To Trevor, RE the Watkins Woofer
Bill Watkins
tre...@rageaudio.com.au says...
>Even one of RAO's favourite sons (Bill Watkins) in collaboration
>with Infinity, released some of the most diabolical speakers
>ever let loose on the domestic market (impedance-wise).
>Trevor Wilson
>www.rageaudio.com.au
---
Trevor, I believe it's time I explained what happened
here. My dual-drive woofer works so:
A second voice coil (vc-2) is wound over the main voice
coil (vc-1) in the woofer, this second coil having a
single layer and very low impedance. Now vc-2 would
normally have an impedance too low for safe operation.
However around fundamental resonance the impedance of
_any_ coil will ~triple. Now we activate vc-2 _ONLY_
in the region of fundamental resonance (around 45 Hz)
and it rises to ~8 ohms or so (being ~2.5 in the
first place) which is safe. This is accomplished with
an LC circuit tuned to 45 HZ and with the Q of the LC
circuit adjusted to provide the response shape and
impedance desired. Please note that the exact value
of vc-2 and the characteristics of the LC circuit give
_COMPLETE_ control of the impedance. The benefit of
the dual-drive may then be taken in extended bass or
higher efficiency in a given size box, or a smaller
box for a given efficiency or bass extension.
Now I set the parameters of the original QLS-1 in a
prototype and shipped it to Infinity. It had a minimum
impedance of 3.2 ohms, acceptable for a 4 ohm speaker.
At that time we were operating a retail store selling
Infinity. Our first shipment of the QLS-1's arrived,
we tested a pair and found the impedance to be
~1 3/4 ohms from ~50 - 80 HZ. Now, the fun begins...
Mr. Nudell wanted a spec down to 20 HZ, he got to
18, as I recall, by adding ~35 grams of mass under
the dust cap, _BUT_ he did not re-tune LC to the
lower resonant frequency, leaving vc-2 operating
somewhat above the new fundamental resonance, and
creating a low impedance in that area. My name
was already on the royalty agreement, which had no
stipulation to cover such... I did voice my
disapproval to no avail.
If you check, you will find our WE-1, built and
marketed by _my_ company had no impedance problems,
and neither did thousands of other speakers we
built have any impedance problems. Perhaps this
makes things clear for the technical people here.
Bill Watkins
Trevor Wilson
"Bill Watkins" <bwat...@mounet.com> wrote in message
news:slibukr...@corp.supernews.com...
**Thank you, Bill. I was aware of the general principle of your dual drive
system.
>
> Now I set the parameters of the original QLS-1 in a
> prototype and shipped it to Infinity. It had a minimum
> impedance of 3.2 ohms, acceptable for a 4 ohm speaker.
> At that time we were operating a retail store selling
> Infinity. Our first shipment of the QLS-1's arrived,
> we tested a pair and found the impedance to be
> ~1 3/4 ohms from ~50 - 80 HZ.
**That correlates with my measurements. Did you ever measure the RS4.5? They
were worse. Having said that, the QLS1 and Q2 bass drivers (sans the dual
drive circuitry) were my favourite bass drivers of all time. Very, very
clean. What was the coating they used? Mineral loaded clay?
Now, the fun begins...
> Mr. Nudell wanted a spec down to 20 HZ, he got to
> 18, as I recall, by adding ~35 grams of mass under
> the dust cap, _BUT_ he did not re-tune LC to the
> lower resonant frequency, leaving vc-2 operating
> somewhat above the new fundamental resonance, and
> creating a low impedance in that area. My name
> was already on the royalty agreement, which had no
> stipulation to cover such... I did voice my
> disapproval to no avail.
**Not altogether surprising. I was closely invloved with the importer of
Infinity products from around 1978 to about 1985. Many times I suggested
modifications and improvements, to their products. Those suggestions were
ignored. Inductor choice, by Infinity, ranged from adequate, to bizarre. In
a few models, I found that the inductor in series with the bass driver,
saturated at less than 12 VRMS, at some frequencies! The resulting
distortion was instantly audible. For several months, Infinity refused to
acknowledge that there was a problem (presumably until someone actually
measured the damn things).
