@terry9 Thank you very much! And thank you for joining in. I'm having fun learning how other real users think about audio and audio gear. I can't get that here in this countryside location.
Thanks to everyone else also.
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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@rauliruegas Thanks for the links. Great reading material. Seems like companies use whatever measurement protocol they feel is appropriate. This is very similar to the "alphabet soup" of specs that exist in the Optics and Electronics engineering world.
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I thought about starting a new thread, but the conversation on this one is a good intro into my next question.
"How does one choose between belt drive (including string, fishing line etc...), direct drive and idler drive?"
There seems to be two crowds, direct drive vs all the others. I've had both. I had a bad experience with the AS table, but that could be an isolated problem. I really don't have a preference. Very curious to hear ideas! |
@kevemaher : In this forum there are 5-6 threads dedicated to your same question and the issue is not exactly the drive TT design because the kind of drive is only one TT characteristic and yes very important but there are other very important characteristics too like: platter build material or blend materials well damped, well dampend isolated arm board, excellent damped suspension, silent bearing, tec, etc,. At the end no matters the drive design the TT must be inert with out any kind of " sound " by it self . It has to be speed accurated and with good speed stability. I that scnario any of those 3 drive designs can make the job. Design , materials and quality level excecution is more or less the name of the game.
Please do a fast search in Agon forum to find out those TT threads.
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Dear @mijostyn : This is the one for you and for the OP because this is not DD but BD design:
Audio-1986-06.pdf (worldradiohistory.com) page 98.
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- 76 posts total