audio-talk

Some nice stuff here-

https://josephcrowe.com

This is interesting

https://josephcrowe.com/blogs/news/the- ... distortion

Ha ! Take that, Earl Geddes.
That is properly interesting.
Must find some time to have a closer look through this site.

Intermodulation is an "interesting" number, but I have serious doubts about its audibility - at least in how it applies to speakers. Why? Because intermodulation (sum and difference tones) are very much a part of live music. Two trumpets, a brass section, massed strings, voices, a woodwind section, all cause "serious" intermodulation - it is a desired trait among professional musicians in acoustic venues. It helps them tune "on the fly" and create the colors intended by the composers and musicians.
I suppose that one could argue about the audible effects of intermodulations at 4Khz, until we examine the amount of acoustic power through the spectrum and see that this area consists practically only of overtones with respective far lower energy levels.
If we were to want to measure the effects of intermodulation distortion, we would have to use typical frequencies found in live music. That has its own set of issues.
There is a great book on tuning and intermodulation "A Study of Musical Intonation" by Chris Leuba - retired/deceased french horn player with the Chicago Symphony Orchestra (if you are interested, PM me). He documented that in a properly tuned major chord, the intermodulation products are ALL frequencies belonging to that chord, there is no dissonance. A minor chord however, ALWAYS creates dissonance and is designed into the experience by the composer. This fact would certainly make the effects of intermodulation very dynamic and not static - depending on the musical context. Mr. Crowes claim of his measured distortion relating to his listening experience is therefore in my view, pure bullshit. Perhaps there is another "problem" that is related to amplifiers with intermodulation artifacts above a certain level, but that would be subject to more research...

Because intermodulation (sum and difference tones) are very much a part of live music. Two trumpets, a brass section, massed strings, voices, a woodwind section, all cause "serious" intermodulation

How? Where is the non linear mixing in the case of live music?

Even if you say the ear or microphone is the source of the intermod, then doing it twice by repeating the process is not equivalent.

I feel you may be conflicting the wanted dissonance created by the combination of musical intervals and the intermodulation created by the non linear mixing in the reproductive chain,

He documented that in a properly tuned major chord

I guess that would require a non tempered scale then.

+ even a single instrument will suffer if intermodulation is applied during reproduction. There's a finely-tuned balance of fundamental and harmonic content in any instrument ; adding extra tones around the 'correct' ones can only degrade the purity of the sound.

Joseph is actually called Troy. If things go according to plan I will eventually have some speakers based around his big ES290 biradial horns (which were inspired by the Yuichi biradials). I may also make some of the mid bass horns that he has recently posted about. I think he is currently the most interesting horn maker out there. I’m genuinely excited by the prospect of owning some of his horns.

My view on the IM article is that his argument is far too narrowly formed and hence his conclusions are somewhat suspect and subject to variability under testing i.e. different person performing the tests is likely to get different results - I would even suggest that if he did the test again that he would get different results... Why do I think this? Because he isn't measuring speaker IM - he is measuring system IM and its not just changing the amplifier that produces changes at this level - changing the type of speaker cables can have a similar effect - changing the length of the speaker cables from - say 1m cables to 10 m cables can have a similar effect - changing the room temperature from under 5 degrees C to over 25 degrees C can have a similar effect - I have measured all these results when I was commercially producing amplifiers - so, to me, his conclusion is down in the experimental noise caused by system and environmental changes...

So its interesting and informative and strengthens his subjective judgement (in this case where it aligns with his personal preferences) but its not scientifically or engineeringly conclusive...

Its a bit like the Korf site for vinyl playback - interesting, informative, worthwhile and should be read and taken account of but seldom fully conclusive by itself.

Another variable to take into account when doing a subjective evaluation whilst making these system changes is how the system IM interacts with the ear and brain hearing system IM...

Having said that its a great site to read and its great to see someone making these products, producing these measurements and publishing them with his commentary - more strength to his elbow!

James

So its interesting and informative and strengthens his subjective judgement (in this case where it aligns with his personal preferences) but its not scientifically or engineeringly conclusive...

I take your point about the results being open to question. I did wonder if the output impedance of the amps was having an effect as there does seem to be some correlation (a bit).

Well.. I think most well implemented single ended amplifiers sound more lifelike and real than any other type of amplifier, it is no surprise to me that the intermodulation is lower with a good one


And my feeling is its intermodulation that starts removing the realness of the sound.

Low levels of 2nd harmonic are nothing like as damaging to the sound in my view

But as ever opinion varies.
But I think it's actually a fact that most of the experts miss.

Yes.
Ps. the woodworking is really nice. I enjoyed watching the time-lapse of the CNC machine making the 1200Hz bi-radial.

Well.. I think most well implemented single ended amplifiers sound more lifelike and real than any other type of amplifier, it is no surprise to me that the intermodulation is lower with a good one

Well, that was measuring the amp and speaker as a system. In general solid state amps will have lower levels of intermod than a typical SET in simple amp measurements. Intermodulation is just the result on a non linear response, its a static measurement just like THD. Where intermod can reveal problems in solid state amps is if they have a limited gain bandwidth product, so the distortion rises at high frequency as the loop gain falls. A 60Hz + 7KHz test can probe an output transformers LF saturation. A 19k and 20k test can be a good measure of how "crunchy" a solid state amp is going to sound on high frequencies.

Its interesting to look at IM for a loudspeaker system as its not really possible to measure it acoustically without having to take into account the amplifier, the loudspeaker cables and the routing of the cables and in many cases mains borne interference products on the signal ground reference - all of these affect the IM reading when measuring to this level of sensitivity... and then the measurements can vary with loudness and environmental conditions such as STP as well... There are about a dozen different variables that can affect the IM reading and some of these factors vary day by day such as STP

As ever interpretation of the results is key and that means not focussing too narrowly on cause and effect... It would be easier if our hearing was a nice linear system but it is not - it relies on the brain to process the distorted detection of sound that the ear detects and for the brain to interpret that signal to give us the sensation of hearing -fortunately or not the brain can do this to a very fine grained level and hear very small differences even when much higher level signal parts are present - unfortunately this means that objective measurement often misses the point...

This in no way invalidates the work done on the site - it is informative just not definitive... pedants drool... as always...



James

I wonder if a more interesting IM test for a loudspeaker would be a surface. x = first tone swept from 20Hz to 20Hz, y = second tone also swept 20Hz to 20kHz, z - total energy outside current x and y frequency, Would need someone used to writing GPIB or some similar control language (eg not me).

And what about cancelling distortion (more or less ) using a SE tube amp and a single moving coil speaker with reversed polarity as described in this article (Why SE tube amps?)? Also explains why speaker systems with active x-overs sound generally better.

https://www.audiopax.com/e/Article.html

I can clearly hear the difference going from passive x-over horn speakers to active x-over horn speakers/OB to single driver BLH with reversed polarity. Worst is passive x-over, best the reversed polarity. But it's not always a100% clear case and depends also on the music/recording which would corroborate with what the article says as the phase cancellation cannot be 100%.