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Old 30th March 2013, 04:40 PM   #37581
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PMA those boards were done about 30 years ago on the Schlumberger computer. That is the top part of the board, almost all the connections are on the BOTTOM side of the board.
It might also be said that these boards are HAND STUFFED ONLY with oversize resistors in many positions, compared to today. You don't want to condense it too much. Too hard to build.

Last edited by john curl; 30th March 2013 at 04:57 PM.
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Old 30th March 2013, 05:21 PM   #37582
gpapag is offline gpapag  Greece
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Interesting concept in the first Tech Review article. Makes me think of the Poynting vector in electromagnetics.
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Originally Posted by simon7000 View Post
George.
The Bruel and Kjaer sound intensity probes were a big deal when first introduced and are a great tool for acoustical speech intelligibility problems among other uses.

ES

Brad and Ed
The weakness of capturing the reality through pressure sensitive mikes, is shown by eq. (1.1). The reality is illustrated by eq.(A.1), (A.2) and (A.7). The journey starts then to become clear with Append. C,D,E,F. (appendices here, have to be read before the main article )
Capturing a scalar quantity vs. capturing a vector complex quantity. The technique with the two closely spaced mikes, brings out the phase component (Blumlein’s micing was "playing" with the idea but couldn't come close enough ).

I wonder if one miniature (MEMS) wire anemometer could be used to read instantaneous particle complex velocity , combined with a single pressure sensitive mic for reading instantaneous pressure. This would be a highly directional combination.
A step further, two such wire anemometers could do all the work by their selves. This would be a directionally flexible combination, which probably would not pose frequency limits due to inter spacing, as both uniquely read instantaneous particle complex velocity. Easy signal processing can give out any desired combination of velocity/pressure attributes.

Ed
Have you experimented yourself with sound intensity probes? If they are good in discriminating speech intelligibility problems in an acoustical space, why and how they are not good -or that good- to be used as proper (and expensive) all-around mics there?

George
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Old 30th March 2013, 05:35 PM   #37583
rsavas is offline rsavas  Canada
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Hello John & others,

Even though that you say that you do not actually do layout itself, I am sure that you either document the layout rules/guidelines prior to placement/routing and then review the layout during and after it is done. I am sure all experienced designers understand that PCB layout design is a iterative process or at least it should be. I have done many designs, more on the digital or mixed signal side where we need to know flight lengths, back annotate to a verilog sim and do worst case timing analysis, IBIS/Spice device modeling, transmission line reflections etc. This is where picoseconds matter.16 layer PCBs, controlled impedance, ECL stuff.
Low frequency analog only design functions, make life easy for an experienced layout person, compared to RF, hi-freq stuff. Don't get me wrong they all have there challenges. I am being general here.
In my mind, being a designer that does there own PCBs are simply just a more rounded designer overall. I have done some ASIC stuff too, it has its similarities.
The ole days of mylar and the royal design handoff to layout guy/group are long gone in my mind. I hated it when they would not let me layout my own designs and forced me to give it to the layout folks. It would take me more time to tell them what I wanted, than if I did it myself. I was in Toronto and layout was being done in Broomfield,Co. It did force a designer to document the layout guidelines with much more detail. What i found in my time as a designer, that many traditional layout folks where not that technical, so many times it was me teaching them design/layout principles.
The first CAD station I designed with was a Cadnetix system, I think it was Sun 4 platform, you know Unix,csh stuff.
For simple analog stuff, audio :-) I could probably get away with Eagle, for elaborate designs, multi-gig, something like Cadence Allegro or Mentor Expedition/DX Designer. I think that DX Designer was based on the original Cadnetix stuff.

Take care
Rick

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Old 30th March 2013, 05:36 PM   #37584
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The continuing frustration of the hi-end PCB designer: if it looks like eye candy, it's not optimal.
Unfortunately, eye candy is all the reviewers can see.


se
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Old 30th March 2013, 05:37 PM   #37585
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You don't want to condense it too much. Too hard to build.
For an amateur maybe. But surely not too hard to build for a PROFESSIONAL.

se
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Old 30th March 2013, 06:15 PM   #37586
gpapag is offline gpapag  Greece
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But yet you can say that they're so much more sophisticated than amateur layouts that there's little comparison. That's just a flat out insult, John.
se
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For an amateur maybe. But surely not too hard to build for a PROFESSIONAL.
se
My understanding is that “amateur” is for J.C. a conjugate to “professional” . But “professional” is not one and the same for him to a designer of High End equipment.

George
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Old 30th March 2013, 06:37 PM   #37587
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Originally Posted by john curl View Post
It might also be said that these boards are HAND STUFFED ONLY with oversize resistors in many positions, compared to today. You don't want to condense it too much. Too hard to build.
John, I don't think you wanted to give the impression that ease of stuffing has priority over performance

jan
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Old 30th March 2013, 06:46 PM   #37588
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Brad and Ed


I wonder if one miniature (MEMS) wire anemometer could be used to read instantaneous particle complex velocity , combined with a single pressure sensitive mic for reading instantaneous pressure. This would be a highly directional combination.
A step further, two such wire anemometers could do all the work by their selves. This would be a directionally flexible combination, which probably would not pose frequency limits due to inter spacing, as both uniquely read instantaneous particle complex velocity. Easy signal processing can give out any desired combination of velocity/pressure attributes.

