Lowther questions....
 

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?

TIA

(It'll be Don, I suspect - if anyone at all....)

Lowther questions....
 

On Wed, 8 Apr 2009 15:56:08 +0100, "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?

TIA

(It'll be Don, I suspect - if anyone at all....)



Dead right. The efficiency of a speaker is built into the driver when
it is designed. I guess you have heard of the Thiele Small parameters;
they describe the sizes, masses, springiness, damping - all the things
that the designer will choose when he specifies his speaker. Anyway,
efficiency can be calculated straight from a couple of those
parameters (can't remember which right now).

Anyway lets start with return springs. There are two. The first most
obvious one is the rubber suspension and it's easy to see how that
works. You end up with a spring and mass (the cone) which makes for a
resonance called Fs. As soon as you put the driver in a cabinet you
add a second spring alongside the first - this is the springiness of
the air in the cabinet. The net effect is a stiffer overall spring
which moves the frequency of the resonance upwards. The physical
spring of the suspension is described in terms of how big a volume of
air would give the same restoring force. It is called Vas (I'm
guessing that is short for volume, air, spring or somesuch). That's
why small cabinets mean less bass - the air spring is stiffer and the
resonance moves up further.

When you put a port in the cabinet something interesting happens. The
air in the port now becomes a second mass bouncing against the springy
air inside the box. This also resonates, so if you make the frequency
of this the same as that of the speaker you get what is called a
coupled system. When that happens the resonance splits into two, one
moving higher in frequency and the other moving lower. It needs
careful tuning for this to happen accurately, but if you look at the
impedance plot of a properly designed ported speaker you will see the
two peaks at low frequency.

Another way to design a speaker is to attempt an infinite baffle. What
this means in practice is that you put enough air into the box that
its spring effect is so floppy that it leaves the mechanical spring of
the driver essentially unchanged. There are two ways to do this. One
is a huge box, and the other is the transmission line; this simply
absorbs the energy from the back of the speaker over a long enough
distance that it is like it has simply drifted into space. There are
versions that don't absorb all the energy, but allow the line to
resonate, producing a similar effect to the simple port. You've made
several of these.

But none of these things change the fundamental efficiency (sound
power out / electrical power in) of the speaker.

d

Lowther questions....
 

In article 49f6beb7.178501281@localhost, Don Pearce
wrote:
On Wed, 8 Apr 2009 15:56:08 +0100, "Keith G"
wrote:

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...)


Dead right. The efficiency of a speaker is built into the driver when it
is designed. I guess you have heard of the Thiele Small parameters; they
describe the sizes, masses, springiness, damping - all the things that
the designer will choose when he specifies his speaker. Anyway,
efficiency can be calculated straight from a couple of those parameters
(can't remember which right now).

I have my doubts that is the entire story. For a speaker unit in free space
the acoustic coupling between the cone/piston movement and the air will
vary with frequency. The electromechanical efficiency will tell you how
much cone displacement you get for a given electrical signal. IIRC over a
fair range speakers tend to be mass-limited where the wavelength isn't tiny
compared with the cone scale-size.

But then there is the question of how much air pressure variation you
radiate for a given cone displacement/velocity. This also affects the
efficiency.

Thus if you fit a baffle you can prevent air movement being 'short
circuited' around the speaker unit and get larger pressure variations.
Hence - potentially - higher overall efficiency. Unless the pressure rise
simply reduces the movement to compensate exactly. But is that the case if
the speaker movements are mass controlled?

In practice also the efficency may improve if judged in terms of *volts* in
if the change in arrangement drops the impedance. So values quoted in terms
of presuming a given drive *voltage* may not be the same as those based on
the power power into the coil.

Anyway lets start with return springs. There are two. The first most
obvious one is the rubber suspension and it's easy to see how that
works. You end up with a spring and mass (the cone) which makes for a
resonance called Fs. As soon as you put the driver in a cabinet you add
a second spring alongside the first - this is the springiness of the air
in the cabinet. The net effect is a stiffer overall spring which moves
the frequency of the resonance upwards.

Does that always shift the compliance limited range up to wavelengths
significantly shorter than the cone scale size? I assumed not.


But none of these things change the fundamental efficiency (sound power
out / electrical power in) of the speaker.

I am less sure of that. However I've never been though the details. nor
designed any speakers, so you may be correct for all I know. Interested to
see what responses you make to the above.

