John Curl's Blowtorch preamplifier part III

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Speakers don't get discussed much here and drivers are not easily DIY'd. Distortion figures aren't often published. But measuring at the listening position is very informative. Who can or wants to listen nearfield?
Yes, I was thinking more purely of the driver distortions.
Making drivers is an item in my (rather large) bucket list. I even have access to a metal lathe and mill. The problem is the more I read, the more I know I'll never approach the quality of commercially made drivers.

But at least measuring drivers is easier than making them, especially with the computer power to generate and analyze audio.
Seems none here has access to an anechoic chamber.
That would help, but still you can do a lot of measurements without one.

I read somewhere way back when, an article almost certainly in Audio Amateur or Speaker Builder, a description of holding a midrange driver to the ear sideways such that when driven with a sine wave the fundamental would audibly cancel out, and one could hear the harmonics generated by the driver. This was used as a measure of quality.
 
Depends on what you are trying to measure. If you have a fundamental tone at 30 Hz and there is a room resonance at 60 Hz, it would exaggerate the second harmonic.

And not only this. Think about room higher modes
Room modes calculator calculate 3 modes rectangular room control room apps eigenmodes eigenfrequencies formula frequency standing waves room acoustic node equation - sengpielaudio Sengpiel Berlin

This makes response and amplitude of distortion components in a modal range totally messed and is prevented by windowing of impulse response to the 1st reflection, which cuts low frequencies below some 300Hz in a standard room. So, distortion of speakers can be measured only on higher frequencies, in a room, or by a near field measurement and then assemble both. Similar as if you measure frequency response split in near field measurement + windowed far field measurement.
 
So, what kind of ballpark distortion do we have on the audio arriving on the ears for a high fidelity system? -40 to -50 dB? Yet people still perceive -90dB amp distortion. Our ears are simply stunning. 🙂
What did I just write about yesterday ... different 'kinds of distortion' sound different and have different amounts of audibility. You can hear one type through a device that creates a lot of another type.
 
Speaking of distortion cancellations.......is there anything like that going on when you go from one tweeter to two on the same baffle? I know combing effect is there but is there anything that would result in a cancellation of distortion.....because it sure does seem that way.

Awhile go I blew one of my 8ohm tweeters (6.7 measured) and i tried my 4 ohm (3.9) spare tweeters and the xo shift was too drastic, so having four of the 4ohms I tried wiring two per side in series just to ‘see’.

The results of combing is evident but just enough to add dimension to the sound stage....rather nice. But the big thing is the sound is now smoother and clearer?

And the thing is these tweeters were of lesser sound quality than their predecessors (when crossed appropriately) in single use.

I did end up having to chase the phase around a bit and ended up having to turn my sub xo down from 60hz to 40hz.

Jury is still out whether or not this is a good thing?

Any ideas? Here’s a pic.
 

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I read somewhere way back when, an article almost certainly in Audio Amateur or Speaker Builder, a description of holding a midrange driver to the ear sideways such that when driven with a sine wave the fundamental would audibly cancel out, and one could hear the harmonics generated by the driver. This was used as a measure of quality.
Fundamental cancel out.
How is this possible ?
 
Nice point to point wiring, genius class and the most pure sound that you are ever going to get, nice.....(no brass, nickel, lead). Two tweeters/half travel makes for lower distortion, and maybe the new tweeters are not so bad after all ?.

Yes never thought about the half travel......good point.

I’ve been called a lot of things but genius isn’t one of them 😀

I tried soldering the same setup and it was quite dull sounding, I couldn’t figure out why and asking on another forum resulted in the typical bs or ‘it must be wrong’......wire nuts are easier than soldering anyhow!
 
A bark edge plank of sinker cypress tube amp wired ptp would be cool.

It would match the table I made from it......counted the rings and got to 475 before I went cross eyed, then it sat on the bottom of the Apalachicola river for 100+ yrs (some sank as they floated the logs down river) .....now it’s dived up and sawed into some of the most beautiful lumber I’ve ever seen.
 
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