Thanks for the discussion, @kevemaher .
A Few Turntable Measurements using the RPM Android App
I found this Android phone app for TT rotation. Phone is Pixel 4a. Thought I'd try this app out. I'm skeptical of these phone apps. Accuracy is always an issue.
I have four tables. I took 5 readings for the first table in order to see what the repeatability is. The "absolute" RPM, RPM peak to peak, and 2 sigma range readings were very, very repeatable. Consequtive RPM readings differed by a max of 0.01 RPM. Two sigma varied by 0.01% ( 2 sigma means that 86% of the readings were within the stated value). I personally would use 3 sigma, but that's a personal quibble.
I've measured all four of my tables. I am very certain that the results are very repeatable. I measured with no LP, LP rotating, LP on and Stylus engaged, and phone offset from center. RPM was the same for all cases, The 2 sigma showed a 0.01% rise (really small). The reading at the edge of the LP was different. And scary to do!
Here's the results:
1. DD-40 #1, RPM = 33.32, 2 sigma = 0.07% (63 dB)
2. DD-40 #2, RPM = 33.27, 2 sigma = 0.09% (61 dB)
3. Acoustic Signature WOW XXL, RPM = 33.17, 2 sigma = 0.10% (60 dB). This varied 0.02% from reading to reading (after running the table for 10 minutes, this noise diminishes), but the 2 sigma stayed the same.
4. Denon DP-57L, RPM = 33.25, 2 sigma = 0.02% (74 dB).
I then went back to DD-40 #1. Using the RPM app, I set the mean speed to be 33.25. The strobe on the table was slowly moving! I checked against the strobe on the Cardas test LP and yes, the RPM speed accuracy was wrong. I reset TT speed using the strobe. The RPM app measured 33.23 again. I must conclude that although the RPM app is very repeatable, the absolute accuracy is not. The wow result (2 sigma variation) remains the same.
I measured the 45 RPM on DD-40 #1. RPM = 44.91, 2 sigma = 0.05%, so the 45 RPM is fairly accurate and the 2 sigma is lower.
This app makes no distinction between wow and flutter. It's all reported in the wow reading (wow and flutter are the same thing by nature, the only difference is the frequency range).
I'm surprised by the poor performance of the WOW XXL table. This a modern, belt driven table, with a massive platter. It is 5 years old. There's no way for the user to adjust the RPM. The variation in the speed is similar or slightly higher than the 40+ years old Micro Seiki DD-40 tables, which don't have crystal oscillator driven speed control. The WOW XXL takes about 10 minutes before the very high frequency variations settle. Now, I don't know much about the internal workings of the app. Helpful would be better accuracy (or the AC frequency in my house is not 60 Hz). Bandwidth is not reported.
The DP-57L performance is outstanding!. This TT was made in the 80s. And the DD-40 tables are not bad, but are as good as or better than the WOW XXL.
In summary, in my opinion, the RPM Android App is very useful. The absolute accuracy is a bit off, but the repeatability is very good The wow measurement is also quite good.
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I was never an AS fan. I do not care for units that go out of their way to look flashy without obvious benefit. Having said that there are four sources of noise when playing vinyl, the turntable, the record, the environment and lastly electronic. I assume you used the same record for all measurements. The environment is basically the same for each table and to my knowledge none of them have isolating suspensions. Electric noise would also be the same for each table. The conclusion you came to is correct. The AS has a Rumble issue. Rumble is a problem if you can hear it or if it affects the performance of speakers particularly subwoofers. I also think it is a significant marker of overall quality. It is also possible this turntable was damaged. I had an 80s era MS turntable which was wonderful. Its only failure was lack of a suspension. The apartment building I lived in had the worst environmental rumble problem I have ever lived in. The AC compressors were clearly audible in spite of concrete floors, all 19 stories. Because of this I returned to the Linn LP12 which was much quieter as long as you tip - toed around it. Measuring is always the best way to confirm anything. You also discover that “ears” have limited sensitivity when dealing with certain things as it sounds you only identified the problem by measuring. Measuring is also a great way to train your ears. If you really want to have fun get yourself a Dayton Omnimic V2. They are about $300 and worth every cent. You need a PC. The program is free but you need to have a serial # to access it. In the process you download the calibration file for your microphone. You will find it essential for possitioning loudspeakers, adjusting room treatments and writing target curves if you ever get into digital signal processing. |
@mijostyn I use REW for room characterization. It is freeware. The functions appear similar. |
Dear @kevemaher : As you said almost no manufacturer disclose the the whole measurements process they used including the different standards they used. Here some examples:
http://www.thevintageknob.org/technics-SP-10MK3.html
http://www.thevintageknob.org/denon-DP-100M.html On specs this Denon TT is the only that shows Measured spec on speed fluctuations: 0.06% http://www.thevintageknob.org/micro_seiki-DD-100.html
http://www.thevintageknob.org/yamaha-GT-2000.html
http://www.thevintageknob.org/sony-TTS-8000.html
http://www.thevintageknob.org/sony-TTS-8000.html
http://www.thevintageknob.org/garrard-401.html
Your AS 60db is prety " decent " for a BD design and is really close to the DD MS unit. Btw, @mijostyn my vintage AS TTs never showed that rumble you mentioned is reflected in the subs not only that I do not noted by " eyes " but neither with my fingers against the Denon DP 80 and the Technics SP 10MK2. I think that the OP really puts the " finger " where it hurts when posted:
"" How low do wow, flutter, and rumble have to be before they become inaudible in a "typical" listening situation? ""
That is in true the real issue for us MUSIC lovers and audiophiles and for what I know I think that no one measured till today with the same standards/process.
I remember that in cartridges the separation spec that normally is measured over the frequency range but manufacturers only gives the measure at 1khz and main reason ( I think all we know it. ) is that at both/near frequency ranges the " figure is way lower over the " figure " showed by the manufacturer that today I think no one gives as in the past when the cartridges came with athe measured diagram of frequency response and separation from 20hz to 20khz and with the test record used, at what temperature, VTF and the like and speed velocity of the diagram. In those " gold " times audiophiles were way better infortmed to decide what to buy and in those times and talking of cartridge separation specs with severaltests and measures was accepted that the minum separation spec must be 20db with no " difference " if that figure goes to 30db because separation is not linear/flat. Lyra Atlas Lambda SL shows 35db on that spec but Allaerts Formula 1 is 70db at 100hz and 20khz and " only " 60db at 1khz but neither manufacturer disclose the measurement process about.
R.
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