Diffuse vs. Free Field post
Stephen Paul
May not be reproduced electronically, mechanically, or by any other means without
express permission of the author. Partial reposting within =this newsgroup= is
permitted.
OK dudes and dudettes,
I asked for six, and gotta Baker's dozen concerning posting something about the
difference between diffuse field and free field omnidirectional microphones and the
applications for which they are suited.
So here goes. (Deep Breath.) First of all, as two or three of the other luminaries on
the newsgroup have already pointed out, the most obvious difference between the two
types of microphones is the frequency response on the zero axis. While I realize that
many of you may already know this, in order to make sure that the post is understood
by everyone, I may say some rather obvious things in order that some of you who are
not technically proficient will understand. So please bear with me I don't think
you're idiots, I just want to give the beginners a chance too.
Essentially, zero axis means that the sound impinging on the microphone is exactly
parallel with the diaphragm of the microphone capsule. Ninety degrees would mean of
course that the microphone diaphragm is perpendicular to the sound source. Okay now
we've gotten that crap out of the way we can move on. <g>
Now I'm going to restate what has already been stated by myself and others in order to
make this coherent. Again, forgive any repetitions or seeming idiocy on my part.
A free field microphone has a rise in the top end usually topping out at 5 or 6 dB at
20 kHz. What is a free field? Well, a free field means that there are no acoustical
returns to the microphone from any surfaces nearby. In other words a free field would
ideally be either an anechoic chamber, outdoors away from reflective walls, or in a
well treated studio with lots of damping.
A diffuse field is exactly the opposite of a free field. In other words, a diffuse
field is a relatively reflective environment such as a concert hall, a church, or in
the case of a recording studio a relatively ' live ' room, such as one with a lot of
hard surfaces which produce a rich number of what acousticians refer to as
eigentones. Now we get a little crazy here. I can just imagine some of you
wondering, "What in the hell are eigentones?" Well, these are not easy to explain or
describe. I will make an attempt clumsy though it may be.
Eigentones may be thought of as sort of the reflections between the lines so to
speak. "What in the hell does he mean by that?" If any of you have ever stood inside
of a live echo chamber you know what a weird experience it is. I have had the good
fortune of having stood in and adjusted many a live chamber. It's quite an
experience. It happens to be a very magical place, (many of you who have read my
articles over the years, or saw the interview I did with Mr. Bonzai in 1987 either in
whole, or in the Mix magazine 20th anniversary issue, where I had the honor of having
a quote from that interview be chosen as the quote of the year from 1987 along with
quotes chosen from such luminaries as George Martin, etc., know that I have a very
strong belief in magic. Not presdidigitation, but real honest to God magic. We won't
go completely into that now at least) which I believe can easily act as a doorway
between worlds.
Now before you all assume I've gone off the deep end, try and understand what I mean
by this. Uh-oh, there he goes again off on some crazy tangent, now we'll never get to
the point! It's alright I assure you, and it is essential in order to understand the
rather slippery concept of eigentones. Let's get into a bit of etymology for a
moment. (No, I do not mean the study of insects. That's entomology anyway.)
Etymology is of course the study of the roots of language. In this case let's take a
quick look at the word enchantment. Enchantment, what a beautiful word especially
when said in the original French pronunciation. Let's take a bit and look at the root
of this word. What does it contain? Well, we can definitely see it contains the word
chant. In French the word "to sing" is chanté. In Hebrew, we call the singer of the
temple a cantor. Starting to get the idea? Quite a leap from ancient Hebrew to
French isn't it? And yet it's only the tip of the iceberg. Let's continue.
What do we call the process of a magician calling up whatever he happens to be
calling up dark or light? Usually a little something called an incantation is
involved. Interesting isn't it? Incant. Hmmm. Could this have something to do with
singing? Why, I guess it must. Chanting, incanting, enchanting, cantor, chanteuse,
chanté, enchanté, enchanted, incantation and so on. I'm sure you're starting to get
the idea even though you probably have no idea where we are going with this. That's
okay, stick with me I'll take you there I promise. So. Now back to that echo
chamber. It has long been known by many of the best producers in the world, (myriads
of whom live right here in Southern California,) that when records were recorded at
certain studios which had magical chambers, you had an instant hit record. The song
almost didn't matter, the artist almost didn't matter, and the engineering almost
didn't matter. You put that chamber on the record and you have a hit! I know it
sounds crazy, but when you been around this business as long as I have nothing seems
crazy anymore.
When I was chief engineer at Larabee in West Hollywood, we had four live chambers.
