HOLMImpulse: Measurements in practice

[Pano]

That seems about right. I'll check some of my old measurements, just as a point of comparison.

EDIT: I see H3 and H5 somewhat lower vs THD than that on my drivers. Tho it's very driver dependent. Cones drivers have more H3, compression drivers more H2.

[doug20]

Please check the "Noise" level too. HOLM THD includes that measurement which really isnt part of the speaker measurement normally.

[Pano]

I've always wondered about that "Noise" graph. What is it telling us?

[wintermute]

I suspect that it is background noise, ie stuff that it can't correlate back to the original signal (and harmonics thereof). It seems to be rather high in some of my measurements.

Below is the measurement of my MTM's with current crossover. The thing I found interesting with the noise is that it is highest at the 2Khz point, which co-incidently I have a major problem with my midbass drivers.... Not sure whether that means that there is some sort of 2Khz noise that is interfering with my measurements or what.....

Steve, I see no one answered your last question, though it was a while ago, I suspect maybe you were clipping your soundcard or perhaps overloading your mike or mike preamp. If your horn is a lot more sensitive than the woofer you were measuring it could explain the rather nasty plot you posted

1st pic noise, 2nd pic 2nd harmonic, 3rd pic third harmonic

Tony.

[speakerdoctor]

Wintermute:
Could you pls. explain what each of the 3 plots are of?

I'm guessing they are of three different types of distortion. But which 3?

[Pano]

I see a noise plot that tracks THD pretty closely even with a DAC->ADC loop back on my system. So I'm not sure what it means.

Yes, be careful not to overdrive!

[wintermute]

Speaker doctor, I realised after I posted that it wasn't obvious so edited and added the legend it is in the images but you really have to look closely! Note also that those measurements were done as swept sine with a starting frequency of 100Hz. Look at the noise plot (first pic) below 100Hz!!

Pano, It could be that the THD measurement is THD + noise, and if the non noise component of the THD is low enough in your loopback that the noise may be the dominant factor??

Tony.

[Pano]

I guess it could be. But looking at the same card loopback in ARTA, the noise floor is very low, like -120dB. So I don't know. ???

[speakerdoctor]

Originally Posted by wintermute

Speaker doctor, I realised after I posted that it wasn't obvious so edited and added the legend it is in the images but you really have to look closely!
Tony.

I see some text just above the impulse response plot. Did you add that yourself? If so, how?
I've been somewhat frustrated with my inability to easily add text to images prior to saving as image files.

[speakerdoctor]

Originally Posted by speakerdoctor

I see some text just above the impulse response plot. Did you add that yourself? If so, how?
I've been somewhat frustrated with my inability to easily add text to images prior to saving as image files.

Never mind answering that. I figured out how to do exactly what you did.