No surprise at all
Seems overly complex - and I can see where it did not last long, or penetrate past a very few makers. By the way, Philips speakers were "active" speakers, needing only a pre-amp input.
No surprise at all, back in the day when tube-based amplifier
damping factors were somewhere between 10 and 15 on a good day
with a tailwind, and acoustic suspension was uncommon. The 'cure'
for tubby bass would be some choice between a stiffer spider,
stiffer surround, smaller magnet, shorter excursion, any or all.
Seems overly complex - and I can see where it did not last long,
or penetrate past a very few makers. By the way, Philips speakers
were "active" speakers, needing only a pre-amp input.
Take the (permanent magnet) speaker as a linear motor.
Now, for illustrative purposes, obtain a small DC brush-type motor. Spin it with your fingers. Now, short the leads to the motor. Now, try spinning it again with your fingers.
Not so easy.
That is the function of "damping factor" - As a way to prevent a PM speaker from wobbling like a spring when it is released.
One of the big problems with drivers is that the suspension stiffness
and the magnet's BL product is, for the most part, highly non-linear:
the stiffness increases with excursion, the BL product decreases
with excursion.
Let me give one example that shows why this is true: look at ANY
bass reflex system: let's assume, for the moment, that it is
"optimally" tuned, i.e., that its frequency response is that of a
"perfect" lossless B4 alignment: it's dead flat down to cutoff,
and it rolls off at 24 dB/octave below that. Now, look at what
the cone is doing as it goes down in frequency through the region
of cutoff:
Acceleration: Constant with frequency as you go lower until
you approach the enclosure tuning frequency, at which point
is approaches 0, ad blow which it increases back up to
the same constant as above tuning.
Velocity: Increases as inverse of frequency until you approach
the enclosure tuning frequency, then goes to 0, goes back up for
a bit then starts decreasing with decreasing frequency.
Position: Increases as the inverse square of frequency until
you approach the enclosure tuning, at which point it approaches
0, then below it starts increasing with decreasing frequency.
Well, I "was there" when the the phillips was being marketed, and at
the same time there was an actually reasonably well-implemented B6
system from EV, designed by, I believe D. B. Keele. Neither speaker was >"outstanding", but both were quite reasonable systems, performance-wise.
Both died in the market for a variety of reasons, but, especially with
the Philips, customers resisted it because they wanted to use it with
THEIR amplifier. Often times, they already had a system and wanted to
upgrade speakers, and looked at their existing amplifier as now being
a "waste". And, with the EV, that little EQ box, no matter how technically >sound the approach was, was just an obstacle for most people. To many,
it reminded them of the Bose 901, and for many, that was just too much.
Interesting story. I had two of the smallest Philips MFBs a few years
back, was not impressed with the sound.
Regarding feedback, I remember there was an hobby project long ago to
have a very small R between speaker and GND (GND also being the amp's ground), and using the speaker's back EMF as feedback to correct
excursions. There are some later publications from W.Kippel about it.
The idea is that the speaker's voice coil itself is the sensor. Will
this feedback method work?
bassreflex also?
**No. It doesn't work like that. In a PROPERLY designed enclosure,
so-called "damping" is not dependent on amplifier output impedance.
Damping is supplied by the enclosure itself.
Take the (permanent magnet) speaker as a linear motor.
Now, for illustrative purposes, obtain a small DC brush-type motor.
Spin it with your fingers. Now, short the leads to the motor.
Now, try spinning it again with your fingers.
Not so easy.
That is the function of "damping factor" - As a way to prevent a
PM speaker from wobbling like a spring when it is released.
Regarding feedback, I remember there was an hobby project long ago to
have a very small R between speaker and GND (GND also being the amp's ground), and using the speaker's back EMF as feedback to correct excursions. There are some later publications from W.Kippel about it.
**The first system I saw with that arrangement was the Infinity RS1. It introduced as many problems as it solved. Amplifiers with 'floating'
output stages encountered some problems. Bridged amplifiers too. That
said, the bass extension available from a rather modestly sized, sealed enclosure was impressive.
Ummmmmm.....
A speaker is a linear motor with a magnet, and a commutator
(voice coil).
Just as in a PM Motor, when current is applied,
the motor spins. DC motors spin according to the
polarity of the power applied.
Speakers move in or out depending on the polarity of the current
applied. And, PM motors do, also, have a fixed resistance across
the commutator just like a voice coil.
Now, when current stops being applied, the motor generates
current - acts as a generator as it spins down. If it is
unloaded, that current goes nowhere and does not add additional
resistance to the motor spinning than normal bearing friction.
