Date: Tue Mar 10 20:36:56 2009 Back to Contents ------------------------------------------------------------------------

Author: chuck...

Subject: Re: stereo speakers

Post:

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You are most probably enjoying the effects of reflected sound waves that =
are
superimposing upon the output of the front of the speaker, causing the =
base
to sound louder although arguably a more distorted sound effect. One =
method
to see this might be to put a microphone in front of the speaker and =
look at
the signal with a low frequency spectrum analyzer. =20
=20
For fun, set up the speaker with a small piece of shiny mylar glued to =
the
front of the cone and illuminate it with a lazer pointer or CW lazer and
enjoy the light show...
=20
cheers,
chuck...

_____ =20

From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On
Behalf Of Richard Heckathorn
Sent: Tuesday, March 10, 2009 2:08 PM
To: tap-l@lists.ncsu.edu
Subject: Re: [tap-l] stereo speakers



Greetings,

=20

Chuck. You sure bring back the good old days or was it, when in high =
school
it was cool to place two speakers (no case) on the back ledge of the =
back
window of the car . Then one day many years later I investigated the =
effect
of the case. Sure had no clue of the physics of speakers.

=20

For those interested, I took 4 similar 4-inch radio shack speakers, =
mounted
one with no case, mounted a second in side a =BD inch plywood case that =
just
covered the speaker and the third and fourth in a =BE particle board =
case, 14
x 22 inches x 8 inches deep. In one I put insulation, the other not. =
Sure
could tell the difference.

=20

Dick

=20

=20

Helping teachers who facilitate, motivating students who learn.

Dick Heckathorn 14665 Pawnee Trail Middleburg Hts, OH 44130 =
440-826-0834

http://web.cvcaroyals.org/~rheckathorn/=20

Adjunct Physics Teacher - Baldwin Wallace College

Physics is learning how to communicate with ones environment so that it =
will
talk back.

=20

-----Original Message-----
From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On
Behalf Of chuck britton
Sent: Tuesday, March 10, 2009 4:02 PM
To: tap-l@lists.ncsu.edu
Subject: Re: [tap-l] stereo speakers

=20

Demo - experiment Speaker question

=20

Regarding the (obvious) entreaty to 'Never throw a 2-inch speaker away' =
I'd
like to suggest an exercise.

=20

I've always enjoyed hooking a bare 1 inch speaker to an amp output just =
to
show the class how lousy the sound can be from a cheap speaker.

=20

THEN by merely cupping your hands around the perimeter of the speaker - =
the
Bass Response jumps dramatically and it is no longer the tinny, tiny =
speaker
that it used to be.

=20

I've always explained this as sound wave interference. Long bass waves
defract more and destructively interfere from the front wave and the =
back
wave.

=20

NOW I want someone to watch the voltage vs current output on =
a
'scope and see if the 'hand-cupping' makes a visible effect.

And if so - what IS the effect??

=20

Clearly - I'm too lazy to try it right now - but someone =
will
try it sometime and hopefully get back to us with fascinating results =
and/or
more questions.

=20

=20

On Mar 10, 2009, at Mar 10(Tue) 8:30 , Zani, Gerald wrote:

=20

=20

A speaker is not a good introductory example of Ohm's law because it is =
not
a purely resistive load. The phase between the voltage and the current =
does
not allow the use of the term resistance.





Some Articles:

=20

How things work=97Never throw a 2-inch speaker away: It has many uses =20

H. Richard Crane Editor=20

Phys. Teach. 30 375 (1992)


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You are most probably enjoying the effects = of=20 reflected sound
waves that are superimposing upon the output of the = front of
the=20 speaker, causing the base to sound louder although arguably a
more = distorted=20 sound effect. One method to see this might be
to put a microphone = in=20 front of the speaker and look at the
signal with a low frequency = spectrum=20 analyzer.



For fun, set up the speaker with a small piece = of shiny=20 mylar
glued to the front of the cone and illuminate it with a lazer =
pointer or=20 CW lazer and enjoy the light show...



cheers,

chuck...


------------------------------------------------------------------------
*From:* tap-l-owner@lists.ncsu.edu=20
[mailto:tap-l-owner@lists.ncsu.edu] *On Behalf Of *Richard=20 Heckathorn
*Sent:* Tuesday, March 10, 2009 2:08 PM
*To:* = tap-l@lists.ncsu.edu
*Subject:* Re: [tap-l] stereo=20 speakers



Greetings,



Chuck. You = sure bring=20 back the good old days or was it, when in
high school it was cool to = place two=20 speakers (no case) on the
back ledge of the back window of the car . = Then one=20 day many
years later I investigated the effect of the case. Sure had no =
clue of=20 the physics of speakers.



For those = interested, I=20 took 4 similar 4-inch radio shack
speakers, mounted one with no case, = mounted a=20 second in side a
=BD inch plywood case that just covered the speaker and = the
third=20 and fourth in a =BE particle board case, 14 x 22 inches x 8
inches deep. = In one I=20 put insulation, the other not. Sure could
tell the = difference.



Dick





*Helping = teachers who=20 facilitate, motivating students who learn.***

Dick Heckathorn 14665 = Pawnee=20 Trail Middleburg Hts, OH 44130
= 440-826-0834

*http://web.cvcaroyals.org/~rheckathorn/=20 ***

Adjunct Physics Teacher - Baldwin = Wallace=20 College

Physics is learning how to = communicate with=20 ones environment so
that it will talk back.



-----Original=20 Message-----
*From:*=20 tap-l-owner@lists.ncsu.edu
[mailto:tap-l-owner@lists.ncsu.edu] *On Behalf Of *chuck = britton
*Sent:* Tuesday, March 10, 2009 = 4:02=20 PM
*To:*=20 tap-l@lists.ncsu.edu
*Subject:*=20 Re: [tap-l] stereo speakers



Demo - experiment Speaker=20 question



Regarding the (obvious) = entreaty to 'Never=20 throw a 2-inch
speaker away' I'd like to suggest an=20 exercise.



I've always enjoyed hooking a = bare 1 inch=20 speaker to an amp
output just to show the class = how lousy the=20 sound can be from
a cheap speaker.



THEN by merely cupping your = hands around=20 the perimeter of the
speaker - the Bass Response jumps = dramatically=20 and it is no
longer the tinny, tiny speaker that it used to=20 be.



I've always explained this as = sound wave=20 interference. Long
bass waves defract more=20 and destructively interfere from the
front wave and the back=20 wave.



= NOW I want someone to watch the voltage vs current =
output=20 on a 'scope and see if the 'hand-cupping' makes a
visible=20 effect.

= And if so - what IS the effect??



= Clearly - I'm too lazy to try it right now - but =
someone=20 will try it sometime and hopefully get back to us with
fascinating = results=20 and/or more questions.





On Mar 10, 2009, at Mar 10(Tue) = 8:30 ,=20 Zani, Gerald wrote:





A speaker is not a good = introductory=20 example of Ohm's law
because it is not a purely resistive load. The phase between
the = voltage and=20 the current does not allow the use of the
term=20 resistance.



Some=20 Articles:



How things work=97Never throw a = 2-inch=20 speaker away: It has
many uses

H. Richard Crane Editor

Phys. Teach. 30 375=20 (1992)

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From tap-l-owner@lists.ncsu.edu Tue Mar 10 20:36:56 2009

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