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Old 6th October 2013, 05:31 PM   #11
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I didn't see where anybody measured a known signal so the measurements can be referenced to anything. Audacity tells you dB in terms of full signal, but you need to tie that to some known displacement or the number is meaningless. (though I could have missed it!) Don't forget to apply weighting if comparing to commercial weighted numbers. (one of the best sites is http://www.diracdelta.co.uk/science/...ng/source.html)

I've looked at the Thorens rumble coupler measurement device and in all honesty I don't understand how the thing can exceed the performance of a well designed and fabricated bearing. IMO, making a near-perfect bearing isn't that difficult. Eliminating motor coupling is a whole 'nuther story, and that signal should probably be described as something other than rumble. A lot of modern motors generate stuff in the hundreds of Hz.
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Last edited by Conrad Hoffman; 6th October 2013 at 05:33 PM.
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Old 6th October 2013, 08:21 PM   #12
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Default thanks for all of the replies...

To respond to some:
1) Method: Yes, this process records the subsonic signals generated by the less than perfectly smooth uncut vinyl. But keeping in mind that under the best of conditions, this vinyl can be as flat and will tend to mirror the surface roughness of the stamper die that pressed it. With that considered the HFN001 copy I have appears to be a very flat record,..... as far as records go.

2) Right. This method can not be compared directly to any published "weighted" values that turntable manufacturers used to reference back in the day when rumble measurements were actually taken. As I see it, its' only repeatable reference will be within the scope of my own listening room while using the same group of equipment. Example, using the same test conditions while recording from a different turntable. then comparing the spectrum plot generated between them. Or, better yet, same turntable after refurbishment has been carried out.

I have to admit that I thought I'd see a "noisier" decible figure from this TD124. something around -40 db weighted would have been appropriate. And my spectrum plot is, I think, unweighted raw data. Even that is useful provided the same conditions of the test are adhered to from one player to the next.

3) The Masterlink. It would be possible to feed the line level signal coming out of the phono preamp directly into the sound card of a suitable PC. Thus eliminating the need for the ML9600. However, not all PC sound cards are created equal. Some are more agreeable with audiophile pursuits than are others. In my case, I just have standard issue sound cards on the computers in my care. The Masterlink, on the other hand, was designed to record high quality sound. So, on that general assumption, I presume it to be as good a bet for getting the "unpolluted data" into Audacity as any other available to me. also, this particular model is long out of production. It was expensive when new. but now, 2nd hand samples may be found and purchased for around a few hundred usd. And that is how I got mine.

4) known signal. The test records I have are rather limited. Two of these offer tracks with unmodulated grooves. The HFN001 record calls this track system residual noise. An older test record I have, Allied Radio, calls their unmodulated groove track a rumble test. but when you look at that track in good lighting it can be seen that there is some very slight modulation within those grooves. Rumble from the mastering lathe. But the HFN001 record does not show any visible evidence of modulation within its residual noise track.

It has been suggested that I use this method to analyze a 1000hz signal. Unfortunately none of the test records I have offer this. Although the HFN001 does offer a 300 hz signal at various different amplitudes. I suspect that a steady tone signal could be used to examine more than the mechanical noise of the turntable. But it could be used to determine performance in the domain of time. Like wow and flutter. So it does seem like a good idea to get a test record that does offer a 1000hz track. Fwiw, the Allied Radio test record (actually 3 records) does offer some wow/flutter tracks. These consist of a single piano note being sustained. This is probably useful for computer analysis. I'm just not certain what software would be the best choice for this test. (wow/flutter)

re: some references available on the web.
http://www.theanalogdept.com/images/...Resonances.pdf
this is the Bruel and Kjaer document that is widely available on the web. Afaik, this company still carries out audio testing and offers its equipment to do so. But none of this is available to me at a price that would make sense.

-Steve
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Old 6th October 2013, 08:29 PM   #13
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Quote:
Originally Posted by Frank Berry View Post
You can't measure turntable rumble just by playing a disc. You must have a device which can measure only the low frequency noise from the platter.
Only valid measure of rumble is for that picked up by cartridge, thus platter must be in motion, and stylus in contact.
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Old 7th October 2013, 03:42 AM   #14
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Default Repeatable measurement.