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Lowther questions....
 

"Don Pearce" wrote in message
news:49f6beb7.178501281@localhost...
On Wed, 8 Apr 2009 15:56:08 +0100, "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?

TIA

(It'll be Don, I suspect - if anyone at all....)



Dead right. The efficiency of a speaker is built into the driver when
it is designed. I guess you have heard of the Thiele Small parameters;
they describe the sizes, masses, springiness, damping - all the things
that the designer will choose when he specifies his speaker. Anyway,
efficiency can be calculated straight from a couple of those
parameters (can't remember which right now).

Anyway lets start with return springs. There are two. The first most
obvious one is the rubber suspension and it's easy to see how that
works. You end up with a spring and mass (the cone) which makes for a
resonance called Fs. As soon as you put the driver in a cabinet you
add a second spring alongside the first - this is the springiness of
the air in the cabinet. The net effect is a stiffer overall spring
which moves the frequency of the resonance upwards. The physical
spring of the suspension is described in terms of how big a volume of
air would give the same restoring force. It is called Vas (I'm
guessing that is short for volume, air, spring or somesuch). That's
why small cabinets mean less bass - the air spring is stiffer and the
resonance moves up further.

When you put a port in the cabinet something interesting happens. The
air in the port now becomes a second mass bouncing against the springy
air inside the box. This also resonates, so if you make the frequency
of this the same as that of the speaker you get what is called a
coupled system. When that happens the resonance splits into two, one
moving higher in frequency and the other moving lower. It needs
careful tuning for this to happen accurately, but if you look at the
impedance plot of a properly designed ported speaker you will see the
two peaks at low frequency.

Another way to design a speaker is to attempt an infinite baffle. What
this means in practice is that you put enough air into the box that
its spring effect is so floppy that it leaves the mechanical spring of
the driver essentially unchanged. There are two ways to do this. One
is a huge box, and the other is the transmission line; this simply
absorbs the energy from the back of the speaker over a long enough
distance that it is like it has simply drifted into space. There are
versions that don't absorb all the energy, but allow the line to
resonate, producing a similar effect to the simple port. You've made
several of these.

But none of these things change the fundamental efficiency (sound
power out / electrical power in) of the speaker.

d


OK Don, many thanks for taking the trouble with that very comprehensive
reply.

I was starting to respond when I saw summat from Jimbo come in, just now -
I'll scrute that before I say more but what I had started to type was:

Just to be crystal clear: The phrase "They are very efficient - in a
cabinet, the PM7 hits over 103dB/watt." as per the article is *blx* then, if
the driver itself is only quoted at 96 dB??

Does that bit hold up OK? - Because what I have is a clear and direct
contradiction between the implication of the phrase in the article I
referenced above and what I was told by the *better half* of WA a little
while back and what you seem to be saying - that the cabinet doesn't come
into it..??!!

Lowther questions....
 

On Wed, 08 Apr 2009 17:11:00 +0100, Jim Lesurf
wrote:

In article 49f6beb7.178501281@localhost, Don Pearce
wrote:
On Wed, 8 Apr 2009 15:56:08 +0100, "Keith G"
wrote:

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...)


Dead right. The efficiency of a speaker is built into the driver when it
is designed. I guess you have heard of the Thiele Small parameters; they
describe the sizes, masses, springiness, damping - all the things that
the designer will choose when he specifies his speaker. Anyway,
efficiency can be calculated straight from a couple of those parameters
(can't remember which right now).

I have my doubts that is the entire story. For a speaker unit in free space
the acoustic coupling between the cone/piston movement and the air will
vary with frequency. The electromechanical efficiency will tell you how
much cone displacement you get for a given electrical signal. IIRC over a
fair range speakers tend to be mass-limited where the wavelength isn't tiny
compared with the cone scale-size.

Nothing is ever the entire story, but all I have done so far with
speakers suggests that as a first approximation it seems to work out.

But then there is the question of how much air pressure variation you
radiate for a given cone displacement/velocity. This also affects the
efficiency.

Thus if you fit a baffle you can prevent air movement being 'short
circuited' around the speaker unit and get larger pressure variations.
Hence - potentially - higher overall efficiency. Unless the pressure rise
simply reduces the movement to compensate exactly. But is that the case if
the speaker movements are mass controlled?


