[John L Stewart]

The earlier post on the Collosus reminded me of my experience at IBM.

Before I became an electrical engineer I joined the service crew at IBM. That was in the Summer of 1953. At the time most data processing was done using electro-mechanical & relay logic.

The data was stored on perforated cards. IBM had the patent on electrical reading of the data on the cards. Other people were at a real disadvantage since their cards had to be read mechanically. You older guys out there probably saw lots of these over time. Later there were mark sense cards, which a user could mark with a carbon pencil. Both card types could be read directly by making an electrical contact by the sorter or whatever data processing equipment they were run thru.

Each card had 80 columns in which the holes were punched by both manual & electric punched card machines. Both numeric & alphabetical information could be stored on the card. One hole would store a decimal digit while a second hole in the appropriate place in the same column would be alpha information. End of line & other commands were also possible.

Each of these card types had its own operator for data entry (ie IBM 024). There was a corresponding set of verifying machines (ie IBM 026), again with their own operator.

The data processing equipment included sorters, collaters, tabulators, line printers (guess where LPT came from!) & so on. Arithmetic was performed by the tabulater printer combo (IBM 402 or 405) using what was known as ‘9s compliment’ computation.

None of these could be bought. The customer had to rent. Because of the patent on the electrical card reading system IBM had a captive market, a monopoly.

Not long before, Thomas J Watson, President of IBM had mused that the World would never need more than five or six computers. Thomas J had started out as a hot shot piano salesman in upper New York state, something he was very good at. But I guess his background did not prepare him for the future, much like many of us now.

The first computer if you could call it that, which I had the pleasure to work on was the IBM 602A. It was an electromechanical beast, lots of relays, cams, gears & so on. Compared to today it doesn’t seem like much but it did replace an acre of girls on mechanical calculators. It could add, subtract & multiply & sweat like hell doing simple division. But it could still get the payroll or inventory out on time provided there were no card jams.

Later the IBM 604 showed up. It was electronic & used the 6J6 as a binary flip-flop. Depending on the application there were 900 to 1500 6J6s in each 604. Each 6J6 was mounted in a plug-in assembly, complete with all the R’s & C’s required to complete the flip-flop. That helped a lot when trouble shooting since the whole assembly could be quickly changed. All computations were done in decimal. The binaries were connected in groups of four. So with some feedforward & feedback to the correct place four 6J6s ran as binary to decimal in 1-2-4-8.

Heater supply was thru a regulated PS using saturable reactors. These driven in a NFB circuit by a 6L6 (metal).

Many of these data processing machines used the 25L6 (metal) in the punch card reading circuits.

The Scopes we used were from Waterman, long gone out of business. They had a 3 inch CRT & perhaps 300 KHz bandwidth. Vertical amplifier is a pair of diff amp 6J6s connected in two stages. But they did the job, I think the IBM 604 processor if you could call it that ran only 50-100 KHz. I’ve still got my IBM voltmeter to which I later added a 1.5 volt range. Sensitivity is actually 10K ohms/volt, not bad for 1953. But it looks kind of used now!

Luckily for me I moved on after a year & half to Ferranti where some real research was being done. By then they had discovered the transistor, even though it was a surface barrier type, the SB100. But that is another story to bore all of you.

BTW, there is no test on this!

[[email protected]]

On Mar 29, 9:05*pm, John L Stewart John.L.Stewart.
wrote:
The earlier post on the Collosus reminded me of my experience at IBM.

Before I became an electrical engineer I joined the service crew at IBM.
That was in the Summer of 1953. At the time most data processing was
done using electro-mechanical & relay logic.

The data was stored on perforated cards. IBM had the patent on
electrical reading of the data on the cards. Other people were at a real
disadvantage since their cards had to be read mechanically. You older
guys out there probably saw lots of these over time. Later there were
mark sense cards, which a user could mark with a carbon pencil. Both
card types could be read directly by making an electrical contact by the
sorter or whatever data processing equipment they were run thru.

Each card had 80 columns in which the holes were punched by both manual
& electric punched card machines. Both numeric & alphabetical
information could be stored on the card. One hole would store a decimal
digit while a second hole in the appropriate place in the same column
would be alpha information. End of line & other commands were also
possible.

Each of these card types had its own operator for data entry (ie IBM
024). There was a corresponding set of verifying machines (ie IBM 026),
again with their own operator.

The data processing equipment included sorters, collaters, tabulators,
line printers (guess where LPT came from!) & so on. Arithmetic was
performed by the tabulater printer combo (IBM 402 or 405) using what was
known as ‘9s compliment’ computation.

None of these could be bought. The customer had to rent. Because of the
patent on the electrical card reading system IBM had a captive market, a
monopoly.

Not long before, Thomas J Watson, President of IBM had mused that the
World would never need more than five or six computers. Thomas J had
started out as a hot shot piano salesman in upper New York state,
something he was very good at. But I guess his background did not
prepare him for the future, much like many of us now.

The first computer if you could call it that, which I had the pleasure
to work on was the IBM 602A. It was an electromechanical beast, lots of
relays, cams, gears & so on. Compared to today it doesn’t seem like much
but it did replace an acre of girls on mechanical calculators. It could
add, subtract & multiply & sweat like hell doing simple division. But it
could still get the payroll or inventory out on time provided there were
no card jams.

Later the IBM 604 showed up. It was electronic & used the 6J6 as a
binary flip-flop. Depending on the application there were 900 to 1500
6J6s in each 604. Each 6J6 was mounted in a plug-in assembly, complete
with all the R’s & C’s required to complete the flip-flop. That helped a
lot when trouble shooting since the whole assembly could be quickly
changed. All computations were done in decimal. The binaries were
connected in groups of four. So with some feedforward & feedback to the
correct place four 6J6s ran as binary to decimal in 1-2-4-8.

Heater supply was thru a regulated PS using saturable reactors. These
driven in a NFB circuit by a 6L6 (metal).

Many of these data processing machines used the 25L6 (metal) in the
punch card reading circuits.

The Scopes we used were from Waterman, long gone out of business. They
had a 3 inch CRT & perhaps 300 KHz bandwidth. Vertical amplifier is a
pair of diff amp 6J6s connected in two stages. But they did the job, I
think the IBM 604 processor if you could call it that ran only 50-100
KHz. I’ve still got my IBM voltmeter to which I later added a 1.5 volt
range. Sensitivity is actually 10K ohms/volt, not bad for 1953. But it
looks kind of used now!

Luckily for me I moved on after a year & half to Ferranti where some
real research was being done. By then they had discovered the
transistor, even though it was a surface barrier type, the SB100. But
that is another story to bore all of you.


You can still find those Waterman scopes at hamfests pretty readily.

Both FORTRAN and Lisp owe a lot of their workings to the fact they
originally ran on these vacuum tube IBM monsters.

[Roger Jones]

On Apr 1, 9:07*pm, wrote:
On Mar 29, 9:05*pm, John L Stewart John.L.Stewart.









wrote:
The earlier post on the Collosus reminded me of my experience at IBM.

Before I became an electrical engineer I joined the service crew at IBM..
That was in the Summer of 1953. At the time most data processing was
done using electro-mechanical & relay logic.

The data was stored on perforated cards. IBM had the patent on
electrical reading of the data on the cards. Other people were at a real
disadvantage since their cards had to be read mechanically. You older
guys out there probably saw lots of these over time. Later there were
mark sense cards, which a user could mark with a carbon pencil. Both
card types could be read directly by making an electrical contact by the
sorter or whatever data processing equipment they were run thru.

Each card had 80 columns in which the holes were punched by both manual
& electric punched card machines. Both numeric & alphabetical
information could be stored on the card. One hole would store a decimal
digit while a second hole in the appropriate place in the same column
would be alpha information. End of line & other commands were also
possible.

