the HFNRR is worthless because the resonance tones are not accurate. They've been independently tested by two people over at vinylasylum.
Second, I thought I was clear, but maybe not. The definition of arm mass is the mass of the arm. The cartridge is not included. Whenever arm mass is published, it does not include the cartridge. The headshell is included because on many arms it is an integral part of the arm and is not removable. This is the value you use to estimate the best match to the compliance of a cartridge.
The ranges I gave for arm mass are just arm mass, not including the cartridge. These are my best guess for the verbal description of the arm mass ranges.
For our purposes, I consider the cartridge to be a constant 6g. If it's not, subtract or add the difference to the arm mass. That's the only way the mass of the cartridge matters when estimating a match--it's relative. Adding the total mass of the cartridge to the arm mass is irrelevant unless plugging it into the resonance formula.
As to tracking forces, I'd call 1-1.5g low, 1.5-2g medium and 2-2.5g high.
So lets take an example.
AT-110E
Mass: 7.2g
Median Tracking force 1.5g
The tracking force is low/medium (high/medium compliance). This would mate well with an arm that is low/medium mass. Since the cartridge mass is 7.2g, add 1.2g (7.2g-6g) to the mass of your arm for the estimation. So if your arm is normally 12g, for this cartridge you'd call it an effective 13.2g. What would be an ideal match? Probably an effective arm mass around 10g. 13.2 would be acceptable, probably fine. There's overlap, it's not an exact science, just to make sure you're in the ball park. If you're using a 22g arm, this isn't the cartridge for you.
AT-95E
Mass 6.5g
Median TF: 2g
The TF is medium/high, meaning low/medium compliance, suitable for a medium/high mass arm. It's .5g over the average of 6g so add .5g to your arm mass. So this is suited to am arm around 15g, but certainly a little more or less would be fine. How about a 7g arm? No, not a good match.
Ortofon OM20
Mass: 5g
Median TF: 1.5g
Medium/low TF meaning medium/high compliance. Subtract a gram from the arm mass for comparisons because the cartridge is a gram under the 6g average. In this case, the lower mass of the cartridge makes this more usable on arms that might be a bit on the high side. Not that 1g is that significant, but every little bit helps. So If your arm is 12g, now it's effectively 11g, and a better match than a heavier cart with a stylus of the same compliance.
This is an estimable unified theory designed to avoid major mismatches. If you accept that my quick and dirty method of estimating arm mass is close enough, the only way to hone this to higher accuracy is to use a reliable test record and measure the resonant frequency. Shure Era IV is reliable but only gives tones in 2Hz intervals. I believe the Shure Era V does 1Hz intervals.
Second, I thought I was clear, but maybe not. The definition of arm mass is the mass of the arm. The cartridge is not included. Whenever arm mass is published, it does not include the cartridge. The headshell is included because on many arms it is an integral part of the arm and is not removable. This is the value you use to estimate the best match to the compliance of a cartridge.
The ranges I gave for arm mass are just arm mass, not including the cartridge. These are my best guess for the verbal description of the arm mass ranges.
For our purposes, I consider the cartridge to be a constant 6g. If it's not, subtract or add the difference to the arm mass. That's the only way the mass of the cartridge matters when estimating a match--it's relative. Adding the total mass of the cartridge to the arm mass is irrelevant unless plugging it into the resonance formula.
As to tracking forces, I'd call 1-1.5g low, 1.5-2g medium and 2-2.5g high.
So lets take an example.
AT-110E
Mass: 7.2g
Median Tracking force 1.5g
The tracking force is low/medium (high/medium compliance). This would mate well with an arm that is low/medium mass. Since the cartridge mass is 7.2g, add 1.2g (7.2g-6g) to the mass of your arm for the estimation. So if your arm is normally 12g, for this cartridge you'd call it an effective 13.2g. What would be an ideal match? Probably an effective arm mass around 10g. 13.2 would be acceptable, probably fine. There's overlap, it's not an exact science, just to make sure you're in the ball park. If you're using a 22g arm, this isn't the cartridge for you.
