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  #1   Report Post  
Ron
 
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Default Damping Material Question

I always thought the purpose for damping material was to keep sound
waves from bouncing off of the back/sides of the enclosure and back into
the driver causing distortion.

What is the deal with using damping material to fool the enclosure into
thinking it is bigger? If you add something to a box, doesn't it make it
smaller? LOL

  #2   Report Post  
Fred
 
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Default Damping Material Question


"Ron" wrote in message
...
I always thought the purpose for damping material was to keep sound
waves from bouncing off of the back/sides of the enclosure and back into
the driver causing distortion.


Its purpose is to reduce standing waves within the enclosure that would
affect the frequency response. This applies to mid-to-high range of the
audio spectrum. I don't think distortion is an issue.

What is the deal with using damping material to fool the enclosure into
thinking it is bigger? If you add something to a box, doesn't it make it
smaller? LOL


At lower frequencies where standing waves and reflections aren't an issue
because the enclosure dimensions prevent them anyway, the addition of
damping material will increase the enclosures effective size


  #3   Report Post  
thelizman
 
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Default Damping Material Question

Ron wrote:
I always thought the purpose for damping material was to keep sound
waves from bouncing off of the back/sides of the enclosure and back into
the driver causing distortion.

What is the deal with using damping material to fool the enclosure into
thinking it is bigger? If you add something to a box, doesn't it make it
smaller? LOL


The idea is that the thermal insulation aspect of "stuffing" (usually
polyfill, though fiberglass insulation has been used in some home
speakers I've seen - not hot on the idea of glass fibers being propelled
into my atmosphere) absorbs some of the acoustic output of the speaker
in the same way the air in a larger enclosure would.

In theory, it ads 15-25%. In actual practice...well...you can make up
your own mind, but I've never measured any actual noticable change that
couldn't also be accounted for by other factors.

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
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  #4   Report Post  
thelizman
 
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Default Damping Material Question

Fred wrote:

Its purpose is to reduce standing waves within the enclosure that would
affect the frequency response. This applies to mid-to-high range of the
audio spectrum. I don't think distortion is an issue.


At lower frequencies where standing waves and reflections aren't an issue
because the enclosure dimensions prevent them anyway, the addition of
damping material will increase the enclosures effective size


How many 15 foot subwoofer boxes have you ever seen? It's not about
"standing waves", unless you're building a full range box.

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
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  #5   Report Post  
Fred
 
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Default Damping Material Question


"thelizman" wrote in message
...
Fred wrote:

Its purpose is to reduce standing waves within the enclosure that would
affect the frequency response. This applies to mid-to-high range of the
audio spectrum. I don't think distortion is an issue.


At lower frequencies where standing waves and reflections aren't an

issue
because the enclosure dimensions prevent them anyway, the addition of
damping material will increase the enclosures effective size


How many 15 foot subwoofer boxes have you ever seen? It's not about
"standing waves", unless you're building a full range box.


You wanna read my post again? See the part about mid-to-high range of the
audio spectrum?




  #6   Report Post  
Don Hills
 
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Default Damping Material Question

In article ,
thelizman wrote:

In theory, it ads 15-25%. In actual practice...well...you can make up
your own mind, but I've never measured any actual noticable change that
couldn't also be accounted for by other factors.


Actually, if you use the right density of stuffing, you do get about 15 to
25% effective size increase. The stuffing slows down the propagation of the
sound waves within the enclosure. The effect is more commonly used to
advantage in "transmission line" style home enclosures, allowing the use of
a shorter line for a given bass extension. I've got a technical paper
somewhere here with suggested densities for various types of stuffing. I
expect there'll be useful information on web sites that discuss home
construction of hi-fi speakers, too.

--
Don Hills (dmhills at attglobaldotnet) Wellington, New Zealand
  #7   Report Post  
thelizman
 
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Default Damping Material Question

Fred wrote:

You wanna read my post again? See the part about mid-to-high range of the
audio spectrum?


You wanna explain to me where mid to high frequencies occur in a
subwoofer system, ya moron?

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
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  #8   Report Post  
Nousaine
 
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Default Damping Material Question

(Don Hills) wrote:

In article ,
thelizman wrote:

In theory, it ads 15-25%. In actual practice...well...you can make up
your own mind, but I've never measured any actual noticable change that
couldn't also be accounted for by other factors.