Each of these card types had its own operator for data entry (ie IBM
024). There was a corresponding set of verifying machines (ie IBM 026),
again with their own operator.

The data processing equipment included sorters, collaters, tabulators,
line printers (guess where LPT came from!) & so on. Arithmetic was
performed by the tabulater printer combo (IBM 402 or 405) using what was
known as ‘9s compliment’ computation.

None of these could be bought. The customer had to rent. Because of the
patent on the electrical card reading system IBM had a captive market, a
monopoly.

Not long before, Thomas J Watson, President of IBM had mused that the
World would never need more than five or six computers. Thomas J had
started out as a hot shot piano salesman in upper New York state,
something he was very good at. But I guess his background did not
prepare him for the future, much like many of us now.

The first computer if you could call it that, which I had the pleasure
to work on was the IBM 602A. It was an electromechanical beast, lots of
relays, cams, gears & so on. Compared to today it doesn’t seem like much
but it did replace an acre of girls on mechanical calculators. It could
add, subtract & multiply & sweat like hell doing simple division. But it
could still get the payroll or inventory out on time provided there were
no card jams.

Later the IBM 604 showed up. It was electronic & used the 6J6 as a
binary flip-flop. Depending on the application there were 900 to 1500
6J6s in each 604. Each 6J6 was mounted in a plug-in assembly, complete
with all the R’s & C’s required to complete the flip-flop. That helped a
lot when trouble shooting since the whole assembly could be quickly
changed. All computations were done in decimal. The binaries were
connected in groups of four. So with some feedforward & feedback to the
correct place four 6J6s ran as binary to decimal in 1-2-4-8.

Heater supply was thru a regulated PS using saturable reactors. These
driven in a NFB circuit by a 6L6 (metal).

Many of these data processing machines used the 25L6 (metal) in the
punch card reading circuits.

The Scopes we used were from Waterman, long gone out of business. They
had a 3 inch CRT & perhaps 300 KHz bandwidth. Vertical amplifier is a
pair of diff amp 6J6s connected in two stages. But they did the job, I
think the IBM 604 processor if you could call it that ran only 50-100
KHz. I’ve still got my IBM voltmeter to which I later added a 1.5 volt
range. Sensitivity is actually 10K ohms/volt, not bad for 1953. But it
looks kind of used now!

Luckily for me I moved on after a year & half to Ferranti where some
real research was being done. By then they had discovered the
transistor, even though it was a surface barrier type, the SB100. But
that is another story to bore all of you.

*You can still find those Waterman scopes at hamfests pretty readily.

*Both FORTRAN and Lisp owe a lot of their workings to the fact they
originally ran on these vacuum tube IBM monsters.

I did all my graduate EE work on an IBM7090 then on a 7094 (NOT a tube
m/c) in Fortran IV. All 80 col. punched cards, batch run.
Back in the day, I did walk inside a working tube computer. Might
have been an English Electric "Deuce" but I forget where it was... I
thought it was at Harwell, UK, the atomic energy research station. Not
sure now, as I don't think Harwell had one. It had a mercury delay-
line memory. One felt like a slice of bread being toasted!
Cheers,
Roger .

[Arny Krueger[_4_]]

wrote in message
...
On Mar 29, 9:05 pm, John L Stewart John.L.Stewart.
wrote:
Each card had 80 columns in which the holes were punched by both manual
& electric punched card machines. Both numeric & alphabetical
information could be stored on the card. One hole would store a decimal
digit while a second hole in the appropriate place in the same column
would be alpha information. End of line & other commands were also
possible.

Not exactly. The card had 12 rows of punches, and 80 columns. A traditional
card character occupied 1 column. 10 rows were numbered 0-9, with the
remaining two rows being called "zone" punches. If there were no zones, then
the character was either a number 0-9 or blank. The zones were used to
modify the numeric values to form 3 additional sets of non-numeric
characters.

There was also a means for punching binary code on cards that came far
later, and pretty much streamed binary data at the card, obviating the
number/zone scheme.

Each of these card types had its own operator for data entry (ie IBM
024). There was a corresponding set of verifying machines (ie IBM 026),
again with their own operator.

Incorrect model numbers. 024 was the non-printing card punch, 026 was the
printing card punch, and the 056 was the verifier. Every card was keyed once
to punch, and again to verify. There were also the new tech punch and
verifier - the 029 and the 059. The 024/026/056 was based on wire contact
relay logic with 4 vacuum tube solenoid drivers (50L6?) and no power
transformer. The 029/059 was based on reed relays.

[John L Stewart]

Incorrect model numbers. 024 was the non-printing card punch, 026 was the
printing card punch, and the 056 was the verifier. Every card was keyed once
to punch, and again to verify. There were also the new tech punch and
verifier - the 029 and the 059. The 024/026/056 was based on wire contact
relay logic with 4 vacuum tube solenoid drivers (50L6?) and no power
transformer. The 029/059 was based on reed relays.[/quote]

Arny is correct, I screwed up some of those IBM data product model numbers. Some others I recall were the 001 & 031. The IBM 001 was a very simple portable hand operated card punch, nothing electrical at all. Handy on the desktop if only a few cards were needed. The IBM 031 was electrical with solenoid driven punches & auto card feed, the predecessor to the much nicer IBM 024.

Most of the rectifiers used were selenium stacks, usually full bridge. Not many failures at all.

IBM had just built a new facility at Don Mills, a suburb of Toronto. The building is ¼ mile long. The building is still in use but IBM has long moved.

IBM Hardware Research locally was one of my biggest accounts while with HP. Today IBM Research here is all in software, far as I know.

There was a card cutting department where the card stock came in as huge rolls. Then the equipment cut & printed the cards. The noise was terrible. Probably some who worked there became prematurely deaf.

Roger mentioned the mercury delay line as a memory device. At Ferranti Canada in 1956 a lot of research went into various ideas for memory, since the transistor was still not a sure thing. These included the magnetostrictive delay line, a wire of nickel-steel. The data was launched from one end as a series of magnetic pulses & a short time later retrieved at the other. Can’t remember how many data bits per foot, but I guess it didn’t fly. Other work included both cylindrical & disc quartz. Multiple reflections were possible in the quartz disc by using critical angel reflection. There was also some work with cylindrical rotating drums (Hum Drum) running on compressed air bearings. Data was stored on the magnetic surface, much like a mag disc today.

Logic circuits were built based on magnetic cores. Shift registers, various gates & flip-flops were all based on core logic. These had to be driven by fairly large & clocked current pulses, as I recall using lots of EL86s.

In 1957 I went to U of Toronto Physics to work on a core memory project. The objective was to build a memory wherein the magnetic cores in the core plane did not have to be refreshed after each read cycle. That went well but by then the transistor had been better developed. I did get an invite to work on Illiac at U of Illinois but didn’t make the move. There was still the danger of being drafted. But I was amazed at the resources in money & equipment there compared to what we had in Toronto.

There was a Ferranti computer at U of T Physics, all vacuum tube. A full time Ferranti employee road shot gun on that thing. Not sure what the mean time between failures was but he kept it going. It used CRT storage among other things.

One of the guys in the Toronto lab built some logic using 3-element neon bulbs. They look same as an NE2, but three wires. The stuff could run at about 50 KHz I recall. I did have some data & reference to these 3-element bulbs in my library but its buried somewhere. Couldn’t find the stuff on the web either. But its out there, that’s where I got mine.

For further reading I recommend Father, Son & Company by Thomas J Watson Jr. A good history of how IBM evolved & their relation to NCR & Toledo Scales.

Also IBM & The Holocaust by Edwin Black. IBM equipment in Europe was used openly in WW2 in the organization & transport of the Jews. In 1945 IBM resumed operation with all their European assets, no questions asked.