>
> If you check, you will find our WE-1, built and
> marketed by _my_ company had no impedance problems,
> and neither did thousands of other speakers we
> built have any impedance problems. Perhaps this
> makes things clear for the technical people here.
**Having worked with many, many Infinity models, over many years, I am not
at all surprised at what you found. Good engineering and success, do not
necessarily go hand in hand.
For the record, I am a technical person. Only Mr Kreuger casts doubt on this
fact.
--
Trevor Wilson
www.rageaudio.com.au
Bill Watkins
tre...@rageaudio.com.au says...
> "Bill Watkins" <bwat...@mounet.com> wrote in message
> news:slibukr...@corp.supernews.com...
>> In article <5PU55.5406$Sn2....@news-server.bigpond.net.au>,
>> tre...@rageaudio.com.au says...
>>
>>
>>>Even one of RAO's favourite sons (Bill Watkins) in collaboration
>>>with Infinity, released some of the most diabolical speakers
>>>ever let loose on the domestic market (impedance-wise).
>>>Trevor Wilson
>>>www.rageaudio.com.au
>>
>>
>>
>> Trevor, I believe it's time I explained what happened
>> here. My dual-drive woofer works so:
>> A second voice coil (vc-2) is wound over the main voice
>> coil (vc-1) in the woofer, this second coil having a
>> single layer and very low impedance. Now vc-2 would
>> normally have an impedance too low for safe operation.
>> However around fundamental resonance the impedance of
>> _any_ coil will ~triple. Now we activate vc-2 _ONLY_
>> in the region of fundamental resonance (around 45 Hz)
>> and it rises to ~8 ohms or so (being ~2.5 in the
>> first place) which is safe. This is accomplished with
>> an LC circuit tuned to 45 HZ and with the Q of the LC
>> circuit adjusted to provide the response shape and
>> impedance desired. Please note that the exact value
>> of vc-2 and the characteristics of the LC circuit give
>> _COMPLETE_ control of the impedance. The benefit of
>> the dual-drive may then be taken in extended bass or
>> higher efficiency in a given size box, or a smaller
>> box for a given efficiency or bass extension.
>
>**Thank you, Bill. I was aware of the general principle of your
>dual drive system.
You are welcome. In reality, it's a simple concept, but
not so easy to analyze in mathmetical ways. It doesn't
violate Mr. Kloss's "Hofmann's Iron Law", but circumvents it.
Richard Small, from down your way did an analysis of the
operational principle after I had finalized it. Seventeen
pages of it to establish the theoretical maximum gain...
Henry Kloss with Advent originally wanted the license, and ask
one of his helpers to send me pole pieces, plates, magnets,
etc for his woofer of that era, with which I was to impliment
dual-drive into it. I never received the parts, decided
he had lost interest, and went with Infinity. Months later
he contacted me, to check the progress. Turned out his
man had packed the parts up, dropped the ball and they were
in the back room, his man having forgotten to ship them...
Not too long after that, Mr. Kloss sold out and moved on,
so likely fortune was on my side. What type business
exactly are you in?
>> I set the parameters of the original QLS-1 in a
>> prototype and shipped it to Infinity. It had a minimum
>> impedance of 3.2 ohms, acceptable for a 4 ohm speaker.
>> At that time we were operating a retail store selling
>> Infinity. Our first shipment of the QLS-1's arrived,
>> we tested a pair and found the impedance to be
>> ~1 3/4 ohms from ~50 - 80 HZ.
>
>**That correlates with my measurements. Did you ever measure the RS4.5? They
>were worse. Having said that, the QLS1 and Q2 bass drivers (sans the dual
>drive circuitry) were my favourite bass drivers of all time. Very, very
>clean. What was the coating they used? Mineral loaded clay?
