Multitone or IMD potential?

[ErinH]

Bill,
I think everyone in audio agrees that while HD plots help you learn more about a driver, it doesn't do as good a job as really illuminating trouble areas regarding distortion as much as multitone or IMD testing does.

I realize that you almost have to have software to really pull a measurement like this off in order to set a fixed tone and a sweep range for IMD or set tones for multitone testing, but I was wondering if this is something you had considered doing. Given the way your software works, I was thinking that maybe there is a way to provide test tracks that have multiple tones in them, in spaces? Maybe something like a track with 74, 79, 83, 87, 91hz altogether. Further test tracks with higher frequency content could be used. The good thing is that if you have 5 or 6 tracks, the data always remains constant because those tracks and the tones within them are always constant. One could play the multitone track and use the standard FR window to collect the data and see just how the distortion components attribute the makeup of the driver's output.
I know you know exactly what I'm talking about and to a MUUUUUUUCH better degree since Praxis actually had the capability to do this (I used Praxis and loved the features, but OM is so much simpler which may be it's downfall in this kind of testing's regard) so forgive me if I'm overreaching but I thought it couldn't hurt to toss it out there.

Something like this (borrowed from Mark K's site):






Truth be told, if there were a way to be able to extract more non-linear distortion data from test drivers, I'd pretty much have no reason to keep using the Klippel for my purposes. I love OM for it's ease and if there were one thing I'd like to be able to do with it, this topic would be it for me.
Between OM and DATs, I'm pretty much set. I realize there are other packages but when it boils down to time, these 2 products take the cake for me. I've been through a LOT of test gear over the past couple years and can't beat the simplicity of OM, even with the tradeoffs given.
I actually hope to use these two products on my website (medleysmusings.com; shameless plug) after I get it off the ground a bit. Maybe you guys wouldn't mind me using your logo on the site.

Thanks,
Erin

[bwaslo]

Hi Erin,

You could always just play a set of tones (from a CD maybe? Praxis could be used to generate the wav files even in "demo/free" mode) into a speaker and use OM in the FFT --on the SPL tabpage-- to show the spectrum like you show.

There is a way to show odd-order IM via a sweep, like is done for HD, but it's not a walk in the park to program or to operate, and besides no one would know what it meant. (Most don't know what HD really means, either, for that matter. They think it will show how something will sound, while usually it just shows when you are getting past the volume capability limits of a speaker when compared to an HD measured at lower level).

[ErinH]

that's a good idea, Bill!

I downloaded a tone generator program a while back and used it to generate multi-tones. I went outside to the garage to give it a rough shot and I'm not sure exactly how well it will work, but I'll have to give it a go when I get the full test set up going again. I'll post back whenever I have a chance to do that.