Note the almost perfect Mean Frequency Response against the recorded 3150Hz and the impressive .01% speed deviation. It makes you wonder if you're measuring the speed stability of your turntable, the lathe that cut the test record, or both. Perhaps this is a benefit of the Timeline. Your measurements are not hindered by lathe inaccuracy. There has to be some lathe inaccuracy. If there wasn't, wouldn't we all be listening to records on lathes or turntable with record lathe type drives? If your Timeline was 31" from a wall, a speed error of .01% would appear as a 0.02" (0.5mm) laser deviation per revolution. |
Also note that even if your speed is off by 0.1Hz, it will take 945 minutes of running time for your platter to gain/lose one rotation. Nothing against the timeline, just that your turntable would have to run for almost a day with the timeline to see how accurate it is. These plots show you results in a matter of seconds. It's not quite that bad. If your TT is 3' from the wall and your laser deviation is 1.5mm per revolution, your speed is off by 0.1Hz. 1.5 mm may be hard to see, but if you let it run for 10 revolutions and divide your total deviation by 10 you should be able to determine a 0.1Hz error pretty easily (if you have my Timeline Calculator Excel file that I posted about in this thread): http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1327029459 The phone app sounds pretty cool, though. It is actually not just an iPhone app. I just discovered that you can get it for Android devices, too. I may have to try it out. |
I was wondering if someone with two tonearms can do a simple test with the Feikert Android/iphone app. Play the test tone with the first tonearm and begin recording. After some data has been collected, drop the second stylus onto the record and see what happens to the tone. If the app is sensitive enough, this might show how much the platter slows due to the additional stylus pressure, how quickly it recovers, and how much it overshoots. It would be really interesting to do the exact same test on a number of different TTs. |
Halcro, Thanks a lot! I was actually waiting to respond until I had some time to really study your results so I wouldn't ask any stupid questions, but all I have done so far was to take a quick look. So, a stupid question. Is the app capable of outputting frequency versus time data instead of a graph? It might be interesting to see changes over very small units of time. When I requested the test, I thought it might be useful in seeing micro speed changes, but I'm not sure if that will be possible. What do you think? the DD table seems to like a little more load perhaps Does your DD table have an oil filled bearing well? If it actually does like a little more load on it, it might be possible to improve its speed stability by using a higher viscosity oil. This is getting interesting! |
Keep in mind too, like I said before; the Timeline needs to run for several hours on your tt in order to get a reasonable data set for evaluation. You need thousands of rotations to conclude anything in the 0.01% range or else you will be seeing those fairies dancing around. Tony, I said this earlier in the thread: If your Timeline was 31" from a wall, a speed error of .01% would appear as a 0.02" (0.5mm) laser deviation per revolution. So, if you played a 20 minute record side, the platter would have made 666.66 revolutions. 666.66 * 0.02" = a total deviation during that one record side of 13.3". What if the total deviation was half that (6.65")? Your speed error is 0.005%. What if it was a quarter (3.25")? Your speed error is 0.0025%. |
Tony, I'm not totally sure what you're trying to say. There is no problem or error with the pencil marks. You make one mark on the wall at the beginning of the record and you make another mark on the wall at the end of the record and measure between them. If the two marks are 3.25" apart after 20 minutes and your turntable's spindle is 31" from the wall, your total speed error over those 20 minutes is 0.0025%. I haven't even tried aftermarket power cords. We both use Thiels, solid state power amps, and ARC tube preamps. Can you recommend a "cheap" aftermarket power cord for one of my components that will make me think I'm even more abnormal? Sorry for the diversion. Back to speed stability... |
Richard, Great post about the arrival time difference between our ears of a sound 15 degrees away from straight ahead. It really made me think about how sensitive our ears and brains are. I'm kind of surprised that I never thought about this. I wonder if this has something to do with components that soundstage and image very well. It could just be that the component processes or amplifies (whatever the component is doing whether it be an DAC or an amplifier) all frequencies and gets them to the output terminals in exactly the same amount of time. The component would also have to have the same exact, non-wavering processing time for the right and left channels. I checked the math (twice) and got a time difference of 0.00008 seconds between the left and right ears, though, not 0.0000053 seconds as you calculated. I may have made the same error twice or maybe not. It still doesn't change the fact that the time difference is extremely small for a sound that is 15 degrees away from straight ahead. For those who didn't do the math, at a distance of 4 meters, 15 degrees is equal to the sound source being about 1 meter away from straight ahead. 1 meter is a reasonable distance to use for this calculation. I think anyone could tell if something is straight ahead or 1 meter to the right with their eyes closed. We are probably capable of hearing even smaller changes in distance. |
We can tell the direction of a sound source by the arrival time difference between our ears. A sound source 15 degrees to the right of straight ahead at a distance of 4 meters will reach the right ear slightly sooner, but this is not all that clues us into where the sound is coming from. The sound will also be louder in the right ear because there is a more direct path into the right ear. It's more than likely both things that help us determine where sounds are coming from- time differences and volume differences. |
