Have another question here......

I found an somewhat old 3-way speaker downstairs which hadnt been used
for a while. Anyway, I opened it up, to find the following:

The audio signal (+ and - ) connects to both terminals of the woofer.
Then from the +ve (of the woofer), there is an 1uF electrolytic cap
connected to the +ve of the mid range. There is also two 4uF caps in
series connecting to the tweeter +ve (from the woofer this is). All the
negatives connect back to the negative woofer.

Is this normal for the crossover ???? Or very very basic?

I am new to audio, but am learning alot .... have not looked in too
many speakers yet and so just wondered. I would have expected there to
be an inductor - but is this not needed as the main audio signal feeds
into the woofer, and so instead the mids and high frequency is
'removed' and sent to the mid-driver and tweeter???

"andrew_h" wrote in message
oups.com...
Have another question here......

I found an somewhat old 3-way speaker downstairs which hadnt been
used
for a while. Anyway, I opened it up, to find the following:

The audio signal (+ and - ) connects to both terminals of the
woofer.
Then from the +ve (of the woofer), there is an 1uF electrolytic cap
connected to the +ve of the mid range. There is also two 4uF caps in
series connecting to the tweeter +ve (from the woofer this is). All
the
negatives connect back to the negative woofer.

Is this normal for the crossover ???? Or very very basic?

I am new to audio, but am learning alot .... have not looked in too
many speakers yet and so just wondered. I would have expected there
to
be an inductor - but is this not needed as the main audio signal
feeds
into the woofer, and so instead the mids and high frequency is
'removed' and sent to the mid-driver and tweeter???


I think you should substitute 'cheap' for 'old' - although that is the
way it was done in cheap speakers in the old days!

The full frequency signal is being fed to the bass unit and they are
relying upon the mechanical inability of that unit to handle anything
much above bass.

The mid-range is probably the most efficient unit so has only 1uF so
as to limit the power to that speaker as well as modfying the signal
being fed to it, although why it is an electrolytic is a puzzle.. They
are also relying on the mechanical inability of the speaker to handle
real bass and real treble.

The tweeter has two capacitors in series so as to allow more power to
get through and again to modify the signal feed but largely relying
upon mechanics to do the filtration. Two electrolytics in series will
halve the resultant capacity but if connected + to + (or - to -) they
effectively become unpolarised - which is what I would have expected
on the mid-range.

Overall the sound, compared with almost any modern speaker, will be
pretty awful. Modern speakers, even cheap ones, will usually have some
sort of relatively complex crossover.


--
Woody

harrogate3 at ntlworld dot com

On 19 Mar 2006 00:21:16 -0800, "andrew_h"
wrote:

I found an somewhat old 3-way speaker downstairs which hadnt been used
for a while. Anyway, I opened it up, to find the following:

The audio signal (+ and - ) connects to both terminals of the woofer.
Then from the +ve (of the woofer), there is an 1uF electrolytic cap
connected to the +ve of the mid range. There is also two 4uF caps in
series connecting to the tweeter +ve (from the woofer this is). All the
negatives connect back to the negative woofer.

Is this normal for the crossover ???? Or very very basic?

It is normal for cheap speakers. And is indeed very basic.

It's pretty cheap to just use capacitors, but if the drivers are designed
for it and it is done right, it works OK. Remember the voice coils are
inductors themselves. So an arrangement like this is very minimalist, but it
will give you 6dB per oct. rolloff. If you look at some of the very esoteric
speaker designs, some people believe that less is more. If you are willing
to do a lot of measuring and testing, this arrangement can work well.

James. )


"andrew_h" wrote in message
oups.com...
Have another question here......

I found an somewhat old 3-way speaker downstairs which hadnt been used
for a while. Anyway, I opened it up, to find the following:

The audio signal (+ and - ) connects to both terminals of the woofer.
Then from the +ve (of the woofer), there is an 1uF electrolytic cap
connected to the +ve of the mid range. There is also two 4uF caps in
series connecting to the tweeter +ve (from the woofer this is). All the
negatives connect back to the negative woofer.

Is this normal for the crossover ???? Or very very basic?

I am new to audio, but am learning alot .... have not looked in too
many speakers yet and so just wondered. I would have expected there to
be an inductor - but is this not needed as the main audio signal feeds
into the woofer, and so instead the mids and high frequency is
'removed' and sent to the mid-driver and tweeter???

"andrew_h" wrote in message
oups.com...
Have another question here......