Thank you. The coating was aquaplaz. Yes, I measured
the 4.5. With all due respect to Mr. Nudell, in that
era he didn't put the degree of priority on impedance
that some other designers did.
>> Now, the fun begins...
>> Mr. Nudell wanted a spec down to 20 HZ, he got to
>> 18, as I recall, by adding ~35 grams of mass under
>> the dust cap, _BUT_ he did not re-tune LC to the
>> lower resonant frequency, leaving vc-2 operating
>> somewhat above the new fundamental resonance, and
>> creating a low impedance in that area. My name
>> was already on the royalty agreement, which had no
>> stipulation to cover such... I did voice my
>> disapproval to no avail.
>
>**Not altogether surprising. I was closely invloved with the importer of
>Infinity products from around 1978 to about 1985. Many times I suggested
>modifications and improvements, to their products. Those suggestions were
>ignored. Inductor choice, by Infinity, ranged from adequate, to bizarre. In
>a few models, I found that the inductor in series with the bass driver,
>saturated at less than 12 VRMS, at some frequencies! The resulting
>distortion was instantly audible. For several months, Infinity refused to
>acknowledge that there was a problem (presumably until someone actually
>measured the damn things).
My impression was that Mr. Nudell was the tinkerer
(a pretty good one), and he may have left some of the
"details" to helpers. The 20 mh inductor in the dual-drive
circuit was my design, air-gapped, grain oriented steel,
and showed no hysteresis distortion to above 200 watts
RMS, a safe enough spec for that era.
>> If you check, you will find our WE-1, built and
>> marketed by _my_ company had no impedance problems,
>> and neither did thousands of other speakers we
>> built have any impedance problems. Perhaps this
>> makes things clear for the technical people here.
>**Having worked with many, many Infinity models, over many years, I am not
>at all surprised at what you found. Good engineering and success, do not
>necessarily go hand in hand. For the record, I am a technical person.
>Only Mr Kreuger casts doubt on this fact.
>Trevor Wilson
>www.rageaudio.com.au
Mr. Krueger generally works above my head in the technical aspects.
My way is to go about it in the simplest form first.
Bill Watkins
Trevor Wilson
> What type business
> exactly are you in?
**The majority of my income is derived from solving peoples hi fi problems
and service to same. I suplement that with fixing manufacturer's mistakes
and corner cutting (plenty of room to move there!). Lastly I sell a small
range of equipment, including the only amp, available in Australia, during
the late 1970's, which could survive the impedance presented by Infinity's
implementation of your technology. I recall how I presented the importer
with one of these amps, for his Imfinty RS4.5's. Several Phase Linear's,
Yamaha's and a few others had either shut down, or blown up, in response to
the absurd impedance curve delivered by these monsters. In fact the amp, I
supplied expired after a few weeks too. The manufacturer scratched his head,
since his amp was rated to deliver 100 Amps. In those days, no current
limiters were used. After measuring the impedance curve of the 4'5's,
current limiters were installed in all production models, post haste.
>
>
> Thank you. The coating was aquaplaz. Yes, I measured
> the 4.5. With all due respect to Mr. Nudell, in that
> era he didn't put the degree of priority on impedance
> that some other designers did.
>
**Yep. I think he was big on tubes. They certainly don't suffer the same
pyrotechnic results, when driven into tricky loads. The 4.5 woofers were
dogs, though.
>
> My impression was that Mr. Nudell was the tinkerer
> (a pretty good one), and he may have left some of the
> "details" to helpers. The 20 mh inductor in the dual-drive
> circuit was my design, air-gapped, grain oriented steel,
> and showed no hysteresis distortion to above 200 watts
> RMS, a safe enough spec for that era.
**None of the laminated steel inductors caused any problems. I was never
able to get them into saturation. It was the ferrite types, which caused all
the problems.
--
Trevor Wilson
www.rageaudio.com.au
Howard Ferstler
> > What type business
> > exactly are you in?