Actually, if you use the right density of stuffing, you do get about 15 to
25% effective size increase. The stuffing slows down the propagation of the
sound waves within the enclosure. The effect is more commonly used to
advantage in "transmission line" style home enclosures, allowing the use of
a shorter line for a given bass extension.


Actually slowing down sound has nothing to do with it this effect (I've
conducted experiments that show up to 36% apparent enclosure size increase ----
1.5 lbs per cubic foot @ 1.5 ft3 enclosure.) It has to do with keeping thermal
conditions in the enclosure closer to isothermal as opposed to adiabatic.

But, so far, all the effects are relative to small signal response ....
Theile/Small parameters. It's time to investigate large signal conditions.

I've got a technical paper
somewhere here with suggested densities for various types of stuffing. I
expect there'll be useful information on web sites that discuss home
construction of hi-fi speakers, too.

--
Don Hills (dmhills at attglobaldotnet) Wellington, New Zealand


1 to 1.5 pounds per cubic foot appears to be optimal and stuffing tupe
(fiberglas, rockwool, wool or polyester) idicates that polyester is as good as
the others and has no disadvantages.
  #9   Report Post  
Fred
 
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Default Damping Material Question


"thelizman" wrote in message
...
Fred wrote:

You wanna read my post again? See the part about mid-to-high range of

the
audio spectrum?


You wanna explain to me where mid to high frequencies occur in a
subwoofer system, ya moron?


When you show me where the original post mentioned a subwoofer you totally
stupid ****wit. He said "enclosure" not subwoofer!


  #10   Report Post  
Les
 
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Default Damping Material Question


"Fred" wrote in message You wanna read my
post again? See the part about mid-to-high range of
the
audio spectrum?


You wanna explain to me where mid to high frequencies occur in a
subwoofer system, ya moron?


When you show me where the original post mentioned a subwoofer you totally
stupid ****wit. He said "enclosure" not subwoofer!


He does not have to say subwoofer, it is implied. It is called reading
comprehension skills. Do they not teach that anymore? Therefore high
frequencies really have nothing to do with the question posed.

Les




  #11   Report Post  
Fred
 
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Default Damping Material Question


"Les" wrote in message
...

"Fred" wrote in message You wanna read my
post again? See the part about mid-to-high range of
the
audio spectrum?

You wanna explain to me where mid to high frequencies occur in a
subwoofer system, ya moron?


When you show me where the original post mentioned a subwoofer you

totally
stupid ****wit. He said "enclosure" not subwoofer!


He does not have to say subwoofer, it is implied. It is called reading
comprehension skills. Do they not teach that anymore? Therefore high
frequencies really have nothing to do with the question posed.

Les


No implication in the original post at all. You have interpreted your way
and I have interpreted it as it was written. It has nothing to do with
comprehension at all. If **** was electricity you'd be a walking, talking
power station.


  #12   Report Post  
Don Hills
 
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Default Damping Material Question

In article ,
(Nousaine) wrote:

Actually slowing down sound has nothing to do with it this effect (I've
conducted experiments that show up to 36% apparent enclosure size increase ----
1.5 lbs per cubic foot @ 1.5 ft3 enclosure.) It has to do with keeping thermal
conditions in the enclosure closer to isothermal as opposed to adiabatic.


Er... No. I refer you to the seminal works on the topic:

[1] A. R. Bailey: "Non Resonant Loudspeaker Enclosure", Wireless World,
October 1965, and "The Transmission Line Enclosure", Wireless World, May 1972.

[3] L. J .S. Bradbury: "The Use of Fibrous Materials in Loudspeaker
Enclosures", JAES Vol. 24 No. 3, April 1976.

Both found (Bailey by experiment, Bradbury by theoretical work) that about
0.5 lb per cubic foot was optimum, and reduced the speed of sound to
around half of its free air value. This amount of reduction cannot be solely
due to isothermal versus adiabatic effects, as the theoretical maximum
reduction in apparent velocity is only on the order of 15%. Someone did some
research into the reasons for the discrepancy, and it is this paper which
I'm currently looking for in what I jokingly call a filing system. Dick
Pierce did some work on this, maybe he knows - are you listening, Dick?