Cheers to all, John

[Phil Allison[_3_]]

"John L Stewart"

Did an Impedance Plot for the speaker. I need to get me a white & pink
noise source. Would make that kind of measurement easier.

** How so ??

Impedance plots are best done with a slow sine wave sweep while feeding the
speaker from a high impedance ( 600ohms plus) source.



..... Phil

[Patrick Turner]

On Apr 13, 11:01*am, "Phil Allison" wrote:
"John L Stewart"

Did an Impedance Plot for the speaker. I need to get me a white & pink
noise source. Would make that kind of measurement easier.

** How so ??

Impedance plots are best done with a slow sine wave sweep while feeding the
speaker from a high impedance ( 600ohms plus) source.

For speaker Z measurements, I use a sine wave sig gene feeding a power
amp with 1k0 series R to speaker. I set the amp to 10Vrms. Then a
nearly constant 10mA rms flows, and Z can be plotted while watching a
trace on CRO, or by measuring with wideband volt meter. If VLs =
0.08Vrms, then Z = 0.08V / 0.01A = 8 ohms, easy to do mentally, and
sound in speakers is not loud while testing, and voltages measured are
large enough to measure and display on CRO easily. To avoid noise at
higher F, using a 0.05 uF across the LS is wise, assuming speaker Z
100 ohms above 5kHz.

For speaker acoustic response I use pink noise and for crossover
electronic response, sine waves from amp, both with amp with Rout 1
ohm.

The trick is to get the crossovers electronic response tailored to
give a flat acoustic response, while making the speakers present a
mainly resistive load to amp, and be free of serious dips in Z along
the band. Not easy, and something many manufacturers get entirely
wrong, and a classic bad example are AR9 speakers from 1975.

Patrick Turner.

.... *Phil

[Don Pearce[_3_]]

On Fri, 13 Apr 2012 11:01:21 +1000, "Phil Allison"
wrote:


"John L Stewart"

Did an Impedance Plot for the speaker. I need to get me a white & pink
noise source. Would make that kind of measurement easier.

** How so ??

Impedance plots are best done with a slow sine wave sweep while feeding the
speaker from a high impedance ( 600ohms plus) source.



.... Phil


It is also vital that the speaker be placed well clear of the floor
and any other obstructions. Anything like that will show up as an
error in the impedance plot.

d

[Phil Allison[_3_]]

"Don Pearce"
"Phil Allison"

"John L Stewart"

Did an Impedance Plot for the speaker. I need to get me a white & pink
noise source. Would make that kind of measurement easier.

** How so ??

Impedance plots are best done with a slow sine wave sweep while feeding
the
speaker from a high impedance ( 600ohms plus) source.



It is also vital that the speaker be placed well clear of the floor
and any other obstructions. Anything like that will show up as an
error in the impedance plot.

** ********.

[Phil Allison[_3_]]

"John L Stewart"

** DO NOT SNIP THE CONTEXT !!!!!!!

Over in thread IBM 1953 Phil said-

** No ****ing way did I post ANYTHING in that tread !!!

Now: RESTORING the ESSENTIAL CONTEXT !!!

" Did an Impedance Plot for the speaker. I need to get me a white & pink
noise source. Would make that kind of measurement easier. "


** How so ??

Impedance plots are best done with a slow sine wave sweep while feeding
the speaker from a high impedance ( 600ohms plus) source.


PV Speaker Test Hookup

For the speaker impedance test run I used an HP 200CD (600 ohm) as the
audio source. Connected that thru a Hammond 1700 Series OPT so that
there was a conversion from 2500 ohms to 16 ohms. Then another 150R
straight into the 16 ohm box, much as Phil suggested.

All done with the speaker box outside (open field) in order to avoid
reflections. Can't afford & don't need an anechoic chamber, long as it
don't rain.

The results were stored with the Pico Technology ADC216 Virtual
Instrument set to Peak mode. Very time consuming.


** Huh ??

Impedance curves for a woofer (with no box) or guitar speaker take about 2
minutes using only an audio generator and a scope.

There is a single impedance peak at resonance and a broad dip around 150 to
400Hz - then it climbs doubling for every two octaves. Plot about a dozen
spots and you have it.


I think with a good
audio noise source one could set up the equipment & let it run to
completion.


** I still see no sign of an explanation of what the **** you are on about.

Wot a tedious ******.


.... Phil

[Don Pearce[_3_]]

On Sat, 14 Apr 2012 10:20:37 +1000, "Phil Allison"
wrote:


"Don Pearce"
"Phil Allison"

"John L Stewart"

Did an Impedance Plot for the speaker. I need to get me a white & pink
noise source. Would make that kind of measurement easier.

** How so ??

Impedance plots are best done with a slow sine wave sweep while feeding
the
speaker from a high impedance ( 600ohms plus) source.



It is also vital that the speaker be placed well clear of the floor
and any other obstructions. Anything like that will show up as an
error in the impedance plot.

** ********.


Not ******** at all. Particularly with a high efficiency speaker, you
can see the impedance plot squirm as you move things around near the
speaker. Bear in mind that it is a two way device, and can operate as
a sort of audio version of RADAR.

d

[Phil Allison[_3_]]

"Don Pearce"
"Phil Allison"
"Don Pearce"
"Phil Allison"

"John L Stewart"

Did an Impedance Plot for the speaker. I need to get me a white & pink
noise source. Would make that kind of measurement easier.

** How so ??

Impedance plots are best done with a slow sine wave sweep while feeding
the
speaker from a high impedance ( 600ohms plus) source.



It is also vital that the speaker be placed well clear of the floor
and any other obstructions. Anything like that will show up as an
error in the impedance plot.

** ********.


Not ******** at all.

** It is utter ********.

You asinine PEDANTIC ****.


.... Phil

[Patrick Turner]

On Apr 14, 4:15*pm, "Phil Allison" wrote:
"Don Pearce"
"Phil Allison"





"Don Pearce"
"Phil Allison"

"John L Stewart"

Did an Impedance Plot for the speaker. I need to get me a white & pink
noise source. Would make that kind of measurement easier.

** How so ??

Impedance plots are best done with a slow sine wave sweep while feeding
the
speaker from a high impedance ( 600ohms plus) source.

It is also vital that the speaker be placed well clear of the floor
and any other obstructions. Anything like that will show up as an
error in the impedance plot.

** ********.

Not ******** at all.

** *It is utter ********.

* *You asinine PEDANTIC *****.

... *Phil- Hide quoted text -

- Show quoted text -

Who could ever have hoped that grown men would not argue about speaker
Z measurements? Nobody?

Anyway, keeping speakers away from sound reflecting surfaces does have
a significance. Only a fool would test a driver with its front face
sitting on a bench, or with a wall a foot away.

But what about enclosure effects on drivers?

To make a speaker, ie, enclosure with driver mounted in it, and with
baffles and sound absorbant materials, one needs to know the raw data
about the driver when it is well away from an enclosure or reflecting
wall. Testing in an average room with driver with magnet down and
sitting on a an upright housebrick on a bench, or dangled on a wire
from cieling will negate 95% of effects on Z by nearby objects. The Z
plot will reveal the Fo, the resonance in free air. There are other
tests one can do to determine all of the Thiele and Small parameters,
and then these may be entered into a program like WinISP which will
give you a calculated box size for a predictable bass response. Then
the speaker box + driver fixed in can be completed, and another
impedance test then made with speaker set up in a workshop in similar
situation to how it is used in a typical listening room. It is done
without any crossover, and the use of a power amp set at 10Vrms output
feeding through 1k0 gives a virtually constant 10mAac, and so tweeters
can't be damaged with bass F. The Z at the lowest part of a given
driver's F band will be quite difference from the free air test out of
any box. This Z is the real and relevant Z which must be matched to
work with a crossover filter to give the wanted acoustic response.
Once the Z is known, the acoustic response of each driver in turn can
be tested with pink noise without any X-over with the same level of
applied LOW voltage at all F, ie, with say 0.1Vrms straight from the
amp which has Rout 1 ohm.