I found an somewhat old 3-way speaker downstairs which hadnt been used
for a while. Anyway, I opened it up, to find the following:

The audio signal (+ and - ) connects to both terminals of the woofer.
Then from the +ve (of the woofer), there is an 1uF electrolytic cap
connected to the +ve of the mid range. There is also two 4uF caps in
series connecting to the tweeter +ve (from the woofer this is). All the
negatives connect back to the negative woofer.

Is this normal for the crossover ???? Or very very basic?

Very basic , and flawed wrt any sort of high fidelity. The full range of
frequencies is going to be woofer (and mf driver) , potentially causing
cone-breakup above their designed freq limit, and presenting a pretty wierd
complex load to the amp. Additionally the roll-off to the mf and hf drivers
may not be sufficient to avoid unwanted effects from them too.

geoff

James Lehman wrote:
It's pretty cheap to just use capacitors, but if the drivers are designed
for it and it is done right, it works OK. Remember the voice coils are
inductors themselves.

Not very good ones, they aren't..

Your typical crossover inductor performs far better as an
inductor than a voice coil. The impedance vs frequency
characteristics of such inductors bahve far closer to ideal
inductors in that their impedance does, in fact, double with
each doubling of frequency. Not so with voice coils. Due to
eddy current losses in the metal parts srrounding the gaps,
the impedance rise is proportional to (approximately) the
square root of frequency rather than directly proportional
to frequency. The voice coil impedance phase angle
never comes anywhere near 90 degrees, unlike ordinary
inductors.

So an arrangement like this is very minimalist, but it
will give you 6dB per oct. rolloff. If you look at some of

In reality, it does not, for the reasons outlined above.
Most of the driver's rolloff is simply due to mechanical
issues and radiating area.

the very esoteric speaker designs, some people believe
that less is more. If you are willing to do a lot of measuring
and testing, this arrangement can work well.

In all the many thousans of speakers I have examined and
measured, I have never once encountered an electrodynamic
speaker system using only capacitors in the crossover
that was not also simply extremely cheap, and used such
a crossover design for the sole purpose of saving as much
parts cost as possible.

The speaker desribed by the original poster is quite typical
of the cheapest "multi-way" systems around, and is very
common in the dreaded and to-be-avoided "white van"
style speaker systems.

Thanks for all the great replies!

Yes the speaker is quite old - maybe early ninties. To be honest the
sound isnt too bad - yes, it is nothing like the speakers I'm using in
the lounge (jamo), but the sound isnt HORRIBLE. My main reason for
opening it was to see what the crossover was, being an old speaker.

I'd like to understand this roll-off concept better. I've read about
butterworth filters etc, how they have steady and smooth rolloff - but,
what exactly does 6dB per octave rolloff???

I understand what an octave is (played piano when small and guitar)
..... what does it mean that it will roll off 6dB per octave??

As an example......say the crossover frequency was 2000Hz. In this
example, what would a 6dB/oct rolloff mean?

Thanks!

A dB is a deci Bell, one tenth of a Bell; named for Alexander Graham Bell.
It is a way to measure ratios of power. It's log. The log of 2 is about 0.3
Bells or 3dB. A high pass filter at 1KHz with a -6 dB rolloff will decrease
the power through it to 1/4 at 2KHz, 1/16 at 4KHz.
-6dB is the natural rolloff of a single reactive part; either a cap or a
coil. They are roughly opposites of each other. Caps are high pass and coils
are low pass. The reason it is -6dB is because for every octave up for coils
or down for caps there is twice as much impedance which cuts the voltage in
half. Half the voltage implies half the current flow through the load (the
speaker). Power is current times voltage; so half times a half is a quarter
of the total power; or -6dB. Coils and caps can be put together into more
complex filters with greater slopes. This is why you see slopes that are
multiples of 6.

James. )


"andrew_h" wrote in message
oups.com...
Thanks for all the great replies!

Yes the speaker is quite old - maybe early ninties. To be honest the
sound isnt too bad - yes, it is nothing like the speakers I'm using in
the lounge (jamo), but the sound isnt HORRIBLE. My main reason for
opening it was to see what the crossover was, being an old speaker.

I'd like to understand this roll-off concept better. I've read about
butterworth filters etc, how they have steady and smooth rolloff - but,
what exactly does 6dB per octave rolloff???

I understand what an octave is (played piano when small and guitar)
.... what does it mean that it will roll off 6dB per octave??

As an example......say the crossover frequency was 2000Hz. In this
example, what would a 6dB/oct rolloff mean?

Thanks!