They had been used on innumerable hit records. However, there was a strange thing
about the chambers. Like many others, they were absolutely, positively haunted. Not
only did I experience this for myself, but report after report from engineers,
producers, artists, and studio personnel would experience the sound of footsteps,
thumps, and other very odd noises coming from these extremely acoustically isolated
chambers. One night I remember it got so bad, that I was asked to go up into the loft
of the studio and make sure that there was no one or nothing (such as a rat, mouse or
what have you) up there running around. I'm not kidding, it was that loud and that
bad. Naturally, I searched and searched and found nothing. Well, at least nothing
one could see. There was also a chamber at Conway in Hollywood, which has since been
torn down which was one of the nicest I had ever heard. It was rather large had
completely aparallel walls, rounded corners, and a very very light coating of
varnish. Standing in that room I had the feeling that if I simply took a swan dive,
rather than hit the floor, I would wind up in some other universe. Seriously that's
how deeply I was affected by the feeling of standing in an interdimensional space.
To put this into focus, that room was loaded with extremely intense eigentones.
Beautiful eigentones, so rich and varied in harmonic structure that the sensation of
magical experience hanging in the air and interfacing with other dimensions was
completely overpowering. It seemed to me as though it was like the boundary where two
bubbles meet. When you look at atomic structure in a scanning tunneling microscope,
you realize very quickly that all the action is at the boundaries of the surface under
investigation. Boundaries. A very heavy place. The place where one substance ends
and another begins. Magic! When one understands (as much as anyone can understand)
quantum mechanics, it becomes very evident that matter is energy out of focus. In
other words, the universe is completely vibratory. Our experience of it is completely
based on vibrations. The ear has a dynamic range of nine octaves, representing the
limits of its vibratory capabilities. The eye sees all the colors of the rainbow
ranging from roughly a wavelength of 700 nm at the low end to about 350 nm at the top
end. 700 nm borders on infrared, 350 nm borders on ultraviolet. This translates into
a dynamic range of about one octave!
The atomic clock made by Hewlett-Packard, uses a small Helmholtz resonator with a
speck of cesium 133, a radioactive element whose atoms vibrate at approximately 9
GHz. This gives the atomic clock a resolution of approximately gaining or losing one
minute every 3000 years. Compare that with the 32 kilohertz quartz crystal in the
average electronic watch! You can readily see the difference in resolution. If all
of the atomic particles in the universe stopped vibrating, consciousness, reality, and
the universe itself would simply cease to exist. Thus, matter is energy out of
focus! Okay, onward.
So here we are in our concert hall and we wish to record an orchestra from a fair
distance, in order to balance the direct pickup of the orchestra against the
eigentones of the reflective concert hall. In a case like this we normally would wish
to have a free field microphone. Why? Because of the law of inverse squares. The
law of inverse squares states the following: high frequency response falls off as the
square of the distance increases from the sound source. In order to understand why
this happens think of air as what it is, a compressible fluid. Fluids have several
properties in common with air. One of those properties is viscosity. Another of
those properties is the way waves propagate through fluid mediums. The way physicists
resolve these differences is by using the comparisons between these various mediums in
order to understand the behavior of one through the behavior of another. Thus we can
understand more about how air functions by observing a fluid such as water.
Because of the law of inverse squares, the further we are from a sound source the more
high frequencies roll off due to frictional forces in the air. Friction arises as the
molecules of air literally rub against each other, thereby creating heat, which
dissipates the lower power high frequency waves first. They're dissipated in the form
of heat just like any other frictional force. Physicists call this activity adiabatic
heating. Adiabatic heating simply means that as the viscous property of air causes
friction, sound waves in the open air are free to heat up and cool down as the air is
rarefied and compressed by the succeeding swells and troughs which make up sound. The
opposite of adiabatic activity is called isothermal activity. Isothermal activity
occurs when compression takes place within a material which tends to act as a heat
sink like brass. Thus, in the capillaries of a microphone capsule there is a
combination of isothermal activity at the edges of the capillary walls where the air
tends to stick a bit, and adiabatic activity tends to occur more in the center of the
capillary where the air tends to flow a bit more freely. How freely depends on the
diameter of the capillary vs. the viscosity of the air. Wow! As I once said in one of
my articles, it's a good idea to follow the example of Hansel and Gretel and leave a
trail of breadcrumbs as we go down this crazy path.
