Don Pearce wrote:
Without being able to trace the circuits I can't say for definite, but
that looks like a second order crossover. Are those chokes wound on
ferrite?

Doesn't look like it to me, they've just use a plastic tranformer former
(there's nothing inside)

Eiron wrote:
Serge Auckland wrote:
Don Pearce wrote:

Without being able to trace the circuits I can't say for definite, but
that looks like a second order crossover. Are those chokes wound on
ferrite? If they are, this crossover has a power limit set by the
magnetic saturation of the ferrite. Your other one is a better way of
making a crossover choke.

Completely agree.

Are there any real test results showing the difference between
air and ferrite cored inductors in a crossover or is it another
evanescent chalk and cheese effect?

I can't find the detail I was hoping to amongst my notes (even Noakes
wasn't a lot of help), but I found the following explanation (I've
edited it for space) on the University of Surrey's website

Saturation

Saturation is a limitation occurring in inductors having a ferromagnetic
core. Initially, as current is increased the flux increases in
proportion to it. At some point, however, further increases in current
lead to progressively smaller increases in flux. Eventually, the core
can make no further contribution to flux growth and any increase
thereafter is limited to that provided by μ0 - perhaps three orders of
magnitude smaller. Iron saturates at about 1.6 T while ferrites will
normally saturate between about 200 mT and 500 mT.

It is usually essential to avoid reaching saturation since it is
accompanied by a drop in inductance. In many circuits the rate at which
current in the coil increases is inversely proportional to inductance (I
= V * T / L). Any drop in inductance therefore causes the current to
rise faster, increasing the field strength and so the core is driven
even further into saturation.

Core manufacturers normally specify the saturation flux density for the
particular material used.

Although saturation is mostly a risk in high power circuits it is still
a possibility in 'small signal' applications having many turns on an
ungapped core and a DC bias (such as the collector current of a transistor).

If you find that saturation is likely then you might -

* Run the inductor at a lower current
* Use a larger core
* Alter the number of turns
* Use a core with a lower permeability
* Use a core with an air gap

or some combination thereof - but you'll need to re-calculate the design
in any case.
............................end................... ..................

Consequently, if you want to avoid the risk of saturation, you use an
air-cored inductor which has a much lower permeability than ferrite or iron.

S.

"Eiron" wrote in message
...
Serge Auckland wrote:
Don Pearce wrote:

Without being able to trace the circuits I can't say for definite, but
that looks like a second order crossover. Are those chokes wound on
ferrite? If they are, this crossover has a power limit set by the
magnetic saturation of the ferrite. Your other one is a better way of
making a crossover choke.

Completely agree.

Are there any real test results showing the difference between
air and ferrite cored inductors in a crossover or is it another
evanescent chalk and cheese effect?

**There are big differences, but it depends on the specs of the ferrite. In
one case I worked on, the manufacturer shipped a batch of speakers, with the
wrong type of ferrite fitted. Saturation occurred at around 6 VRMS. Since
the speakers were 4 Ohm types, this corresponded to around 10 Watts input
power. Complaints began arriving that the speakers distorted at modest power
levels. A quick sine wave test confirmed the problem. Replacement with
equivalent resistance air core inductors solved the problem.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

"Don Pearce" wrote in message
...
On Wed, 17 Jan 2007 18:20:24 GMT, (Don Pearce)
wrote:

as they are a little larger and have easy, front access - see the
original
drivers on a nice, easily removed front baffle he

http://www.apah69.dsl.pipex.com/show/originals.JPG


H3310s looks like a Seas pat number, but I can't find any info,
particularly the TS parameters, so I can't offer any help on box
design.

Ah - quite by chance I find that H3310s is not a driver, it is the
part number for the rubber surround, which is used on several drivers.
If you can find another part number somewhere, we might progress.



OK, skinning the rabbit(s) another way.....

I've taken the Ruark woofers (Vifa units, crude as **** to look at and 8
ohms apparently) out of the speakers I had put them in (Meraks) to replace
the ones a 'high current' Parasound amp had boiled up some time back and
dropped the Seas units in. The Vifas were good, the Seas are gooder - sounds
very nice and very 'bouncy' in the bass!! (Well usable for ss/digital I
would have thought and I doubt anybody would fault them as such - playing
right now: Yello 'The Eye' and they sound fine to me...)