For the apparent enclosure size increase, your experimental figures are
quite close to the theoretical maximum (about 40%).

1 to 1.5 pounds per cubic foot appears to be optimal and stuffing tupe
(fiberglas, rockwool, wool or polyester) idicates that polyester is as good as
the others and has no disadvantages.


As the man with a wooden leg said, "That's a matter of a pinion." grin

--
Don Hills (dmhills at attglobaldotnet) Wellington, New Zealand
  #13   Report Post  
thelizman
 
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Default Damping Material Question

Fred wrote:

No implication in the original post at all. You have interpreted your way
and I have interpreted it as it was written. It has nothing to do with
comprehension at all. If **** was electricity you'd be a walking, talking
power station.


You're an idiot. Just admit it. Anyone who starts talking about standing
waves in a box for a car is an idiot for multiple reasons.

Be quiet now.

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
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  #14   Report Post  
thelizman
 
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Default Damping Material Question

Don Hills wrote:

As the man with a wooden leg said, "That's a matter of a pinion." grin


Isn't that also the same man who said "har, whars th' cabin boyee, aye
need t'sheath me sword"?

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
is forbidden.
  #15   Report Post  
Nousaine
 
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Default Damping Material Question

(Don Hills) wrote:

In article ,
(Nousaine) wrote:

Actually slowing down sound has nothing to do with it this effect (I've
conducted experiments that show up to 36% apparent enclosure size increase

----
1.5 lbs per cubic foot @ 1.5 ft3 enclosure.) It has to do with keeping

thermal
conditions in the enclosure closer to isothermal as opposed to adiabatic.


Er... No. I refer you to the seminal works on the topic:

[1] A. R. Bailey: "Non Resonant Loudspeaker Enclosure", Wireless World,
October 1965, and "The Transmission Line Enclosure", Wireless World, May
1972.


Bailey's work was with open enclosures.

[3] L. J .S. Bradbury: "The Use of Fibrous Materials in Loudspeaker
Enclosures", JAES Vol. 24 No. 3, April 1976.

Both found (Bailey by experiment, Bradbury by theoretical work) that about
0.5 lb per cubic foot was optimum, and reduced the speed of sound to
around half of its free air value. This amount of reduction cannot be solely
due to isothermal versus adiabatic effects, as the theoretical maximum
reduction in apparent velocity is only on the order of 15%.


I'll bow to Bradbury. Haven't read that for several years now.

Someone did some
research into the reasons for the discrepancy, and it is this paper which
I'm currently looking for in what I jokingly call a filing system. Dick
Pierce did some work on this, maybe he knows - are you listening, Dick?

For the apparent enclosure size increase, your experimental figures are
quite close to the theoretical maximum (about 40%).


Indeed they were; which probably meant that the highest stuffing density may
have
somehow added mass to the system. Which is why I use 25% as a rule of thumb.

1 to 1.5 pounds per cubic foot appears to be optimal and stuffing tupe
(fiberglas, rockwool, wool or polyester) idicates that polyester is as good

as
the others and has no disadvantages.


As the man with a wooden leg said, "That's a matter of a pinion." grin

--
Don Hills (dmhills at attglobaldotnet) Wellington, New Zealand


I'll amend that to 1 lb/ft3.


  #16   Report Post  
Eddie Runner
 
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Default Damping Material Question

give him hell Don!
Tom wrote a paper for a car audiuo magazine that seemed to
me to be just a sensationalized (exagerated!) plagerizm of the
original fellows that you quote below...

I tried to point this out to him several
times but he wont put up any of his test data and only wants to
belittle my expertise on the matter...

I have been trying to drag him into a good conversation on this
topic for quite some time so I could do some testing and post a
web page on just how wrong he is... But he wont discuss it at
all he just wants to say he is right and everyone else is wrong.

Tom gets these old tech papers and he appearantly thinks no one
else on here is gonna have the same papers so he embelishes them
for his own purposes and tells his falsehoods....

He tried it on me quoting Beraneks book... I think I suprised
the crap outa him when I actually had the book and I posted some drawings
and text from the same book which proved him totally wrong on some
standing wave issues...