If one builds a 3 way speaker, the acoustic responses of LF, MF and HF
should tell you where the lowest level of sound is made between 40Hz
and 20kHz. You might find these F are where LF and tweeter are -3dB.
In a typical speaker, you may find there is a level response ( +/-
2dB ) between say 80Hz and 200Hz and that this level is lower than
anywhere else above 200Hz and below 20kHz, so this acoustic level sets
the sensitivity of the completed speakers. Its not unusual for LF, MF
and HF drivers to have peaks in their response +12dB above the
REFERENCE level of say 80Hz to 200Hz. So some means of attenuating the
amp voltage reaching all drivers has to be designed to ensure a flat
input voltage gives a flat acoustic response, and that the L&C used
are "terminated" by sufficient R to avoid dips in Z due to resonances,
and that the driver always "see" a lowest possible R as it source. So
the work of making a good crossover is NEVER easy, and NEVER is a
simple task done by an online calculator, with no understanding or
experience with LCR theory.

Most ppl just shove a resistor in series with MF and HF to reduce the
higher acoustic output of MF and HF over the low bass output from most
bass drivers. Let us assume each and every driver has an R+C Zobel
strapped across it so that its mid band Z value is maintained at all F
above the midband. The Zobel adding is called "impedance equalizing,
and makes the driver look more like a pure resistance above the mid
band Z, and equal in ohms to the midband Z.

Let us assume the equalised Z of a driver in a box = 7 ohms. Just
adding say 7 ohms in series makes the total Z roughly 14 ohms, giving
6dB attenuation. The driver is now driven by 7 ohms plus amp Rout so
perhaps by 8 ohms source resistance. People could say this is no good,
because the damping factor has become hopelessly low, only about 1.0
in this case, when theory says we should have DF 10. The LC filter
designed for 7 ohms will have very different attenuation slope rates
and X-over points if loaded with 14 ohms. One might then decide to
make the Z "seen by" the preceeding LC filter to be 7 ohms, and have
the driver "see a lower source R". This means that after the LC, one
has 3.5 ohms in series with driver and its parallel R&C zobel, but
with an additional 7 ohms across the driver, to make the driver Z look
like 3.5 ohms. The driver sees 3.5 ohms plus 7 ohms in parallel and
the F below the midband Z, ie, 2.67 ohms, and the driver is better
damped, and amp sees 7 ohms, and LC sees 7 ohms, and everyone is
happy, except that the sensitivity has halved for the driver. Well, if
you want a truly flat response with 3 drivers, you usually have to
sacrifice some power lost heating resistors if you are determined to
have a flat response. No free breakfast.

There are other ways to avoid losses in speakers due to driver Z
variatons and R losses. One might use tri-amping, very expensive with
tubes, and you'll waste fat more heat, or you have an audio speaker
voltage transformer for MF and HF. It usually is never necessary to
attenuate bass levels, considering so many speakers are bass deficent,
because they have been designed to sell well and be marketted easily
with high quoted sensitivity figures of at least 87dB/W@1M. The tranny
to attenuate MF and treble can have Fsat at 50Hz, at say 50Vrms input,
and have a series C between its primary and amp. It will need to be
very carefully designed so there is not a horrible low Z formed at the
Fo between the series C and primary inductance. Taps down a winding at
1.5dB steps are wise, giving 0dB to -12dB. By this means, the
crossovers and the following drivers are driven by a source resistance
lower than the amp Rout, so DF improves, ie, gets higher. The amp then
sees a higher load, welcomed, because most tube amps function best if
load R is higher. So if one has 2:1 tranny voltage ratio, with sec
load = 7 ohms, the amp will see 28 ohms, and no losses occur in series
& shunting R.

I don't know ONE manufacturer who uses transformer attenuators for
multi drivered dynamic speakers.
The exceptions are for ribbons and ESL which form a tiny % of speakers
sold.

So sure, speaker impedance is hugely important, if we wish to save our
amplifiers from overheating, and if we wish to hear the best sound,
from using the available electric energy most efficiently. Efficiency
becomes important when the Watts become expensive, or when we have
made the decision to have so few Watts at the outset, ie, chosen a
lone 300B to fill a large room with divorce causing sound levels at
low distortion.

Patrick Turner.

[Don Pearce[_3_]]

On Sat, 14 Apr 2012 16:15:40 +1000, "Phil Allison"
wrote:


"Don Pearce"
"Phil Allison"
"Don Pearce"
"Phil Allison"

"John L Stewart"

Did an Impedance Plot for the speaker. I need to get me a white & pink
noise source. Would make that kind of measurement easier.

** How so ??

Impedance plots are best done with a slow sine wave sweep while feeding
the
speaker from a high impedance ( 600ohms plus) source.



It is also vital that the speaker be placed well clear of the floor
and any other obstructions. Anything like that will show up as an
error in the impedance plot.

** ********.


Not ******** at all.

** It is utter ********.

You asinine PEDANTIC ****.


... Phil


So I've measured the utter ******** for you (still in dB form because
Audition won't do the calculation needed to turn it to impedance).

http://www.soundthoughts.co.uk/look/speaker_imp.png

The speaker is fed via a 100 ohm resistor, and the output is read
across the speaker terminals themselves.

What you see here is the same speaker (Kef Cresta II) measured twice,
once with a book held a foot away from the cone. There are two effects
evident. The first is that the frequencies of the impedance peaks have
shifted up slightly with the book in place (blue trace), and secondly
there is considerable disturbance to the actual impedance, mainly at
the lower peak and the intermediate dip - but also in a considerable
modification to the upper slope of the top peak where there is a bit
of a wobble.

So yes, it is important to keep the area around the speaker clear of
clutter when you measure the impedance.

I have no doubt that Phil will try to come back with some guttersnipe
defence of his position, but as you see it is untenable.

d

[Don Pearce[_3_]]

On Sun, 15 Apr 2012 09:48:56 GMT, (Don Pearce) wrote:


So I've measured the utter ******** for you (still in dB form because
Audition won't do the calculation needed to turn it to impedance).

http://www.soundthoughts.co.uk/look/speaker_imp.png

The speaker is fed via a 100 ohm resistor, and the output is read
across the speaker terminals themselves.

What you see here is the same speaker (Kef Cresta II) measured twice,
once with a book held a foot away from the cone. There are two effects
evident. The first is that the frequencies of the impedance peaks have
shifted up slightly with the book in place (blue trace), and secondly
there is considerable disturbance to the actual impedance, mainly at
the lower peak and the intermediate dip - but also in a considerable
modification to the upper slope of the top peak where there is a bit
of a wobble.

So yes, it is important to keep the area around the speaker clear of
clutter when you measure the impedance.

I have no doubt that Phil will try to come back with some guttersnipe
defence of his position, but as you see it is untenable.

d

And while we are at it, just for interest, here is a Monitor Audio
RX2, measured with and without the port damper fitted. The port damper
is a light foam plug about 40mm long, which is a loose fit in the
reflex port. It has clearly been designed with care, because it does a
perfect job of removing the coupled resonance from the speaker.

http://www.soundthoughts.co.uk/look/port_damping.png

d

[Phil Allison[_3_]]

"Patrick Turner"


Who could ever have hoped that grown men would not argue about speaker
Z measurements? Nobody?


** Anybody who has EVER dared to post a simple fact on usenet.

The one place you are most likely to be crucified for so doing.

