"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?

Keith G wrote:

As is being repeatedly pointed out in this group, I am
something of an ignoramus when it comes to certain (most)
things 'audio' -some because I couldn't care less about
them (CD) and others because I haven't devoted a lifetime
to studying/working in audio and I'm too damn old to start
now!

But I do have a couple of questions - surprisingly
perhaps, I like Lowther speakers (as any number of others
have done for the last 70 or 80 years it appears, but
there ya go) and I was skimming through this article (yes,
I know....)

http://www.hi-fiworld.co.uk/hfw/olde...hornspkrs.html

The phrase "They are very efficient - in a cabinet, the
PM7 hits over 103dB/watt." comes up.

Now, this has always mystified me, especially since I
asked an 'expert' at a famous (but fairly recently changed
hands) 'speaker company' about this very thing and he
didn't think the sensitivity of a speaker (Fostex in the
Buschhorn cabinet, at the time) could be changed
(increased *or* decreased) by the enclosure it was used
in! So, who is right here? (Makers claim for the PM7A is a
sensitivity of 96 dB at 1m/1kHz/1 watt...)

And this phrase also: "This relied on the same basic
twin-cone driver allied to the new PM4 magnet unit, which
has the most unbelievably powerful gap-flux of
24,000Gauss - stronger than anything else I have ever
seen."

...is interesting because one of my pairs of Lowthers has
a 'Flux density' figure of 2.1 Tesla (where 1
Tesla=10,000 Gauss) which is pretty close and implies
*plenty beeg cojones* in some way, but what does it mean?
What does it do? In my ignorance, I imagine it is the
'strength of the return spring' of the speaker's 'motor' -
ie how quickly it can be snapped back from an excursion??

How silly or wide of the mark is that?


Seems to me that as long as the speaker is radiating
directly into the room then the amount of sound it makes
depends on how big the cone is and how far it travels.
Nothing you can do to the box behind it can make the cone
bigger or travel further in a way that is not dependent on
frequency. The box can be used to extend the frequency
range for which the max SPL is realised, and using a
combination
of box resonance and venting, you could get considerable
increase in SPL at some particular frequency, but you
probably wouldn't want to do that, and I suppose it could
damage the driver if you did. Maybe the speaker had a huge
peak where he measured it, and sounded crap in consequence.

The magnet isn't on its own like a spring. A simple way of
looking at it would be to see the force on the cone arising
from the field strength of the magnet, the number of turns
on the coil, and the current through the coil. The stronger
the magnet, the less turns you need, or the less current, or
both, for the same force. One consequence is that coil
resistance becomes less significant, and that should improve
electrical damping.

What's this got to do with a spring? AFAIK the only spring
that snaps your cone back to its centre point is the same
mechanical suspension that stops it from falling out of its
basket.

More analogous to an improvement in the shock absorber, I
would have thought. The difference is that a spring produces
an opposing force dependent on distance, whereas a shock
absorber (aka damper) produces an opposing force dependent
on velocity. An important consequence of this distinction is
that a damper dissipates energy, whereas a spring doesn't.

Seems to me that coil resistance damps the operation of the
electrical damping, but I would be interested if anyone can
help me get a clearer picture of what that means...but I
guess the damping force created by self-induced current in
the coil is stronger without it.

And how significant is it compared with the mechanical
damping provided by the movement of the cone in air, and the
squidgy suspension?

If you've ever toyed with the suspension settings on your
bikes, maybe you should know this kind of stuff?

I suppose we could look it up if we were desperate to know.

Ian

Ian Iveson wrote:

And how significant is it compared with the mechanical
damping provided by the movement of the cone in air, and the
squidgy suspension?


That squidgy suspension issue interests me for a practical reason.

I've just repaired a pair of 30 year old Wharfedale 12 inch drivers. I
replaced the original neoprene suspension with foam sourrounds which seem
much more squidgy. They do sound great now but I'm wondering what overall
effect this has had on their original performance. Improved, degraded or no
difference ? They were out of use for 3-4 years so difficult to judge from
memory....

"Ian Iveson" wrote


snip

What's this got to do with a spring? AFAIK the only spring
that snaps your cone back to its centre point is the same
mechanical suspension that stops it from falling out of its
basket.


Surely not...???


If you've ever toyed with the suspension settings on your bikes, maybe you
should know this kind of stuff?


