Geddes on Waveguides

[jzagaja]

I agree. What about higher harmonic distortions? Can they be equally or more audible than 3nd? I'm not sensitive to 2nd but 3nd is probably what I hear from JXR6 (more than it's small ringing) - a kind of harmonic distortion CSD is useful tool here. Appended photo illustrates the problem - ca. 2V peak to peak.

[gedlee]

Originally posted by jzagaja
I agree. What about higher harmonic distortions? Can they be equally or more audible than 3nd? I'm not sensitive to 2nd but 3nd is probably what I hear from JXR6 (more than it's small ringing) - a kind of harmonic distortion CSD is useful tool here. Appended photo illustrates the problem - ca. 2V peak to peak.

You appear to be unaware of my work in this area - its not simple and reading the AES papers is the best way to educate yourself. To make a long story short, yes the higher harmonics are more audible, but it also depends on other factors.

[jzagaja]

I had in mind something simple - music sample and % threshold with digitally added distortions. You're referring to your Gm(f) metric so please write more how you can evaluate by this loudspeakers and amplifiers. Theory is fine as long you can use it practically.

I've got Sony CDPXA50ES AA filters spectra and time. With Mr Manger we used 3A aliasing filter which is non-symmetric and has no pre-ringing that is commonly applied these days in traditional mastering. New kind of mastering like DSD and switching amplifiers make it probably worse. So my question is have ever bothered with this kind of delicate distortion? So many people claim that analogue record has better spatial image. Same effect with 24/196 playback (see dcsltd.co.uk white papers). If Summa has good time resolution then it should be possible to examine this subject.

[jzagaja]

I shouldn't put DSD so low. The ringing is smallest achievable:

http://www.dddac.de/files/dsd_ringing.pdf

[gedlee]

Originally posted by jzagaja
I had in mind something simple - music sample and % threshold with digitally added distortions. You're referring to your Gm(f) metric so please write more how you can evaluate by this loudspeakers and amplifiers. Theory is fine as long you can use it practically.

What you suggest is what we did and we did apply it in "practice". I don't think it a good use of my time to reiterate things that have been published and are readily available from the AES. Just go to www.aes.org and order copies of my preprints. They are cheap.

[Patrick Bateman]

Originally posted by gedlee



HOM - Higher Order Mode, its a term that I coined to define waves that propagate in a waveguide that do not go down the axis, but travel by bouncing off of the walls. They are not predicted by the Horn Equation, so most people didn't even know that they existed (I was the first person to hypothesize there existance). The Waveguide Theory predicts them, and low and behold, it turns out that they are quite significant to audibility. Minimizing them yields a far better sound quality. But with "horns" its not possible to minimize them because you don't know what to do - the equations aren't rigorous enough to predict them so they are simply ignored.

So a HOM is simply a sound wave that has reflected inside the horn or waveguide, right? When using a foam plug on my waveguides, I noticed that the reproduction sounded more articulate. For example, I was able to discern words in songs that I hadn't noticed before. My hypothesis is that the reflected waves muddy the articulation due to the time difference between the initial wave and it's reflections.

Imagine a good pair of headphones, and you get the general idea. Diffraction is a bad thing kids.

[jzagaja]

Can we use burst decay (similar to CSD) for HOMs? It shows reflections more clear. Here is an example.

[gedlee]

Originally posted by Patrick Bateman


So a HOM is simply a sound wave that has reflected inside the horn or waveguide, right? When using a foam plug on my waveguides, I noticed that the reproduction sounded more articulate. For example, I was able to discern words in songs that I hadn't noticed before. My hypothesis is that the reflected waves muddy the articulation due to the time difference between the initial wave and it's reflections.

Imagine a good pair of headphones, and you get the general idea. Diffraction is a bad thing kids.

Agreed - What I noticed was how readily I could hear flaws in music that I knew very well. For instance, with the Summas it's quite clear that Van Morrison is clipping the microphone signal on a few passages of Moondance, but I never noticed it before - more than thirty years of listening to that same song.

[freddi]

makes sense -what losses vs frequency are seen with foam plug versus none?

can some old-school HF horn be viewed as adding a type of "reverb"? - how about basshorn?

[Patrick Bateman]

Originally posted by freddi
makes sense -what losses vs frequency are seen with foam plug versus none?

Everyone looks at the foam, and wonders what effect it will have on the frequency. But all the magic is in the time domain. So let me explain...

The foam simply acts as a low pass filter. If your waveguide is only 4 inches across, the effect will be pretty subtle. If your wavguide is 15" in diameter, it will be pretty dramatic. HOWEVER, it's effect on the frequency response can be UNDONE with a corresponding filter.

It's effect on the time domain is where the magic happens. Picture a sound wave going down the length of the waveguide. A great deal of energy is reflected BACK to the throat. That energy is delayed in time, and psychoacoustic research demonstrates that these timing errors are very audible.

The foam simply absorbs those reflected waves. While the primary wave is absorbed ONCE, the reflected waves are absorbed a MINIMUM of THREE times. Draw it on paper and it makes more sense.

I could sweaaaar that I posted before & after measurements of the foams effect on my Unity waveguides. But for the life of me, I can't find the post. I also posted it on a thread about my old tractrix horns, which used it, but not so extensively.

http://www.audiogroupforum.com/csfor...ad.php?t=62789

Originally posted by freddi
can some old-school HF horn be viewed as adding a type of "reverb"? - how about basshorn?

Good questions! Yes, it is something like reverb. But the HOMs have a different response than the initial wave, due to the reflections. So it's kind of like reverb, except it sucks.

As for the effect on a basshorn, psychoacoustically we are very sensitive to EARLY reflections. Late reflections, like in a basshorn, are not as obnoxious.