Toms not a bad guy, he is just a little overzealous in his embelishing
of facts so he can publish his own papers in largely non technical
magazines for profit...

Don Hills wrote:

In article ,
(Nousaine) wrote:

Actually slowing down sound has nothing to do with it this effect (I've
conducted experiments that show up to 36% apparent enclosure size increase ----
1.5 lbs per cubic foot @ 1.5 ft3 enclosure.) It has to do with keeping thermal
conditions in the enclosure closer to isothermal as opposed to adiabatic.


Er... No. I refer you to the seminal works on the topic:

[1] A. R. Bailey: "Non Resonant Loudspeaker Enclosure", Wireless World,
October 1965, and "The Transmission Line Enclosure", Wireless World, May 1972.

[3] L. J .S. Bradbury: "The Use of Fibrous Materials in Loudspeaker
Enclosures", JAES Vol. 24 No. 3, April 1976.

Both found (Bailey by experiment, Bradbury by theoretical work) that about
0.5 lb per cubic foot was optimum, and reduced the speed of sound to
around half of its free air value. This amount of reduction cannot be solely
due to isothermal versus adiabatic effects, as the theoretical maximum
reduction in apparent velocity is only on the order of 15%. Someone did some
research into the reasons for the discrepancy, and it is this paper which
I'm currently looking for in what I jokingly call a filing system. Dick
Pierce did some work on this, maybe he knows - are you listening, Dick?

For the apparent enclosure size increase, your experimental figures are
quite close to the theoretical maximum (about 40%).

1 to 1.5 pounds per cubic foot appears to be optimal and stuffing tupe
(fiberglas, rockwool, wool or polyester) idicates that polyester is as good as
the others and has no disadvantages.


As the man with a wooden leg said, "That's a matter of a pinion." grin

--
Don Hills (dmhills at attglobaldotnet) Wellington, New Zealand


  #17   Report Post  
Les
 
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Default Damping Material Question


"Fred" wrote in message

No implication in the original post at all. You have interpreted your way
and I have interpreted it as it was written. It has nothing to do with
comprehension at all. If **** was electricity you'd be a walking, talking
power station.



So what do you think the OP is talking about? A box for his tweeters? He
mentioned a box and an enclosure, ie things you would normally place a
subwoofer in. He also mentions 2 phenomenoms that are associated with
subwoofers. So there are 4 things associated with a subwoofer system. Now I
can stretch one, maybe two of those things to include midbass drivers. But
how can you stretch it that much to think he is talking mid/high drivers?
You need to take a reading for comprehension class.

BTW: OP, you should just google for this topic as it has been discussed many
times here.

Les


  #19   Report Post  
Don Hills
 
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Default Damping Material Question

In article ,
Eddie Runner wrote:
give him hell Don!


Why? I'm aware of his history, and he does appear to be what many claim him
to be, but he's made his reputation and now he has to live with it.
As you well know, I generally confine myself to gently pointing out the
misconceptions some people expound from time to time. Have you figured out
how a bridged amp works yet? big grin And notice how the "should I fasten
down my sub box" thread went quiet? bigger grin I could see the light
bulbs lighting up from way over here...

Toms not a bad guy, he is just a little overzealous in his embelishing
of facts so he can publish his own papers in largely non technical
magazines for profit...


Thanks for the concise potted history. Google Groups filled in the gaps.
I saw some of the arguments that Tom has been in while I was looking for
clues as to the title of the paper I can't find. (I did find an on-topic
post by Dick Pierce from 1985...)

--
Don Hills (dmhills at attglobaldotnet) Wellington, New Zealand
"I don't use Linux. I prefer to use an OS supported by a large multi-
national vendor, with a good office suite, excellent network/internet
software and decent hardware support."
  #20   Report Post  
Eddie Runner
 
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Default Damping Material Question

Don Hills wrote:

Have you figured out
how a bridged amp works yet? big grin


Please notice that thanks to my persistance it is now
VERY RARE to find someone saying that bridging
halves the resistance....

And notice how the "should I fasten
down my sub box" thread went quiet? bigger grin


I dont remember that thread was I in that one..??