I think we can assume mass control - which is true for the majority of
the operating range. But compliance control is what you use to
calculate the dimensions of the box. at Fs.

In practice also the efficency may improve if judged in terms of *volts* in
if the change in arrangement drops the impedance. So values quoted in terms
of presuming a given drive *voltage* may not be the same as those based on
the power power into the coil.

Anyway lets start with return springs. There are two. The first most
obvious one is the rubber suspension and it's easy to see how that
works. You end up with a spring and mass (the cone) which makes for a
resonance called Fs. As soon as you put the driver in a cabinet you add
a second spring alongside the first - this is the springiness of the air
in the cabinet. The net effect is a stiffer overall spring which moves
the frequency of the resonance upwards.

Does that always shift the compliance limited range up to wavelengths
significantly shorter than the cone scale size? I assumed not.


I wouldn't have thought so.


But none of these things change the fundamental efficiency (sound power
out / electrical power in) of the speaker.

I am less sure of that. However I've never been though the details. nor
designed any speakers, so you may be correct for all I know. Interested to
see what responses you make to the above.


There is a standard equation that derives sensitivity (dB at 1 metre
for 1 watt)

112 + 10 * LOG(9.64 * 10^(-10) * Fs^3 * Vas/Qes)

I don't have the derivation for it, but if you check pretty much any
speaker manufacturer's data, the published sensitivity will match.

It occurs to me that horn loading will change this considerably, but
it really isn't equivalent because it sort of alters the assumptions
inherent in the T/S parameters by severely increasing the air mass
(equivalent density, if you like).

d

Lowther questions....
 

On Wed, 8 Apr 2009 17:34:47 +0100, "Keith G"
wrote:

OK Don, many thanks for taking the trouble with that very comprehensive
reply.

I was starting to respond when I saw summat from Jimbo come in, just now -
I'll scrute that before I say more but what I had started to type was:

Just to be crystal clear: The phrase "They are very efficient - in a
cabinet, the PM7 hits over 103dB/watt." as per the article is *blx* then, if
the driver itself is only quoted at 96 dB??

Does that bit hold up OK? - Because what I have is a clear and direct
contradiction between the implication of the phrase in the article I
referenced above and what I was told by the *better half* of WA a little
while back and what you seem to be saying - that the cabinet doesn't come
into it..??!!



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.

See my reply to Jim, where I concede that if the thing is attached to
a horn (front loading, not the type you made) things are different.

d

Lowther questions....
 

"Don Pearce" wrote in message
news:49f9d301.183695000@localhost...
On Wed, 8 Apr 2009 17:34:47 +0100, "Keith G"
wrote:


Just to be crystal clear: The phrase "They are very efficient - in a
cabinet, the PM7 hits over 103dB/watt." as per the article is *blx* then,
if
the driver itself is only quoted at 96 dB??

Does that bit hold up OK? - Because what I have is a clear and direct
contradiction between the implication of the phrase in the article I
referenced above and what I was told by the *better half* of WA a little
while back and what you seem to be saying - that the cabinet doesn't come
into it..??!!



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.

See my reply to Jim, where I concede that if the thing is attached to
a horn (front loading, not the type you made) things are different.


Well then, buggrit - is the guy in the HFW article right or wrong then with
the phrase 'in a cabinet...' which is vague, if nothing else. When I asked
about the Fostex drivers and was told categorically the cabinet could and
did not influence the sensitivity of the drive unit, the cabinet was
specifically the type called 'back loaded horns' which you prefer to call
TLs (Buschhorn Mk2).

Actually 'categorically' is a bit strong - IIRC, it was more a case of 'I
don't see how it [the cabinet] could alter the sensitivity' or somesuch!

(I'll have to have a shufti at the other stuff later, my day's suddenly
caught up with me!!)

Lowther questions....
 

"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....

??

I gotta stop reading this and get my chores done, I'm all behind!!

Lowther questions....
 

"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?

Lowther questions....
 

In article 49f8d005.182930703@localhost, Don Pearce
wrote:
On Wed, 08 Apr 2009 17:11:00 +0100, Jim Lesurf
wrote:

In article 49f6beb7.178501281@localhost, Don Pearce
wrote:
On Wed, 8 Apr 2009 15:56:08 +0100, "Keith G"
wrote:


Thus if you fit a baffle you can prevent air movement being 'short
circuited' around the speaker unit and get larger pressure variations.
Hence - potentially - higher overall efficiency. Unless the pressure
rise simply reduces the movement to compensate exactly. But is that the
case if the speaker movements are mass controlled?