Tbh, other than adjusting the preload I have never bothered even with
top-quality (top price, at any rate) stuff like Ohlins; the normal 'factory'
settings usually work sufficiently well for most people in most situations -
it's a bit like audio, you can tweak stuff all you like but the original was
probably plenty good enough for most people at the outset!



I suppose we could look it up if we were desperate to know.


No, don't bother but here's another example of the 'depends on cabinet
design' school of thought (4th para):

http://www.lowther.com.hk/


See why I query it...??

"Keith G" wrote in message
...

"Ian Iveson" wrote


snip

What's this got to do with a spring? AFAIK the only spring
that snaps your cone back to its centre point is the same
mechanical suspension that stops it from falling out of its
basket.


Surely not...???

Yes, because there is nothing magnetic in the cone system, except the
interaction of the current in the coil with the magnet. If the current
reverses then the coil (and with it the cone) are *driven* back. As an
analogy consider a double-acting steam engine, the piston is driven both
ways, there is no "spring".

David.

"David Looser" wrote in message
...
"Keith G" wrote in message
...

"Ian Iveson" wrote


snip

What's this got to do with a spring? AFAIK the only spring
that snaps your cone back to its centre point is the same
mechanical suspension that stops it from falling out of its
basket.


Surely not...???

Yes, because there is nothing magnetic in the cone system, except the
interaction of the current in the coil with the magnet. If the current
reverses then the coil (and with it the cone) are *driven* back.


Yes. That's what I was referring to - the foams on some/many speakers are
usually in a state of being knackered, part knackered or on their way to
becoming part knackered in any case. (Not to mention those people who use
speakers with long rips in the foam and who say they love the sound!)


As an
analogy consider a double-acting steam engine, the piston is driven both
ways, there is no "spring".


I am very happy with that - if you apply a voltage to a speaker with the
polarity reversed, the cone is sucked (driven) *in*, is it not?

Keith G

What's this got to do with a spring? AFAIK the only
spring
that snaps your cone back to its centre point is the
same
mechanical suspension that stops it from falling out of
its
basket.


Surely not...???

Yes, because there is nothing magnetic in the cone
system, except the interaction of the current in the coil
with the magnet. If the current reverses then the coil
(and with it the cone) are *driven* back.


Yes. That's what I was referring to - the foams on
some/many speakers are usually in a state of being
knackered, part knackered or on their way to becoming part
knackered in any case. (Not to mention those people who
use speakers with long rips in the foam and who say they
love the sound!)


As an
analogy consider a double-acting steam engine, the piston
is driven both ways, there is no "spring".


I am very happy with that - if you apply a voltage to a
speaker with the polarity reversed, the cone is sucked
(driven) *in*, is it not?

And it follows, pretty much by logic with no need for
science, that with no voltage there will be no force and so
it will stay wherever it is, unless there is a spring to
return it. I believe there are at least two springs: one on
the periphery of the cone that you can see, and one near the
centre that you can't. Between them, they ensure that the
cone stays central and moves in a straight line along its
axis. I assume it's the one near the centre that plays the
main role in returning the cone to its rest position, and
the one on the periphery is there mainly to stop that end
from drooping or flopping about sideways.

I think the principle is that the coil is in a position with
respect to the magnet such that, wherever it moves, the
field strength is the same. The force produced is
proportional to coil current, and you hope current is
proportional to voltage. You also hope the spring is linear,
so that the force it produces is proportional to
displacement. It would then follow that displacement is
proportional to voltage. There is a complication in that
there is a delay between current and voltage, but that kind
of comes out in the wash if you think in terms of amplitude
rather than position.

One good thing about a big magnet is that there is a bigger
place where the field is linear, I suppose, which allows for
greater cone movement whilst maintaining linearity.

Anyway, to get back to the matter of "how quickly it can be
snapped back from an excursion"...that depends on quite what
you mean.

After you hit a bump, it's the spring that returns your
suspension to its rest position, and not the damper which
tends to slow it down on the way. So the fastest snap-back
is without any damping, you could say. However, if you mean
how quickly it returns *to rest*, then the damper is crucial
to the speed of return. Without it, you bounce up and down
for ages. The quickest return to any particular
approximation to the rest position is always slightly
underdamped...just a touch of bounce. This applies not only
to how your speaker cone returns to centre in the absence of
a signal, but also to how it makes its way to any position
as it follows the signal. I suppose everyone more or less
knows these things because they apply to pretty much
everything in the universe that anyone knows anything about.