So we can see because of the high frequency rolloff, due to friction, that a high
frequency rise in the microphone is desirable when placed at a distance from the sound
source. However, we run into a rather complex problem. This problem is exactly what
gave birth to the original idea of the venerated Neumann M-50 microphone. Here's the
problem in a nutshell. In nature because of the law of inverse squares, reverberation
rarely has frequencies above 5 kHz, and more often than not acoustically correct
spaces for orchestras etc. are treated so that high frequency reflections tend to be
even further damped then they would be by air friction. Therefore, what we really
wish in order to resolve the room correctly is a diffuse field microphone so that the
reflections don't sound unnatural. Unfortunately, this would result in rather a muddy
sounding recording of the orchestra even though it would avoid the rather hollow sound
of exaggerating the high frequency response of the reflections in the concert hall.
See the problem? The M-50 addressed this problem by the use of the now famous Perspex
(or what we now might call acrylic) 52 mm or so sphere surrounding the capsule. How
does this help? Well, it's an interesting thing. In the large dual diaphragm
condenser microphones, there is an acoustic labyrinth in all of the dual backplate
designs which act as low pass filters as well as delay lines through the capsule. The
reason has to do with the driving force of a cardioid style microphone, which is a
vector, or what is commonly known as a gradient or pressure gradient action. Very
simply stated it is the difference in air pressure between the front of the capsule
and the rear of the capsule which provides the driving force of the diaphragm. In an
omnidirectional microphone (otherwise jokingly referred to by us capsule designers as
fast acting barometers) the driving force is simply pressure. In a large diaphragm
microphone, the actual physical size of the capsule starts to interfere with the
wavelength of sound impinging on it, as the wavelength approaches the square of the
radius of the diaphragm. Think of it as if you're standing outside on a cloudy day.
Notice that your shadow has soft edges. This is the result of light rays being
diffused and refracted or bent around your body, because the cloud cover has diffused
and softened the light from the sun, spreading out the source of light. This is
analogous to the effect of lower frequency wavelengths. On a sunny day when your
shadow has sharp edges, it's because the light ceases to bend around your body,
because the source is no longer as diffuse. This effect is analogous to the higher
frequencies. (Actually, it's more the resulting appearance that's analogous, as
opposed to the reason for the result. I'm simply using it to illustrate the effects
of low-frequency diffraction, vs. high frequency shadowing.)
The same thing happens with sound. Waves which are large enough to diffuse or refract
around the edge of the capsule create a gradient or pressure difference between the
front and rear. Waves however, which are small enough to be stopped or shadowed by
the capsule, will start to exhibit a much narrower pickup pattern, and, for the
sharper of you out there, if the high frequencies did not come to a stop at the
diaphragm, above a certain frequency they would otherwise roll off. In order to fix
this problem and make a cardioid pattern consistent as possible through the audio
range, the labyrinth is designed to cut off frequencies above the transition frequency
at which this happens. This causes the transducer to transition from a cardioid to an
omnidirectional pattern above the transition frequency, thus assuring a more even off
axis pickup pattern as the frequencies rise. There are other reasons for the delay
line but these are not relevant to the present discussion.
In the M-50, exactly the opposite effect is achieved by the sphere. In other words
the microphone is omnidirectional at lower frequencies, but at higher frequencies as
we move around the ball, the rolloff starts to approach the curve of a diffuse field
microphone. This ensures a clearer recording of the orchestra at a distance, while
taming the tendency to exaggerate the high frequency content of the reflecting
eigentones impinging on the microphone from the walls, the ceiling, and the corners of
the hall. Well, we learn something every day!
So what do we do if we don't have the wealth of Solomon and a whole bunch of M-50s to
record with? Well, we can take a microphone which has a free field type response, and
angle it until we get a nice compromise between a clean recording of the sound source,
and a reasonable representation of the space in which we're recording.
So where does this leave a diffuse field microphone? Well, let's say we're in a
studio that is a particularly live one. In this case, a diffuse field microphone
would be the right solution. The reason? Because, in this case we can move the
microphone closer to the sound source, and because the microphone is flat on axis it
will roll off naturally as sound waves impinge at increasing angles to the diaphragm.
This makes it possible to get a reasonable sound image and still take advantage of a
nice live room. Of course, if you can afford an M-50, hell, go for it!<g> Whew! This
post took the spank out of me, that's for damn sure. Damn, I'm exhausted how about
you? Blech.
Anyway, I hope that kind of explains why we would choose a diffuse field mike over a
free field one, under certain circumstances, and why we would really hunger after and
drool over and kill for an M-50!
