[net.audio] extra speakers: test methodology

winograd@nbires.UUCP (Steve Winograd) (04/06/84)

Here is a suggested methodology to follow when conducting the "extra
speaker" test.  The object of the test is to determine the effect, if any,
on the sound of a hi-fi system when speakers other than the ones to which
you are listening are present in the room.  I hope that some people will take
the trouble to do the test for themselves and then post their results.  I 
have posted an article after this one in which I report what I heard when I
did the test on my system this week.  If you want to avoid the possibility
that what I say might influence you, skip that article and don't read it
until you have done the test for yourself.

0. Choose a pair of speakers (if you have more than one) which you like and
   connect them to your system.  These are the "active" speakers.  Use them
   for all your testing and do not move them at any time during testing.
1. Remove all extra speakers from the room.  This may take some doing! Some
   obvious places where speakers are found are radios, TV's, and tape
   recorders.  Some much less obvious places are telephones and answering
   machines, electronic doorbells, home computers and terminals, electronic
   games, talking clocks, and digital watches.  Take all such speakers into
   another room and close the door.  If there is a speaker which you can't
   remove (like the one in a built-in microwave oven which makes those
   cute beeps) then cover it up as best you can.
2. Find a few selections from records which you like and use them for all
   your testing.  A minute or two of music from each is probably enough.
3. Find a comfortable place to sit where the system sounds good and sit there
   for all your testing.
4. Find settings for the volume, balance, and other controls which you like
   and do not change them at any time during testing.
5. Choose a speaker for use as the "extra" speaker.  You only need one.  It
   can be any of the ones which you removed from the room in step 1.  It
   will not be connected to anything.
6. For each of your musical selections:
   a. Listen to the selection with the extra speaker removed.
   b. Bring the extra speaker in and place it near the active speakers.  One
      good possibility is to set it on the floor between them.
   c. Listen to the selection with the extra speaker present.
   d. Remove the extra speaker from the room again.
   Repeat steps a-d as often as you want.  Start out with the extra speaker
   present if you want.  The important thing is to listen for the difference,
   if any, in sound which the presence/abscence of the extra speaker makes.
7. Repeat step 6 for each of your musical selections. 

Here are some things to listen for in determining what effect, if any, an
extra speaker has on the sound:

1. Are the instruments/voices in tune?  Is the pitch steady or does it waver?
2. How tight is the ensemble?  Are the musicians together?  Does it sound like
   they are listening to each other?  Are they are enjoying themselves or just
   trying to finish the performance so they can go get a beer?
3. Is the tempo steady or does it vary?
4. Can you hear the beginning and end of each note?
5. Do the instruments sound like real instruments?  Can you hear the sharp,
   percussive attack of a stick on a drum?  The guitarist's fingers running
   along the strings?  The bass player's fingernails plucking the string?
   The sax player's breathing?  The individual voices in a choir?  
6. How do you feel about the music?  What emotions does it stir in you?
   Are you moved, bored, angered, pleased?

				Steve Winograd
				{ucbvax|hao|allegra}!nbires!winograd

rcd@opus.UUCP (04/06/84)

<>
Steve (nbires!winograd) omitted one important part of a test methodology.
The test ABSOLUTELY MUST be done with the help of another person to remove
and replace the extra speaker.  You (or whoever is doing the critical
listening) must not know whether the speaker is present or not.  Use a
blindfold if you need to (honest, it won't affect audio perception that
much!) but try to make the test unbiased.  If you know when the speaker is
present and when it isn't, you may not be able to be objective.

Suggestion:  Blindfold the listener.  Have the assistant go to the room
where the extra speaker is kept, and either bring the speaker out or not.
Try the test selection.  Remove the speaker or not, but the assistant must
go to the room where the speaker would be kept, and return.  The assistant
should be a skeptic of the phenomenon, if possible.  Be aware of subtle
cueing of the assistant's actions.  For example, if the extra speaker is a
substantial one in an enclosure, it may be that the assistant will make
some noises from the exertion of carrying the speaker.  (If you can arrange
for the tester to stop his ears as well while the change is/isn't being
made, so much the better.)   Remember that testing involving human beings
is the most difficult to control, because unconscious cues are often hard
to find.

One variation of the test which has been suggested to me is to compare with
the speaker always present, but sometimes with the terminals shorted and
sometimes not - this SHOULD show a difference, though not as much as
predicted for removing the speaker entirely, if I understand the arguments
right.

Use a pseudo-random sequence of changes.  (Come on, everyone out there
should know how to set this up, right?)  That is, if 1=speaker present and
0=speaker absent, don't use a sequence like 010101010101.  Instead, use
something like 0101111000101011100.  In fact, runs of "speaker present" or
"speaker absent" are good for checking whether the listener really hears a
difference and is convinced of it.
---
"Nothing left to do but smile, smile, smile."
{hao,ucbvax,allegra}!nbires!rcd
-- 
"Nothing left to do but smile, smile, smile."
{hao,ucbvax,allegra}!nbires!rcd

winograd@nbires.UUCP (Steve Winograd) (04/07/84)

The reply from nbires!rcd about my suggested "extra speaker test" methodology
gives me a welcome chance to try to avoid some potential disagreements which
would divert peoples' attention from the matter before us, namely whether
having extra speakers in the room affects the sound of a hi-fi system.

My suggested methodology is only a suggestion.  I do not claim that it is the
best or the only way to do the test.  Make your own variations!  Use tapes or
CD's or something other than records as the source if you think that multiple
consecutive plays of a record may be undesirable.  Be creative!