Eddie



  #22   Report Post  
Don Hills
 
Posts: n/a
Default Damping Material Question

In article ,
Eddie Runner wrote:

Please notice that thanks to my persistance it is now
VERY RARE to find someone saying that bridging
halves the resistance....


Ah, but that doesn't mean you're right. just kidding

I dont remember that thread was I in that one..??


Nope. Sancho and Lizard were. Look in Google for "How to secure a sub
enclosure", started 2 weeks ago.

--
Don Hills (dmhills at attglobaldotnet) Wellington, New Zealand
  #23   Report Post  
Eddie Runner
 
Posts: n/a
Default Damping Material Question



Don Hills wrote:

In article ,
Eddie Runner wrote:

Please notice that thanks to my persistance it is now
VERY RARE to find someone saying that bridging
halves the resistance....


Ah, but that doesn't mean you're right. just kidding


a few years back everyone said bridging halves speakers
impedance.. it was on tech websites, manufacturers web sites,
(some of my best argueing was with some of the JL techs) and
even in amp install manuals.... Thanks to my persistance none
of that is there anymore, folks have learned the truth... Damn
I am good.... ;-)

I dont remember that thread was I in that one..??


Nope. Sancho and Lizard were. Look in Google for "How to secure a sub
enclosure", started 2 weeks ago.


Ahhh...
I try not to argue with morons...


Eddie

  #24   Report Post  
gregs
 
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Default Damping Material Question

In article , Eddie Runner wrote:


Don Hills wrote:

In article ,
Eddie Runner wrote:

Please notice that thanks to my persistance it is now
VERY RARE to find someone saying that bridging
halves the resistance....


Ah, but that doesn't mean you're right. just kidding


a few years back everyone said bridging halves speakers
impedance.. it was on tech websites, manufacturers web sites,
(some of my best argueing was with some of the JL techs) and
even in amp install manuals.... Thanks to my persistance none
of that is there anymore, folks have learned the truth... Damn
I am good.... ;-)


Aw but you rarely hear what bridging really does.It
doubles the voltage!

greg
  #25   Report Post  
Scott Gardner
 
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Default Physics of bridging an amplifier - was: Damping Material Question

On Sat, 20 Mar 2004 03:27:53 GMT, (gregs)
wrote:

In article , Eddie Runner wrote:


Don Hills wrote:

In article ,
Eddie Runner wrote:

Please notice that thanks to my persistance it is now
VERY RARE to find someone saying that bridging
halves the resistance....

Ah, but that doesn't mean you're right. just kidding


a few years back everyone said bridging halves speakers
impedance.. it was on tech websites, manufacturers web sites,
(some of my best argueing was with some of the JL techs) and
even in amp install manuals.... Thanks to my persistance none
of that is there anymore, folks have learned the truth... Damn
I am good.... ;-)




Aw but you rarely hear what bridging really does.It
doubles the voltage!

greg


True, and I've always wondered why it's not explained that way more
often in the first place. I used to see that "halving the impedance"
crap all the time too, when the correct explanation is so much simpler
- you double the voltage swing, which quadruples the output power.
(Obviously, the *total* power only doubles, since you're going from
two channels to only one when you bridge the amp.)

Liz - I'm saddened to hear that the JL techs were arguing with you
about how amp bridging works. I can understand it if the marketing
types were confused, and maybe even the manual writers, but the techs
and engineers should know better. How hard is it to understand that
power equals voltage squared divided by impedance?

Scott Gardner




  #26   Report Post  
 
Posts: n/a
Default Physics of bridging an amplifier - was: Damping Material Question



True, and I've always wondered why it's not explained that way more
often in the first place. I used to see that "halving the impedance"
crap all the time too, when the correct explanation is so much simpler
- you double the voltage swing, which quadruples the output power.
(Obviously, the *total* power only doubles, since you're going from
two channels to only one when you bridge the amp.)

Liz - I'm saddened to hear that the JL techs were arguing with you
about how amp bridging works. I can understand it if the marketing
types were confused, and maybe even the manual writers, but the techs
and engineers should know better. How hard is it to understand that
power equals voltage squared divided by impedance?

Scott Gardner



Power does not equal voltage squared divided by impedance..... sorry,
but power equalss voltage squared divided by resistance...

impedance and resistances are different...

