Sorry to post this here, but most of the people who would know the answer to this come here so thats where I decided to post it. If it gets long then maybe it should be moved.
I was making some measurements today - using Holm - and I kept see glitchs at various frequencies. Now I know that I have a hum problem because you can hear it. But oddly enough, the glitches were at eaxactly 70 Hz and 280 Hz. Now this got my attention because if this were 60 Hz and 240 Hz then I'd know what it was, but it wasn't at those frequencies.
Is it possible that the AC mains are actualy at 70 Hz. temporarily? Can this every happen? I didn't think that this was possible.
Clock error in the sound card?
Any ideas how this could occur?
I was making some measurements today - using Holm - and I kept see glitchs at various frequencies. Now I know that I have a hum problem because you can hear it. But oddly enough, the glitches were at eaxactly 70 Hz and 280 Hz. Now this got my attention because if this were 60 Hz and 240 Hz then I'd know what it was, but it wasn't at those frequencies.
Is it possible that the AC mains are actualy at 70 Hz. temporarily? Can this every happen? I didn't think that this was possible.
Clock error in the sound card?
Any ideas how this could occur?
The thing is that there is a lot of stuff synchronous to the 60 Hz. mains. Changing it would mess all that up.
This was a fluk that pop'd up and then went away on a sample of a speaker that I have measured hundreds of times. Its not in the speaker, that I am positive of. And, its gone now. I went back to try and track it down and POOF!! All gone!
This was a fluk that pop'd up and then went away on a sample of a speaker that I have measured hundreds of times. Its not in the speaker, that I am positive of. And, its gone now. I went back to try and track it down and POOF!! All gone!
I saw this a few years ago on a documentary on power generation. (now I'm guessing they may have said 5/10/15%?)(BTW, wouldn't you guys be getting into winter?)
On the other hand mine sits quite predictably on 50Hz. My measurements remind me of a tent on a pole.
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I use hbx6 and arta, and also got the strange results some times. I think it is a timing problem of hardware and software during measuring.
But you have to watch where your measurement window is with the start of the mls-impulse. That is also a source for strange results.
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Hi Earl, do you have a CRT monitor, and if so what is the refresh rate set to? I was measuring noise on my power-supply, and had a big spike at 100Hz, funny thing was it didn't go away when I switched off the power!! After a lot of head scratching I changed the refresh rate on my monitor from 100Hz to 90Hz and the noise spike was at 90Hz. The device being measured was at least 10 feet from the monitor too!
Tony.
Tony.
I've had a measurement system before that screwed up the frequency of the output and input. It would make the output frequency half of what it was supposed to be and the input frequency twice what it actually was (or vice versa), so when you took a loop measurement it looked okay but the speaker was being driven at half the frequency specified. It turned out to be some weird interaction between the soundcard and the industrial motherboard in the computer, but it was totally repeatable. So probably not helpful to you, but interesting...
The monitor is LCD - Does anyone still have a CRT? Not very energy efficient.
I have to believe that if its possible for the mains to go to 70 Hz then that was it, because I have seen this exact thing before, but only at 60 Hz. AND I can hear the problem - unfortunately I don't have perfect pitch.
So CAN the mains ever go to 70 Hz? Anyone know for sure? Any Power Engineers out there?
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For power to go to 70 Hz the generators would have to increase in rpm accordingly.
Power generating stations are held in very close (near perfect) sync so generators can be added or removed depending on load demands.
If they were not held in perfect sync, this would not be possible, not to mention there would be lots of complaints from anyone using synchronous clocks or Hammond organs.
In my business of sound and lighting, we used to have fun "bumping" around 120 1K par lights on and off while using large portable generators. The generator would lurch, and fart black smoke, (we were able to get 2 of four wheels off the ground if we timed it right) but would not loose rpm.
If you were in some Banana Republic powered by a single generator, frequency fluctuations of a few % would be possible, but not here in the USA.
Art
Been using a beautiful 21" CRT with no plans to change. The relays just began faltering which I've fixed although I managed to throw the focus out in the process. I hope I can bring it back because I'm not ready for an LCD yet. Call me cynical, but my TV is a plasma.
Yes, mains will shift, by tenths of a HZ at max. No more. If it went to 70, gad that would cause major grid faults. I could easily see a PC clock error. Try measuring your mains frequency, with sufficient voltage divider and "one in the pocket" safety methods. ( Or just a loop of wire not actually attached the line. Much safer. )
I still use CRT's I much prefer them as I can set the resolutions at 1600x1200 or better.
I Like not being able to see the dots.
I can't get this kind of resolution on the LCD's with out spending a ton of money or in a small format, as I can pick up a good CRT display usually for free that still has decent color to them.
But they do generate a bit of noise though.
So, I just turn them off or use my one LCD panel when I do the measurements.
Right now I have 3 computers setup and each with two display units and 24 bit cards installed.
I have a couple of real good CRT Displays that I use strictly for photo editing as their colors are extremely good.
A calibrated CRT for photos can run as high as $35,000!!
Yes, They are big and heavy but they are still working great!
Just my honest opinion For what it's worth.
jer
I Like not being able to see the dots.
I can't get this kind of resolution on the LCD's with out spending a ton of money or in a small format, as I can pick up a good CRT display usually for free that still has decent color to them.
But they do generate a bit of noise though.
So, I just turn them off or use my one LCD panel when I do the measurements.
Right now I have 3 computers setup and each with two display units and 24 bit cards installed.
I have a couple of real good CRT Displays that I use strictly for photo editing as their colors are extremely good.
A calibrated CRT for photos can run as high as $35,000!!
Yes, They are big and heavy but they are still working great!
Just my honest opinion For what it's worth.
jer
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