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

"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!! :-)

"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)....

;-)

"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

"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!!

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

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

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

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.

"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'!