Phase One complete.

Now for Phase Two:

I will now put the Ruark/Vifa woofers back in their own boxes (to keep all
the critics quiet about the TS stuff) and, using the Ruark crossover, will
fit the T27s in place of the Vifa tweets which were fried one night when
Shiny Nigel was round! That way I get 2 pairs of speakers from Rob's 1 pair
which (sorry Rob) were not even as good in the bass as the above-mentioned
Meraks!!

Now, am I just hitting lucky so far or can you really *not* just chuck
anything about the same size in? Also, I am suspecting tweeter differences
of the same type and size are almost neglible...??

OK, we'll see - not so easy now, it's getting a bit *gynaecological*......!!
:-)

Mora non....

On Thu, 18 Jan 2007 16:06:14 -0000, "Keith G"
wrote:


"Don Pearce" wrote in message
...
On Wed, 17 Jan 2007 18:20:24 GMT, (Don Pearce)
wrote:

as they are a little larger and have easy, front access - see the
original
drivers on a nice, easily removed front baffle he

http://www.apah69.dsl.pipex.com/show/originals.JPG


H3310s looks like a Seas pat number, but I can't find any info,
particularly the TS parameters, so I can't offer any help on box
design.

Ah - quite by chance I find that H3310s is not a driver, it is the
part number for the rubber surround, which is used on several drivers.
If you can find another part number somewhere, we might progress.



OK, skinning the rabbit(s) another way.....

I've taken the Ruark woofers (Vifa units, crude as **** to look at and 8
ohms apparently) out of the speakers I had put them in (Meraks) to replace
the ones a 'high current' Parasound amp had boiled up some time back and
dropped the Seas units in. The Vifas were good, the Seas are gooder - sounds
very nice and very 'bouncy' in the bass!! (Well usable for ss/digital I
would have thought and I doubt anybody would fault them as such - playing
right now: Yello 'The Eye' and they sound fine to me...)

Phase One complete.

Now for Phase Two:

I will now put the Ruark/Vifa woofers back in their own boxes (to keep all
the critics quiet about the TS stuff) and, using the Ruark crossover, will
fit the T27s in place of the Vifa tweets which were fried one night when
Shiny Nigel was round! That way I get 2 pairs of speakers from Rob's 1 pair
which (sorry Rob) were not even as good in the bass as the above-mentioned
Meraks!!

Now, am I just hitting lucky so far or can you really *not* just chuck
anything about the same size in? Also, I am suspecting tweeter differences
of the same type and size are almost neglible...??

OK, we'll see - not so easy now, it's getting a bit *gynaecological*......!!
:-)

Mora non....



When you have drivers of the same size and general type, you've got a
fighting chance that their resonances will fall at somewhere near the
same frequency, and that is what matters. The tolerance of frequency
between two drivers that are nominally the same is pretty wide anyway.

I don't know the difference between the T27s and the Vifas, but the
important thing with tweeters is not to give them stuff that is lower
than they can cope with - that is the road to early death. I think you
should be pretty safe with the T27s though.

d

--
Pearce Consulting
http://www.pearce.uk.com

"Don Pearce" wrote in message
...
On Thu, 18 Jan 2007 16:06:14 -0000, "Keith G"
wrote:


Now, am I just hitting lucky so far or can you really *not* just chuck
anything about the same size in? Also, I am suspecting tweeter differences
of the same type and size are almost neglible...??

OK, we'll see - not so easy now, it's getting a bit
*gynaecological*......!!
:-)

Mora non....



When you have drivers of the same size and general type, you've got a
fighting chance that their resonances will fall at somewhere near the
same frequency, and that is what matters. The tolerance of frequency
between two drivers that are nominally the same is pretty wide anyway.



OK, that's the gamble I took, but the first pair are still on and really do
sound good - I might grab a snatch off 'em and post it later....



I don't know the difference between the T27s and the Vifas, but the
important thing with tweeters is not to give them stuff that is lower
than they can cope with - that is the road to early death. I think you
should be pretty safe with the T27s though.



