distortion at 4 ohms vs. 8 ohms?

M

Michael

Guest
I got a hi-fi amplifier (Harman Kardon AVR45) off Craigslist (what a
deal), and am running it on four 4-ohm speakers within the house.
(Two 10" subs, rated at 200+ W continous; two 6-1/2" speakers rated at
300W continuous). The manual specs say the following:

Five-Channel Surround Mode
Power Per Individual Channel

Front L&R channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz–20kHz into 8 ohms

Center channel:
55 Watts, @ < 0.07% THD, 20Hz–20kHz into 8 ohms

Surround channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz–20kHz into 8 ohms


It sounds great on 4 ohm speakers.

I was wondering, what kind of increased distortion numbers am I
looking at, running at 4 ohms?

I know not to overdrive it too much, since it will get hot. Most of
the time I listen to George Winston piano solos, but during the
occasional party, ... well, it still works...

Thanks,

Michael
 
On Sep 22, 3:23 pm, Michael <mrdarr...@gmail.com> wrote:
I got a hi-fi amplifier (Harman Kardon AVR45) off Craigslist (what a
deal), and am running it on four 4-ohm speakers within the house.
(Two 10" subs, rated at 200+ W continous; two 6-1/2" speakers rated at
300W continuous).  
Click to expand...

Correction - two 6-1/2" speakers rated at 30 W continuous.

They're all car audio speakers.
 
On Sep 22, 3:23 pm, Michael <mrdarr...@gmail.com> wrote:
I got a hi-fi amplifier (Harman Kardon AVR45) off Craigslist (what a
deal), and am running it on four 4-ohm speakers within the house.
(Two 10" subs, rated at 200+ W continous; two 6-1/2" speakers rated at
300W continuous).  The manual specs say the following:

Five-Channel Surround Mode
Power Per Individual Channel

Front L&R channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz–20kHz into 8 ohms

Center channel:
55 Watts, @ < 0.07% THD, 20Hz–20kHz into 8 ohms

Surround channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz–20kHz into 8 ohms

It sounds great on 4 ohm speakers.

I was wondering, what kind of increased distortion numbers am I
looking at, running at 4 ohms?

I know not to overdrive it too much, since it will get hot.  Most of
the time I listen to George Winston piano solos, but during the
occasional party, ... well, it still works...

Thanks,

Michael
Click to expand...
If the power supply doesn''t droop from the 4 ohm loads, the power
output will be double what it is for 8 ohms. Audio amps are voltage
amplifiers and will 'adjust' the current to the load. E^2/4 is twice
as big as E^2/8. Distortion will not be significantly higher as long
as you're under clipping.

G˛
 
On Tue, 22 Sep 2009 15:23:54 -0700 (PDT), Michael
<mrdarrett@gmail.com> wrote:

I got a hi-fi amplifier (Harman Kardon AVR45) off Craigslist (what a
deal), and am running it on four 4-ohm speakers within the house.
(Two 10" subs, rated at 200+ W continous; two 6-1/2" speakers rated at
300W continuous). The manual specs say the following:

Five-Channel Surround Mode
Power Per Individual Channel

Front L&R channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz=9620kHz into 8 ohms

Center channel:
55 Watts, @ < 0.07% THD, 20Hz=9620kHz into 8 ohms

Surround channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz=9620kHz into 8 ohms


It sounds great on 4 ohm speakers.

I was wondering, what kind of increased distortion numbers am I
looking at, running at 4 ohms?

I know not to overdrive it too much, since it will get hot. Most of
the time I listen to George Winston piano solos, but during the
occasional party, ... well, it still works...
Click to expand...
Just using 4 ohms instead of 8 should not cause
increased distortion at normal listening levels.
The problem with 4 ohm speakers is that you can
drive the amp beyond its rated power output. If
it doesn't have adequate limiting and shutdown
circuitry, you could smoke the output stages.

I'd guess this will not be a problem unless you
really work at getting loud. You'll probably get
clipping on peaks that will make it sound "gritty"
well before you get it loud enough to do damage,
and you'll naturally back off the volume when you
hear that (I hope!).

Possible exception: I seem to recall amps that
were unstable at 4 ohms, back in the "early days".
Doesn't seem likely here, though.

Best regards,



Bob Masta

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!
 
