It occurs to me that, since an isobaric sub has two drivers, then there are
two options for connection, series and parallel, which results in two
options for impedance - 4 and 16 ohms.

In the interest of giving the amplifier the best chance of maintaining tight
control of the drivers, is one impedance preferable to the other? For
example, what would happen if I put a 16 ohm speaker on an amp that expected
8 ohms?

The amplifier will likely be solid state, 50-100W per channel, maybe with a
low-pass filter at the input (because that seems like a good place to put
it - all of the amp's work is going into the wanted frequencies).


--
Wally
www.art-gallery.myby.co.uk
On webcam: Black Cat In Coal Cellar

"Wally" wrote
It occurs to me that, since an isobaric sub has two drivers, then there
are
two options for connection, series and parallel, which results in two
options for impedance - 4 and 16 ohms.
More like 4ish(f)+/-jX(f) or 16ish(f)+/-jX(f) ohms.

In the interest of giving the amplifier the best chance of maintaining
tight
control of the drivers, is one impedance preferable to the other? For
example, what would happen if I put a 16 ohm speaker on an amp that
expected
8 ohms?
4ish+/-jX ohms may blow your amp or at least demand high current from it.
16ish+/-jX ohms will have lower damping as each driver is driven from
8ish+/-jX ohms.
Best option would be a separate power amp for each driver. Make sure out of
phase.
Second best option is in parallel but note comment above.

The amplifier will likely be solid state, 50-100W per channel, maybe with
a
low-pass filter at the input (because that seems like a good place to put
it - all of the amp's work is going into the wanted frequencies).
Yes, this will reduce IMD too.

HTHAB,
Pete

"Wally" wrote
It occurs to me that, since an isobaric sub has two drivers, then there
are
two options for connection, series and parallel, which results in two
options for impedance - 4 and 16 ohms.
More like 4ish(f)+/-jX(f) or 16ish(f)+/-jX(f) ohms.

In the interest of giving the amplifier the best chance of maintaining
tight
control of the drivers, is one impedance preferable to the other? For
example, what would happen if I put a 16 ohm speaker on an amp that
expected
8 ohms?
4ish+/-jX ohms may blow your amp or at least demand high current from it.
16ish+/-jX ohms will have lower damping as each driver is driven from
8ish+/-jX ohms.
Best option would be a separate power amp for each driver. Make sure out of
phase.
Second best option is in parallel but note comment above.

The amplifier will likely be solid state, 50-100W per channel, maybe with
a
low-pass filter at the input (because that seems like a good place to put
it - all of the amp's work is going into the wanted frequencies).
Yes, this will reduce IMD too.

HTHAB,
Pete

Ewar Woowar wrote:
"Wally" wrote
It occurs to me that, since an isobaric sub has two drivers, then
there are two options for connection, series and parallel, which
results in two options for impedance - 4 and 16 ohms.
More like 4ish(f)+/-jX(f) or 16ish(f)+/-jX(f) ohms.

Yes, 4 or 16 nominally, for the purpose of drawing a basic comparison.



In the interest of giving the amplifier the best chance of
maintaining tight control of the drivers, is one impedance
preferable to the other? For example, what would happen if I put a
16 ohm speaker on an amp that expected 8 ohms?

4ish+/-jX ohms may blow your amp or at least demand high current from
it. 16ish+/-jX ohms will have lower damping as each driver is driven
from 8ish+/-jX ohms.
Best option would be a separate power amp for each driver. Make sure
out of phase.
Second best option is in parallel but note comment above.

In other words, the best option is the one where the impedance if of the
drivers and amp are matched? If so, what about using an amp that wants 4 or
16 - could there be any differences, in terms of driver control, between
them?


The amplifier will likely be solid state, 50-100W per channel, maybe
with a low-pass filter at the input (because that seems like a good
place to put it - all of the amp's work is going into the wanted
frequencies).

Yes, this will reduce IMD too.

Cool. That sounds like a good thing to have.


--
Wally
www.art-gallery.myby.co.uk
On webcam: Black Cat In Coal Cellar

Ewar Woowar wrote:
"Wally" wrote
It occurs to me that, since an isobaric sub has two drivers, then
there are two options for connection, series and parallel, which
results in two options for impedance - 4 and 16 ohms.
More like 4ish(f)+/-jX(f) or 16ish(f)+/-jX(f) ohms.

Yes, 4 or 16 nominally, for the purpose of drawing a basic comparison.



In the interest of giving the amplifier the best chance of
maintaining tight control of the drivers, is one impedance
preferable to the other? For example, what would happen if I put a
16 ohm speaker on an amp that expected 8 ohms?

4ish+/-jX ohms may blow your amp or at least demand high current from
it. 16ish+/-jX ohms will have lower damping as each driver is driven
from 8ish+/-jX ohms.
Best option would be a separate power amp for each driver. Make sure
out of phase.
Second best option is in parallel but note comment above.

In other words, the best option is the one where the impedance if of the
drivers and amp are matched? If so, what about using an amp that wants 4 or
16 - could there be any differences, in terms of driver control, between
them?


The amplifier will likely be solid state, 50-100W per channel, maybe
with a low-pass filter at the input (because that seems like a good
place to put it - all of the amp's work is going into the wanted
frequencies).

Yes, this will reduce IMD too.

Cool. That sounds like a good thing to have.


