Crossover questions
 

Chris Morriss wrote:

I've got 'WinSpeakerz' on the pc, so if you let me know the box
volume I could give you a reasonable idea of the LF response.

I'm looking at doing a Nautilus-style tubular enclosure. Some pictures...

http://www.wally.myby.co.uk/audio/sp...ExpoCab-01.jpg
http://www.wally.myby.co.uk/audio/sp...ExpoCab-02.jpg
http://www.wally.myby.co.uk/audio/sp...ExpoCab-03.jpg


If the prog can do such a shape, the dims are, in mm...

length - 400
dia large - 180
dia small - 40

The volume of the cab as drawn is 2.85 litres, which is too small for
extending the bass - KEF say 4L for a midrange box, 5-10 for bass/mid. So,
I'm wondering what could be acheived by keeping the narrow end of the pipe
open, like a sort of transmission line with some damping due to the rear
opening having a small area.


--
Wally
www.artbywally.com
www.wally.myby.co.uk/music

Crossover questions
 

Old Fart at Play wrote:

3-way speaker, but two amps. I'm considering a cabinet which will
roll off the mid naturally, so no low-end cut, just a mid/top
crossover. The bass would have some kind of filter before the amp.

That doesn't sound like a very good solution.
Better to use an active crossover (4th order Linkwitz-Riley) before
the poweramps and make the B110 have a flat response down to
an octave or so below the crossover frequency.

Wouldn't there be issues with matching to the B139 where the filter kicks
in?


I have a scan of the R50 crossovers from my old B139/B110/T27
project if you are interested.

That would be handy - I'll email you.


Why not make replicas of the LS3/5a crossover for your new boxes.
I believe they enjoyed a certain reputation once!

Indeed they did. How would they fare with a 20W valve amp? I have to say
that I am on something of a minimalist thing with this...


--
Wally
www.artbywally.com
www.wally.myby.co.uk/music

Crossover questions
 

On Sat, 28 Feb 2004 15:36:40 -0000, "Wally"
wrote:

Given that my speaker rebuild fantasy is gradually taking shape, I'm
starting to think about what to do about crossovers. The plan is to bi-amp,
one amp to the B139 drivers, the other to the B110/T27. I'd rather ditch the
orginal KEF DN12 units and make new ones for the mid/top, probably keeping
to the spec crossover frequency. So, I have some questions about
components...

Am I right in thinking that air-cored inductors are better than those with
some sort of ferrite(?) core? For the same value, would an air-cored version
be physically larger? If so, is that because it requires more turns?

What is the best type of capacitor to use wthin sensible cost limits?

Others have addressed the component issues. For crossover topology, I
suggest you review Siegfried Linkwitz' articles on these drivers which
appeared in Wireless World and, later, in SpeakerBuilder. He analyzes
and designs an active crossover for the B139 and B110.

Kal

Crossover questions
 

In message , Wally
writes
Chris Morriss wrote:

I've got 'WinSpeakerz' on the pc, so if you let me know the box
volume I could give you a reasonable idea of the LF response.

I'm looking at doing a Nautilus-style tubular enclosure. Some pictures...

http://www.wally.myby.co.uk/audio/sp...ExpoCab-01.jpg
http://www.wally.myby.co.uk/audio/sp...ExpoCab-02.jpg
http://www.wally.myby.co.uk/audio/sp...ExpoCab-03.jpg


If the prog can do such a shape, the dims are, in mm...

length - 400
dia large - 180
dia small - 40

The volume of the cab as drawn is 2.85 litres, which is too small for
extending the bass - KEF say 4L for a midrange box, 5-10 for bass/mid. So,
I'm wondering what could be acheived by keeping the narrow end of the pipe
open, like a sort of transmission line with some damping due to the rear
opening having a small area.


--
Wally
www.artbywally.com
www.wally.myby.co.uk/music



A 'nautilus shell' style enclosure is a difficult beast to analyse, and
it's out of my depth! (a closed, tapered transmission line).

You're right about the enclosure volume being a bit low for the B110 if
it was a simple sealed box, but still OK for a filter -3dB of 500Hz or
so.