Right, hint of 'non-peachyness' creeping in to the equation - scrute these
pix:

http://www.apah69.dsl.pipex.com/show/tweeterpic01.JPG

http://www.apah69.dsl.pipex.com/show/tweeterpic02.JPG

http://www.apah69.dsl.pipex.com/show/tweeterpic03.JPG

and you will see:

1) Sawdust everywhere 'cos one of the Seas drivers dropped in to the other
speakers reet lovely and the other one rocked a bit and had to be 'let in' a
tad!

2) The Vifa woofer looking smug - back *home*...

3) That the Vifa tweeter is only 6 oms...!!??

Now, is '3' going to represent a big problem crossoverwise? - I'm intending
to use the original Ruark crossover and the T27 is 8 ohms, as you can
see/already knew....

My money's on them sounding OK, but I don't know what to expect from the
T27's higher rating - 'vanishingly' less treble? A small but devastating
explosion? Loss of libido....?? Dry skin...??

Incidentally, when I fried the tweeter I contacted Ruark and some old dear
told me I got *no chance* of a replacement - old model and all the bloody
drivers (Focal, Dynaudio, Vifa in various models, to my knowledge) are
non-standard, 'Ruark tweaked' apparently!! I asked about using a 'near miss'
tweeter and got a *telephone shrug*...!! :-)

On Thu, 18 Jan 2007 16:59:10 -0000, "Keith G"
wrote:


"Don Pearce" wrote in message
...
On Thu, 18 Jan 2007 16:06:14 -0000, "Keith G"
wrote:


Now, am I just hitting lucky so far or can you really *not* just chuck
anything about the same size in? Also, I am suspecting tweeter differences
of the same type and size are almost neglible...??

OK, we'll see - not so easy now, it's getting a bit
*gynaecological*......!!
:-)

Mora non....



When you have drivers of the same size and general type, you've got a
fighting chance that their resonances will fall at somewhere near the
same frequency, and that is what matters. The tolerance of frequency
between two drivers that are nominally the same is pretty wide anyway.



OK, that's the gamble I took, but the first pair are still on and really do
sound good - I might grab a snatch off 'em and post it later....



I don't know the difference between the T27s and the Vifas, but the
important thing with tweeters is not to give them stuff that is lower
than they can cope with - that is the road to early death. I think you
should be pretty safe with the T27s though.



Right, hint of 'non-peachyness' creeping in to the equation - scrute these
pix:

http://www.apah69.dsl.pipex.com/show/tweeterpic01.JPG

http://www.apah69.dsl.pipex.com/show/tweeterpic02.JPG

http://www.apah69.dsl.pipex.com/show/tweeterpic03.JPG

and you will see:

1) Sawdust everywhere 'cos one of the Seas drivers dropped in to the other
speakers reet lovely and the other one rocked a bit and had to be 'let in' a
tad!

2) The Vifa woofer looking smug - back *home*...

3) That the Vifa tweeter is only 6 oms...!!??


Well, the Vifa is often recommended as an upgrade for the T27, so I
really wouldn't be too fussed about the impedance difference. Just be
prepared for it to be a bit on the loud side, though - you may need a
series resistor yet.

Now, is '3' going to represent a big problem crossoverwise? - I'm intending
to use the original Ruark crossover and the T27 is 8 ohms, as you can
see/already knew....

Nope, don't worry about that.

My money's on them sounding OK, but I don't know what to expect from the
T27's higher rating - 'vanishingly' less treble? A small but devastating
explosion? Loss of libido....?? Dry skin...??

Incidentally, when I fried the tweeter I contacted Ruark and some old dear
told me I got *no chance* of a replacement - old model and all the bloody
drivers (Focal, Dynaudio, Vifa in various models, to my knowledge) are
non-standard, 'Ruark tweaked' apparently!! I asked about using a 'near miss'
tweeter and got a *telephone shrug*...!! :-)



A shrug is all you will get from anyone. For sure they are going to
work a sight better than a busted pair of Vifas - although it may be
worth your while seeing f they can be fixed. They're rated and worth
money.

d

--
Pearce Consulting
http://www.pearce.uk.com

Don Pearce wrote:
On Thu, 18 Jan 2007 16:59:10 -0000, "Keith G"
wrote:

"Don Pearce" wrote in message
...
On Thu, 18 Jan 2007 16:06:14 -0000, "Keith G"
wrote:

Now, am I just hitting lucky so far or can you really *not* just chuck
anything about the same size in? Also, I am suspecting tweeter differences
of the same type and size are almost neglible...??