If you wanna be talking about impedences...you gotta take into account
PF angles... which means you arent really dealing with Power anymore,
your dealing V-A (volt-amps). Just what i gathered at Electrical
eng. school.

Never did understand why speakers are rated in WATTS and impedences.

Can anyone explain this to me? Or is the 5 text books i spent ,which
seems to be, unlimited hours reading...wrong?


  #27   Report Post  
Eddie Runner
 
Posts: n/a
Default Physics of bridging an amplifier - was: Damping MaterialQuestion

Scott Gardner wrote:

Liz - I'm saddened to hear that the JL techs were arguing with you
about how amp bridging works.


Liz..????????????

No Scott, it was me! Eddie Runner!

In the old days EVERYONE said inpedance halves when bridging
an amplifier (thats how bridging works)... Many amp manuals
said so.. Many web sites said so. Most all installers said so...
And RAC said so every day!

Anyone that was around back then will remember my relentless
debates and arguements over why it was not so... It is doubling the
voltage, not halving the impedance!

If youve been around to see me in some big arguements here then
let me tell you the recent arguements are nothing compared to the
size and length of the arguements over bridging that we used to have,
those were the whoppers!! Since EVERYONE was against me, I
sometimes argued against 5 or 6 guys at the same time, it was
overwhelming but I stuck it out and eventually won just about everyone
over to the truth....

Alot of folks back then called me the bridging guy.

After a while when someone would come on and say bridging halves
the impedence, someone would say DONT LET EDDIE SEE YOU
SAY THAT!! ha ha ha

Nowdays I almost never hear that anymore... For a while I know folks
were afraid I would jump on them if they said it... ;-) Now, it may just
be because amps arent bridged that much anymore, the class D amps
are so common......

Get it right in the history books, it was Eddie Runner, not Liz!

Eddie

  #29   Report Post  
Scott Gardner
 
Posts: n/a
Default Physics of bridging an amplifier - was: Damping Material Question

On Sat, 20 Mar 2004 15:30:52 GMT, wrote:



True, and I've always wondered why it's not explained that way more
often in the first place. I used to see that "halving the impedance"
crap all the time too, when the correct explanation is so much simpler
- you double the voltage swing, which quadruples the output power.
(Obviously, the *total* power only doubles, since you're going from
two channels to only one when you bridge the amp.)

Liz - I'm saddened to hear that the JL techs were arguing with you
about how amp bridging works. I can understand it if the marketing
types were confused, and maybe even the manual writers, but the techs
and engineers should know better. How hard is it to understand that
power equals voltage squared divided by impedance?

Scott Gardner



Power does not equal voltage squared divided by impedance..... sorry,
but power equalss voltage squared divided by resistance...

impedance and resistances are different...

If you wanna be talking about impedences...you gotta take into account
PF angles... which means you arent really dealing with Power anymore,
your dealing V-A (volt-amps). Just what i gathered at Electrical
eng. school.

Never did understand why speakers are rated in WATTS and impedences.

Can anyone explain this to me? Or is the 5 text books i spent ,which
seems to be, unlimited hours reading...wrong?


"Power" is a valid term for describing both AC and DC circuits - the
units just differ. "Power" is simply the rate of energy flow in a
circuit (first derivative of energy with respect to time, or p=dw/dt).
This rate of energy flow is always called "power", whether we're
talking about DC or AC circuits. The load in question can be purely
resistive, purely reactive, or a combination of the two - "power" is
still a valid term to describe the rate of energy flow through the
load.

In AC power equations, you have "true power", "reactive power", and
"apparent power" (this is the infamous "power triangle"). "Apparent
power" is the hypotenuse of the triangle, and "true power" and
"reactive power" are the two legs.

True power comes from the resistive portion of the load, and reactive
power comes from the reactive portion of the load. True power is
measured in Watts, and reactive power is measured in VAR (volt-amps
reactive). Apparent power is the combination of the two, and as
you've mentioned, is properly measured in VA (volt-amps).

Impedance is a combination of resistance and reactance. The same
formula applies throughout, though.

True power is voltage squared divided by resistance.
Reactive power is voltage squared divided by reactance.
Apparent (or total) power is voltage squared divided by impedance.