Worse by far than Nazi Germany, Stalin's Russia or Communist China.

But maybe just tad safer than being a traitor to Scientology.



..... Phil

[Arny Krueger[_4_]]

"Don Pearce" wrote in message
...

So I've measured the utter ******** for you (still in dB form because
Audition won't do the calculation needed to turn it to impedance).

http://www.soundthoughts.co.uk/look/speaker_imp.png

The speaker is fed via a 100 ohm resistor, and the output is read
across the speaker terminals themselves.

What you see here is the same speaker (Kef Cresta II) measured twice,
once with a book held a foot away from the cone. There are two effects
evident. The first is that the frequencies of the impedance peaks have
shifted up slightly with the book in place (blue trace), and secondly
there is considerable disturbance to the actual impedance, mainly at
the lower peak and the intermediate dip - but also in a considerable
modification to the upper slope of the top peak where there is a bit
of a wobble.

Looks like a pretty small differnce to me.

Proof of the pudding would be comparison of T/S parameters calculated from
each plot.

[Don Pearce[_3_]]

On Sun, 15 Apr 2012 15:42:35 -0400, "Arny Krueger"
wrote:


"Don Pearce" wrote in message
...

So I've measured the utter ******** for you (still in dB form because
Audition won't do the calculation needed to turn it to impedance).

http://www.soundthoughts.co.uk/look/speaker_imp.png

The speaker is fed via a 100 ohm resistor, and the output is read
across the speaker terminals themselves.

What you see here is the same speaker (Kef Cresta II) measured twice,
once with a book held a foot away from the cone. There are two effects
evident. The first is that the frequencies of the impedance peaks have
shifted up slightly with the book in place (blue trace), and secondly
there is considerable disturbance to the actual impedance, mainly at
the lower peak and the intermediate dip - but also in a considerable
modification to the upper slope of the top peak where there is a bit
of a wobble.

Looks like a pretty small differnce to me.


I wish I was permitted such large tolerances in my design work. It's
an error. That's all the claim I made.

Proof of the pudding would be comparison of T/S parameters calculated from
each plot.


Good luck with that. These are speakers in cabinets.

d

[Phil Allison[_3_]]

"Arny Krueger"
"Don Pearce"
So I've measured the utter ******** for you (still in dB form because
Audition won't do the calculation needed to turn it to impedance).

http://www.soundthoughts.co.uk/look/speaker_imp.png

The speaker is fed via a 100 ohm resistor, and the output is read
across the speaker terminals themselves.

What you see here is the same speaker (Kef Cresta II) measured twice,
once with a book held a foot away from the cone. There are two effects
evident. The first is that the frequencies of the impedance peaks have
shifted up slightly with the book in place (blue trace), and secondly
there is considerable disturbance to the actual impedance, mainly at
the lower peak and the intermediate dip - but also in a considerable
modification to the upper slope of the top peak where there is a bit
of a wobble.

Looks like a pretty small differnce to me.


** SFA in fact.

The guitar speaker system in question is intended to sit on a floor - so
THAT IS HOW it should be when you measure its impedance.



..... Phil

[Patrick Turner]

On Apr 15, 7:48*pm, (Don Pearce) wrote:
On Sat, 14 Apr 2012 16:15:40 +1000, "Phil Allison"
wrote:







"Don Pearce"
"Phil Allison"
"Don Pearce"
"Phil Allison"

"John L Stewart"

Did an Impedance Plot for the speaker. I need to get me a white & pink
noise source. Would make that kind of measurement easier.

** How so ??

Impedance plots are best done with a slow sine wave sweep while feeding
the
speaker from a high impedance ( 600ohms plus) source.

It is also vital that the speaker be placed well clear of the floor
and any other obstructions. Anything like that will show up as an
error in the impedance plot.

** ********.

Not ******** at all.

** *It is utter ********.

* You asinine PEDANTIC *****.

... *Phil

So I've measured the utter ******** for you (still in dB form because
Audition won't do the calculation needed to turn it to impedance).

http://www.soundthoughts.co.uk/look/speaker_imp.png

The speaker is fed via a 100 ohm resistor, and the output is read
across the speaker terminals themselves.

*What you see here is the same speaker (Kef Cresta II) measured twice,
once with a book held a foot away from the cone. There are two effects
evident. The first is that the frequencies of the impedance peaks have
shifted up slightly with the book in place (blue trace), and secondly
there is considerable disturbance to the actual impedance, mainly at
the lower peak and the intermediate dip - but also in a considerable
modification to the upper slope of the top peak where there is a bit
of a wobble.

So yes, it is important to keep the area around the speaker clear of
clutter when you measure the impedance.

I have no doubt that Phil will try to come back with some guttersnipe
defence of his position, but as you see it is untenable.

The differences between red line and blue lines with and without a
book held near a speaker are to my mind quite negligible, leading some
ppl to argue that claiming significant Z differences due to nearby
objects is "********", aka as bull**** or horse manure, bovine
fertilizer or even hiefer dust, ( the latter to not offend sensitive
older female farmers who'd always frown on the vulgarities speiled out
by the male species. ).

Presumably, a speaker box will affect the Z far more than a book held
a foot away. In fact, the Z curve with driver suspended in free air,
and in the geometric centre of a large room is somewhat a useless
curve to draw apart from deriving T&S parameters. The Z with driver in
box is VERY important.

Patrick Turner.


d- Hide quoted text -

- Show quoted text -

[Patrick Turner]

On Apr 15, 8:13*pm, (Don Pearce) wrote:
On Sun, 15 Apr 2012 09:48:56 GMT, (Don Pearce) wrote:
So I've measured the utter ******** for you (still in dB form because
Audition won't do the calculation needed to turn it to impedance).

http://www.soundthoughts.co.uk/look/speaker_imp.png

The speaker is fed via a 100 ohm resistor, and the output is read
across the speaker terminals themselves.

What you see here is the same speaker (Kef Cresta II) measured twice,
once with a book held a foot away from the cone. There are two effects
evident. The first is that the frequencies of the impedance peaks have
shifted up slightly with the book in place (blue trace), and secondly
there is considerable disturbance to the actual impedance, mainly at
the lower peak and the intermediate dip - but also in a considerable
modification to the upper slope of the top peak where there is a bit
of a wobble.

So yes, it is important to keep the area around the speaker clear of
clutter when you measure the impedance.

I have no doubt that Phil will try to come back with some guttersnipe
defence of his position, but as you see it is untenable.

d

And while we are at it, just for interest, here is a Monitor Audio
RX2, measured with and without the port damper fitted. The port damper
is a light foam plug about 40mm long, which is a loose fit in the
reflex port. It has clearly been designed with care, because it does a
perfect job of removing the coupled resonance from the speaker.

http://www.soundthoughts.co.uk/look/port_damping.png

Blocking the port in any way between not at all, and totally has a
profound effect on Z at the resonance at the low end of the band below
100Hz in your example. But hardly any effect on the F above 140Hz.

When building a speaker we need to know Fs, resonant F in free air,
and Fb, predictable resonance of the box with its port or without.
Transmission lines are where the box becomes the port, and the spead
of sound in air in the long port, or line, is artificially reduced by
hanging loose fill material in the line air, thus creating desired
phase relationship between output from the line end away from driver,
and the acoustic phase from the front of the cone. Correct me if I am
wrong, but the TL speaker is the only type which lowers the apparent
resonant F of speaker in an enclosure, and thus extends the mid band Z
over a lower range of F and thus making the speaker in box nearer to a
resistance load and thus loading the amp better, and all the while
making better sunding bass as so many transmission line fetishists
proclaim, while they throw turds at anyone persisting with a sealed
box, aperiodic port, or normal reflex port.
I've tried TL, and heard no bass improvements.