Now some quotes from nbires!rcd and my reactions:

 > The test ABSOLUTELY MUST be done with the help of another person to
 > remove and replace the extra speaker.  You (or whoever is doing the
 > critical listening) must not know whether the speaker is present or not.
 > Use a blindfold if you need to . . . but try to make the test unbiased.
 > If you know when the speaker is present and when it isn't, you may not 
 > be able to be objective.

I don't think that the test ABSOLUTELY MUST be done as he says, but I have
no objection to the idea.  I have often done tests on my system while I kept
my eyes closed and another person made changes.

 > One variation of the test . . .is to compare with the speaker always
 > present, but sometimes with the terminals shorted and sometimes not -
 > this SHOULD show a difference, though not as much as predicted for
 > removing the speaker entirely, if I understand the arguments right.

I don't know what rcd understands the arguments to be, but I don't claim to
know exactly why the extra speaker does what I have heard it do.  Shorting the
terminals may or may not do anything.  Some other net people, without ever
trying the test for themselves, have attempted to discredit the extra speaker
idea by first attributing any difference to sound absorption by the extra
speaker and then arguing that its absorption could not possibly have a
significant effect.  That is a totally invalid method of argument:
setting up a straw man and then demolishing it.

 > Use a pseudo-random sequence of changes. . .  That is, if 1=speaker
 > present and 0=speaker absent, don't use a sequence like 010101010101.
 > Instead, use something like 0101111000101011100.  In fact, runs of
 > "speaker present" or "speaker absent" are good for checking whether
 > the listener really hears a difference and is convinced of it.

Sounds like a good idea to me.

			Steve Winograd
			{ucbvax,hao,allegra}!nbires!winograd

trb@masscomp.UUCP (04/07/84)

I did a double-dumb test on my stereo to determine the effect of my
GTI's passive radiator (well, it just sat there) on my stereo.  I
drove my GTI into my bedroom and just parked it between the speakers
(Symdex Sigmas, no subwoofers).  The transcription device was a ratty
old Connoisseur BD2A with a worn out belt and stylus.  I closed the
windows in my bedroom, and made my bed, to ensure minimal experimental
aberration.

My test selections:

The Royal Symphony Orchestra: "Hooked on Audiophile Drivel."
The Doors: "L.A. Woman"

My findings:

1. Are the instruments/voices in tune?  Is the pitch steady or does it
waver?

   The passive radiator had a definite effect here, Jim Morrison always
   sounded a bit flat.  His pitch was pretty steady, but my mood sort
   of trailed off the more I listened.

2. How tight is the ensemble?  Are the musicians together?  Does it
   sound like they are listening to each other?  Are they are enjoying
   themselves or just trying to finish the performance so they can go
   get a beer?

   Hey, man, the Doors sounded tight to me, no lie.  Up tight, all
   right, outasite.  Morrison sounded kinda loosely wrapped, I guess.
   Are they together?  Well, they were then, but they aren't now.
   Morrison is dead, he choked on his own puke, you know.

   Does it sound like they are listening to each other?  Gee, I don't
   know what the sound of musicians listening to each other is.  When I
   listen to one, I sound very quiet.  If they were listening to each
   other, then the sound of them listening to each other was drowned
   out by their music.  I think I'd have to buy a real good expensive
   stereo to be able to actually hear them listening to each other.

   They didn't sound like they were exactly enjoying themselves.  I
   think they wanted to finish the performance, I suspect that they
   were looking forward to a beer to complement the barbiturates that
   they were all using.  Ya know, I have a such a good ear I can
   actually tell you what kind of beer they were going to get after
   they finished the performance.

3. Is the tempo steady or does it vary?

   Oh, the tempo varied, there were some songs with a fast tempo, and
   some had a kinda, ya know, slow tempo.  But I liked it.  You could
   dance to it, it had a good beat.  I'd give it a 78.  What do I win?

4. Can you hear the beginning and end of each note?

   Of course, you just listen to the note, and the very very first part
   you hear is the beginning, the last part is the end.  Got it?  I
   know you would.

5. Do the instruments sound like real instruments?  Can you hear the
   sharp, percussive attack of a stick on a drum?  The guitarist's
   fingers running along the strings?  The bass player's fingernails
   plucking the string?  The sax player's breathing?  The individual
   voices in a choir?

   Well, it sounded like a real stereo.  I think that's pretty
   important, since that's what I payed for.

6. How do you feel about the music?  What emotions does it stir in
   you?  Are you moved, bored, angered, pleased?

   Yes, that's it!  I was moved, bored, angered and pleased.


	Andy Tannenbaum   Masscomp Inc  Westford MA   (617) 692-6200 x274

jj@rabbit.UUCP (04/09/84)

How very interesting!  You heard pitch shifting from the 4" speaker
in the room with your stereo.  That's interesting.  VERY interesting.

Care to tell me HOW it happened?  Maybe the extra speaker was moving at
a considerable percentage of the speed of sound? <maybe you had
Walter Johnston toss it past the room?>

Methinks that psychoacoustics once again strikes.
-- 
TEDDY BEARS ARE NICER THAN PEOPLE--HUG YOURS TODAY!
(If you go out in the woods today ... )
 
(allegra,harpo,ulysses)!rabbit!jj

ron@brl-vgr.ARPA (Ron Natalie <ron>) (04/09/84)

Actually, to do this right, you should do it double blind.  Place two
cassette decks in another room.  In one place an empty speaker grill,
in the other a monitor speaker.  Without letting the assistant know which
deck he's bringing in, have him bring one to the subject.

-Ron

ron@brl-vgr.ARPA (Ron Natalie <ron>) (04/09/84)

Foo.  You don't need to exploit the doppler effect to shift pitch.
All you have to do is have the other speaker vibrate at a different
frequency than the source.

-Ron