So, voltage squared divided by impedance is a valid equation for
Apparent (or total) power in an AC circuit. You are correct that in
AC circuits, there will be phase and time components in the voltage
and reactance to deal with as well.

As to your question about why speakers are rated using "Watts" and
"impedence", they're half-correct. Speaker loads have both a
resistive component and a reactive component. This combination of
resistance and reactance is "impedance", so they're correct to use
"impedance" to describe a speaker.

However, since speakers loads are both resistive and reactive, the
power delivered to them is both true power and reactive power. Thus,
the total power delivered to the speaker is the combination of the
two, or "apparent power". Apparent power should be measured in V-A,
not Watts. Technically, stereo amplifiers should be rated in V-A as
well. I figure more consumers understand "Watts" as a unit of power
than volt-amps, and as long as the amp manufacturers and speaker
manufacturers are on the same page, there's no real harm done in using
"Watts" instead of the correct "volt-amps"

Scott Gardner







  #30   Report Post  
Tha Ghee
 
Posts: n/a
Default Damping Material Question

"thelizman" wrote in message
...
Fred wrote:

You wanna read my post again? See the part about mid-to-high range of

the
audio spectrum?


You wanna explain to me where mid to high frequencies occur in a
subwoofer system, ya moron?

if you have a metal cone sub there can be hi-freq content. look at the lab
graphs, so he's not a moron you may be.




  #31   Report Post  
Tha Ghee
 
Posts: n/a
Default Damping Material Question

"thelizman" wrote in message
...
Fred wrote:

No implication in the original post at all. You have interpreted your

way
and I have interpreted it as it was written. It has nothing to do with
comprehension at all. If **** was electricity you'd be a walking,

talking
power station.


You're an idiot. Just admit it. Anyone who starts talking about standing
waves in a box for a car is an idiot for multiple reasons.

Be quiet now.

are you saying there are no standing waves in sub encs.??


  #32   Report Post  
Kevin Murray
 
Posts: n/a
Default Physics of bridging an amplifier - was: Damping Material Question

Speakers are rated in watts in order to tell you how much electrical power they
can dissipate. Over 95% of the power delivered to a loudspeaker is dissipated as
heat by it's resistive element and can quickly barbecue the voice coil. Reactive
power (V-A) is what does all the work in a speaker. Since the reactive power is
not converted to heat, the maximum V-A delivered to a speaker will vary
depending on several things such as enclosure type, signal frequency, and driver
x-max among others. In this case the driver will reach it's excursion limit and
mechanically destroy itself.

Since your average loudspeaker is only about 5% efficient at best, it's
satisfactory to only provide it's maximum power rating in watts. If a speaker
bottoms out it will sound like crap and the listener will turn down the volume.
This inherent "built-in protection" protects the speaker from mechanical damage
resulting from excessive V-A.

Kevin Murray

wrote in message
...


True, and I've always wondered why it's not explained that way more
often in the first place. I used to see that "halving the impedance"
crap all the time too, when the correct explanation is so much simpler
- you double the voltage swing, which quadruples the output power.
(Obviously, the *total* power only doubles, since you're going from
two channels to only one when you bridge the amp.)

Liz - I'm saddened to hear that the JL techs were arguing with you
about how amp bridging works. I can understand it if the marketing
types were confused, and maybe even the manual writers, but the techs
and engineers should know better. How hard is it to understand that
power equals voltage squared divided by impedance?

Scott Gardner



Power does not equal voltage squared divided by impedance..... sorry,
but power equalss voltage squared divided by resistance...

impedance and resistances are different...

If you wanna be talking about impedences...you gotta take into account
PF angles... which means you arent really dealing with Power anymore,
your dealing V-A (volt-amps). Just what i gathered at Electrical
eng. school.

Never did understand why speakers are rated in WATTS and impedences.

Can anyone explain this to me? Or is the 5 text books i spent ,which
seems to be, unlimited hours reading...wrong?




  #33   Report Post  
thelizman
 
Posts: n/a
Default Damping Material Question

Tha Ghee wrote:
"thelizman" wrote in message
...

are you saying there are no standing waves in sub encs.??


Not at subwoofer frequencies. Prove me wrong.