--
Wally
www.art-gallery.myby.co.uk
On webcam: Black Cat In Coal Cellar

In other words, the best option is the one where the impedance if of the
drivers and amp are matched? If so, what about using an amp that wants 4
or
16 - could there be any differences, in terms of driver control, between
them?
Simplifying things, let's say the amp output impedance is zero ohms and it
tries to maintain its voltage gain whatever the load. So whether the
speaker is 4 or 16 ohms, it has the same voltage across the terminals.
Using Ohms Law, I = V/R, using a 4 ohm load demands more current from the
amp.

If you have two drivers in parallel, the ~4 ohm load may mean the amp cannot
source enough instantaneous current producing poor bass quality. However,
the back emf from each driver is shorted by the source which damps down the
oscillations in the driver improving driver control.

If the two drivers are in series, then the amp would find it easier to
source the current and therefore maintaining voltage gain. The source
impedance for each driver is now zero ohms plus 8 ohms, which will change
the damping in the drivers ie. poorer driver control.

By good driver control, lets assume we require the instantaneous air
pressure pushed by both drivers in enclosure is proportional to the
instantaneous voltage level at the power amp input. I would therefore put
both drivers in parallel and ensure your power amp can drive a 4 ohm load
for better driver control. ie choose an amp that can source large current.


The amplifier will likely be solid state, 50-100W per channel, maybe
with a low-pass filter at the input (because that seems like a good
place to put it - all of the amp's work is going into the wanted
frequencies).

Yes, this will reduce IMD too.

Cool. That sounds like a good thing to have.
IMD is just another form of distortion caused when 2 or more frequencies go
through a non-linear system.

In other words, the best option is the one where the impedance if of the
drivers and amp are matched? If so, what about using an amp that wants 4
or
16 - could there be any differences, in terms of driver control, between
them?
Simplifying things, let's say the amp output impedance is zero ohms and it
tries to maintain its voltage gain whatever the load. So whether the
speaker is 4 or 16 ohms, it has the same voltage across the terminals.
Using Ohms Law, I = V/R, using a 4 ohm load demands more current from the
amp.

If you have two drivers in parallel, the ~4 ohm load may mean the amp cannot
source enough instantaneous current producing poor bass quality. However,
the back emf from each driver is shorted by the source which damps down the
oscillations in the driver improving driver control.

If the two drivers are in series, then the amp would find it easier to
source the current and therefore maintaining voltage gain. The source
impedance for each driver is now zero ohms plus 8 ohms, which will change
the damping in the drivers ie. poorer driver control.

By good driver control, lets assume we require the instantaneous air
pressure pushed by both drivers in enclosure is proportional to the
instantaneous voltage level at the power amp input. I would therefore put
both drivers in parallel and ensure your power amp can drive a 4 ohm load
for better driver control. ie choose an amp that can source large current.


The amplifier will likely be solid state, 50-100W per channel, maybe
with a low-pass filter at the input (because that seems like a good
place to put it - all of the amp's work is going into the wanted
frequencies).

Yes, this will reduce IMD too.

Cool. That sounds like a good thing to have.
IMD is just another form of distortion caused when 2 or more frequencies go
through a non-linear system.

In article , Wally
wrote:


In other words, the best option is the one where the impedance if of the
drivers and amp are matched?

Depends upon what you mean by 'matched'. Most power amps will have an
output impedance well below the 4 to 16 Ohm range.

It also depends what you mean by 'best'. :-)

For a given output voltage from the amp:

Having the units electrically in series will draw less current than having
the in parallel, but will output less power, and means the amp will
probably reach its voltage limits before its current limits.

Having the units electrically in parallel will draw more current and more
power for a given voltage, so you may run into current limiting. It may
also mean the finite output impedance of the amp has more effect.

The speakers will be coupled acoustically, so the output and impedance may
now vary as you'd expect simply by assuming electrical parallel or series.

If so, what about using an amp that wants 4 or 16 - could there be any
differences, in terms of driver control, between them?

The amount of control will depend upon the output impedance of the
amplifier. The meaning of "wants 4 or 16" is ambiguous in this context.
Power amps assert the required output voltage pattern, and then should
supply whever current the load then demands when you assert this voltage.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

In article , Wally
wrote:


In other words, the best option is the one where the impedance if of the
drivers and amp are matched?

Depends upon what you mean by 'matched'. Most power amps will have an
output impedance well below the 4 to 16 Ohm range.

It also depends what you mean by 'best'. :-)

For a given output voltage from the amp:

Having the units electrically in series will draw less current than having
the in parallel, but will output less power, and means the amp will
probably reach its voltage limits before its current limits.

Having the units electrically in parallel will draw more current and more
power for a given voltage, so you may run into current limiting. It may
also mean the finite output impedance of the amp has more effect.

The speakers will be coupled acoustically, so the output and impedance may
now vary as you'd expect simply by assuming electrical parallel or series.

If so, what about using an amp that wants 4 or 16 - could there be any
differences, in terms of driver control, between them?

The amount of control will depend upon the output impedance of the
amplifier. The meaning of "wants 4 or 16" is ambiguous in this context.
Power amps assert the required output voltage pattern, and then should
supply whever current the load then demands when you assert this voltage.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

On Wed, 07 Jan 2004 16:05:31 +0000 (GMT)
Jim Lesurf wrote:


The speakers will be coupled acoustically, so the output and impedance may
now vary as you'd expect simply by assuming electrical parallel or series.

may *not* I assume you mean...

--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with ketchup.