John Curl's Blowtorch preamplifier part II - Page 2887 - diyAudio
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Old 3rd November 2012, 06:38 AM   #28861
RNMarsh is offline RNMarsh  United States
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Originally Posted by Esperado View Post
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But i can assure you that my enclosure present no more colorations (and may-be less) or "distorted feeling" despite no care had be taken about those mysterious HOMs, reason of my joke about.

On the contrary, they are more "free" and "easy", gives more "air", localization is the same order of quality, with a little more space between instruments. As the Gedlee's, i use to listen to them with an angle from the axis (20° on mine).
Basses, nothing to compare, of course.
I
I would also like to buy/build/listen to your system as well. Is it available to buy or to build from plans? Thx-RNM
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Old 3rd November 2012, 06:43 AM   #28862
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No, sorry. Are they good ?
Yes, they are. The best studio monitors I ever heard. But they are different. The point is, to compare two completely different approaches that can lead to very similar results.
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Old 3rd November 2012, 10:46 AM   #28863
RNMarsh is offline RNMarsh  United States
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Who is a genius?

Marilyn vos Savant - certified by the Guiness Book of World records has the highest recorded IQ of any living person. But, never inspired a new genre in any field. Many exceptional achievers do not attain genius-level IQs. W. Shockley had an IQ well below 140. But, B.Pascal IQ was in the 180's. So, IQ is not the best indicator of genius.

Genius goes to those who produce original and exemplary accomplishments.

Interesting research on creativity -Scientific American Mind: Think Like a Genius. How exceptional intelligence and creativity arise. Nov/Dec 2012.

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Old 3rd November 2012, 11:58 AM   #28864
gpapag is offline gpapag  Greece
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Originally Posted by bcarso View Post
For example, when optical/EM phenomena propagate without an elastic medium, versus acoustical phenomena that rely upon one.
Good point. But if air is treated as an elastic medium being worked by pressure variations in it’s linear range, would things differ much or at all from optical/EM phenomena (apart from philosophical issues)?

Problem is when air is stressed in closed or semi- closed "conduits", we enter the territory of it’s local non linear behavior. Time scale of phenomena play a role there too.

(this is a question from my part: In electromagnetics, with high energy, short time bursts, does vacuum properties (eo, μο) change values locally?)

George
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Old 3rd November 2012, 12:44 PM   #28865
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I would also like to buy/build/listen to your system as well. Is it available to buy or to build from plans? Thx-RNM
It is a sad story.
The author had leaved the shop, long time ago. After a while, the bass loudspeaker was not available any more. A new guy started to redesign-it with a new loudspeaker and a new filter.
The original filter was pretty complex, with correction for response curve and flat impedance, symmetrical, big coils...The new one look to simple to be honnest :-) Too, i doubt if they continue to sort and pair the JBL drivers too...It is a sad story...

The machined plain wood big horn is available, i believe it has not changed...
There is some pairs of enclosures on the second hand market, but need to be sure it was the good version.
My version at home is unique. Active filter now.
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Old 3rd November 2012, 12:47 PM   #28866
DF96 is offline DF96  England
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I believe the vacuum is linear for EM until you get to astonishingly high energies, like the interior of collapsed stars.
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Old 3rd November 2012, 01:20 PM   #28867
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About digital active filters, how many of you use them ? And , if some, what is your comments about equalization and group delay tuning ?

I had some trouble at the begining with coherency between the transducers at hight transients... until i used the same power supply for the two ways power amps (bass+treble).
Same feeling that the stereo image stability problems with mono-blocs.
Am-i alone to prefer a unique PSU for the 2 stereo ways ?
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Old 3rd November 2012, 05:05 PM   #28868
gedlee is offline gedlee  United States
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Originally Posted by Esperado View Post
Some candid questions about those HOMs.

- About comparing with optics, are horns something else than a lens ?
Any HOM in a lens ? Something else than chromatic aberration ?
I do not think that a lens is a good comparison. Chromatic aberation is comparable to frequency response aberation, but that's about all.

Quote:
- Is the front of pressure supposed to be pseudo spherical (depending of the driver) by JMLC, reflect itself on the walls of the horn ?
Or is-it more like a wave on the water with well known diffraction phenomenas if it hits obstacles ?
The lowest mode in a waveguide is spherical, but the HOMs are not. HOMs are created when the boundaries of the device deviate from those that allow a spherical wavefront to develope. There is precisely one boundary that allows for the developement of a spherical wavefront from a flat circular source and that is the OS. The physics of wave motion will decide what the shape has to be for this to happen, not the horn designer. One cannot simply assume that a wave will follow a given boundary, the correct boundary has to be determined not specified.
Quote:

- What about the different waves lengths Vs the throat diameter ?
The radius of the throat determines the cut-in frequency of the modes. This is all discussed in detail in my papers and my book. My book is now avaialble on-line at Geddes on Audio
Quote:
Lets suppose that the sound is like some kind of photons bouncing on the walls of the horn when out of axis. (fiber comparison)
Any chance those photons to finish their course in the axis with a exponential horn ?
Sound is a wave not a particle, this analogy is not valid.
Quote:

So some sound arrive with some delay in some axes ? We can see the distortion induced by the delay and the change of level at this frequency when added with strait signal: No accident in the response curve we can measure ?

Problems with the non linearity of air with crossed waves ? Again no way to measure distortion ?
The nonlinearity of air is not an issue at reasonable SPL levels.

Quote:
There are simulation tools witch shows the pressure repartition at different frequencies VS angle. We can see effects of diffractions in space.

Why those mysterious HOMs are not measurable, i mean at least their effects ?

Did i missed something ?
I did not say that they were not measureable, I said that they were very hard to measure. I have done some tests that show some results, but its like looking for a needle in a haystack. It takes very high resolution and complex signal processing.

The question is, to me at least, what would be the point? Just to prove to people that what I have been saying is correct. I am not in any doubt. All of the theory has played out so far why would HOMs be any different? In my designs I know the HOMs are as low as they can be, hence measuring them is not going to change that. Do measurements to compare them to other designs? I'm not interested in that either. I know my designs and I've see the results form others, I am not interested the alternatives. I am not new to this, I have been studying and writing about horns and waveguides for more than 40 years now. There is not much left for me to learn. There are some things that I am doing, but as all know research takes time.

Last edited by gedlee; 3rd November 2012 at 05:14 PM.
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Old 3rd November 2012, 05:09 PM   #28869
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Originally Posted by Esperado View Post
until i used the same power supply for the two ways power amps (bass+treble).
Hi, how do you deal with the ground loops in this case? Or is it a non-issue?
Maybe the inputs of your amps are differential and you lift the shield of the cables?

Thanks
-Alex

Last edited by Alexandre; 3rd November 2012 at 05:11 PM.
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Old 3rd November 2012, 07:20 PM   #28870
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Originally Posted by Alexandre View Post
Hi, how do you deal with the ground loops in this case? Or is it a non-issue?
Maybe the inputs of your amps are differential and you lift the shield of the cables?
Where is the difference between preamp and amp on this point ? Star grounding.

I use symmetric cables, and the shields are connected only source side (no current). If asymmetrical cabling, the second signal cable carry the reference.
In amps circuits themselves, it is better to have separated ground returning to the ground point for input stages including VAS and power stages. It is well known.

I use to measure, before connecting elements, the AC leakages between them respective grounds, and chose the AC sens of oultlets measuring the less V. Toroidal transformers are not the best regarding this problem of AC leakages.
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