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Default Null speaker test

Years ago I read about something called a null speaker test.

It was a way to detect differences between amps by connecting 2 amps to a
single speaker. If there were differences between the 2 amps then the
speaker would generate sound.

Does anyone know of this test and can you give details?


  #2   Report Post  
James Lehman
 
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In order to do this you better be sure that BOTH amps are of the old style
of 2 prong, floating ground with the speaker negative and the chassis ground
common. Tie the amp chassis together with a ground strap.

Lots of people use to create a fake center channel by connecting a speaker
across the positive terminals L and R of their stereo amp.

New amp designs have both negative and positive signals; voltage between
both wires and chassis ground. You'll blow up an amp like this.

James. )


" wrote in message
link.net...
Years ago I read about something called a null speaker test.

It was a way to detect differences between amps by connecting 2 amps to a
single speaker. If there were differences between the 2 amps then the
speaker would generate sound.

Does anyone know of this test and can you give details?




  #3   Report Post  
Trevor Wilson
 
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" wrote in message
link.net...
Years ago I read about something called a null speaker test.

It was a way to detect differences between amps by connecting 2 amps to a
single speaker. If there were differences between the 2 amps then the
speaker would generate sound.

Does anyone know of this test and can you give details?


**Such a test is highly likely to destroy one or both amps. Signals should
ONLY be combined at low signal levels, then listened through a power amp.
There have been several methods in which this can be accomplished. Hafler
proposed quite a good system. You have either been misled, or your memory is
flawed.


--
Trevor Wilson
www.rageaudio.com.au


  #4   Report Post  
Barry Mann
 
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In .net, on 10/11/05

at 10:58 PM, " said:



Years ago I read about something called a null speaker test.


It was a way to detect differences between amps by connecting 2 amps
to a single speaker. If there were differences between the 2 amps
then the speaker would generate sound.


Does anyone know of this test and can you give details?


At first glance, this is a very clever trick, however, I don't think it
is worth the (very minimal) trouble.

Others have warned about things that could go wrong with this sort of
adventure. I share some of these misgivings, especially if you attempt
to do this with equipment designed for cars. Home audio amplifiers are
a better risk, unless they are bridged or "dual Mono".

In any case, I don't think this is a very sensitive test. What if there
was a slight time delay between amplifiers? If so, the test speaker
would be quite noisy, even if the amplifiers were otherwise identical.
In a few cases one amplifier might be inverting, while the other is
not. Sensitivity will also be tied to speaker efficiency, speaker
frequency response, room response, and your own sensitivities.

Assuming the above considerations are not show stoppers, which
amplifier is better? All you know is that they are "different".

In my opinion, the only interesting feature about this sort of test is
that one can use music as the test signal. Music is much more complex
than the usual test tones.

-----------------------------------------------------------
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wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13 (Barry Mann)
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-----------------------------------------------------------

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Stewart Pinkerton
 
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On Tue, 11 Oct 2005 22:58:48 GMT, "
wrote:

Years ago I read about something called a null speaker test.

It was a way to detect differences between amps by connecting 2 amps to a
single speaker. If there were differences between the 2 amps then the
speaker would generate sound.

Does anyone know of this test and can you give details?


That's extremely likely to destroy *both* amplifiers. The classic null
test uses an attenuator at the output of the amp, exactly matched to
the gain and phase characteristics of the amp, and the output of the
attenuator is then summed with the input signal. the output from this
summing junction will be any amplifier artifacts.
--

Stewart Pinkerton | Music is Art - Audio is Engineering
  #8   Report Post  
GregS
 
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In article .net, " wrote:
Years ago I read about something called a null speaker test.

It was a way to detect differences between amps by connecting 2 amps to a
single speaker. If there were differences between the 2 amps then the
speaker would generate sound.

Does anyone know of this test and can you give details?


I think it sounds like an interesting idea. Having a wide range speaker with two separate
voice coils would do it. Since the fields null, the speaker impedance will be flatter.
I would suggest lower drive levels. Having low level nulling transformation sampling the amps,
might be better. Amplifiers would tend to shwo differences at the higher frequencies.
In any case, I would like to hear more about this sort of testing vs humanoid ABX comparison.

greg
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Arny Krueger
 
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"Barry Mann" wrote in message
om

In any case, I don't think this is a very sensitive test.


As Peter Irwin mentioned Peter Walker of Quad advocated this
test as a demonstration
that the best amplifiers have distortion products which are
inaudible even in the absence of signal.

David Hafler revisited this type of test as alluded to here,
and many other places

http://www.audioasylum.com/audio/cab...es/100288.html

http://www.snippets.org/pipermail/di...ry/009563.html

What if there was a slight time delay between amplifiers?


Unlikely in the narrow sense, but in the broader sense of
phase shift, then this is a serious problem that Hafler ran
into and tried to manage.