>
> and service to same. I suplement that with fixing manufacturer's mistakes
> and corner cutting (plenty of room to move there!). Lastly I sell a small
> range of equipment, including the only amp, available in Australia, during
> the late 1970's, which could survive the impedance presented by Infinity's
> implementation of your technology. I recall how I presented the importer
> with one of these amps, for his Imfinty RS4.5's. Several Phase Linear's,
> Yamaha's and a few others had either shut down, or blown up, in response to
> the absurd impedance curve delivered by these monsters. In fact the amp, I
> supplied expired after a few weeks too. The manufacturer scratched his head,
> since his amp was rated to deliver 100 Amps. In those days, no current
> limiters were used. After measuring the impedance curve of the 4'5's,
> current limiters were installed in all production models, post haste.
>
> >
> >
> > the 4.5. With all due respect to Mr. Nudell, in that
> > era he didn't put the degree of priority on impedance
> > that some other designers did.
> >
>
> pyrotechnic results, when driven into tricky loads. The 4.5 woofers were
> dogs, though.
>
> >
> > (a pretty good one), and he may have left some of the
> > "details" to helpers. The 20 mh inductor in the dual-drive
> > circuit was my design, air-gapped, grain oriented steel,
> > and showed no hysteresis distortion to above 200 watts
> > RMS, a safe enough spec for that era.
>
> able to get them into saturation. It was the ferrite types, which caused all
> the problems.
I thoroughly enjoyed reading this series of posts between
you and Bill.
Howard Ferstler
Tony Loban
----snip----
> In reality, it's a simple concept, but
> not so easy to analyze in mathmetical ways. It doesn't
> violate Mr. Kloss's "Hofmann's Iron Law", but circumvents
it.
> Richard Small, from down your way did an analysis of the
> operational principle after I had finalized it. Seventeen
> pages of it to establish the theoretical maximum gain...
----snip----
bill, i guess the 'short course' here is that your dual-drive
system lowered the impedance of the woofer around fundamental
resonance, making it easier for amplifiers to power the woofer
at and below resonance. yes?
the question i have is this: imo, when you drive a system below
resonance there is an inevitable rise in harmonic distortion,
since, in essence, the voice-coil is no longer in complete
control of the motion of the cone(the 'stiffness' of the air in
the enclosure becomes a larger and larger factor with decreasing
frequency-which is why the system is 'rolling off' with
decreasing frequency absent your dual-drive system or some form
of eq.)did your dual-drive system include steps to decrease this
rise in(speaker generated)distortion?
Got questions? Get answers over the phone at Keen.com.
Up to 100 minutes free!
http://www.keen.com
No User
On Tue, 27 Jun 2000, Trevor Wilson wrote:
> [...]
>
> For the record, I am a technical person. [...]
Answer my questions on feedback first. You will be asked to address impedance later.
--
Anon E. Mouse
Trevor Wilson
"No User" <no....@anon.xg.nu> wrote in message
news:26d36818d427ca27...@anon.xg.nu...
1) I have no record of a question from you.
2) I do not carry on a discussion with unidentified people.
3) Be polite, or into the killfile you will go.
--
Trevor Wilson
www.rageaudio.com.au
Bill Watkins
>> Trevor wrote:
>> **None of the laminated steel inductors caused any problems. I was never
>> able to get them into saturation. It was the ferrite types, which caused
all
>> the problems.
>Howard wrote:
>I thoroughly enjoyed reading this series of posts between
>you and Bill.
---
Thanks Howard.
Bill Watkins
Bill Watkins
tre...@rageaudio.com.au says...
>**The majority of my income is derived from solving peoples hi fi problems
>and service to same. I suplement that with fixing manufacturer's mistakes
>and corner cutting (plenty of room to move there!). Lastly I sell a small
>range of equipment, including the only amp, available in Australia, during
>the late 1970's, which could survive the impedance presented by Infinity's
>implementation of your technology. I recall how I presented the importer
>with one of these amps, for his Imfinty RS4.5's. Several Phase Linear's,
>Yamaha's and a few others had either shut down, or blown up, in response to
>the absurd impedance curve delivered by these monsters. In fact the amp, I
>supplied expired after a few weeks too. The manufacturer scratched his head,
>since his amp was rated to deliver 100 Amps. In those days, no current
>limiters were used. After measuring the impedance curve of the 4'5's,
>current limiters were installed in all production models, post haste.