Ed
Have you experimented yourself with sound intensity probes? If they are good in discriminating speech intelligibility problems in an acoustical space, why and how they are not good -or that good- to be used as proper (and expensive) all-around mics there?

George
Hot wire anemometers have very poor high frequency response. The used to be used for artillery detectors. Today that is a handheld instrument.

The sound intensity probes are only useful over a limited frequency range. In acoustics you can easily see an impulse response, but once you have identified problems then they are you need to know direction.

The best example I can give as to why this is not as simple as it seems is a local church. It was built with sound absorbing material on the ceiling. An "Expert" had them renovate and cover all of it with plaster to improve the organ's sound. Well speech intelligibility dropped to pretty bad (.55-.65 CIS). The organ also was too loud and not balanced.

The next crop of "Experts" said to use a highly directional loud speaker, when that didn't work then to use many distributed loudspeakers. When that didn't work to cover the back wall with fur (or some equivalent.)

It turns out the issue was not total absorption or directional control but rather that frequencies between 200 - 1000 hz were hanging around too long. The transepts of the church were not very long and about 20% of the length of the entire nave. The tops were arches. The nave had an "A" style sloped ceiling. Well when you have transepts shaped like a whistle, guess what the resonate! (See you thought I was going to say whistle ) Placing a small amount of absorption at the top of the arched ceiling on both sides solved the problem.

So not just knowing what the problem is but where it is coming from can be very difficult to determine without the proper knowledge or equipment.

OK for those of you who can't name the parts of a church a bit of explanation.

The front end of a Catholic church often has a piece of artwork with a figure on two sticks or at least the sticks. This area is raised and contains a table that has been blessed and is used as non-sacrificial altar. Since this is a holy area it is raised above the heads of the congregation. There is a rail or a screen to keep folks out of this area (Until things changed for some at least.)

Just past the edge of the sanctuary is in many churches a pulpit and a lectern. Now the pulpit can be higher as only those who have been blessed (Priest etc.) use it, The only speaking from here is religious readings or commentary. The lectern is ground level and is used by "Lay" people and is used for everything else from pray response to general announcements.

Farther out comes the seating. In a big church or Basilica the floor plan is cross shaped and the seating area perpendicular to the rest of the church is the transept. It is used in some places for the lower clergy (monks, nuns etc.) to sit. Many churches do not have transepts. This one did but very short compared to the normal cross ratios.

The main body of seating is called the Nave. Behind this is the lobby area called the Narthex. Sometimes above the Narthex is a balcony for a "Lay" choir. Other times it may be in the transepts in some churches it is in or above the sides of the Sanctuary.

In very large churches there may be side balconies along the Nave. Most of the side balconies were for the monks or nuns to sing all day long.

Now the quiz, what is a reredos?

Last edited by simon7000; 30th March 2013 at 06:51 PM.
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Old 30th March 2013, 06:53 PM   #37589
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Originally Posted by john curl View Post
PMA those boards were done about 30 years ago on the Schlumberger computer. That is the top part of the board, almost all the connections are on the BOTTOM side of the board.
It might also be said that these boards are HAND STUFFED ONLY with oversize resistors in many positions, compared to today. You don't want to condense it too much. Too hard to build.
The code date says early 1989.

Jan,

Who is it that keeps saying 741s aren't used anymore? You seem to be getting use out of one, for an image at least.

Last edited by simon7000; 30th March 2013 at 06:56 PM.
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Old 30th March 2013, 07:39 PM   #37590
gpapag is offline gpapag  Greece
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Originally Posted by simon7000 View Post
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Now the quiz, what is a reredos?
(and the rest of your illustrative description)
I smile as I can’t help but remembering Vitruvius script.

Quote:
Hot wire anemometers have very poor high frequency response. The used to be used for artillery detectors. Today that is a handheld instrument.
That’s why I wrote MEMS construction. Orders of magnitude shorter time constants possible.

Quote:
The sound intensity probes are only useful over a limited frequency range.
Agree, with the typical construction we see (mic inter-spacing issue).

Quote:
In acoustics you can easily see an impulse response, but once you have identified problems then they are you need to know direction.
This is my point in my question at the bottom Ed. Precisely this !

Proper Impulse response (time correct and proper freq response too) and phase info (direction too, plus real/imaginary components) is what I think of is needed.
What else you imply is needed for a good mic apparatus for picking-up the maximum of reality? (Yes, max pressure levels handling, S/N ratio and distortion figures are issues but only technical issues. I am asking about conceptual issues)

I have the outmost respect for people dealing with real problems in acoustics and don’t get my theorising wrong

George
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Last edited by gpapag; 30th March 2013 at 07:46 PM.
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