Making good bass in most rooms is a very uncertain undertaking, and
rooms affect bass response profiles pretty badly. But I prefer large
bass drivers in reflex box where there are two peaks in Z each side of
the Fb which if possible should be below 20Hz, as it is in most good
sub-woofers. This means everything produced about 35Hz is mainly from
the front of the cone, and from a driver looking mainly resistive in
Z.
Not all drivers of say 300mm dia will work the same in a given box and
port. Thiele and Small worked out what was going on mathematically to
give audio engineers some hope to make a box and port to optimise bass
productions. Luckily, today's world of online calculators liberates
most ppl from working out endless equations in which they are prone to
mistakes, especially if the don't much understand the concepts of what
Thiele and Small knew, and which could then be mathematicized.

Patrick Turner.

d- Hide quoted text -

- Show quoted text -

[Patrick Turner]

On Apr 15, 10:09*pm, "Phil Allison" wrote:
"Patrick Turner"

Who could ever have hoped that grown men would not argue about speaker
Z measurements? Nobody?

** Anybody who has *EVER *dared to post a simple fact on usenet.

The one place you are most likely to be crucified for so doing.

Worse by far than Nazi Germany, Stalin's Russia or Communist China.

But maybe just tad safer than being a traitor to Scientology.

.... *Phil

Ah, so If Jesus Christ walked amoung us now, the last thing 'he'd
wanna do is post about religious issues at r.a.t.

He knew first hand what dreadful things can happen if you speak your
mind.

I'd like to see Jesus have a debate with Richard Dawkins. Since Jesus
is due to arrive any minute now in what ppl call a "second coming",
why don't you book an auditorium for the debate, and phone Auntie ABC
to lend us the Q&A team to run the debate?

Patrick Turner.

[Patrick Turner]

On Apr 16, 5:01*pm, "Phil Allison" wrote:
"Arny Krueger"





"Don Pearce"
So I've measured the utter ******** for you (still in dB form because
Audition won't do the calculation needed to turn it to impedance).

http://www.soundthoughts.co.uk/look/speaker_imp.png

The speaker is fed via a 100 ohm resistor, and the output is read
across the speaker terminals themselves.

What you see here is the same speaker (Kef Cresta II) measured twice,
once with a book held a foot away from the cone. There are two effects
evident. The first is that the frequencies of the impedance peaks have
shifted up slightly with the book in place (blue trace), and secondly
there is considerable disturbance to the actual impedance, mainly at
the lower peak and the intermediate dip - but also in a considerable
modification to the upper slope of the top peak where there is a bit
of a wobble.

Looks like a pretty small differnce to me.

** SFA in fact.

The guitar speaker system in question is intended to sit on a floor - *so
THAT *IS *HOW *it should be when you measure its impedance.

.... *Phil- Hide quoted text -

- Show quoted text -

Guitar amp speakers are a little odd because they usually have an open
backed cab, so placing them up against a wall will change bass
response and Z considerably, but then most guitar amp bass drivers
have quite high Fs, and no matter what anyone does, they won't go
really low, and besides, most guitar bass notes don't go lower than
41Hz.

Phil's right, Z should be measured with speaker put into a normal
operating position and condition, and at most venues, it'll be on the
floor and away from rear walls, ( if there is one; if a previous Dark
Metal band has played ear crushingly LOUD in the previous bracket, the
rear wall may have been blasted off tha building ) But hey, there are
no strict rules about anything here involving non-hi-fi, ie, noise
musicians make using geetahs and amps. Have another beer. Forget Z.
See if you can score the blonde staring at you while ya play.

Patrick Turner.

[Don Pearce[_3_]]

On Mon, 16 Apr 2012 03:11:42 -0700 (PDT), Patrick Turner
wrote:

On Apr 15, 8:13*pm, (Don Pearce) wrote:
On Sun, 15 Apr 2012 09:48:56 GMT, (Don Pearce) wrote:
So I've measured the utter ******** for you (still in dB form because
Audition won't do the calculation needed to turn it to impedance).

http://www.soundthoughts.co.uk/look/speaker_imp.png

The speaker is fed via a 100 ohm resistor, and the output is read
across the speaker terminals themselves.

What you see here is the same speaker (Kef Cresta II) measured twice,
once with a book held a foot away from the cone. There are two effects
evident. The first is that the frequencies of the impedance peaks have
shifted up slightly with the book in place (blue trace), and secondly
there is considerable disturbance to the actual impedance, mainly at
the lower peak and the intermediate dip - but also in a considerable
modification to the upper slope of the top peak where there is a bit
of a wobble.

So yes, it is important to keep the area around the speaker clear of
clutter when you measure the impedance.

I have no doubt that Phil will try to come back with some guttersnipe
defence of his position, but as you see it is untenable.

d

And while we are at it, just for interest, here is a Monitor Audio
RX2, measured with and without the port damper fitted. The port damper
is a light foam plug about 40mm long, which is a loose fit in the
reflex port. It has clearly been designed with care, because it does a
perfect job of removing the coupled resonance from the speaker.

http://www.soundthoughts.co.uk/look/port_damping.png

Blocking the port in any way between not at all, and totally has a
profound effect on Z at the resonance at the low end of the band below
100Hz in your example. But hardly any effect on the F above 140Hz.

When building a speaker we need to know Fs, resonant F in free air,
and Fb, predictable resonance of the box with its port or without.
Transmission lines are where the box becomes the port, and the spead
of sound in air in the long port, or line, is artificially reduced by
hanging loose fill material in the line air, thus creating desired
phase relationship between output from the line end away from driver,
and the acoustic phase from the front of the cone. Correct me if I am
wrong, but the TL speaker is the only type which lowers the apparent
resonant F of speaker in an enclosure, and thus extends the mid band Z
over a lower range of F and thus making the speaker in box nearer to a
resistance load and thus loading the amp better, and all the while
making better sunding bass as so many transmission line fetishists
proclaim, while they throw turds at anyone persisting with a sealed
box, aperiodic port, or normal reflex port.
I've tried TL, and heard no bass improvements.

Making good bass in most rooms is a very uncertain undertaking, and
rooms affect bass response profiles pretty badly. But I prefer large
bass drivers in reflex box where there are two peaks in Z each side of
the Fb which if possible should be below 20Hz, as it is in most good
sub-woofers. This means everything produced about 35Hz is mainly from
the front of the cone, and from a driver looking mainly resistive in
Z.
Not all drivers of say 300mm dia will work the same in a given box and
port. Thiele and Small worked out what was going on mathematically to
give audio engineers some hope to make a box and port to optimise bass
productions. Luckily, today's world of online calculators liberates
most ppl from working out endless equations in which they are prone to
mistakes, especially if the don't much understand the concepts of what
Thiele and Small knew, and which could then be mathematicized.


You may be right, you may be wrong. I'll never know because there is
that about you which means I will never read a word you write.

d

[Don Pearce[_3_]]

On Mon, 16 Apr 2012 02:46:46 -0700 (PDT), Patrick Turner
wrote:

On Apr 15, 7:48*pm, (Don Pearce) wrote:
On Sat, 14 Apr 2012 16:15:40 +1000, "Phil Allison"
wrote:







"Don Pearce"
"Phil Allison"
"Don Pearce"
"Phil Allison"

"John L Stewart"

Did an Impedance Plot for the speaker. I need to get me a white & pink
noise source. Would make that kind of measurement easier.

** How so ??

Impedance plots are best done with a slow sine wave sweep while feeding
the
speaker from a high impedance ( 600ohms plus) source.

It is also vital that the speaker be placed well clear of the floor
and any other obstructions. Anything like that will show up as an
error in the impedance plot.