Remember, no matter what Lexicon or anyone else does, short of a convolver, and even
considering a convolver, the best echo in the world is the Real Thing. In my humble
opinion anyway... Nothing on this earth can come close to the real thing, especially a
bunch of shift registers, some taps, some filters, and endless fooling around with
someone else's idea of an algorithm that's supposed to replicate nature. That's about
all I have to say on this subject, I hope it was enlightening, because it was
certainly exhausting, hee hee. What the hell am I laughing at, I'm ready to fall
over! I think I will, and besides it's almost time for Stargate. It's what I live
for!
Well it's been nice chattin' with ya, keep a tight... oops! Gotta watch that Zap
comic stuff! It could really get me into trouble one of these days, Har! KNUTZ
signing off:
Later folks...
--
SP
"The Quest for Truth is never lost... only sued or hounded out of existence..."
-SP
Harvey Gerst
>Stephen Paul <sp...@primenet.com> wrote:
>? 1999 Stephen Paul
>chant. In French the word "to sing" is chante. In Hebrew, we call the singer of the
>temple a cantor. Starting to get the idea? Quite a leap from ancient Hebrew to
>French isn't it? And yet it's only the tip of the iceberg. Let's continue.
>
>What do we call the process of a magician calling up whatever he happens to be
>calling up dark or light? Usually a little something called an incantation is
>involved. Interesting isn't it? Incant. Hmmm. Could this have something to do with
>singing? Why, I guess it must. Chanting, incanting, enchanting, cantor, chanteuse,
>chante, enchante, enchanted, incantation and so on. I'm sure you're starting to get
Stephen Paul
Harvey Gerst wrote:
>
> So, would an AKG C3000 be a good general use microphone for vocals or guitar?
>
You're kidding, right?
Say, now that I think of it, is there something you don't want to tell
me about the CD? Something happen to it? I haven't heard or seen a word
from you about it since you called...
Just wondering...
David Josephson
very informative post from Stephen that tells lots of good stories and
clears up a lot of confusion -- but unfortunately there are some areas
where, um, let's say his and my understanding of things differ. I'll
try to make it short, and hope that no one takes offense ... and if
someone has better ideas, I hope they post them.
Inverse square only applies to amplitude -- the loss in HF with distance
is due to higher transmission loss of the air particles at high frequencies.
A freefield mic is intended to have a _flat_ response on-axis, for
measuring sounds in a free (anechoic) field. A diffuse field mic is the
one with the high frequency boost, and initially was intended for taking
a spatial average of the sounds in a diffuse (reverberant) field. To
do this properly you actually need to rotate the mic around the surface
of a sphere, averaging the sound received over the whole measurement.
A typical freefield mic is the B&K 4133, a typical diffuse field mic is
the B&K 4134 -- these are instrumentation mics, which can also work
very well for music.
If you want to use the mic up close, and want a flat response, you use a
freefield mic. If it's at a distance, and you want to compensate for the
HF loss *or* just add 6 dB of high end, you use a diffuse field mic. But
as always, this is music and not measurement, and you need to make the
determination based on what you hear, not some formula.
Most omni mics sold for music are actually a compromise between free
field and diffuse -- not because they are intended to be, but because when
you use a plastic diaphragm of 1/2 to 3/4", about the best you can do is
+3 or so at 12k and -2 or so at 20k.
--
David Josephson / Josephson Engineering / San Jose CA / da...@josephson.com
Harvey Gerst
>
>
>Harvey Gerst wrote:
>>
>> So, would an AKG C3000 be a good general use microphone for vocals or guitar?
>>
>>You're kidding, right?
Yup, I couldn't resist. <g>
>Say, now that I think of it, is there something you don't want to tell
>me about the CD? Something happen to it? I haven't heard or seen a word
>from you about it since you called...
>
>Just wondering...
>SP
Stephen,
If you've been following the r.a.p. thread, I'm trying to get the new 7 disc set
out, so I haven't had too much chance to relisten to it and actually post a
review of your new album.
Do I like it? Well, I liked it enough to call you long distance and talk your
ear off for two solid hours, telling you personally how great I thought the
album was!! <g> Now that I just sent out the first 100 sets, I can breath
easier and get around to some decent postings rather than having to constantly
apologize for this thing being about 4 months late. "The Awakening" is a killer
album. Great music, great musicianship. That's the bottom line.