Sounds like you have an interesting series of things
going on. RE current limiters, I have preferred the
simple circuits, meaning I prefer no limiters.
Unfortunately, such is sometimes needed for the
marketplace. The 4.5 was Mr. Nudells baby, after
my time with him. However I did work later with
Cary Christie on the bass end of the Renaissance
80 and 90.
>**None of the laminated steel inductors caused any problems. I was never
>able to get them into saturation. It was the ferrite types, which caused all
>the problems.
>--
>Trevor Wilson
>www.rageaudio.com.au
I would never use a ferrite core inductor other than
in a low bass filter, then it would have to be huge.
A bar ~1"x1"x4" is needed to get even 100 watts
through cleanly. Grain oriented laminated steel
inductors are expensive, but they measure and sound
clean.
Bill Watkins
Trevor Wilson
>
> Sounds like you have an interesting series of things
> going on. RE current limiters, I have preferred the
> simple circuits, meaning I prefer no limiters.
> Unfortunately, such is sometimes needed for the
> marketplace. The 4.5 was Mr. Nudells baby, after
> my time with him. However I did work later with
> Cary Christie on the bass end of the Renaissance
> 80 and 90.
**Two models, which Infinity finally got right, after the old RS4b. The
Renaissance were very under-rated products (here in Australia).
--
Trevor Wilson
www.rageaudio.com.au
Bill Watkins
says...
>bill, i guess the 'short course' here is that your dual-drive
>system lowered the impedance of the woofer around fundamental
>resonance, making it easier for amplifiers to power the woofer
>at and below resonance. yes?
The benefits of the dual-drive are mainly:
1. Extended bass, higher efficiency, smaller enclosure,
or a combination of the above.
2. In any case, a flatter impedance, and almost purely resistive
load in the bass. For example, one can achieve 6 ohms
+/- .5 ohm easily from 10 Hz through 200 Hz if desired.
The typical woofer would vary from 6 to 20 ohms or so.
Thus the dual-drive removes the highly inductive load
of ordinary woofers in the region of resonance and allows
the amplifier to deliver more power into the woofer.
>the question i have is this: imo, when you drive a system below
>resonance there is an inevitable rise in harmonic distortion,
>since, in essence, the voice-coil is no longer in complete
>control of the motion of the cone(the 'stiffness' of the air in
>the enclosure becomes a larger and larger factor with decreasing
>frequency-which is why the system is 'rolling off' with
>decreasing frequency absent your dual-drive system or some form
>of eq.)did your dual-drive system include steps to decrease this
>rise in(speaker generated)distortion?
The 12" dual-drive exhibits the lowest harmonic distortion
I have ever measured at 90 dB 1 meter, 10 through 200 HZ.
This is due mainly to linear drive by the motor however.
I know of no way to significantly decrease the increasing
distortion with lowering frequency below resonance, other
than to extend the linear magnetic field the voice coil is
immersed in. It is a function of increased cone/coil motion
with lowering frequency and the coil goes further and
further fron the linear magnetic field.
Bill Watkins
Bill Watkins
tre...@rageaudio.com.au says...
To elaborate on your question about woofer operation:
The theory of such is a little difficult to describe, in
laymans terms at least, but here is my assessmant. Let's
look at a quality 8" woofer in a sealed enclosure ~10"
wide and examine its frequency response from ~1,500 Hz
downward. Response will be flat by nature down to ~300 Hz,
even without an inductor in the crossover, assuming the
proper voice coil configuration and intrinsic inductance.