However, if the motor is loaded, there will be additional friction.
Similarly the (conventional) speaker. Try it some time with a
sensitive VOM. The bigger the driver, the more easily this is
observed. Just a few taps on the speaker cone will show you.
All and at the same time, DF is only one (1) single factor in
how amplifiers interact with speakers.
And, today in 2019, the issues that drove speaker design in the
era after field-coil speakers were dominant up until the development
of acoustic suspension are not particularly relevant as much
evolution is taken for granted (and usually is granted). However,
as one who spends as much time with electronics from the 1930s
as from the the 1970s and up, I see all sorts of variations on
how to control large speaker overshoot, sagging, and similar
problems.
A 15" Zenith speaker driven by a single-ended 6F6 is
an entirely different animal than a 12" Long-throw woofer from an AR3a.
On Thursday, November 7, 2019 at 4:32:20 PM UTC-5, Trevor Wilson wrote:
Regarding feedback, I remember there was an hobby project long ago to
have a very small R between speaker and GND (GND also being the amp's
ground), and using the speaker's back EMF as feedback to correct
excursions. There are some later publications from W.Kippel about it.
**The first system I saw with that arrangement was the Infinity RS1. It
introduced as many problems as it solved. Amplifiers with 'floating'
output stages encountered some problems. Bridged amplifiers too. That
said, the bass extension available from a rather modestly sized, sealed
enclosure was impressive.
May well be the case, but it wasn't because of feedback. If there
was anything done electronically, it was EQ which, itself, is a
completely legitimate way of getting bandwidth, if done properly*.
* Which, of course, is subject to Dick Pierce's First Law
of Acoustics: Anny idiot can design a loudspeaker and,
unfortunately, many do.
Ummmmmm.....of the current applied. And, PM motors do, also, have a fixed resistance across the commutator just like a voice coil.
A speaker is a linear motor with a magnet, and a commutator (voice coil). Just as in a PM Motor, when current is applied, the motor spins. DC motors spin according to the polarity of the power applied. Speakers move in or out depending on the polarity
Now, when current stops being applied, the motor generates current - acts as a generator as it spins down. If it is unloaded, that current goes nowhere and does not add additional resistance to the motor spinning than normal bearing friction. However,if the motor is loaded, there will be additional friction.
Similarly the (conventional) speaker. Try it some time with a sensitive VOM. The bigger the driver, the more easily this is observed. Just a few taps on the speaker cone will show you.suspension are not particularly relevant as much evolution is taken for granted (and usually is granted). However, as one who spends as much time with electronics from the 1930s as from the the 1970s and up, I see all sorts of variations on how to
All and at the same time, DF is only one (1) single factor in how amplifiers interact with speakers. And, today in 2019, the issues that drove speaker design in the era after field-coil speakers were dominant up until the development of acoustic
On 9/11/2019 6:50 am, Peter Wieck wrote:polarity of the current applied. And, PM motors do, also, have a fixed resistance across the commutator just like a voice coil.
Ummmmmm.....
A speaker is a linear motor with a magnet, and a commutator (voice coil). Just as in a PM Motor, when current is applied, the motor spins. DC motors spin according to the polarity of the power applied. Speakers move in or out depending on the
if the motor is loaded, there will be additional friction.Now, when current stops being applied, the motor generates current - acts as a generator as it spins down. If it is unloaded, that current goes nowhere and does not add additional resistance to the motor spinning than normal bearing friction. However,
suspension are not particularly relevant as much evolution is taken for granted (and usually is granted). However, as one who spends as much time with electronics from the 1930s as from the the 1970s and up, I see all sorts of variations on how toSimilarly the (conventional) speaker. Try it some time with a sensitive VOM. The bigger the driver, the more easily this is observed. Just a few taps on the speaker cone will show you.
All and at the same time, DF is only one (1) single factor in how amplifiers interact with speakers. And, today in 2019, the issues that drove speaker design in the era after field-coil speakers were dominant up until the development of acoustic
**And again: It is the output impedance that is important. The so-called 'damping factor' of an amplifier has (almost) nothing to do with damping
a speaker.
The reason why speakers sound different on high output
impedance amplifiers (like most valve amps) is due to the frequency
response variations, caused by the interaction of the output impedance
of the amplifier and the impedance variations over the audible range of
the speaker system.
Locate a speaker that exhibits an almost resistive load and check for yourself. Maggies are a pretty good start. As is almost anything that
uses ribbon HF drivers (obviously, LF variations will depend on what
kind of bass driver/s is used). Maggies exhibit a highly resistive load
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