** ********.

Not ******** at all.

** *It is utter ********.

* You asinine PEDANTIC *****.

... *Phil

So I've measured the utter ******** for you (still in dB form because
Audition won't do the calculation needed to turn it to impedance).

http://www.soundthoughts.co.uk/look/speaker_imp.png

The speaker is fed via a 100 ohm resistor, and the output is read
across the speaker terminals themselves.

*What you see here is the same speaker (Kef Cresta II) measured twice,
once with a book held a foot away from the cone. There are two effects
evident. The first is that the frequencies of the impedance peaks have
shifted up slightly with the book in place (blue trace), and secondly
there is considerable disturbance to the actual impedance, mainly at
the lower peak and the intermediate dip - but also in a considerable
modification to the upper slope of the top peak where there is a bit
of a wobble.

So yes, it is important to keep the area around the speaker clear of
clutter when you measure the impedance.

I have no doubt that Phil will try to come back with some guttersnipe
defence of his position, but as you see it is untenable.

The differences between red line and blue lines with and without a
book held near a speaker are to my mind quite negligible, leading some
ppl to argue that claiming significant Z differences due to nearby
objects is "********", aka as bull**** or horse manure, bovine
fertilizer or even hiefer dust, ( the latter to not offend sensitive
older female farmers who'd always frown on the vulgarities speiled out
by the male species. ).

Presumably, a speaker box will affect the Z far more than a book held
a foot away. In fact, the Z curve with driver suspended in free air,
and in the geometric centre of a large room is somewhat a useless
curve to draw apart from deriving T&S parameters. The Z with driver in
box is VERY important.

Patrick Turner.


More blah blah blah.

d

[jh[_3_]]

Am 16.04.2012 12:32, schrieb Patrick Turner:
On Apr 16, 5:01 pm, "Phil wrote:
"Arny Krueger"





"Don Pearce"
So I've measured the utter ******** for you (still in dB form because
Audition won't do the calculation needed to turn it to impedance).

http://www.soundthoughts.co.uk/look/speaker_imp.png

The speaker is fed via a 100 ohm resistor, and the output is read
across the speaker terminals themselves.

What you see here is the same speaker (Kef Cresta II) measured twice,
once with a book held a foot away from the cone. There are two effects
evident. The first is that the frequencies of the impedance peaks have
shifted up slightly with the book in place (blue trace), and secondly
there is considerable disturbance to the actual impedance, mainly at
the lower peak and the intermediate dip - but also in a considerable
modification to the upper slope of the top peak where there is a bit
of a wobble.

Looks like a pretty small differnce to me.

** SFA in fact.

The guitar speaker system in question is intended to sit on a floor - so
THAT IS HOW it should be when you measure its impedance.

.... Phil- Hide quoted text -

- Show quoted text -

Guitar amp speakers are a little odd because they usually have an open
backed cab, so placing them up against a wall will change bass
response and Z considerably, but then most guitar amp bass drivers
have quite high Fs, and no matter what anyone does, they won't go
really low, and besides, most guitar bass notes don't go lower than
41Hz.

Phil's right, Z should be measured with speaker put into a normal
operating position and condition, and at most venues, it'll be on the
floor and away from rear walls, ( if there is one; if a previous Dark
Metal band has played ear crushingly LOUD in the previous bracket, the
rear wall may have been blasted off tha building ) But hey, there are
no strict rules about anything here involving non-hi-fi, ie, noise
musicians make using geetahs and amps. Have another beer. Forget Z.
See if you can score the blonde staring at you while ya play.

Patrick Turner.



Patrick,

the Dark Metal Band will most propably have played sealed 4x12" cabinets....

*No* open back cabs allowed in this kind of music ;-)

The back of the building is completely save....


regards

Jochen

[John L Stewart]

My Grandsons PV JSX that I worked on has 4X 12 inch speakers with the back closed. There is a wooden post from the center of the front panel to the rear, just a bit too long. So it is preloaded. Stiffens things up a bit, so hopefully no rattling. Or perhaps some rock bands would want that!

The PV JSX Amp has a variable full loop NFB system. But operator variable.

With all this theory being spouted did anyone mention that DF don't matter much beyond about 10 because speaker R gets in the way. Something about Thevenin's Theorem. Better give Norton honorable mention too!

And the rock bands don't care much, they will do the damndest things to make the equipment sound the way they want anyway.

Still can't figure out what all this has to do with IBM in 1953!

[Phil Allison[_3_]]

"Patrick Turner"

Guitar amp speakers are a little odd because they usually have an open
backed cab,

** The VAST majority of *separate* speaker cabinets used for guitar or
bass guitar have sealed backs. Combo amps that use SS circuitry also have
sealed back cabinets, in the main.

It is only valve guitar amps that are combos where open back cabinets are
the norm - and then mainly to allow air to get to the inverted valves to
cool them.

JLS has not revealed whether his example of the PV JSX is a combo or a
head - but a resonant peak in the impedance at 137Hz suggests it is a head
with a sealed cabinet.


.... Phil

[flipper]

On Mon, 16 Apr 2012 03:32:22 -0700 (PDT), Patrick Turner
wrote:



Guitar amp speakers are a little odd because they usually have an open
backed cab,

It's called open baffle and used to be common as dirt, including the
gazillion Hi-Fi consoles that were virtually everywhere. And then
there were free standing units like the famous Wharfedale SFB/3 with a
published response of 30 C/S to 20000 C/S.

The biggest problem is baffle size but if one can live with it they're
very efficient and Warfedale advertised "full domestic volume from a
small amplifier, tape recorder, or any good radio set with more than 3
Watt output."

[jh[_3_]]

Am 17.04.2012 03:47, schrieb John L Stewart:
My Grandsons PV JSX that I worked on has 4X 12 inch speakers with the
back closed. There is a wooden post from the center of the front panel
to the rear, just a bit too long. So it is preloaded. Stiffens things up
a bit, so hopefully no rattling. Or perhaps some rock bands would want
that!

The PV JSX Amp has a variable full loop NFB system. But operator
variable.

With all this theory being spouted did anyone mention that DF don't
matter much beyond about 10 because speaker R gets in the way. Something
about Thevenin's Theorem. Better give Norton honorable mention too!

And the rock bands don't care much, they will do the damndest things to
make the equipment sound the way they want anyway.

Still can't figure out what all this has to do with IBM in 1953!


+-------------------------------------------------------------------+
|Filename: PV Speaker Box 7W.jpg |
|Download: http://www.audiobanter.com/attachment.php?attachmentid=283|
+-------------------------------------------------------------------+





I don't know what IBM 1953 has to do with it, for the "invention" of
the 4x12 took place in 1962....;-)

It's simply the "smallest" convenient enclosure for 4 12" drivers. The
slanted one (Marshall 1960A) had the slant only, because the amplifier
head (Marshall JTM45) looked "funny" sitting on top of the cab...

No technical explanation there - although the "explanation" for the
slant was "to project the sound over the crowd so the last rows can hear
something too".... when Jim Marshall and his crew was asked by curios
musicians.

BTW they can sound good on big stages. Almost useless in small venues.
The ears of the people sitting in the center of the "beaming area" are
almost "pierced"; the other ones - including the guitar hero don't hear
much of it....

"i can't hear my guitar" - "no i did not turn it up"

regards

Jochen

PS: and yes - they are noise generators - have nothing to to with sound
reproduction. Guitar speakers are part of the instrument - and a very
important one. Far from "perfect".

[Phil Allison[_3_]]

"jh"


It's simply the "smallest" convenient enclosure for 4 12" drivers. The
slanted one (Marshall 1960A) had the slant only, because the amplifier
head (Marshall JTM45) looked "funny" sitting on top of the cab...

