Date: Wed Mar 11 08:06:47 2009 Back to Contents ------------------------------------------------------------------------

Author: Bernard Cleyet

Subject: Re: stereo speakers

Post:


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A box is an infinite baffle, with its own resonances, hence the =20
absorbing insulation. The resonance is useful it if matches the =20
decrease in response in the bass of the speaker, especially if =20
ported, so some of the "rear" energy is added to the front.

http://en.wikipedia.org/wiki/Bass_reflex

For best sensitivity (efficiency) A Z transformer is necessary, e.g. =20
the Klipsch Horn.


http://en.wikipedia.org/wiki/Klipsch

The best budget system I've heard was six 6 X 9" speakers mounted on =20=

a 1/4 box (no back and the sides about 1/4 the sides of the baffle =20
(~3' X 3' X 1')]. The speakers were wired series parallel w/ the =20
assumed equal potential nodes shorted. The speakers were selected =20
to have different resonances so the nodes were not equipotential, =20
thereby, affording mutual damping.

bc

p.s. Your mirror system is a phonodyke (or dike), which w/ a rotating =20=

mirror was one of the methods (manometric flame is another) of =20
analyzing sound before the advent of the kinescope. I have a brand =20
name phonodike (phonelescope) patented in 1912.


On 2009, Mar 10, , at 17:34, chuck... wrote:

> You are most probably enjoying the effects of reflected sound waves =20=

> that are superimposing upon the output of the front of the speaker, =20=

> 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 =20
> in front of the speaker and look at the signal with a low frequency =20=

> spectrum analyzer.
>
> For fun, set up the speaker with a small piece of shiny mylar glued =20=

> 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 [mailto:tap-l-=20
> 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,
>
> Chuck. You sure bring back the good old days or was it, when in =20
> high school it was cool to place two speakers (no case) on the back =20=

> ledge of the back window of the car . Then one day many years later =20=

> I investigated the effect of the case. Sure had no clue of the =20
> physics of speakers.
>
> For those interested, I took 4 similar 4-inch radio shack speakers, =20=

> mounted one with no case, mounted a second in side a =BD inch plywood =20=

> case that just covered the speaker and the third and fourth in a =BE =20=

> particle board case, 14 x 22 inches x 8 inches deep. In one I put =20
> insulation, the other not. Sure could tell the difference.
>
> Dick
>
>
> Helping teachers who facilitate, motivating students who learn.
> Dick Heckathorn 14665 Pawnee Trail Middleburg Hts, OH 44130 =20
> 440-826-0834
> http://web.cvcaroyals.org/~rheckathorn/
> Adjunct Physics Teacher - Baldwin Wallace College
> Physics is learning how to communicate with ones environment so =20
> that it will talk back.
>
> -----Original Message-----
> From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-=20
> 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
>
> Demo - experiment Speaker question
>
> Regarding the (obvious) entreaty to 'Never throw a 2-inch speaker =20
> away' I'd like to suggest an exercise.
>
> I've always enjoyed hooking a bare 1 inch speaker to an amp output =20=

> just to show the class how lousy the sound can be from a cheap =20
> speaker.
>
> THEN by merely cupping your hands around the perimeter of the =20
> speaker - the Bass Response jumps dramatically and it is no longer =20
> the tinny, tiny speaker that it used to be.
>
> I've always explained this as sound wave interference. Long bass =20
> waves defract more and destructively interfere from the front wave =20
> and the back wave.
>
> NOW I want someone to watch the voltage vs current =20
> output 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 =20
> someone will try it sometime and hopefully get back to us with =20
> fascinating results and/or more questions.
>
>
> On Mar 10, 2009, at Mar 10(Tue) 8:30 , Zani, Gerald wrote:
>>
>>
>> A speaker is not a good introductory example of Ohm's law because =20
>> it is not a purely resistive load. The phase between the voltage =20
>> and the current does not allow the use of the term resistance.
>
>
> Some Articles:
>
> How things work=97Never throw a 2-inch speaker away: It has many uses
> H. Richard Crane Editor
> Phys. Teach. 30 375 (1992)


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A box is an infinite baffle, with its own resonances, hence the =
absorbing insulation. =A0The=A0resonance=A0is useful it if matches the =
decrease in response in the bass of the speaker, especially if ported, =
so some of the "rear" energy is added to the =
front.