I think we can assume mass control - which is true for the majority of
the operating range. But compliance control is what you use to calculate
the dimensions of the box. at Fs.

I'm not thinking of any specific 'box'. Just of the more general question
of how the efficience will alter when you place any kind of box, baffle,
etc, around the cone.

Consider two assumptions:

1) That the scale size of the speaker is not significantly larger than the
radiated wavelength.

2) That the movement is mass dominated.

Under those conditions anything you place around the cone can be expected
to change the efficiency as it changes the amount of pressure variation
that a given cone movement produces.

As I said, I've never designed a speaker. But I have put speaker units into
surrounds or baffles. The increase in sound level at mid-low frequencies
has been quite noticable. However I have no idea if that takes you to the
kind of values Keith asked about originally.




But none of these things change the fundamental efficiency (sound
power out / electrical power in) of the speaker.

I am less sure of that. However I've never been though the details. nor
designed any speakers, so you may be correct for all I know. Interested
to see what responses you make to the above.


There is a standard equation that derives sensitivity (dB at 1 metre for
1 watt)

112 + 10 * LOG(9.64 * 10^(-10) * Fs^3 * Vas/Qes)

I don't have the derivation for it, but if you check pretty much any
speaker manufacturer's data, the published sensitivity will match.

Again, I have the feeling that simply isn't the whole story. The coupling
efficiency between cone movement and sound pressure is surely going to be
frequency dependent and also be affected by items which alter the air flow
near the cone.

It occurs to me that horn loading will change this considerably, but it
really isn't equivalent because it sort of alters the assumptions
inherent in the T/S parameters by severely increasing the air mass
(equivalent density, if you like).

Maybe in your terms, using a box or baffle *also* alters the parameters.
:-)

There is also the question of the effect of a surround, box, etc on the
speaker input impedance, thus altering the 'efficiency' when regarded in
terms of input voltage - output sound pressure. (As distinct from input
electrical power - output pressure.)

Why do people put cones into boxes if that has no effect on the sound level
radiated at low frequencies?... ;-

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Lowther questions....
 

On Thu, 09 Apr 2009 10:13:43 +0100, Jim Lesurf
wrote:

In article 49f8d005.182930703@localhost, Don Pearce
wrote:
On Wed, 08 Apr 2009 17:11:00 +0100, Jim Lesurf
wrote:

In article 49f6beb7.178501281@localhost, Don Pearce
wrote:
On Wed, 8 Apr 2009 15:56:08 +0100, "Keith G"
wrote:


Thus if you fit a baffle you can prevent air movement being 'short
circuited' around the speaker unit and get larger pressure variations.
Hence - potentially - higher overall efficiency. Unless the pressure
rise simply reduces the movement to compensate exactly. But is that the
case if the speaker movements are mass controlled?


I think we can assume mass control - which is true for the majority of
the operating range. But compliance control is what you use to calculate
the dimensions of the box. at Fs.

I'm not thinking of any specific 'box'. Just of the more general question
of how the efficience will alter when you place any kind of box, baffle,
etc, around the cone.

Consider two assumptions:

1) That the scale size of the speaker is not significantly larger than the
radiated wavelength.

2) That the movement is mass dominated.

Under those conditions anything you place around the cone can be expected
to change the efficiency as it changes the amount of pressure variation
that a given cone movement produces.

As I said, I've never designed a speaker. But I have put speaker units into
surrounds or baffles. The increase in sound level at mid-low frequencies
has been quite noticable. However I have no idea if that takes you to the
kind of values Keith asked about originally.




But none of these things change the fundamental efficiency (sound
power out / electrical power in) of the speaker.

I am less sure of that. However I've never been though the details. nor
designed any speakers, so you may be correct for all I know. Interested
to see what responses you make to the above.


There is a standard equation that derives sensitivity (dB at 1 metre for
1 watt)

112 + 10 * LOG(9.64 * 10^(-10) * Fs^3 * Vas/Qes)

I don't have the derivation for it, but if you check pretty much any
speaker manufacturer's data, the published sensitivity will match.

