Using REW for sub distortion meaurements

[Chrisbee]

Hi

I've used John M's advice to take distortion measurements at stepped frequencies and output levels using REW's "Frequency follows cursor" while leaving the distortion and frequency boxes open.

The problem is that with rising levels the SPLs become very serious indeed because they go on for so long!

I wait for the distortion measurement to settle. Then average the max and min in my head. Then write down the measurements longhand against a simple form showing F, dB & %. Taking measurements much above 100dB takes far more nerve than I can bring to bear for the time it takes to get each new figure!

I doubt the drivers like being subjected to so much abuse. The voice coils must be heating up from running continuously at these low frequencies at such high levels. I'm not sure the house likes it much either and I know my wife doesn't.

Wouldn't it be nice to be able to measure harmonic distortion automatically (on the fly) using the REW frequency sweep?

[JohnM]

Chris,

Good news and bad news. The good news is harmonic distortion measurement via the sweep is on the features list, though don't know when I'll get to it. The bad news is there is a bug in the SPL meter display code which means the 3rd harmonic distortion is not being displayed (always shows <0.01%). I've fixed it for the next release.

[Chrisbee]

JohnM wrote:

Chris,

Good news and bad news. The good news is harmonic distortion measurement via the sweep is on the features list, though don't know when I'll get to it. The bad news is there is a bug in the SPL meter display code which means the 3rd harmonic distortion is not being displayed (always shows <0.01%). I've fixed it for the next release.

JohnM

Thankyou for taking my post so seriously. It was more of a wish than an expectation.

I noted the 3rd harmonic figure didn't move but had assumed that since my 2nd harmonic reading were so low that 3rd didn't even register. Had I pushed my levels above 105dB(C) I might have noticed its absence.

It would be nice to be able to produce distortion graphs like Ilkka's in only a few brief seconds. It would add another layer of sophistication to our discussions about real-world subwoofer performance. And lead to an increase in IB building and further experimentation.

I hope you realise how much the AV community appreciates your excellent work on REW?

Regards
Chris

[terry j]

Chrisbee wrote:

JohnM


I hope you realise how much the AV community appreciates your excellent work on REW?

Regards
Chris

Hear hear!