Harvey Gerst
Indian Trail Recording Studio
http://ITRstudio.com/
Stephen Paul
> Now here I am in a dilemma. We have a highly entertaining and mostly
> very informative post from Stephen that tells lots of good stories and
> clears up a lot of confusion -- but unfortunately there are some areas
> where, um, let's say his and my understanding of things differ. I'll
> try to make it short, and hope that no one takes offense ... and if
> someone has better ideas, I hope they post them.
>
> Inverse square only applies to amplitude -- the loss in HF with distance
> is due to higher transmission loss of the air particles at high frequencies.
>
David:
It happens that according to all sources I have, that inverse squares also applies to
the frictional loss computation for high frequencies as well, though there are
additional calculations to separate that area from amplitude. You are correct in that
it naturally also applies to amplitude in general, but I wanted to not overcomplicate
the post with too much technical confusion... If you like however, (though I'm still
living outof boxes right now) I will find one or two sources, (one of them an old book
by B&K) giving the exact computations for the high end falloff due to distance, which
includes the inverse square law.
> A freefield mic is intended to have a _flat_ response on-axis, for
> measuring sounds in a free (anechoic) field. A diffuse field mic is the
> one with the high frequency boost, and initially was intended for taking
> a spatial average of the sounds in a diffuse (reverberant) field. To
> do this properly you actually need to rotate the mic around the surface
> of a sphere, averaging the sound received over the whole measurement.
> A typical freefield mic is the B&K 4133, a typical diffuse field mic is
> the B&K 4134 -- these are instrumentation mics, which can also work
> very well for music.
This is also correct, and I never rechecked the post to make certain my nomenclature
was correct, as I slapped it together in too much of a hurry... I stand corrected
here, you simply need to read free-field where I said diffuse etc... and that goes for
the earlier mention of these...
I had meant to go over the thing with my search and replace function, (if I thought
they were backwards,) but it was late for me, I was very tired, and I used the 4033
and 4 many times in the past for calibrating, and am aware of this. (Not to mention
for recording Rosmini!) It does get confusing, and I will repost with the reversed
nomenclature in order to correct the misunderstanding. Thanks for pointing that out,
as I have often said, I am not infallible, nor a god, and should know better than to
post anything quickly in the state I'm in right now. (Sick as a dog<g>.) This is
precisely why I have taken so long over the 87 post, as I can't afford to let
something like this go by there.
If I learned one thing from my late, great friend Deane Jensen, it was to always
=double check anything= I was going to publish, and I violated that rule here, and
have been quite rightly corrected. Glad you're here, and I'm sure everyone else is
too... or this may have gone past for at least a week or so before I noticed it. I had
intended to check it over, but I really should have before posting, as this has
-always- been damnably confusing!<g> Sorry if I added to it. I even have pictures of
B&Ks diffuse room and panels etc. of the time, so I really should have remembered to
double check.
Gonna take a week off and rest and be very exact on every detail in the future, rest
assured. I guess that's all I can say, except that I do endeavor to be accurate, and
to my knowledge, rereading the post, everything else is.
To anyone whom I may have confused with this, I apologize, and will rectify the error.
> Most omni mics sold for music are actually a compromise between free
> field and diffuse -- not because they are intended to be, but because when
> you use a plastic diaphragm of 1/2 to 3/4", about the best you can do is
> +3 or so at 12k and -2 or so at 20k.
>
Actually, though, the 53s were most definitely diffuse-field mikes. They use a
resonaator in the backplate to achieve the correct rise in the top that qualifies them
as full-tilt (no pun intended) flat at 90 degree mikes. (Even when we've replaced the
aluminum with 1 micron plastic.) Many don't know that Neumann also made their own
measurement mikes. Strange looking things they were too... I think they were MM
something-or-others... kinda looked like giraffes.
Guess if I could have I shoulda stuck to playing music... <rueful grin>
Stephen Paul
> Stephen Paul <sp...@primenet.com> wrote:
>
> >
> >
> >Harvey Gerst wrote:
> >>
> >> So, would an AKG C3000 be a good general use microphone for vocals or guitar?
> >>
> >>You're kidding, right?
>
> Yup, I couldn't resist. <g>
>
> >Say, now that I think of it, is there something you don't want to tell
> >me about the CD? Something happen to it? I haven't heard or seen a word
> >from you about it since you called...
> >
> >Just wondering...
> >SP
>
> Stephen,
>
> If you've been following the r.a.p. thread, I'm trying to get the new 7 disc set
> out, so I haven't had too much chance to relisten to it and actually post a
> review of your new album.