If so, the test speaker would be quite noisy, even if the
amplifiers were otherwise identical. In a few cases one
amplifier might be inverting, while the other is not.


That's the basic problem - there are so many variables that
lead to sound that survives simplistic nulling that has
nothing to do with distortion.


When I tried to come up with a way to increase the
audibility of errors in power amps, I came up with the
process of sending the music through the amp again and
again, to allow the errors to build up.

Here are some real-world examples that people can simply
download and listen to:

http://www.pcabx.com/product/amplifiers/index.htm


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"Trevor Wilson" wrote in message
...

" wrote in message
link.net...
Years ago I read about something called a null speaker test.

It was a way to detect differences between amps by connecting 2 amps to a
single speaker. If there were differences between the 2 amps then the
speaker would generate sound.

Does anyone know of this test and can you give details?


**Such a test is highly likely to destroy one or both amps. Signals should
ONLY be combined at low signal levels, then listened through a power amp.
There have been several methods in which this can be accomplished. Hafler
proposed quite a good system. You have either been misled, or your memory
is flawed.


--

It's been at least a dcade since I read the article that descibed the set
up, soo it's entirely possible my memory is flawed, but not about the basic
premise.





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"Don Pearce" wrote in message
. ..
On Tue, 11 Oct 2005 22:58:48 GMT, wrote:

Years ago I read about something called a null speaker test.

It was a way to detect differences between amps by connecting 2 amps to a
single speaker. If there were differences between the 2 amps then the
speaker would generate sound.

Does anyone know of this test and can you give details?


Despite what the others have told you, there is a way to do this without
danger. I'm presuming the amplifiers are niminally similar, or you
wouldn't
even be trying this.

The way you do this is to connect the amplifers in a bridged formation.
Ignore the ground terminals at the amplifier outputs, and connect the
speaker between the two live terminals. Now connect the audio source to
both amplifier inputs in parallel. There should be no net audio on the
output if the amps are the same. Use an oscilloscope on one of the outputs
to see just what signal level is present while you are doing this.

I'm not really sure I'll try it in any case, I just thought it would be
agood topic of discussion, particularly if my memory of it only producing
sound when there is a difference is correct.

The output will not be zero. In a good amplifier, the gain is set by a
pair
of resistors - the feedback network. If good 1% resistors are used for
these, you can expect to hear a signal perhaps 40dB below that from a
normally wired amplifier. You can trim the level to one amplifier (the one
with the higher gain) slightly to null out the remaining residue of
signal.
What remains now will be slight frequency response differences and
distortions.

d

Hopefully I can find the issue of the magazine where I saw this setup
mentioned, and reveal the whole thing to one and all.

I thought it might offer some alternative to those who get their panties in
a twist at the metion of ABX.


  #12   Report Post  
Barry Mann
 
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In k.net, on
10/13/05
at 12:15 AM, " said:

[ ... ]

I thought it might offer some alternative to those who get their
panties in a twist at the metion of ABX.


I'm not sure if the null speaker test could satisfy many listeners.
Generally, one wants to discover which is best "A" or "B". In the null
test one can only establish that there is a difference.

The null test might be an interesting way to compare a production
reference amplifier to a newly manufactured unit as part of a
comprehensive final test procedure.

-----------------------------------------------------------
spam:
wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13 (Barry Mann)
[sorry about the puzzle, spammers are ruining my mailbox]
-----------------------------------------------------------

  #13   Report Post  
DaveL
 
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It's like bridging the amps but not inverting one of them. If one has
higher gain than the other you would get some sound. But this test does not
make much sense to do.

DaveL


" wrote in message
hlink.net...

"Don Pearce" wrote in message
. ..
On Tue, 11 Oct 2005 22:58:48 GMT, wrote:

Years ago I read about something called a null speaker test.

It was a way to detect differences between amps by connecting 2 amps to
a
single speaker. If there were differences between the 2 amps then the
speaker would generate sound.

Does anyone know of this test and can you give details?


Despite what the others have told you, there is a way to do this without
danger. I'm presuming the amplifiers are niminally similar, or you
wouldn't
even be trying this.

The way you do this is to connect the amplifers in a bridged formation.
Ignore the ground terminals at the amplifier outputs, and connect the
speaker between the two live terminals. Now connect the audio source to
both amplifier inputs in parallel. There should be no net audio on the
output if the amps are the same. Use an oscilloscope on one of the
outputs
to see just what signal level is present while you are doing this.

I'm not really sure I'll try it in any case, I just thought it would be
agood topic of discussion, particularly if my memory of it only producing
sound when there is a difference is correct.

The output will not be zero. In a good amplifier, the gain is set by a
pair
of resistors - the feedback network. If good 1% resistors are used for
these, you can expect to hear a signal perhaps 40dB below that from a
normally wired amplifier. You can trim the level to one amplifier (the
one
with the higher gain) slightly to null out the remaining residue of
signal.
What remains now will be slight frequency response differences and
distortions.

d

Hopefully I can find the issue of the magazine where I saw this setup
mentioned, and reveal the whole thing to one and all.

