Measuring Turntable Rumble

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gold
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Measuring Turntable Rumble

Post: # 31952Unread post gold
Wed Oct 22, 2014 10:21 pm

I have looked for standards and methods of measuring turntable rumble without much success. I know there was a Neumann RU75 measurement system with a calibrated test record. I have never seen one let alone one for sale. I've spoken to Bruel & Kjer at the AES shows about it. They said that they did have a measurement system but of course it's obsolete.

I haven't found any AES standards for rumble measurement. Does anyone know what the standards were and where they were published?

Does anyone have any experience measuring turntable rumble?

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dubcutter89
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Re: Measuring Turntable Rumble

Post: # 31965Unread post dubcutter89
Thu Oct 23, 2014 12:07 pm

The Neumann thing was is called RUMS75 - RUmpel Mess System? RUmble Measuring System?? Don't know..
A little pricey and probably without documentation...

ebay: 201038532550

Maybe you can borrow it just to let them know if it works...

I look if I find something about rumble and how to measure...interesting topic!

Lukas
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gold
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Re: Measuring Turntable Rumble

Post: # 31966Unread post gold
Thu Oct 23, 2014 12:59 pm

It's nice to see one but without the test record it is a historical curiosity. Way too expensive for something that can't work.

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dubcutter89
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Re: Measuring Turntable Rumble

Post: # 31967Unread post dubcutter89
Thu Oct 23, 2014 1:04 pm

yup

btw, I've seen at least 3 units for sale within the last year (and also for more realistic prices...)
already reading some papers - will come back to you when I have the information distilled.

Lukas
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Re: Measuring Turntable Rumble

Post: # 31968Unread post dubcutter89
Thu Oct 23, 2014 1:30 pm

BTW, do you want to measure rumble of any turntable or of your lathe?
if it is for measuring TTs then you can make one on your own...

Lukas
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Re: Measuring Turntable Rumble

Post: # 31969Unread post gold
Thu Oct 23, 2014 1:50 pm

It's more of a general question but I would like to be able to measure the lathe. It seems like there are rumblings (ha!) of an SP02 replacement. I don't think anyone can actually measure and quantify rumble. Without being able to measure rumble designing a replacement seems like a fools errand.

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Re: Measuring Turntable Rumble

Post: # 31970Unread post dubcutter89
Thu Oct 23, 2014 2:08 pm

Hmm, non-native me is now wondering - do you talk about that ?rumblings?:
http://www.flokason.ch/fs_directdrive.html
(btw, already saw the prototype - nice!)

Of course you can measure rumble!
You need:
- Turntable (DUT-Device under Test)
- A tonearm + PU attached to it
- RUMS66 or RUMS75 or
- A computer + audio interface
- DIN 45 544 Record or
- Cut a record with silence and 315 Hz @ 5,42 cm/s (DIY DIN RECORDINGs (C)2014 Dubcutter89)
- Brain
- A place with no rumble...

Measure:
- PU in air
- PU on record (not spinning)
- Playback 315 Hz @ blabla
- Playback of silent groove

Now it's time to add filters and do the math - details on request; after thinking break.

Lukas
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Re: Measuring Turntable Rumble

Post: # 31971Unread post gold
Thu Oct 23, 2014 2:58 pm

What is the reference level for measuring rumble? I don't think obtaining a DIN record in good shape will be possible. Is the RUM75 like a distortion analyzer with the notch filter at 315Hz?

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Re: Measuring Turntable Rumble

Post: # 31972Unread post dubcutter89
Thu Oct 23, 2014 3:43 pm

Getting the DIN records is hard, and probably wasted money...
Searching for Info I also found that some companies claimed that they used reference cuts because the pressed test records were not good enough for measuring...

Reference Level is 5,42cm/s @ 315 Hz (that's what the DIN Record says...) NOTE: 300Hz is -5,5dB (RIAA) -> 5,42 would be the same as 10cm/s at 1kHz (or +6dB over standard 5cm/s reference)
You compare the unmodulated groove with the reference. all measurements are weighted with a filter.
not a notch at 315hZ, more the opposite...
it is a 2nd order low pass at 315 Hz and either:
a 2nd order high pass at the same 315 Hz (Rumpel-Geräuschspannungsabstand) or
a 1st order high pass at 10Hz (Rumpel-Fremdspannungsabstand)

Easy way: cut +6dB 315Hz (if your VU is reading 0 at 5cm/s@1kHz), cut silence, Playback and record to DAW, add filters, measure recorded files...
(my personal add was to measure PU on disk without spinning motors etc. aslo to get another reference...)

Lukas

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Re: Measuring Turntable Rumble

Post: # 31973Unread post dubcutter89
Thu Oct 23, 2014 3:45 pm

a graph says more than thousand words...
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Re: Measuring Turntable Rumble

Post: # 31974Unread post gold
Thu Oct 23, 2014 4:04 pm

Very helpful. Thanks!

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Stevie342000
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Re: Measuring Turntable Rumble

Post: # 32001Unread post Stevie342000
Sat Oct 25, 2014 3:52 am

Ah excellent now I know what my copy of DIN 45 544 Rumpel - Mess - Schallapatte is for, it's all in German which is no surprise as I am sure that is where my copy came from.

I picked a copy of this on eBay earlier this year, I have been collecting test discs for awhile. I have most of the common ones.

Including RCA technical test disc which is the standard reference disc for setting up RIAA.

In addition of nearly a full set of the EMI Techinical Test Discs as well as the Decca Mono and stereo test discs. As well as an American one with pictures of cutting lathes and associated equipment on the front which I think is mono, its called for Hifi Bugs it's on Transworld.