AT-95E
Mass 6.5g
Median TF: 2g
The TF is medium/high, meaning low/medium compliance, suitable for a medium/high mass arm. It's .5g over the average of 6g so add .5g to your arm mass. So this is suited to am arm around 15g, but certainly a little more or less would be fine. How about a 7g arm? No, not a good match.
Ortofon OM20
Mass: 5g
Median TF: 1.5g
Medium/low TF meaning medium/high compliance. Subtract a gram from the arm mass for comparisons because the cartridge is a gram under the 6g average. In this case, the lower mass of the cartridge makes this more usable on arms that might be a bit on the high side. Not that 1g is that significant, but every little bit helps. So If your arm is 12g, now it's effectively 11g, and a better match than a heavier cart with a stylus of the same compliance.
This is an estimable unified theory designed to avoid major mismatches. If you accept that my quick and dirty method of estimating arm mass is close enough, the only way to hone this to higher accuracy is to use a reliable test record and measure the resonant frequency. Shure Era IV is reliable but only gives tones in 2Hz intervals. I believe the Shure Era V does 1Hz intervals.
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Thanks Howard.
That's pretty much what I expected but I needed someone with much greater experience to validate.
Do you have any answers to my observed differences in vert vs lateral resonances? How do vert and lateral complainces compare?
My observations are that lateral resonance occurs at lower freq than vertical which implies that lateral compliance is greater (softer) than vertical (stiffer).
I would think that to preserve linearity the two would need to be kept equal.
Enlightened opinions (facts!) anyone?
That's pretty much what I expected but I needed someone with much greater experience to validate.
Do you have any answers to my observed differences in vert vs lateral resonances? How do vert and lateral complainces compare?
My observations are that lateral resonance occurs at lower freq than vertical which implies that lateral compliance is greater (softer) than vertical (stiffer).
I would think that to preserve linearity the two would need to be kept equal.
Enlightened opinions (facts!) anyone?
gkimeng
Forum Mod, ClassicSpeakerPages.net
Are there any more credentials available for these people besides the fact that they hang out on vinylasylum?
hakaplan
Needs professional help
Both are long time members, very knowledgeable, and have been involved with numerous discussions about theory and electronics. They have scoped the tones and both came to the identical conclusions and listed all the tones as announced on the record and the actual measured frequency. If you want their names, PM me and I'll let you know who they are.
I don't know if anyone ever contacted HiFi News with this information--hard to believe that no one else knows about this, but I suppose people can't imagine that a company so respected in the hi-fi world could put out a defective test record, so who would think to test the tones? It's really scandalous when you thing about it--betraying the trust of your customers. What's worse is that they put out a new record a couple of years ago, and the tones are the same (defective) on that one, as well.
gkimeng
Forum Mod, ClassicSpeakerPages.net
That's ok, it's been years since I felt the need to pull mine out and use it anyway. I was just wondering if they were pros or amateurs.
gusten
Addicted Member
The fact is that it´s normally so that lateral res. is lower than vert. The figures I have seen published, and my own figures, show a diff. of about 3-5Hz.
The reasons for this are mainly speculations, one reason could be that the compliance is lower, as a part of the spring vert. is already used for VTF. There could be several other explanations as well.
We cannot assume this diff. in res. is causing any linearity issue IMO; if the diamond isn´t loosing contact with groove walls, which we cannot assume it does, or the azimuth isn´t changed, why should there be.
gusten
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Thanks for making me (re)think!
I bring my thinking from racecar suspension tuning where the unsprung weight (stylus) is a significant percentage of the sprung weight (tonearm), and the spring rate very large and transmits much energy/movement to the sprung weight.
With such a small difference in compliance, and very low spring rates relative to the arm mass, practically speaking there is no difference in needle movement in the two axis and no displacement of the arm mass. Thanks
I bring my thinking from racecar suspension tuning where the unsprung weight (stylus) is a significant percentage of the sprung weight (tonearm), and the spring rate very large and transmits much energy/movement to the sprung weight.
With such a small difference in compliance, and very low spring rates relative to the arm mass, practically speaking there is no difference in needle movement in the two axis and no displacement of the arm mass. Thanks