On Wed, 23 Sep 2009 08:32:02 -0700, Michael wrote:
On Sep 23, 5:00 am, N0S...@daqarta.com (Bob Masta) wrote:

I know not to overdrive it too much, since it will get hot.  Most of
the time I listen to George Winston piano solos, but during the
occasional party, ... well, it still works...

Just using 4 ohms instead of 8 should not cause increased distortion at
normal listening levels. The problem with 4 ohm speakers is that you can
drive the amp beyond its rated power output.  If it doesn't have
adequate limiting and shutdown circuitry, you could smoke the output
stages.

Oh is that all! Ok.

I'd guess this will not be a problem unless you really work at getting
loud.  You'll probably get clipping on peaks that will make it sound
"gritty" well before you get it loud enough to do damage, and you'll
naturally back off the volume when you hear that (I hope!).
Click to expand...
At a certain sound power level, your eardrums will do the clipping as they
bottom out on the peaks. I think this causes damage, however.

Cheers!
Rich
 
On Sep 23, 5:00 am, N0S...@daqarta.com (Bob Masta) wrote:

....

I know not to overdrive it too much, since it will get hot.  Most of
the time I listen to George Winston piano solos, but during the
occasional party, ... well, it still works...

Just using 4 ohms instead of 8 should not cause
increased distortion at normal listening levels.
The problem with 4 ohm speakers is that you can
drive the amp beyond its rated power output.  If
it doesn't have adequate limiting and shutdown
circuitry, you could smoke the output stages.
Click to expand...

Oh is that all! Ok.


I'd guess this will not be a problem unless you
really work at getting loud.  You'll probably get
clipping on peaks that will make it sound "gritty"
well before you get it loud enough to do damage,
and you'll naturally back off the volume when you
hear that (I hope!).
Click to expand...

Yep, if it gets gritty that's no fun to listen to. But I'm impressed
with how clear the sound is, even at max volume. (Granted, the only
time I went max volume was for a fairly soft-sounding song, but
still... clear as a whistle.)


Possible exception:  I seem to recall amps that
were unstable at 4 ohms, back in the "early days".
Doesn't seem likely here, though.
Click to expand...

Seems like a lot of modern amps say "8 ohm speaker only". That's
partly why I went for an older amp model... 4-ohm speakers are way
cheaper than 8-ohm home hi-fi speakers. I got my 6-1/2" speakers for
about $30 at Target in the car section.


Best regards,

Bob Masta

              DAQARTA  v4.51
   Data AcQuisition And Real-Time Analysis
             www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
           FREE Signal Generator
        Science with your sound card!
Click to expand...

Thanks,

Michael
 
On Sep 23, 5:00 am, N0S...@daqarta.com (Bob Masta) wrote:
On Tue, 22 Sep 2009 15:23:54 -0700 (PDT), Michael



mrdarr...@gmail.com> wrote:
I got a hi-fi amplifier (Harman Kardon AVR45) off Craigslist (what a
deal), and am running it on four 4-ohm speakers within the house.
(Two 10" subs, rated at 200+ W continous; two 6-1/2" speakers rated at
300W continuous).  The manual specs say the following:

Five-Channel Surround Mode
Power Per Individual Channel

Front L&R channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz=9620kHz into 8 ohms

Center channel:
55 Watts, @ < 0.07% THD, 20Hz=9620kHz into 8 ohms

Surround channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz=9620kHz into 8 ohms

It sounds great on 4 ohm speakers.

I was wondering, what kind of increased distortion numbers am I
looking at, running at 4 ohms?

I know not to overdrive it too much, since it will get hot.  Most of
the time I listen to George Winston piano solos, but during the
occasional party, ... well, it still works...

Just using 4 ohms instead of 8 should not cause
increased distortion at normal listening levels.
The problem with 4 ohm speakers is that you can
drive the amp beyond its rated power output.  If
it doesn't have adequate limiting and shutdown
circuitry, you could smoke the output stages.

I'd guess this will not be a problem unless you
really work at getting loud.  You'll probably get
clipping on peaks that will make it sound "gritty"
well before you get it loud enough to do damage,
and you'll naturally back off the volume when you
hear that (I hope!).

Possible exception:  I seem to recall amps that
were unstable at 4 ohms, back in the "early days".
Doesn't seem likely here, though.