>
> Do I like it? Well, I liked it enough to call you long distance and talk your
> ear off for two solid hours, telling you personally how great I thought the
> album was!! <g> Now that I just sent out the first 100 sets, I can breath
> easier and get around to some decent postings rather than having to constantly
> apologize for this thing being about 4 months late. "The Awakening" is a killer
> album. Great music, great musicianship. That's the bottom line.
>
> Harvey Gerst
> Indian Trail Recording Studio
> http://ITRstudio.com/
Thanks Harvey...
I was just concerned because in the last batch I made I had one or two pieces of bad
media that crapped after a few plays... wanted to make sure yours wasn't one of 'em...
Kodak since discontinued those, and now I guess I know why...
j.taylor
I knew there was some reason I keep hangin' around this group.
..besides my crappy recording chops-
ya learn something weird every day.....
the action's on the boundaries, eh????
take it out there, people.......
Merci Stephen
Will Hunt
David Josephson
>> A typical freefield mic is the B&K 4133, a typical diffuse field mic is
>> the B&K 4134 -- these are instrumentation mics, which can also work
>> very well for music.
>This is also correct, and I never rechecked the post to make certain my nomenclature
>was correct, as I slapped it together in too much of a hurry... I stand corrected
>here, you simply need to read free-field where I said diffuse etc... and that goes for
>the earlier mention of these...
>I had meant to go over the thing with my search and replace function, (if I thought
>they were backwards,) but it was late for me, I was very tired, and I used the 4033
>and 4 many times in the past for calibrating, and am aware of this. (Not to mention
Careful there, friend -- 4033 and 4034 are little DPA mics; 4133 and 4134
are the real B&K stuff (which they are in the process of discontinuing,
claiming that their new welded steel-alloy diaphragms are better).
>as I have often said, I am not infallible, nor a god, and should know better than to
>post anything quickly in the state I'm in right now. (Sick as a dog<g>.) This is
>precisely why I have taken so long over the 87 post, as I can't afford to let
>something like this go by there.
Stephen, as long as this medium remains two-way, we can correct and advise
each other and the truth will out... we all learn that way. Not to worry.
>Actually, though, the 53s were most definitely diffuse-field mikes. They use a
>resonaator in the backplate to achieve the correct rise in the top that qualifies them
>as full-tilt (no pun intended) flat at 90 degree mikes. (Even when we've replaced the
>aluminum with 1 micron plastic.) Many don't know that Neumann also made their own
>measurement mikes. Strange looking things they were too... I think they were MM
>something-or-others... kinda looked like giraffes.
Correct again. Lots of the *early* omni's were diffuse field, and a lot of
the old time Tonmeisters still prefer them, because nearly all of their
use *was* in the diffuse field (i. e. more than a couple wavelengths from
the sound source). The MM 1, MM 2 etc measurement mics sort of look like
today's Gefell measurement mic capsules on a two foot stalk attached to
the top of a Neumann bottle mic.
>"The Quest for Truth is never lost... only sued or hounded out of existence..."
That's it. Hoping this still counts for quest rather than hounding,
Cheers,
Stephen Paul
David Josephson wrote:
>Careful there, friend -- 4033 and 4034 are little DPA mics; 4133 and 4134
>are the real B&K stuff (which they are in the process of discontinuing,
>claiming that their new welded steel-alloy diaphragms are better).
Well, there ya go... It was nearly 15 years ago, and I have all my
perdonal books in boxesd, and the ol' memory is slippin' fast. Yes,
these were the nickel 1/4" dudes with the rectangular tube cathode
follower amps in 'em, and of course the 40xx series are them electret
'studio' things... so once again, I'm gettin' outta here for a while so
I can recuperate...
I didn't want to mention this, but part of my editing problem with
exactly this kinga thing is that I'm also fighting a cystoid edema in my
left retina, and stuff is getting by me that I just don't see well
wnough to edit. In case you haven't noticed my normally punctilious
spelling has pretty much gone to hell with my memory for exactitude, and
I can barely see the spell xhecker so the hell with thsat thing!
Also, I thought I'd caught the M-50 ball diameter error, (it's about
42mm not 52mm) but I guess thast got by me too. Anyway, I'm outta
here!!!! Can't see worth a samn this morning, and I'm going to go back
to bed...
And to think this eye was 20/10 once!
I will write back all who emailed, never gear, but I'M GONNA DICTATE
THAT to Tony... my eye is a lot worse than it was just a few days ago,
and it's time to quit ;ooking at computer screens!
That's all folks! And if my spelling sucks, no this is not a rib, just
ignore it, hopefully dome rest'll fix me up there...