OK, we'll see - not so easy now, it's getting a bit
*gynaecological*......!!
:-)

Mora non....


When you have drivers of the same size and general type, you've got a
fighting chance that their resonances will fall at somewhere near the
same frequency, and that is what matters. The tolerance of frequency
between two drivers that are nominally the same is pretty wide anyway.


OK, that's the gamble I took, but the first pair are still on and really do
sound good - I might grab a snatch off 'em and post it later....


I don't know the difference between the T27s and the Vifas, but the
important thing with tweeters is not to give them stuff that is lower
than they can cope with - that is the road to early death. I think you
should be pretty safe with the T27s though.


Right, hint of 'non-peachyness' creeping in to the equation - scrute these
pix:

http://www.apah69.dsl.pipex.com/show/tweeterpic01.JPG

http://www.apah69.dsl.pipex.com/show/tweeterpic02.JPG

http://www.apah69.dsl.pipex.com/show/tweeterpic03.JPG

and you will see:

1) Sawdust everywhere 'cos one of the Seas drivers dropped in to the other
speakers reet lovely and the other one rocked a bit and had to be 'let in' a
tad!

2) The Vifa woofer looking smug - back *home*...

3) That the Vifa tweeter is only 6 oms...!!??


Well, the Vifa is often recommended as an upgrade for the T27, so I
really wouldn't be too fussed about the impedance difference. Just be
prepared for it to be a bit on the loud side, though - you may need a
series resistor yet.

Now, is '3' going to represent a big problem crossoverwise? - I'm intending
to use the original Ruark crossover and the T27 is 8 ohms, as you can
see/already knew....

Nope, don't worry about that.

My money's on them sounding OK, but I don't know what to expect from the
T27's higher rating - 'vanishingly' less treble? A small but devastating
explosion? Loss of libido....?? Dry skin...??

Incidentally, when I fried the tweeter I contacted Ruark and some old dear
told me I got *no chance* of a replacement - old model and all the bloody
drivers (Focal, Dynaudio, Vifa in various models, to my knowledge) are
non-standard, 'Ruark tweaked' apparently!! I asked about using a 'near miss'
tweeter and got a *telephone shrug*...!! :-)



A shrug is all you will get from anyone. For sure they are going to
work a sight better than a busted pair of Vifas - although it may be
worth your while seeing f they can be fixed. They're rated and worth
money.

d

Apart from good old Wilmslow, drive units including tweeters can be
repaired/reconed by
http://www.loudspeakersonline.com/re....new/index.htm

They say a typical tweeter recone costs £30. Interestingly, I can't
find any reference to the D25.TG-85 tweeter on the Vifa web site, so
maybe it was produced only as an OEM item.

S.

S.

"Don Pearce" wrote


Well, the Vifa is often recommended as an upgrade for the T27, so I
really wouldn't be too fussed about the impedance difference. Just be
prepared for it to be a bit on the loud side, though - you may need a
series resistor yet.


That I don't get - a higher impedance will result in a *louder* sound...??



Now, is '3' going to represent a big problem crossoverwise? - I'm
intending
to use the original Ruark crossover and the T27 is 8 ohms, as you can
see/already knew....

Nope, don't worry about that.


OK.


A shrug is all you will get from anyone. For sure they are going to
work a sight better than a busted pair of Vifas - although it may be
worth your while seeing f they can be fixed. They're rated and worth
money.


Glad you said that, I was going to *investigate* the innards at the end of
all this!!

Carpetting the Ruark boxes now - the messy bit, I stick it in with Unibond!!

(*Insides*, of course...!! ;-)

Keith G wrote:
"Don Pearce" wrote


Well, the Vifa is often recommended as an upgrade for the T27, so I
really wouldn't be too fussed about the impedance difference. Just be
prepared for it to be a bit on the loud side, though - you may need a
series resistor yet.


That I don't get - a higher impedance will result in a *louder* sound...??

No, all other things being equal, a higher impedance will draw less
power and so produce a lower sound level. One reason why 'speaker
manufacturers like to use 6 ohm drive units is that it gives them a bit
of extra sensitivity over 8 ohm rivals, but without becoming too
strenuous a load for more modest amplifiers which they could well do if
they went for 4 ohm drivers.



S.