John Curl's Blowtorch preamplifier part II

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Where is Iverson's paper? I would like to read it. For ME, even working with the 'GD Wall of Sound system', owning K-horns and talking with Paul Klipsch for years, even Richard Heyser, and spending 1 1/2 years designing speaker systems with John Meyer, it was Barlow who first gave me the insight about speaker enclosure resonance Q.
 
Regarding getting speakers under 'control', this was one of the key elements in progressing my system quality 30 years ago, allowing my thinking on what was important to evolve. Very ordinary but quite decent bookshelf speakers, B&W DM10s, started with internal fixing of the cheap and nasty bits. Which hinted that stabilising the speaker would help, so the task then became to lock the speaker as rigidly to the structure of the house as possible, and dramatically increase its effective mass. Bass quality went up enormously, but now the speaker was highly revealing, every tiny irkiness in the sound was crystal clear - so the battle now moved to eliminating all the electronic 'grubbiness'.

Back then I didn't succeed in resolving all the electrical issues, but those every ordinary speakers were way in front of the preceding chain, in their ability to tell exactly what the quality status of the electronics side was. But when there was momentary alignment of everything that mattered, sound quality that beat everything else that I had ever heard before was there, in the room.

I wouldn't have got those moments, then, unless the work had been done to make the speakers audibly get out of the way, to a large degree - they showed me what was possible ...
 
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Frank, are you taking lessons form KBK?

Three paras above and, to me, they say absolutely NOTHING!

WHAT have you been doing for the last 30 years that makes your hi-fi listenable?

WHY do you have to keep redoing it?

WHY does everything have to be in quotes with added smileys? *

WHY do I bother? Nothing personal, but I just don't geddit, and the same message seems to be in every forum I read. For ever.
 
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Are we truly going to have to go back to the beginning with the construction of rigid bodies here as regards speaker enclosures? I'm sure not aware of much new in the way of enclosure design. Whether they are wood, stone, plastic or composites the rules stay the same. Yes we can have constrained layers but what about any of this is unknown at this point?
 
WHY does everything have to be in quotes with added smileys? *

WHY do I bother? Nothing personal, but I just don't geddit, and the same message seems to be in every forum I read. For ever.
Well, I am trying not to be too deadly serious about all this ... ( virtually not really there :)ey ...)

The geddit, for me, is that most people's thinking is in this game is a**e up - the normal approach is that one keeps worrying about adding bits of quality, fabulous or otherwise, here and everywhere - and if one keeps doing this forever and a day that, magically, at some point out will pop acceptable, or even 'special' sound.

My thinking is quite orthogonal to this: it is that essentially all systems are fully capable of producing quite exceptional sound, but the reason they don't do this 99.999% of the time is there are always a number of flaws holding things back, degrading or limiting the sound. So my technique is not to replace a component of quality 86% with one of 91% and hope that that does the trick, but to track down the problems and resolve them. One by one. This "way" has worked over and over again, for me, so I feel it's worth taking seriously.
 
The graph from Barlow in 1975 that taught me:
 

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Oh dear, I suppose I am getting sucked in, but ...

"but to track down the problems and resolve them"

What does that MEAN? What do you do?
OK, let's take the extremely ordinary PC, and quite decent little Dell monitor speakers I'm using to do these listening tests - I want them to work at their best, to give me a decent chance of picking up the differences that may be there ... and what I've done there.

Switched on from cold, in the morning, raw form - nothing special at all, just your typical, tiny, bedside radio sound - ho hum to the max ...

From experience I know that there are a whole series of things that are giving me that throwaway sound, so I start going through a checklist of things to try, that tell how far that sound can be improved.

First, especially for cheap gear, warmup is terrible important - from cold most of the low end equipment is pretty execrable. So, the 'test' is hammer the equipment hard - put on very aggressive music, lots of HF, as loud as you dare, say, for an hour or two. This conditions the DAC, the power supplies, speaker driver suspension, etc, for the day ... go back to normal listening after the workout, typically gives vastly improved treble, low level detail clarity; subjectively the sound is much, much bigger.

But, usually that greater 'transparency', at this point, comes with unpleasant edginess, 'harsh' recordings will drive you from the room - it's not a sound you can live with ...

This is where poor quality connections become important: if I really want to do it seriously I hardwire everything I can get to easily, if there are still issues I would pull it all to pieces and deal with all the bare metal to metal contacts. To tell me whether a particular contact is giving audible problems I play something which is hovering at the edge of being unpleasant to listen to, and reseat, refresh the connection point while playing. If there is a short term improvement in treble clarity, purity immediately after doing this then you've found a significant weakness.