Conrad is right. It is no good measuring something if you cannot compare it to a known reference. But to make that meaningful the measuring system must be the same and have proved to be repeatable within acceptable criteria. So unless everyone has the same measuring system (that's why I suggested using Audacity.) but even then we would need to use the same computers, the same cable and the sames turntable mounting system, same temperature and humidity. Change any of these and other things and you will vary the result.
i.e. how clean, old is the HFN LP, what is the cartridges output at these low frequencies?
So all in all you can only measure rumble in your own environment for your own system.
What you need to do is measure before you change/upgrade your system. Do the change/upgrade and then remeasure.
Just by upgrading your internal wire of the tonearm will change the rumble heard. But here it will most likely make it a worse result. As hopefully the upgraded wire will give you better signal retrieval!!

So to cut out 80% of the variables I believe the only way to measure rumble and not measure worn cartridge, dirty/old record. Is to measure the single with the arm sitting on the arm rest. At around 2 to 3 o-clock in the morning. With all components switched on then measure again with every component (accept of cause your computer, T/T and phono amp) switched off.
Then you will be able to get a true repeatable idea of your system rumble, Bearing Motor, belt etc,etc.
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Old 7th October 2013, 08:31 PM   #15
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Hi Steve

The following measurements are done with the Thorens messkoppler on a special antivibration table .
All the ,,rumble ,, is between the 0,55 -100 Hz as you can see the motor has two vibration components its own resonance from 23 hz at 50 hz power frequence and the magnetic vibration at 100hz .
Others are from the tonearm, steppulley, idler and its harmonic components.
The first picture is with the normal rubber motor decoupling 100Hz at -65db the second with spring decoupling 100 hz at - 72db . same results at 23 hz motor frequence.

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Old 7th October 2013, 10:22 PM   #16
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Click the image to open in full size.

Good image. and while we have it why not discuss the merits of the rumplemesskoppler. The rumble coupler was designed by Thorens engineers back when it became clear that record players were capable of producing less rumble than many of the mastering lathes still being used to produce records. And so a test record with an un-modulated track was no longer of any use.

But now some have suggested that this device, the "rumplemesskoppler", by itself, does produce some bearing noise. So the question becomes; is the reading taken 'a measurement of the record player' or of the instrument itself? My guess would be that it depends upon the record player being measured. If its' rumble levels are greater than those of the rumplemesskoppler, then those readings should show up on the graph but in addition to the noise produced by the instrument.

Then compare readings taken using this instrument versus the readings taken using a blank flat bit of vinyl while the stylus skates across it. I see two very different reads. And it seems that the frequencies recorded by myself using the later method did generate some very low frequency sound waves. down to below 20 hz, while the rumplemesskoppler did not go that low. But with the Thorens coupler instrument we see noise frequencies consistent with motor vibrations and spinning pulleys and driving idler wheels, etc.

Anyway, just brainstorming. I probably missed an important point or two.

Fwiw could you let us know more about your methodology? What is the signal chain in use to acquire the two charts you show?

Interesting stuff. And that is a great photo of a Rumplemesskoppler in use.

-Steve
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Old 7th October 2013, 10:33 PM   #17
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volken;

How long was the sample period for resolving such clean peaks?

Some assumptions are made about acoustic paths to stylus, but does remove pressing issues with test disc contact.

What does same measurement gain setting show with 300Hz test disc signal? Is modulation apparent?
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Old 8th October 2013, 05:53 AM   #18
volken is offline volken  Netherlands
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[
Fwiw could you let us know more about your methodology? What is the signal chain in use to acquire the two charts you show?

Interesting stuff. And that is a great photo of a Rumplemesskoppler in use.

-Steve[/QUOTE]


Steve the messkoppler is connected to a B@K Response test unit and after that to the HP 35665A Dynamic Signal Analyzer .
I did also measurements with a Denon test record posting follows.

Volken
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Old 11th October 2013, 06:58 AM   #19
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That little Thorens device touches the bearing and contacts the record surface at the same time, so it's not missing any noise paths. i've never seen that before it's a funky little thing.
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Old 11th October 2013, 07:42 AM   #20
volken is offline volken  Netherlands
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Quote:
Originally Posted by Barleywater View Post
volken;

How long was the sample period for resolving such clean peaks?

Some assumptions are made about acoustic paths to stylus, but does remove pressing issues with test disc contact.

What does same measurement gain setting show with 300Hz test disc signal? Is modulation apparent?
With a W@F speed measurement from 3 Khz you get these results .
Restoring and Improving A Thorens TD-124 MKII
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