"Dave Plowman (News)" wrote in message
...
In article ,
Keith G wrote:
Also, I've read your comments on suspension amd springiness again, but
still don't know exactly what it is that is directly affected (or
improved, presumably) by 'high flux density'...??

The movement of a conductor carrying a current is influenced by the flux
density acting on it. In other words the higher the flux density the more
it will move. Which is the efficiency of what is a motor of sorts.


Sure - a linear motor, no?

But you are talking 'amplitude' whereas I get the impression Don is talking
about the strength of an applied force which would more greatly affect the
speed of an excursion (and return therefrom), would it not?

Never mind, Arny'll be along shortly (aka the world-famous big chief
****ting Bull) - he'll put us right.

(Or perhaps, he won't... ;-)

On Thu, 9 Apr 2009 15:05:26 +0100, "Keith G"
wrote:


"Don Pearce" wrote in message
news:4a00f601.258178859@localhost...
On Thu, 9 Apr 2009 14:04:07 +0100, "Keith G"
wrote:

There's another issue, as of this morning - looks like I've got a
microphonic *valve socket* on an amp I have just re-activated and it's got
me wondering about cobbling together one of these 'Tripath' amps pro
temps....?? Just curious - David Holgate (past UKRA poster) was very
enthusiastic about them offlist a while back!!

Don't know the tripath, but when it comes to microphonic, it is always
the valve at fault.


Noop. Simple checking with 3 different valves (out of 4 available)
demonstrates the problem to remain with the socket always. I suspect the
soldering or it just needs proper, tricky cleaning - the problem is that its
PCB mounted, so not trivial to just swap it out and move on!! The nuisance
is that it pops and spits quite hard when its warming up and that ain't good
on a Lowther! (Voice coils wired inside and out and one will fall off with
that sort of behaviour, apparently!)

Ah that is a different problem - a poor pin connection rather than
microphonics. As the valve moves the connection makes and breaks. It
could be a dodgy solder joint or - quite likely when you mount
something as heavy as a valve on a PCB - a fractured track close to
the socket. You will need a jeweller's glass to see that.


Anti-microphonic sockets just provide some
suspension to keep the valve steady. Unfortunately a common error is
to carefully fit a nice anti-microphonic socket, then completely wreck
it by stiff, short wiring anchoring the thing firmly to the chassis.


Sure. Apart from the physical coupling, hardwiring anywhere/anything too
tight in a valve amp which is going to get quite hot is not a good idea!



Also, I've read your comments on suspension amd springiness again, but
still
don't know exactly what it is that is directly affected (or improved,
presumably) by 'high flux density'...??


Flux density? More is better.


Yep. That much is obvious - if nothing else, the figure goes up with the
price!! :-)


The force exerted by the wire is
proportional to it (and the current, and the number of turns in the
coil).


OK, I'm getting the idea - my initial thoughts were probably not to far out
then: I suspected it was like shortening a dog's lead - the higher the flux,
the shorter the lead. Which, I guess, is what give Lowthers their 'speed'
and supreme clarity - or, to put it another way, their entire *lack* of
'flubberiness'!


Unfortunately no - the forces and movements just don't work that way.

d

"Don Pearce" wrote

Don't know the tripath,

There's a fairly comprehensive write-up here, if you are interested:

http://www.tnt-audio.com/ampli/tripath_amps_e.html

(I believe the 'Charlize' amplifier is named in honour of an attractive
actress...??)

But this is what David Holgate was enthusing about - a 'Gainclone':

http://cgi.ebay.co.uk/20W-Stereo-DIY...1%7C240%3A1318


(Try eBay auction No. 310125391530 if that link don't work!)

"Don Pearce" wrote in message
news:4a0201a1.261152296@localhost...
On Thu, 9 Apr 2009 15:05:26 +0100, "Keith G"
wrote:


Noop. Simple checking with 3 different valves (out of 4 available)
demonstrates the problem to remain with the socket always. I suspect the
soldering or it just needs proper, tricky cleaning - the problem is that
its
PCB mounted, so not trivial to just swap it out and move on!! The nuisance
is that it pops and spits quite hard when its warming up and that ain't
good
on a Lowther! (Voice coils wired inside and out and one will fall off with
that sort of behaviour, apparently!)

Ah that is a different problem - a poor pin connection rather than
microphonics. As the valve moves the connection makes and breaks. It
could be a dodgy solder joint or - quite likely when you mount
something as heavy as a valve on a PCB - a fractured track close to
the socket. You will need a jeweller's glass to see that.


I suspect the soldering - the valve is question (6AU6) is about as light as
they come. It's a faff, but I'll flow the solder joints on the socket pins
to see if that clears it. I have been using an old (but nice) Pioneer SS amp
but that's got a bit noisy and hit and miss on the knobs now, so it's a
clean-up either way is why I was thinking of summat different like the
Gainclone for the time being!!


OK, I'm getting the idea - my initial thoughts were probably not to far
out
then: I suspected it was like shortening a dog's lead - the higher the
flux,
the shorter the lead. Which, I guess, is what give Lowthers their 'speed'
and supreme clarity - or, to put it another way, their entire *lack* of
'flubberiness'!


Unfortunately no - the forces and movements just don't work that way.


OK, I'll have to wait for Arnie's 'no upper case/no long words' explanation,
then - he's especially skilled at dealing with the *ignorant*...!!

:-)

Dave Plowman (News) wrote:
In article ,
Keith G wrote:
Also, I've read your comments on suspension amd springiness again,
but still don't know exactly what it is that is directly affected (or
improved, presumably) by 'high flux density'...??

The movement of a conductor carrying a current is influenced by the
flux density acting on it. In other words the higher the flux density
the more it will move. Which is the efficiency of what is a motor of
sorts.