For a simple sealed box of 2.85 litre with the B110, the Qtc is 0.944,
the -3dB point is 94Hz, and there is a broad resonant peak of approx
+1dB centred at 160Hz. (There are a number of flavours of B110. I don't
know how much the parameters vary)

With the right crossover this volume would still be OK as a housing for
the B100 if it was appropriately filtered as a midrange unit. (For
400/500Hz and above)

Perhaps others can help with the analysis of a closed or open ended
tapered TL?

--
Chris Morriss

Crossover questions
 

Jim Lesurf wrote:

I don't know the details of the crossover networks in question.
However if you are going to bi-amp the system it may make sense to
remove some/all the networks between power amps and speakers and,
instead, use networks at the inputs to the power amps. Done
correctly, this may well give much better results that networks that
have to work at high powers in the complex loads.

The plan so far is a low-pass filter before the bass amp, with full range
going to the mid/top through a conventional crossover. There are two
circuits for the B110, depending on whether it's in a 3-way or 2-way setup.
I'm considering copying the 2-way version and rolling off the B110 low end
using cabinet damping. The filter on the bass amp would be configured to
match this roll off.


Am I right in thinking that air-cored inductors are better than those
with some sort of ferrite(?) core?

Depends upon your definition of 'best' and the circumstances.

Better than the ferrite-cored ones in the original DN12. I need to make new
crossovers anyway, and it looks like I can wind my own coils for less than
half the cost of ready-made ones.


Ferrite cores mean you can reduce the length of wire required. This
can mean a physically smaller coil and/or a lower coil resistance
and/or lower resistance due to internal impedance, etc. Hence the
ferrite may improve things on the conductor side. However it may,
itself, increase magnetic 'singing' of the coil and/or introduce some
non-linearity.

Is that an effect the coil has on itself (so to speak)? Can I counteract it
with suitable construction and physical layout?



(That said, it may well be that the speaker units
introduce more distortion than the use of a suitable ferrite.) Sizes
and shapes also affect the amount of coupling from/to a coil and
surrounding components. Ferrite non-linearity or saturation may not
matter much in some circumstances, but make ferrites a poor choice in
other circumstances.

If ferrites either don't matter much, or are a poor choice, does that mean
that air-cored will always be similar or better?


So, "It depends"... :-)

Aye. :-)



For the same value, would an air-cored version be physically larger?
If so, is that because it requires more turns?

and/or a larger cross-sectional area.

Do you mean thicker wire, or something to do with the dimensions of the
coil?


What is the best type of capacitor to use wthin sensible cost limits?

Answer similar to the above. :-)

I think I'm trying to spec the crossover compoenents such that likely
compromises with these are eliminated - it seems that decent parts aren't
too expensive, so, rather that get into esoterica like how much distortion
my old drivers have, I'm tempted to over-engineer the crossovers by using
'known good' stuff.


Are you wishing to compare bipolar electrolytics with other types, or
are you excluding them?

I'm willing to consider anything that will do a good job without being
hugely expensive or overly time-consuming. Maybe I should establish the
shortcomings of the various types...


The advantage of using crossover/equalising networks between pre and
power amps is that you can avoid a lot of the above problems as the
required voltage and current levels in the components will be much
lower. This means you can use smaller, cheaper, and better perfoming
coils/caps.

Since there will be two amps, but 3-way speakers, I'd have to tri-amp to
fully implement the crossovers before the power amps (which would wipe out
the saving). In practical terms, how much improvement is there likely to be
by driving the B110 and T27 from separate amps, compared with using a single
amp to drive both through a conventional crossover built with components of
good repute?

I should mention that the reason for bi-amping is to provide enough power to
the bass speakers and to account for the change in impedance. Making new
crossovers is kinda a knock-on effect from that.


The disadvantage is that producing the correct network may involve a
fair bit of work as it won't be a simple 'copy' of the speaker
arrangement.

But there should be fairly standard circuits/methods out there which will
give similar crossover points and slopes.


--
Wally
www.artbywally.com
www.wally.myby.co.uk/music