Calling DarqueKnight: Test technique questions, please
SciFiTom
Posts: 58
Dear Sir,
if you would be so kind, I have questions about the test conditions you use with your Omnimic, and the FFT shots for the jumper wires in a recent post.
Omnimic:
I expect the results shown were averaged. How many? RTA mode with fast sweep?
Some plots I found are accompanied by the caption, "Room Response." Does that mean they were taken from your favored listening position, or directly in front of the speaker, at 1m, 3m or some other distance? Both channels driven, or only one?
What height did you have the mic at w.r.t. the speaker elements? Perhaps vertically centered on the active elements?
I note that the plots show better than 90dB at low frequency, around 40Hz. Does that mean that you use a fairly high volume while testing, or is the mic that close to the speakers?
In terms of flat response, have you ever chosen to try the Magnepan MG-12s you once mentioned owning, as a comparison?
FFT:
Looking at your recent comparisons of jumpers -
if I read these correctly, the FFT runs to 125kHz., so pretty much the first two vertical divisions are in the audible range, and there seems to be about a 5dB (peak) noise floor. Correct?
Is the concern at higher frequencies in terms of distortion brought about by energy transferred in the super-audible range?
Since these are voltage plots, could it be that external influences are driving some of the signals you see in these plots (EMC)? Did you construct some sort of Faraday cage for these tests?
How did you connect the probe to the jumpers? Where is the ground connection?
I think it would be interesting to try the FFT with a current probe. I have an old Tek AM503/A6302 active current probe, and a TDS2012C. The current probe hasn't been calibrated in a few years, but it should be OK for relative measurements. Unfortunately, the cable trough would only accept about a bare 10 or 12Ga. wire, but If you would be interested, perhaps I could construct a connector with only enough lead to fit the probe over, and a banana jack for the jumpers. If you aren't using some of your older jumpers, and would care to send them to me, I could try out the notion. Otherwise, perhaps I could at least try a few wire types on my own. I was hoping for more of an apples-to-apples comparison.
Thanks for your attention, and the many excellent efforts you've made to enlighten others,
Tom
if you would be so kind, I have questions about the test conditions you use with your Omnimic, and the FFT shots for the jumper wires in a recent post.
Omnimic:
I expect the results shown were averaged. How many? RTA mode with fast sweep?
Some plots I found are accompanied by the caption, "Room Response." Does that mean they were taken from your favored listening position, or directly in front of the speaker, at 1m, 3m or some other distance? Both channels driven, or only one?
What height did you have the mic at w.r.t. the speaker elements? Perhaps vertically centered on the active elements?
I note that the plots show better than 90dB at low frequency, around 40Hz. Does that mean that you use a fairly high volume while testing, or is the mic that close to the speakers?
In terms of flat response, have you ever chosen to try the Magnepan MG-12s you once mentioned owning, as a comparison?
FFT:
Looking at your recent comparisons of jumpers -
if I read these correctly, the FFT runs to 125kHz., so pretty much the first two vertical divisions are in the audible range, and there seems to be about a 5dB (peak) noise floor. Correct?
Is the concern at higher frequencies in terms of distortion brought about by energy transferred in the super-audible range?
Since these are voltage plots, could it be that external influences are driving some of the signals you see in these plots (EMC)? Did you construct some sort of Faraday cage for these tests?
How did you connect the probe to the jumpers? Where is the ground connection?
I think it would be interesting to try the FFT with a current probe. I have an old Tek AM503/A6302 active current probe, and a TDS2012C. The current probe hasn't been calibrated in a few years, but it should be OK for relative measurements. Unfortunately, the cable trough would only accept about a bare 10 or 12Ga. wire, but If you would be interested, perhaps I could construct a connector with only enough lead to fit the probe over, and a banana jack for the jumpers. If you aren't using some of your older jumpers, and would care to send them to me, I could try out the notion. Otherwise, perhaps I could at least try a few wire types on my own. I was hoping for more of an apples-to-apples comparison.
Thanks for your attention, and the many excellent efforts you've made to enlighten others,
Tom