I thought it might offer some alternative to those who get their panties
in a twist at the metion of ABX.


  #14   Report Post  
Don Pearce
 
Posts: n/a
Default

On Thu, 13 Oct 2005 00:15:32 GMT, wrote:

"Don Pearce" wrote in message
. ..
On Tue, 11 Oct 2005 22:58:48 GMT,
wrote:

Years ago I read about something called a null speaker test.

It was a way to detect differences between amps by connecting 2 amps to a
single speaker. If there were differences between the 2 amps then the
speaker would generate sound.

Does anyone know of this test and can you give details?


Despite what the others have told you, there is a way to do this without
danger. I'm presuming the amplifiers are niminally similar, or you
wouldn't
even be trying this.

The way you do this is to connect the amplifers in a bridged formation.
Ignore the ground terminals at the amplifier outputs, and connect the
speaker between the two live terminals. Now connect the audio source to
both amplifier inputs in parallel. There should be no net audio on the
output if the amps are the same. Use an oscilloscope on one of the outputs
to see just what signal level is present while you are doing this.

I'm not really sure I'll try it in any case, I just thought it would be
agood topic of discussion, particularly if my memory of it only producing
sound when there is a difference is correct.

The output will not be zero. In a good amplifier, the gain is set by a
pair
of resistors - the feedback network. If good 1% resistors are used for
these, you can expect to hear a signal perhaps 40dB below that from a
normally wired amplifier. You can trim the level to one amplifier (the one
with the higher gain) slightly to null out the remaining residue of
signal.
What remains now will be slight frequency response differences and
distortions.

d

Hopefully I can find the issue of the magazine where I saw this setup
mentioned, and reveal the whole thing to one and all.

I thought it might offer some alternative to those who get their panties in
a twist at the metion of ABX.


The method is no good for this. It will reveal all sorts of differences
that heave nothing whatever to do with audible differences between
amplifiers. These would be to do with small phase and amplitude differences
between two perfectly competent amplifiers.

d
  #16   Report Post  
 
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Default


"Barry Mann" wrote in message
om...
In k.net, on
10/13/05
at 12:15 AM, " said:

[ ... ]

I thought it might offer some alternative to those who get their
panties in a twist at the mention of ABX.


I'm not sure if the null speaker test could satisfy many listeners.
Generally, one wants to discover which is best "A" or "B". In the null
test one can only establish that there is a difference.


But, if there's no difference, ther's nothing to prefer other than features.
Since there seems to be preicous little in the way of differnce as revealed
by ABX, and since there is a vocal and very nasty cadre of people who scream
that it HIDES difference, it seems to me that a way that doesn't require
blinding or several trials, a simple, objective comparison like a null test,
ought to have some quieting effect on those in denial.

The null test might be an interesting way to compare a production
reference amplifier to a newly manufactured unit as part of a
comprehensive final test procedure.


I'm hoping for a way to drive home the point that the "incredible"
differences that get reported, for the most part simply don't exist, due to
the state of current technology making it simple and inexpenisive to build
amps that are sonically perfect. IOW they pass a signal that is not only
indstinguishable from another reference, but in fact identical.
-----------------------------------------------------------



  #17   Report Post  
Ken Berg
 
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something like page 7 of this?
http://www.hafler.com/techsupport/pd...80_amp_man.pdf


"Barry Mann" wrote in message
om...
In .net, on 10/11/05

at 10:58 PM, " said:



Years ago I read about something called a null speaker test.


It was a way to detect differences between amps by connecting 2 amps
to a single speaker. If there were differences between the 2 amps
then the speaker would generate sound.


Does anyone know of this test and can you give details?


At first glance, this is a very clever trick, however, I don't think it
is worth the (very minimal) trouble.

Others have warned about things that could go wrong with this sort of
adventure. I share some of these misgivings, especially if you attempt
to do this with equipment designed for cars. Home audio amplifiers are
a better risk, unless they are bridged or "dual Mono".

In any case, I don't think this is a very sensitive test. What if there
was a slight time delay between amplifiers? If so, the test speaker
would be quite noisy, even if the amplifiers were otherwise identical.
In a few cases one amplifier might be inverting, while the other is
not. Sensitivity will also be tied to speaker efficiency, speaker
frequency response, room response, and your own sensitivities.

Assuming the above considerations are not show stoppers, which
amplifier is better? All you know is that they are "different".

In my opinion, the only interesting feature about this sort of test is
that one can use music as the test signal. Music is much more complex
than the usual test tones.

-----------------------------------------------------------
spam:
wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13 (Barry Mann)
[sorry about the puzzle, spammers are ruining my mailbox]
-----------------------------------------------------------



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