Best regards,

Bob Masta

              DAQARTA  v4.51
   Data AcQuisition And Real-Time Analysis
             www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
           FREE Signal Generator
        Science with your sound card!
Click to expand...


Since it's a 5.1 amplifier, and I'm only using 4 speakers, what would
happen if for the other powered output I put two more 4-ohm speakers
in series?

Intuitively it seems trivial, but in reality, would this arrangement
increase distortion?

Thanks,

Michael
 
On Thu, 24 Sep 2009 10:18:28 -0700 (PDT), Michael
<mrdarrett@gmail.com> wrote:

On Sep 23, 5:00=A0am, N0S...@daqarta.com (Bob Masta) wrote:
On Tue, 22 Sep 2009 15:23:54 -0700 (PDT), Michael



mrdarr...@gmail.com> wrote:
I got a hi-fi amplifier (Harman Kardon AVR45) off Craigslist (what a
deal), and am running it on four 4-ohm speakers within the house.
(Two 10" subs, rated at 200+ W continous; two 6-1/2" speakers rated at
300W continuous). =A0The manual specs say the following:

Five-Channel Surround Mode
Power Per Individual Channel

Front L&R channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz=3D9620kHz into 8 ohms

Center channel:
55 Watts, @ < 0.07% THD, 20Hz=3D9620kHz into 8 ohms

Surround channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz=3D9620kHz into 8 ohms

It sounds great on 4 ohm speakers.

I was wondering, what kind of increased distortion numbers am I
looking at, running at 4 ohms?

I know not to overdrive it too much, since it will get hot. =A0Most of
the time I listen to George Winston piano solos, but during the
occasional party, ... well, it still works...

Just using 4 ohms instead of 8 should not cause
increased distortion at normal listening levels.
The problem with 4 ohm speakers is that you can
drive the amp beyond its rated power output. =A0If
it doesn't have adequate limiting and shutdown
circuitry, you could smoke the output stages.

I'd guess this will not be a problem unless you
really work at getting loud. =A0You'll probably get
clipping on peaks that will make it sound "gritty"
well before you get it loud enough to do damage,
and you'll naturally back off the volume when you
hear that (I hope!).

Possible exception: =A0I seem to recall amps that
were unstable at 4 ohms, back in the "early days".
Doesn't seem likely here, though.

Best regards,

Bob Masta

=A0 =A0 =A0 =A0 =A0 =A0 =A0 DAQARTA =A0v4.51
=A0 =A0Data AcQuisition And Real-Time Analysis
=A0 =A0 =A0 =A0 =A0 =A0 =A0www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
=A0 =A0 =A0 =A0 =A0 =A0FREE Signal Generator
=A0 =A0 =A0 =A0 Science with your sound card!



Since it's a 5.1 amplifier, and I'm only using 4 speakers, what would
happen if for the other powered output I put two more 4-ohm speakers
in series?

Intuitively it seems trivial, but in reality, would this arrangement
increase distortion?
Click to expand...
Two 4-ohm speakers in series will give you 8 ohms,
which is what the amp is designed for. It
definitely will not increase distortion at normal
levels. But since that channel now has twice the
resistance, it will have half the power output of
the other channels... assuming the same input
voltage. But you probably have a separate volume
control for that channel anyway, so just turn it
up a bit more.

At high levels, the 8-ohm channel will reach
clipping at a lower power output. The amp is
rated at 55W into 8 ohms. Power is V^2 / R,
so V^2 = P * R = 55 * 8 = 440, so V = 21V.

Now with 4 ohms, the max power is V^2 / 4
or 110 W. That's 3 dB louder than 55 W, so
yes, the 8-ohm channel will distort sooner as the
input level approaches maximum. But remember that
you are not supposed to be pulling more than 55 W
per channel out of this amp anyway, so you better
not be running this high!

Best regards,



Bob Masta

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!
 
