sound practices reading club /18

Today, part 2 of Herb Reichert on his quest for an ultra-fi horn system. We are reading Casual Reactions, from sound practices issue 5. In it Herb describes the/his frenzy that the Edgar horn caused, and the ‘blue island system’ is introduced. Then deeper reasons for building a system like this are discussed. Next, an opportunity is described to integrate crossovers into multi-amp systems. After touching on the WAF problem, Herb gives an insight in how he planned to specialise his amps for his set-up. Last, Herb endorses the cheap PR-120 tweeter. The TD-124 part of the article we will cover on another occasion.

teaser quote: ‘I fully expect that the mainstream manufacturers/press coalition will soon discover what tens of thousands of Asian and European music lovers have known for almost two decades: that carefully engineered triode/horn systems will play the hell out of your records in a way that makes “recommended” audio systems seem sterile and emotionally distant.’

my take

Can’t stop Herb Reichert from covering the big picture.

And when talking about sublime architectures, I immediately have to think about the system architecture of a fine music reproduction system. And Herb really works the system architecture here. Out of the choices of putting the crossover before or after the power amps, he spots the opportunity to do more with less and put it inside the amps. Next he takes the opportunity to optimise each amp for its frequency range (remember: ‘no amp plays all 10 octaves perfectly’). But, if you take it apart (e.g. multi amp), you also have to put it back together again, so Herb pays attention to integration of the parallel choices (‘smooth tonal transition’). More system thinking is in that both the amp design and the crossover (1st order, higher order, no crossover) is informed by the speaker each has to drive.

The proposed tweeter amp has an interesting twist with the kathode follower output stage. I guess the point of that is extended high frequency output, providing low impedance drive to overcome parasitics (inductance, capacitance) in the output transformer. Checking out the 500Hz midrange amp, you can see no-coincidence similarities with Herb’s flesh and blood amp, published two issues later.

Last week I promised to discuss why the Edgarhorns have not become the mother of all horns. To quote a high-profile proponent—in those days—of the Edgar midrange horn: ‘the thing about the edgarhorn is that it was as beamy as a laser.’ Some people like this; sitting in the listening chair, with the head in the listening position; the beams lighting up their ears. But yeah: ‘the tone moves when you move,’ which turns loads of people off. So the opposite direction is to have the same sound over a large area of the room, which is liberating in allowing the freedom to enjoy the music anywhere, in any position. Later in this series we will read about how to achieve that.

I think the definite contributions that Bruce Edgar made were:

• highlighting, in comparison, the ‘peaky resonances’ and ‘serious colorations’ in even the best of the classic horns we have read about in the last few weeks;
• in the articles linked to last week, highlighting out the horrible compromises in the design parameters of said classic horns;
• showing that the classic horn texts have errors in the formulas that kept being replicated in newer texts by people who did not do the math. Bruce Edgar, being a scientist by training, did check the math and found it lacking.

practical note: the amp numbering in the text is shifted by one compared to the images (at least in my printed issue).

Also, the formulas for the time constants are just plain naive. [correction, 25-2-2016:] I have now investigated using gain stage time constants for x-over duty. The results are surpassing but clear.

ps: the bliss system makes quite a cameo in Casual Reactions in issue 6.

Now go and read the article, see you next week.