Zaph's distortion measurements

[Dennis H]

Zaph has updated his page with distortion tests of tweeters and 6.5" woofers. He figured out how to set the scale on his SoundEasy distortion sweeps so you can see K 2-5 now. Personally, I find these kind of sweeps very helpful. SL and Mark's tests are great but they are only at a few frequencies and can hide a lot of sins. Zaph is mounting them on an IB and can sweep well above and below any reasonable XO so you can really see what's going on in that region.

A surprise to me was how well the Vifa XG18 performed in the midrange. It looks like a very serious candidate for any 3-way system that relieves it of bass duties.

http://www.zaphaudio.com/

[Mark K]

I've been curious about that Vifa as well. It does not look to be a good performer in the excursion limited frequencies below 80 Hz, but does have very good numbers above. Still, I don't want to fork over ~100 to test one 8O

My measurements generally parallel Zaph's although there are some differences. I realize that it seems more "complete" to do these sweeps. The problem is that they look only at harmonic distortion. IM distortion is in general a better overall marker of distortion. (A gross oversimplification, but generally true.) So what you gain in terms of a continuous sweep you lose in not being able to assess IM and distortion product number.

You can actually do IM sweeps by tracking a specific IM product and sweeping. I've been fooling around with this and, beleive or not, John Risch's nonlinear distortion tests, but I'm not really ready to post anything yet.

[capslock]

The Vifa seems to have a problem with the surround at high excursion, strange as it may sound (double roll shold be better but isn't really). Does John Krutke state the absolute SPL anywhere? 40 to 50 dB midrange separation seem too good to be true for average drivers...

[Dennis H]

He says 0dB is 98dB SPL at 1/2 meter.

[AJINFLA]

and, beleive or not, John Risch's nonlinear distortion tests

as long as this doesn't require you to put sandbags on your praxis computer, I'm looking forward to it .

Cheers,

AJ

[Tommythecat]

Mark, I thought those XG's were only 62 bucks at Madisound (am I tempting you yet? :twisted: ). And for a forum where every other design contemplates using Milleniums and Excel mids....I'm just happy some people are helping us budget restricted members :T . (As my first post, I feel obligated to suck up to someone. So thanks Jon, Mark, Dennis, Graham, and others you're made my lurking very enjoyable but now I must post)

[Dennis H]

The problem is that they look only at harmonic distortion. IM distortion is in general a better overall marker of distortion. (A gross oversimplification, but generally true.) So what you gain in terms of a continuous sweep you lose in not being able to assess IM and distortion product number.

No measurement is perfect but Zaph claims, and it makes sense to me, that a driver with high IM distortion will usually show high levels of the higher harmonics as well.

[KeithM]

There is the XG18 and the XT18 . The XTs are the 100 dollar ones. Zaph tested the XG(62 bucks).