I have collected a small selection of test kit as well to set my cutting lathe system and make sure that is properly aligned. This includes some old BBC equipment including as TS10P (Tone Source) and ATM-1 (Meter measuring system) all with Paignton attenuators and built like tanks to a specification that after approximately 60 years that they still look brand new inside and out. As well as couple of voltage test meters one tube (valve) by Mullard and the other a Leader which is solid state. I have the BBC Technical documents for the BBC equipment as well which tells you how to use them, set them up and including schematics.

Surely rumble tests are only relevant to playback and not to the recording system? These tests are of limited use as far as the cutting system is concerned - generally speaking.

I intend to make some test cuts based on or around the test discs and specific tests such as rumble, frequency response using the equipment I have, as well as making reference of the settings for cutting at a number of velocities, so I can repeat that at a later date. Cutting levels work in conjunction with groove pitch especially if you running in fixed groove and not variable pitch mode.

I have an in between the two pitch situations with the Connoisseur (AR Sugden) cutting lathes as it is vari-groove, pitch running from 100 - 300 lines per inch. So I can do it old school (as in Fine Recording - read as Mercury Records) and change pitch on the fly. Any how I digress.....but at least I now know what DIN 45 544 is now for.

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Re: Measuring Turntable Rumble

Post: # 32006Unread post gold
Sat Oct 25, 2014 6:21 pm

Stevie342000 wrote: Surely rumble tests are only relevant to playback and not to the recording system? These tests are of limited use as far as the cutting system is concerned - generally speaking.
.
Any rumble in the system will be recorded on the disk. It is important for both recording and playback.

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dubcutter89
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Re: Measuring Turntable Rumble

Post: # 32008Unread post dubcutter89
Sun Oct 26, 2014 5:31 am

When measuring rumble of a lathe by cutting a test disk and playback on the same someone might consider that you have up to twice the amount of rumble (record+playback, worst case), so the real numbers can be a few (0-6, probably around 3) dB better... also it is possible to measure different styles of rumble (only vertical/horizontal, left/right ...)

@Stevie

Nice collection! I only have the vinylike test tone record (which is good for almost all calibration etc.)
do you mind making audio files of your records? straight playback into DAW? Would be interesting to compare the different disks...

Lukas
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Stevie342000
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Re: Measuring Turntable Rumble

Post: # 32009Unread post Stevie342000
Sun Oct 26, 2014 2:27 pm

Hi Agreed about minimizing rumble in the cutting system itself but how exactly can you measure that? As it can not be done directly it can only be achieved on playback and then you are measuring the playback system as well, so how exactly do you determine which is playback and which is recorded?

Anyone with a half decent cutting/playback system would be able to hear it on silent grooves or with 315Hz recorded and taking suitable measurements but it is really taking it all a bit too far for most people. Although we need to be aware of it should we come across it in our cutting journey.

It's way too technical for most folks and it slightly outside my comfort zone but am aware of how to measure it and how to remedy it. It clearly falls under maintenance of the cutting system, suspension and platter bearings etc.

Hi Lukas yes not a bad collection, you just have to keep looking there are plenty of copies of all the discs around. They allow me to do some basic tests, align the system and set operating levels. At the moment my cutting system is in the process of being built up, I have two Connoisseur lathes one with Sugden head and the other with Presto 1-D, a Neumann adapter, some of Jerrys steel styli, along with Neumann SX74 cutting stylus new, a Connoisseur (Sugden) CQ20 essentially a Mullard 5-20 design with triode strapped EF86. Along with all the components to build microphone amps, line amps, equalisers, compressor and so on....on my list of projects to complete and get the system up and running. I need one or two pieces to get the other lathe up and running like a cabinet and I need to get a couple ball bearings for platter spindle.

Maybe I could cut copies of the discs, although I may be treading on Copyright territory but trying to learn as much as I can by reading all I can. It's taken me about 30 years to get a cutting lathe so not point in rushing to the end of the road too soon. Thankfully I bought my first complete lathe about 18 months ago just before the major upsurge in interest, the second one was bit pricier but I got the lathe, Presto head, Neumann stylus, Neumann adapter and the Connoisseur amp for roughly 3 times what I paid for the first lathe, I was offered the second lathe when I bought the first one but could not afford it at the time. But I could afford it a few months back so I got the second for spares at worst.

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Stevie342000
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Re: Measuring Turntable Rumble

Post: # 32011Unread post Stevie342000
Sun Oct 26, 2014 2:56 pm

Recorded rumble is kept to a minimum by the mass of the platter and the drive system, which is why a Lyrec motor is so expensive.

If for example you had a turntable/cutter which was belt driven as in Universal you can minimise rumble. Another project I have on the go is from an article in Radio news around 1940-1942, which gives instructions on how to make a belt drive turntable. This can be found on the American Broadcast link found here: http://www.americanradiohistory.com/Radio_News_Master_Page_Guide.htm

Topped off with a Ladegaard parallel tracking air bearing tone arm which can be found here: http://www.dcaudiodiy.com/roscoe/airbearingarm.html

If you're going to cut them that way they should be played back the same way. It would be interesting to measure the rumble on this set up and if/when it gets built will feed back with the data.

One interesting adaption I am considering is to drive the AC Synchronous motor off a tone source with a power amp, so you don't need all those pulleys but change the frequency to change the speed. There are a number of options for this one can be found in Audio in 1962 another can be found in the Radio news again, there is an article on the Fairchild 412, the schemo for that can be found additionally on Vinyl Engine.

I did find a strobedisc calculator for 50 or 60 cycles which you could print out unfortunately I can not locate it right now, very useful. You could punch in the other speeds and print out the strobe disc so you could check speed.

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