Being pedantic...it is the *force* on a current carrying conductor that is
affected by flux density, from F = q v × B, qv is charge movement =
current, B is flux density

Of course, the velocity of the conductor will often be roughly proportional
to the force in the real world...depending on how it is constrained.

On Thu, 09 Apr 2009 14:19:55 +0100, Jim Lesurf
wrote:

In article 49ffe88b.254734781@localhost, Don Pearce
wrote:
On Thu, 09 Apr 2009 10:13:43 +0100, Jim Lesurf
wrote:

[big snip]

OK, now you have me thinking, but I know my brain is going to start
hurting if I go down that route - I won't be able to put it down.

But speaker sensitivity is generally given at 1kHz, well away from all
the cabinet "stuff" occurring around the speaker resonance.

Waving my hands and taking 1000 feet/sec (aargh, non SI alert!) as the
speed of sound I'd expect some loss from the mechanism you mention below
even at 1kHz, and for it to produce a bigger and bigger drop in efficiency
as you go down in frequency. This assumes a speaker unit with a size of
less than 1 ft.

All the box is really doing is stopping the out-of-phase stuff round the
back getting involved.

But that "all" is vital to the output efficiency for wavelengths which
aren't small compared with the cone scale size. i.e. from around 1kHz and
downwards in frequency for typical domestic units.

Boxes certainly do change things to a certain extent by diffraction if
nothing else, but I think the equation above was derived empirically as
the least-worst estimate.

Having said all that, I would be suspicious of a claim of 6dB
improvement just from any mounting method other than a front loaded horn.

I don't know how big the effect might be as I've never really studied this
nor designed a speaker. But below, say, 100 - 200Hz I'd expect the effect
to quite marked with a unit 8 - 10 inches in diameter. Taking a leaf from
Keith's book, that's what my ears have made me think in the past, anyway.
:-)


I think this one has to be moved to the back burner. It would take
access to a speaker manufacturer's R&D lab notes to sort it out.

d

"Jim Lesurf" wrote in message
...
In article , Keith G
wrote:

"Don Pearce" wrote


Also, I've read your comments on suspension amd springiness again, but
still don't know exactly what it is that is directly affected (or
improved, presumably) by 'high flux density'...??

In effect, the flux density affects how much force is applied to the coil
(and hence pushes the cone) for a given current through the coil. But what
that means in practice depends on other things. So the result depends on
some "all else being the same" assumptions. Makers therefore may say "high
flux density" to imply "more cone movement" or "more output efficiency",
but that depends on other details as well.


Hmm, 'more cone movement' is more or less what Plowie was saying, but thanks
for that nice and clear comment, Jimbo - shows your experience and expertise
in shoving knowledge into thick heads effectively!!

As Don says, though - I'm happy to push this to the back burner (= my 'Feck
Nose' pile) and leave it stew. In fact, I'm going to get a 'Probably Fairy
Dust' rubber stamp made up for this sort of thing when it comes up in the
future - I ain't going to live long enough to *play* all my vinyl at this
rate, let alone spend time trying to *understand* it!

In article ,
TonyL wrote:
Dave Plowman (News) wrote:
In article ,
Keith G wrote:
Also, I've read your comments on suspension amd springiness again,
but still don't know exactly what it is that is directly affected (or
improved, presumably) by 'high flux density'...??

The movement of a conductor carrying a current is influenced by the
flux density acting on it. In other words the higher the flux density
the more it will move. Which is the efficiency of what is a motor of
sorts.


Being pedantic...it is the *force* on a current carrying conductor that
is affected by flux density, from F = q v × B, qv is charge movement
= current, B is flux density

Of course, the velocity of the conductor will often be roughly
proportional to the force in the real world...depending on how it is
constrained.

Trying to keep it simple for ol' Keith. A speaker which didn't move when a
current was applied to it wouldn't be much good. ;-)

--
*Caution: I drive like you do.

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
TonyL wrote:
Dave Plowman (News) wrote:
In article ,
Keith G wrote:
Also, I've read your comments on suspension amd springiness again,
but still don't know exactly what it is that is directly affected
(or improved, presumably) by 'high flux density'...??

The movement of a conductor carrying a current is influenced by the
flux density acting on it. In other words the higher the flux
density the more it will move. Which is the efficiency of what is a
motor of sorts.


Being pedantic...it is the *force* on a current carrying conductor
that is affected by flux density, from F = q v × B, qv is charge
movement = current, B is flux density

Of course, the velocity of the conductor will often be roughly
proportional to the force in the real world...depending on how it is
constrained.

Trying to keep it simple for ol' Keith. A speaker which didn't move
when a current was applied to it wouldn't be much good. ;-)


He, he.

So, the higher the flux density the more the voice coil movement will
attempt to track the current flowing through it and the less it will be
affected by the suspension, the air mass that the cone is pushing against,
etc.

"Keith G" wrote in message

"Arny Krueger" wrote in message
...
"Keith G" wrote in message

"Don Pearce" wrote


If "in a cabinet" means a conventional box, then yes it
is probably blx. The cabinet is only really "doing
stuff" at the speaker's resonance. Above that, where
measurements are made, it is simply stopping the stuff
round the back getting to the front.


Which brings us to the subject of Open Baffle
speakers.... ??

With a driver that is has as limited of a range and as
peaky response as a Lowther, does it matter that much?

I know you don't often go outside your Comfort Zone Arny,
but lemme give you a Tip For Life - if you don't know the
answer to a qustion that has been thrown open it is
generally better to keep quiet (or simply say you *don't
know*, if pressed)....

I've had the displeasure of listening to Lowthers, so the lack of discomfort
is reality-based.