Around 300 Hz, the "6 dB response step" takes effect. This
is due to increasing wave length with lowering frequency and
the baffle width determines the frequency at which the
radiation pattern changes from 180 degrees to 360 degrees.
Response will begin a downward slope fron here on down.
Incidentally, how this is handled by a given designer has
a _most profound_ effect on the overall character of the
speaker, perhaps the greatest effect, assuming good design
elsewhere, and dual-drive can be implimented to control
the 6 dB response step effect, as well as low bass response.
Now we approach and reach resonance, maybe 50 Hz in our
example. Resonance in a sealed box is the point where the
stored kinetic energy in the moving parts (the mass of the
cone, coil, and ~1/2 the spider and suspension) is equal
to the stored energy in the elasticity of the suspensions
and the air in the enclosure. This is what occurs:
1. The cone is at rest. Now suppose a negative signal is
applied, the cone moves backward, compressing the air in
the box.
2. The cone reaches its innermost position, the air is
compressed, cone motion approaches zero, and kinetic
energy in the moving mass is zero.
3. The stored energy in the compressed air now pushes the cone
forward, kinetic energy builds up in the moving mass,
and upon reaching the starting position, kinetic energy
is at maximum, and "air energy" is where we started at zero,
being neither compressed or rarfied.
4. This kinetic energy in the moving cone causes it to continue
past center or starting position, which then begins to
"stretch" (rarefy) the air in the box.
5. The cone then reaches its outermost position, cone motion
again approaches zero, kinetic energy in the cone is zero,
but we now have maximum energy stored in the "stretched" air,
and it pulls the cone back inward, again inserting kinetic
energy into the cone.
6. The cone reaches center position, kinetic energy is maximum,
and air energy is again is zero. We are where we started, _BUT_
this time we have kinetic energy in the moving system and it will
continue the above cycling _WITHOUT_ amplifier assistance. In
fact, we have created a perpetual motion machine, except the
resistance (friction) in the system will eventually cause it to
slow and stop.
In summation, at any given instant and cone position either the
moving cone is transfering energy into the air in the box, or the
air in the box is transfering energy into the cone. At resonance,
the two forces are equal, so the cone oscillates unassisted back and
forth. Like a ball tied to a rubber band oscillates up and down.
Now the tricky part. It would appear the amplifier's role around
resonance has diminished, the speaker having taken off on its own.
However, motors also act as generators, and the moving coil
generates a voltage opposite in polarity to the amplifier drive
voltage. called bucking voltage, or back EMF. This back EMF
bucks (opposes) the amplifier output voltage, and in fact, with
a larger motor (magnet and/or coil), the more the back EMF, the
more it opposes the drive voltage, and the less the coin motion and
bass output. I call this the see-saw effect - increase the motor
strength and output increases above resonance but _DECREASES_ at
resonance. Decrease motor strength and output decreases above
resonance but _INCREASES_ at resonance. So typically one must
have a certain size motor for flat response, and response above
resonance is tied to that below and vice-versa. However, with
dual-drive we simply insert a smaller motor to increase bass
(with a second low-impedance coil), _BUT_ let it work around
resonance _ONLY_, so as to not affect output above resonance.
The see-saw "plank" then can be up on both ends. Bass response
can be adjusted _INDEPENDENT_ from response above resonance.
We can go for efficiency with a larger magnet, or we can minipulate
motor, mass, and enclosure volume, and use dual-drive to achieve
extended bass or a smaller enclosure, as well as deal with the
6 dB response step.
This leaves the response below resonance to deal with, and here
resistance from the elasticity of the enclosed air is in control
in a sealed box. The output falls 12 dB per octave, equating
to a 2nd order electrical filter network, and so far as I know,
no one has come up with a means to circumvent this law of physics.
Bill Watkins
No User
Will go?!? Am I not a permanent resident of your kill file(s)? 8-D
--
Anon E. Mouse
Trevor Wilson
**I don't know. Who are you?
--
Trevor Wilson
www.rageaudio.com.au