Again, I have the feeling that simply isn't the whole story. The coupling
efficiency between cone movement and sound pressure is surely going to be
frequency dependent and also be affected by items which alter the air flow
near the cone.

It occurs to me that horn loading will change this considerably, but it
really isn't equivalent because it sort of alters the assumptions
inherent in the T/S parameters by severely increasing the air mass
(equivalent density, if you like).

Maybe in your terms, using a box or baffle *also* alters the parameters.
:-)

There is also the question of the effect of a surround, box, etc on the
speaker input impedance, thus altering the 'efficiency' when regarded in
terms of input voltage - output sound pressure. (As distinct from input
electrical power - output pressure.)

Why do people put cones into boxes if that has no effect on the sound level
radiated at low frequencies?... ;-

Slainte,

Jim

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

d

Lowther questions....
 

"Don Pearce" wrote


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


Don't bust a blood vessel over this, Don - I can continue to live in
*ignorance* of this, it doesn't matter that much; I'll throw it onto the
'Feck Nose' heap with all the other little mysteries I have encountered in
life, but not yet conquered! (As opposed to throwing it on the 'Who GAS'
heap where stuff like CDs lie.... ;-)

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!!

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'...??

(But I guess that can go on the heap also!! :-)

Lowther questions....
 

"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)....

;-)

Lowther questions....
 

"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!!


Or just grab one of these:

http://cgi.ebay.co.uk/High-Quality-C...QQcmdZViewItem

Lowther questions....
 

"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!!


Or just grab one of these:

http://cgi.ebay.co.uk/High-Quality-C...QQcmdZViewItem

??

At that price it ain't worth plugging the iron in, let alone starting to
source the bits!!

Lowther questions....
 

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.
:-)

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Lowther questions....
 

On Thu, 9 Apr 2009 14:04:07 +0100, "Keith G"
wrote:


"Don Pearce" wrote


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


Don't bust a blood vessel over this, Don - I can continue to live in
*ignorance* of this, it doesn't matter that much; I'll throw it onto the
'Feck Nose' heap with all the other little mysteries I have encountered in
life, but not yet conquered! (As opposed to throwing it on the 'Who GAS'
heap where stuff like CDs lie.... ;-)

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. 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.

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

d

Lowther questions....
 

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.

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Lowther questions....
 

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.

--
*Proofread carefully to see if you any words out or mispeld something *

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

Lowther questions....
 

"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!)


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'!

Lowther questions....
 

"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... ;-)

Lowther questions....
 

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

Lowther questions....
 

"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!)

Lowther questions....
 

"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*...!!

:-)

Lowther questions....
 

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.

Lowther questions....
 

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

Lowther questions....
 

"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!

Lowther questions....
 

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.

Lowther questions....
 

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.

Lowther questions....
 

"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.

Lowther questions....
 

In article ,
Arny Krueger wrote:
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.

Could be the poor HF response helps tame the 2nd harmonic distortion from
vinyl, of course. Add in some SET valve technology and you get that nice
mellow tone. Of course a '30s radiogram is a cheaper way of doing it. ;-)

--
*Snowmen fall from Heaven unassembled*

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

Lowther questions....
 

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

Lowther questions....
 

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....

Lowther questions....
 

"Arny Krueger" wrote


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


Ordinarily, my experience is that anyone going to such lengths to avoid the
use of simple and straightforward English is usually telling 'porkies', but
with you Arnie, it's difficult to tell - either way, I suspect you've got
one too many 'dis' in there....

What goes against you, however, is that Lowthers have been making speakers
without major redesign for getting on for a century and people have been
(presumably) buying them, so they can't be anything like as bad as you would
try to have others believe - the usual *feeding frenzy* for nice Lowther
units on eBay kinda says it all, really....

Lowther questions....
 

"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...??

Lowther questions....
 

"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.

Lowther questions....
 

"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?

Lowther questions....
 

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

Lowther questions....
 

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

Lowther questions....
 

"Ian Iveson" wrote in message
...

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.

Traditional speaker design used a thing in the centre, called a "spider",
which acted both to centre the coil in the air-gap and to return the cone to
it's rest position. With a "long-throw" speakers the spider becomes a
problem due to the large excursion that the cone makes at it's centre and so
some more modern designs have dispensed entirely with the spider and relied
on the cone-surround alone to perform both these functions.

David.