So the more precise the damping, the snappier the driver.
Coil resistance and amplifier output resistance are
generally accidents rather than design features, and so are
likely to act against precise damping, so it could plausibly
be said that a stronger magnet makes for a snappier driver
by reducing the significance of coil resistance, although I
don't know how important that is compared to the acoustic
damping of the cone or the plasticity of the spring.

Also, if you can generate a greater force for the same
current, then you can have a stiffer spring and still get
the same displacement, which also makes for more snappiness.
Maybe this is the best interpretation of what you meant?

And the coil can be lighter...more snappy still.

OTOH, doesn't a horn rather slow things down? A long time
ago, I used to play an E-flat bass, and it took so long for
a note to get out that to play anything fast I had to block
its sound out of my mind otherwise I got confused between
what I was playing and what I played a little while ago. It
also carried on playing after I stopped blowing. That's why
they are restricted to umpah, umpah. French horn players in
orchestras must be really clever to play their more complex
passages ahead of time.

Ian

Keith G

What's this got to do with a spring? AFAIK the only
spring
that snaps your cone back to its centre point is the same
mechanical suspension that stops it from falling out of
its
basket.
Surely not...???

If you've ever toyed with the suspension settings on your
bikes, maybe you should know this kind of stuff?

Tbh, other than adjusting the preload I have never
bothered even with top-quality (top price, at any rate)
stuff like Ohlins; the normal 'factory' settings usually
work sufficiently well for most people in most
situations - it's a bit like audio, you can tweak stuff
all you like but the original was probably plenty good
enough for most people at the outset!

Better riders than me sorted my suspension when they
designed the bike, I always find. But if you can use better
quality units than the designers were allowed, there is a
case for using them if you can, and then there is a
legitimate reason to fiddle with the settings. There's not
much scope for adjustment on my jampots or Hagons, and
someone stole my Kwacker, so I don't need to worry.

I suppose we could look it up if we were desperate to
know.


No, don't bother...

Looking stuff up too early spoils the learning
experience...something too many engineers never found out.

...but here's another example of the 'depends on cabinet
design' school of thought (4th para):

http://www.lowther.com.hk/


See why I query it...??

No, it's in Chinese. Do they have paragraphs? Maybe if it's
horn loaded you can get a big bass lift, and that's where it
was measured?

The possibility occurs to me that, maybe, if you can use a
rearward horn to emphasise some frequencies, then it could
be possible to lift the whole audio band, at the expense of
higher and lower Fs that we can't hear? Seems a long shot
though.

Ian

"Ian Iveson" wrote

Better riders than me sorted my suspension when they designed the bike, I
always find. But if you can use better quality units than the designers
were allowed, there is a case for using them if you can, and then there is
a legitimate reason to fiddle with the settings.


Yep.


There's not
much scope for adjustment on my jampots or Hagons, and someone stole my
Kwacker, so I don't need to worry.

???

Sorry to hear that - did the insurance pay out OK?



Looking stuff up too early spoils the learning experience...something too
many engineers never found out.


:-)


...but here's another example of the 'depends on cabinet design' school
of thought (4th para):

http://www.lowther.com.hk/


See why I query it...??

No, it's in Chinese.


Don't let yourself be put off the 'welcome page' - check the links on the
left.

Keith G wrote:

There's not
much scope for adjustment on my jampots or Hagons, and
someone stole my Kwacker, so I don't need to worry.

???

Sorry to hear that - did the insurance pay out OK?

Yes, thanks. It was...maybe still is...a GPz900R, the
original ninja, which became regarded as a classic. I got
slightly more than I paid for it, but only after arguing and
sending a heap of evidence of value. All the same, I would
have rather kept the bike, even though it was scary after
the AJS (jampots) and the BMW with *7 suspension units*
(Hagons), due to leading link forks and a carriage-sprung
sidecar.

...but here's another example of the 'depends on cabinet
design' school of thought (4th para):

http://www.lowther.com.hk/


See why I query it...??

No, it's in Chinese.


Don't let yourself be put off the 'welcome page' - check
the links on the left.

Right, OK, yes.

Ian