On Sep 25, 5:14 am, N0S...@daqarta.com (Bob Masta) wrote:
On Thu, 24 Sep 2009 10:18:28 -0700 (PDT), Michael







mrdarr...@gmail.com> wrote:
On Sep 23, 5:00=A0am, N0S...@daqarta.com (Bob Masta) wrote:
On Tue, 22 Sep 2009 15:23:54 -0700 (PDT), Michael

mrdarr...@gmail.com> wrote:
I got a hi-fi amplifier (Harman Kardon AVR45) off Craigslist (what a
deal), and am running it on four 4-ohm speakers within the house.
(Two 10" subs, rated at 200+ W continous; two 6-1/2" speakers rated at
300W continuous). =A0The manual specs say the following:

Five-Channel Surround Mode
Power Per Individual Channel

Front L&R channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz=3D9620kHz into 8 ohms

Center channel:
55 Watts, @ < 0.07% THD, 20Hz=3D9620kHz into 8 ohms

Surround channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz=3D9620kHz into 8 ohms

It sounds great on 4 ohm speakers.

I was wondering, what kind of increased distortion numbers am I
looking at, running at 4 ohms?

I know not to overdrive it too much, since it will get hot. =A0Most of
the time I listen to George Winston piano solos, but during the
occasional party, ... well, it still works...

Just using 4 ohms instead of 8 should not cause
increased distortion at normal listening levels.
The problem with 4 ohm speakers is that you can
drive the amp beyond its rated power output. =A0If
it doesn't have adequate limiting and shutdown
circuitry, you could smoke the output stages.

I'd guess this will not be a problem unless you
really work at getting loud. =A0You'll probably get
clipping on peaks that will make it sound "gritty"
well before you get it loud enough to do damage,
and you'll naturally back off the volume when you
hear that (I hope!).

Possible exception: =A0I seem to recall amps that
were unstable at 4 ohms, back in the "early days".
Doesn't seem likely here, though.

Best regards,

Bob Masta

=A0 =A0 =A0 =A0 =A0 =A0 =A0 DAQARTA =A0v4.51
=A0 =A0Data AcQuisition And Real-Time Analysis
=A0 =A0 =A0 =A0 =A0 =A0 =A0www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
=A0 =A0 =A0 =A0 =A0 =A0FREE Signal Generator
=A0 =A0 =A0 =A0 Science with your sound card!

Since it's a 5.1 amplifier, and I'm only using 4 speakers, what would
happen if for the other powered output I put two more 4-ohm speakers
in series?

Intuitively it seems trivial, but in reality, would this arrangement
increase distortion?

Two 4-ohm speakers in series will give you 8 ohms,
which is what the amp is designed for.  It
definitely will not increase distortion at normal
levels.  But since that channel now has twice the
resistance, it will have half the power output of
the other channels... assuming the same input
voltage.  But you probably have a separate volume
control for that channel anyway, so just turn it
up a bit more.
Click to expand...

That's a good point that I hadn't considered. Guess it's not worth
the effort cutting two more holes in the ceiling then. Thanks.


At high levels, the 8-ohm channel will reach
clipping at a lower power output.  The amp is
rated at 55W into 8 ohms.  Power is V^2 / R,
so V^2 = P * R = 55 * 8 = 440, so V = 21V.
Click to expand...

+/- 21V? 42V rail-to-rail?


Now with 4 ohms, the max power is V^2 / 4
or 110 W.  That's 3 dB louder than 55 W, so
yes, the 8-ohm channel will distort sooner as the
input level approaches maximum.  But remember that
you are not supposed to be pulling more than 55 W
per channel out of this amp anyway, so you better
not be running this high!

Best regards,

Bob Masta

              DAQARTA  v4.51
   Data AcQuisition And Real-Time Analysis
             www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
           FREE Signal Generator
        Science with your sound card!
Click to expand...

Thanks,

Michael
 
On Fri, 25 Sep 2009 11:40:30 -0700 (PDT), Michael
<mrdarrett@gmail.com> wrote:

On Sep 25, 5:14=A0am, N0S...@daqarta.com (Bob Masta) wrote:
On Thu, 24 Sep 2009 10:18:28 -0700 (PDT), Michael
snip

At high levels, the 8-ohm channel will reach
clipping at a lower power output. =A0The amp is
rated at 55W into 8 ohms. =A0Power is V^2 / R,
so V^2 =3D P * R =3D 55 * 8 =3D 440, so V =3D 21V.


+/- 21V? 42V rail-to-rail?
Click to expand...
Yes. The amp rails are probably a bit more than
that,but not by much.

Best regards,


Bob Masta

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!
 
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