http://en.wikipedia.org/= wiki/Bass_reflex

For best sensitivity = (efficiency) A Z transformer is necessary,
e.g. = the=A0Klipsch=A0Horn.


http://en.wikipedia.org/wiki= /Klipsch

The best budget system I've heard = was six =A06 X 9" speakers
mounted on a 1/4 box (no back and the sides = about 1/4 the sides of
the baffle (~3' X 3' X 1')]. =A0The speakers were = wired series
parallel w/ the assumed equal=A0potential=A0nodes shorted. = =A0 The
speakers were selected to have different resonances so the nodes =
were not equipotential, thereby, affording mutual damping. = =A0

bc

p.s. Your = mirror system is a phonodyke (or dike), which w/ a
rotating mirror was = one of the methods (manometric flame is
=A0another) = of=A0analyzing=A0sound=A0before=A0the advent of the
kinescope. =A0I have = a brand name phonodike (phonelescope)
patented in = 1912.


On 2009, Mar 10, , at 17:34, = chuck... wrote:

You are most probably=A0enjoying 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.=A0 One method to see
this might = be to put a microphone in front=A0of the speaker
and look at the signal = with a low frequency spectrum analyzer.=A0
=A0
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...
=A0
cheers,
chuck...

------------------------------------------------------------------------
*From:*=A0tap-l-owner@lists.ncsu.edu
[mailto:tap-l-owner@lists.ncsu.e= du]=A0*On Behalf =
Of=A0*Richard = Heckathorn
*Sent:*=A0Tuesday, March 10, 2009 2:08 = PM
*To:*=A0tap-l@lists.ncsu.edu
*Subjec= t:*=A0Re: [tap-l] stereo = speakers

=A0
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.

=A0

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.

=A0

Dick

=A0

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

Dick = Heckathorn=A0 14665 Pawnee Trail=A0 Middleburg Hts, OH=A0
44130=A0 = 440-826-0834
*http://web.cvcaroyals.org= /~rheckathorn/*
Adjunct Physics Teacher - = Baldwin Wallace College
Physics is learning how to = communicate with ones environment
so that it will talk = back.

=A0

=A0tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.e=
du]=A0*On Behalf Of=A0*chuck = britton
*Sent:*=A0Tuesday, March 10, 2009 4:02 = PM
*To:*=A0tap-l@lists.ncsu.edu
*Subject:*=A0Re: [tap-l] stereo = speakers

Demo - experiment Speaker = question

=A0

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

=A0

I've always enjoyed hooking = a bare 1 inch speaker to an amp
=A0output just to show the class = how=A0lousy=A0the sound can be
from a cheap = speaker.

=A0

THEN by merely cupping your = hands around the perimeter of the
speaker - the Bass=A0Response=A0jumps = dramatically and it is no
longer the tinny, tiny speaker that it used to = be.

=A0

I've always explained this = as sound wave interference. Long bass
waves=A0defract=A0more = and=A0destructively=A0interfere from the
front wave and the back = wave.

=A0

=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0NOW I = want someone to watch
the voltage vs current output on a 'scope and see = if =A0the
'hand-cupping' makes a visible effect.
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0An= d if so - what IS the effect??

=A0

=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0Clearly - = 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.

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

=A0

A speaker is not a good = introductory example of Ohm's law
because it is not a purely resistive = load.=A0=A0The phase
between the = voltage and =A0 =A0the current does not allow the
= use of the term resistance.



Some = Articles:

=A0

How things work=97Never throw a 2-inch speaker away: It has many =
uses=A0=A0
<= div style=3D"font-size: 12pt; margin-top: 0in; margin-right: 0in; =
margin-bottom: 0pt; margin-left: 0in; font-family: 'Times New Roman'; =
">H. Richard Crane Editor=A0
<= div style=3D"font-size: 12pt; margin-top: 0in; margin-right: 0in; =
margin-bottom: 0pt; margin-left: 0in; font-family: 'Times New Roman'; =
">Phys. Teach. 30 375 = (1992)

=

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From tap-l-owner@lists.ncsu.edu Wed Mar 11 08:06:47 2009

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