No technical explanation there - although the "explanation" for the slant
was "to project the sound over the crowd so the last rows can hear
something too".... when Jim Marshall and his crew was asked by curios
musicians.


** The slant front 4 x 12 cab was built after requests from guitarists who
regularly played in venues that were cinemas. Typical cinemas of the era
were converted ( or doubled as) live theatres and so had " front stalls " at
ground level and a " dress circle " upstairs. Folk up stairs were missing
out on the higher tones from straight fronted cabs.

http://i55.tinypic.com/16acdg6.jpg

Many Fender combo amps were built with two, steel legs that allowed to amp
to tilt backwards at about 30 degrees for similar reasons - eg.

http://www.stratopastor.org.uk/strat...istiltback.jpg


..... Phil

[jh[_3_]]

Am 17.04.2012 10:12, schrieb Phil Allison:
"jh"


It's simply the "smallest" convenient enclosure for 4 12" drivers. The
slanted one (Marshall 1960A) had the slant only, because the amplifier
head (Marshall JTM45) looked "funny" sitting on top of the cab...

No technical explanation there - although the "explanation" for the slant
was "to project the sound over the crowd so the last rows can hear
something too".... when Jim Marshall and his crew was asked by curios
musicians.


** The slant front 4 x 12 cab was built after requests from guitarists who
regularly played in venues that were cinemas. Typical cinemas of the era
were converted ( or doubled as) live theatres and so had " front stalls " at
ground level and a " dress circle " upstairs. Folk up stairs were missing
out on the higher tones from straight fronted cabs.

http://i55.tinypic.com/16acdg6.jpg

Many Fender combo amps were built with two, steel legs that allowed to amp
to tilt backwards at about 30 degrees for similar reasons - eg.

http://www.stratopastor.org.uk/strat...istiltback.jpg


..... Phil





....you don't believe Jim Marshall's own words?

[Phil Allison[_3_]]

"jh"


** The slant front 4 x 12 cab was built after requests from guitarists
who
regularly played in venues that were cinemas. Typical cinemas of the era
were converted ( or doubled as) live theatres and so had " front stalls "
at
ground level and a " dress circle " upstairs. Folk up stairs were missing
out on the higher tones from straight fronted cabs.

http://i55.tinypic.com/16acdg6.jpg

Many Fender combo amps were built with two, steel legs that allowed to
amp
to tilt backwards at about 30 degrees for similar reasons - eg.

http://www.stratopastor.org.uk/strat...istiltback.jpg



...you don't believe Jim Marshall's own words?


** I am quoting him, from at least two magazine articles.

You bull****ting idiot.



.... Phil

[Phil Allison[_3_]]

"John L Stewart"

My Grandsons PV JSX that I worked on has 4X 12 inch speakers with the
back closed.

** Told ya.....

A few hours ago I posted this:

" JLS has not revealed whether his example of the PV JSX is a combo or a
head - but a resonant peak in the impedance at 137Hz suggests it is a head
with a sealed cabinet. "


With all this theory being spouted did anyone mention that DF don't
matter much beyond about 10 because speaker R gets in the way.


** Never come across a tube guitar amp with a DF of more than 5.

Some ( eg the VOX AC30 ) have a DF of about 0.1.



.... Phil

[jh[_3_]]

Am 17.04.2012 12:29, schrieb Phil Allison:
"jh"


** The slant front 4 x 12 cab was built after requests from guitarists
who
regularly played in venues that were cinemas. Typical cinemas of the era
were converted ( or doubled as) live theatres and so had " front stalls "
at
ground level and a " dress circle " upstairs. Folk up stairs were missing
out on the higher tones from straight fronted cabs.

http://i55.tinypic.com/16acdg6.jpg

Many Fender combo amps were built with two, steel legs that allowed to
amp
to tilt backwards at about 30 degrees for similar reasons - eg.

http://www.stratopastor.org.uk/strat...istiltback.jpg



...you don't believe Jim Marshall's own words?


** I am quoting him, from at least two magazine articles.

You bull****ting idiot.



.... Phil



Phil,

The history of Marshall has been quite consistent over the last 30+
years.... Not many contradictions by Mr. Marshall. He almost always told
his story the same way.

BTW - where is your source - as you're "quoting him" ???

For example: I have a german copy of "Jim Marshall - the father of loud"
2004 - handsigned by the man himself. There is a quote with this exact
content. Cosmetics was the intention.
The possibility, that the projection might improve, was purely by
accident. This told by "the man himself"

Unfortunately neither you nor me can ask him anymore...

So please leave baiting and show *your* sources

kindest regards

Jochen

[Phil Allison[_3_]]

"jh"

...you don't believe Jim Marshall's own words?


** I am quoting him, from at least two magazine articles.

You bull****ting idiot.

BTW - where is your source - as you're "quoting him" ???

** You quoted no source at all.


For example: I have a german copy of "Jim Marshall - the father of loud"
2004 - handsigned by the man himself.


** But not written by him - so useless.

**** off ****head.

[jh[_3_]]

Am 17.04.2012 15:23, schrieb Phil Allison:
"jh"

...you don't believe Jim Marshall's own words?


** I am quoting him, from at least two magazine articles.

You bull****ting idiot.

BTW - where is your source - as you're "quoting him" ???

** You quoted no source at all.

you did not either

where's your source -eh? written by him?



Phil - it's so easy with you - you have always been pretty predictable
- especially, when you're running out of arguments.




For example: I have a german copy of "Jim Marshall - the father of loud"
2004 - handsigned by the man himself.


** But not written by him - so useless.

**** off ****head.

NO

:-)


Doyle the history of marshall - several interviews etc pp.
#

[Phil Allison[_3_]]

"jh"


...you don't believe Jim Marshall's own words?


** I am quoting him, from at least two magazine articles.

You bull****ting idiot.

BTW - where is your source - as you're "quoting him" ???

** You quoted no source at all.

you did not either


** FFS - get cause and effect figured out, ****head.

Then GO DROP ****ING DEAD !!

You revolting, wog nut case retard.

[jh[_3_]]

Am 17.04.2012 15:56, schrieb Phil Allison:
"jh"


...you don't believe Jim Marshall's own words?


** I am quoting him, from at least two magazine articles.

You bull****ting idiot.

BTW - where is your source - as you're "quoting him" ???

** You quoted no source at all.

you did not either


** FFS - get cause and effect figured out, ****head.

Then GO DROP ****ING DEAD !!

You revolting, wog nut case retard.





exactly....

** FFS - get cause and effect figured out, ****head.

Jim Marshall himself said several times, that he "invented" the slant
simply because he did not like the optics of the (fairly small) JTM45
head sitting on the straight cab. (for example: Page 12 - The History of
Marshall - and proofread by JM himself!!)

Your arguments? TGDFD??? You don't ´need to...



read back again in this thread - you chimed in, trying to prove that i'm
wrong - so back it up - nothing yet

baaah

[Phil Allison[_3_]]

"jh" = RABID ****ING NUTTER


Jim Marshall himself said several times, that he "invented" the slant
simply because he did not like the optics of the (fairly small) JTM45 head
sitting on the straight cab. (for example: Page 12 - The History of
Marshall - and proofread by JM himself!!)


** All depend what the ****ing QUESTION was - you ****ing ASD ****ed
****wit !!!!!!!!!!!

The **PURPOSE** of the slanted front is to project sound upwards to an
elevated audience.

Now, whether or not Jim actually thought of it before making the suggestion
to his workers is MOOT !!!

FFS - Jim Marshall was a ****ING DRUMMER with NO CLUE AT ALL about
either amplifiers or how sound works.


FFS - get cause and effect figured out, ****head.

Then GO DROP ****ING DEAD !!

You revolting, wog nut case ****ing retard.