Question on measuring speakers

[gedlee]

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?

[RockLeeEV]

is it isolated to the speaker or is it the same results regardless? - Is there any possibility of issue with inductor placement/orientation/build quality?

[Keriwena]

I read once that power companies increase the frequency during the day to send more power down the lines when it's needed, then drop it at night to get everyone's clocks back right.


I read it on an audiophile's site, so it must be true!

[gedlee]

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!

[paulspencer]

Earl,
For some strange reason I've found Holm to be a bit unreliable at times. It sometimes comes up with really bizarre and obviously wrong results. Press the button again and it's gone. I've never had that problem with anything else.

[Pano]

Ditto what Paul says. It can get glitchy for no reason. Close it and start again.
Mostly I get glitches from Windows interrupts. But they are inconsistent, but regular.
No way the mains will be a 70Hz, ever.

[AllenB]

Originally Posted by Keriwena

I read once that power companies increase the frequency during the day to send more power down the lines when it's needed, then drop it at night to get everyone's clocks back right.

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.

[Helmuth]

Originally Posted by paulspencer

Earl,
For some strange reason I've found Holm to be a bit unreliable at times. It sometimes comes up with really bizarre and obviously wrong results. Press the button again and it's gone. I've never had that problem with anything else.

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.

[wintermute]

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.

[Pano]

Good thinking Tony!
FWIW, my soldering station throws out noise everywhere. I have to turn it off for good electrical measurements.