Luckily, with the PC monitors I've managed to get reasonable quality replay by cleaning the obvious connections and using contact enhancer. The other obvious weakness are the pots, but they're good enough for the moment, I set them at the end of their travel to get the best out of them as is.

Then there are interference effects, cheap gear again is not brilliant. Easy to test for: use a 'challenging' recording which quickly becomes difficult to listen to because there is an irritating quality about it, and switch off all possible sources of interference that you can, one by one. And then add back possibly interfering elements, like placing a mobile phone next to the equipment. If no audible change, then the gear is good to go, or, more likely the sound is not 'transparent' enough yet to hear the effect. In the case of my PC I've reorganised all the cables, where they're plugged in, and what is switched off, disconnected when I listen more closely.

Power supplies inside gear is a biggy, older stuff is usually pretty dreadful in this regard - I've done a lot of playing with this over the years. Fortunately, newer gear seems a lot better; one can get away with what is standard more often it seems. The wall wart, plus Dell active amps are quite reasonable, the sound degrades quite gracefully when voltages are overtaxed, it's quite easy to judge a perfectly adequate max. volume setting for a particular recording.

Another little 'fudge': the plastic enclosures are shaped and have only nominal resonance; they're Blu Tacked at the corners to the solid desk top - a bass guitar solo sounds quite decent! Also, pulled off the covers - but, everyone does that ... ;)

So, I looked at: warmup behaviour, poor connections, external interference, obvious power supply failings, stabilising of speakers - as a start. That's got me a long way with the 'ratty' PC sound - at its best it easily outshines a lot of what I heard at the recent hifi show ... it gets somewhat close to being 'invisible speakers' at times - if I wanted that next step I would need to do more of the same on the inside of the enclosures.

Note, I haven't opened the boxes, or changed any circuitry so far ...
 
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To summarise, you know you have a problem when you can't hear the musical detail in a recording that you know is there, from hearing it on a "superior" system. Or, if the detail is there, but it's too unpleasant to listen to at decent listening volumes.

As far as I'm concerned, that's a major part of this audio game ...
 
In the 1960's, I started out with an AR-1 loudspeaker that was one of the first 'acoustic suspension' designs. It was a fiberglass filled wooden cabinet. I doubt that it had any extra bracing inside. Then I sold and installed custom cabinets made by Klipsch. They didn't seem to have any extra bracing inside and the thickness of the wood was not to great. Then, in 1970, I was introduced to the Grateful Dead custom cabinets that was proudly made with 15 ply Finnish birch. They were heavy, sturdy, and seemingly inflexible, but they did have a 'signature' that I still remember today. It was years after I left the Grateful Dead, and was designing my own speaker cabinets that I came across D.A. Barlow's papers at the Lon.1975 AES and noted that the Q did NOT really change with the thickness or even the hardness of the material that made the enclosure.
Some sort of 'damping layer' had to be put inside the cabinet to lower the Q, and not just some fiberglass stuffing, as I normally used.
For those of you who want to note what I learned please look at the graph that shows the response with different thicknesses of wood.
Then note the other graph that shows the advantage of dissimilar materials making a composite cabinet material.
Dave Wilson's speaker cabinets are light years ahead of 1975.
 

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It was years after I left the Grateful Dead, and was designing my own speaker cabinets that I came across D.A. Barlow's papers at the Lon.1975 AES and noted that the Q did NOT really change with the thickness or even the hardness of the material that made the enclosure.
Some sort of 'damping layer' had to be put inside the cabinet to lower the Q, and not just some fiberglass stuffing, as I normally used.

Yes, because the two perform completely different tasks. The fiberglass used inside the cabinets is to absorb sound within the cabinet. It's called dampening. Something quite different from damping, which involves adding loss to a resonant system in order to damp said resonance.

For those of you who want to note what I learned please look at the graph that shows the response with different thicknesses of wood.

Yes. For a given size panel, if you use thicker material, the panel becomes stiffer and it raises the resonant frequency. Which is a good thing as it tends to be easier to damp a higher frequency resonance than a low frequency resonance.

Then note the other graph that shows the advantage of dissimilar materials making a composite cabinet material.

It's not so much about using a dissimilar material, but rather using a lossy, elastometric material to better damp the resonance.

As I said, this is just some pretty basic physics. Didn't you already have a BA in physics by 1975?

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John I hope you enjoy your new speakers. I the end the disconnect between MSRP and BOM in the high end is not going to be resolved. I liked the guy from Raal, and I see they still show the $90,000 speakers now sporting an even more interesting "enclosure". As to the sound, demonstrated too loud in an untreated space, I could not judge (though I liked the avant guard Eastern European music they played).
 
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