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
is forbidden.
  #34   Report Post  
thelizman
 
Posts: n/a
Default Physics of bridging an amplifier - was: Damping MaterialQuestion

Kevin Murray wrote:
If a speaker
bottoms out it will sound like crap and the listener will turn down the volume.
This inherent "built-in protection" protects the speaker from mechanical damage
resulting from excessive V-A.


You would think, anyway. What most often happens is the listener ignores
it, thinks its part of the source, or because the subs are in the trunk
they don't even notice. Thats why as an installer I was such a fan of
Alpine's (or was it JBL's?)old soft-clip design. The speaker never
bottomed out per-se, it just got harder to push.

It's also worth pointing out that IME 75% of the time a speaker blows,
its not the voice coil that went bad, but the mechanical portion of the
speaker which couldn't handle the abuse. Spiders and surrounds come
unglued, get worn out, or the cone itself becomes warped. I've even seen
some speakers where the leads get ripped out of the speaker terminal in
subs that have high Xmax, but don't cut the leads long enough. Power
handling in a voice coil is rarely a problem. Thats why I tell people
not to worry about an amp thats too big, you can always turn it down
when things start to go "thwack!".

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
is forbidden.
  #35   Report Post  
Les
 
Posts: n/a
Default Damping Material Question


"Tha Ghee" wrote in message if you have a metal cone
sub there can be hi-freq content. look at the lab
graphs, so he's not a moron you may be.


No Ghee, you and Fred are morons. Do you not run a crossover on a sub? Are
you that dumb? Let's say you run your crossover unusually high at 140Hz, do
you consider that high frequency? We are talking application here, not what
a sub could potentially do in a lab if the conditions are right.

Les




  #36   Report Post  
Nousaine
 
Posts: n/a
Default Physics of bridging an amplifier - was: Damping Material

thelizman
wrote:

Kevin Murray wrote:
If a speaker
bottoms out it will sound like crap and the listener will turn down the

volume.
This inherent "built-in protection" protects the speaker from mechanical

damage
resulting from excessive V-A.


If the speaker "bottoms" meaning striking some part of the basket it is often
already damaged.


You would think, anyway. What most often happens is the listener ignores
it, thinks its part of the source, or because the subs are in the trunk
they don't even notice.


That's common; an overload condition isn't "heard" until the driver quits.

Thats why as an installer I was such a fan of
Alpine's (or was it JBL's?)old soft-clip design. The speaker never
bottomed out per-se, it just got harder to push.

It's also worth pointing out that IME 75% of the time a speaker blows,
its not the voice coil that went bad, but the mechanical portion of the
speaker which couldn't handle the abuse. Spiders and surrounds come
unglued, get worn out, or the cone itself becomes warped. I've even seen
some speakers where the leads get ripped out of the speaker terminal in
subs that have high Xmax, but don't cut the leads long enough. Power
handling in a voice coil is rarely a problem. Thats why I tell people
not to worry about an amp thats too big, you can always turn it down
when things start to go "thwack!".

--
thelizman "I didn't steal the FAQ either"


FWIW; in speaker testing the most common failure mode is melting voice coil
glue. I drive every woofer to its maximum SPL capability using a ramped sine
wave ( a demanding but non-purposfully threatening) that has characteristics
similar to musical programs.

Using a Crown Macro-Tech 5000VZ I've blown up dozens of woofers but have only
damaged suspensions on a few occasions. It's true that this represents a lab
condition and not repeated abuse over a long time. But, thinking about it,
nearly all woofers have more Xsus (linear suspension stroke) than Xmag (linear
motor travel) so it's hard to imagine a situation where a limited stroke motor
woukd tear out a suspension with more travel.

Not saying that it doesn't happen; I'd just like to know more about the
circumstance.
  #37   Report Post  
Eddie Runner
 
Posts: n/a
Default Physics of bridging an amplifier - was: Damping Material

Nousaine wrote:

Not saying that it doesn't happen; I'd just like to know more about the
circumstance.


Tom, I think Liz, and maybe other installers may be mistaken here..
As installers working in the bay we do see alot of speakers with
worn out surrounds and alot of problems other than burned VCs.

But I think your right this time Tom, the things other than burned VCs
like surrounds coming apart are usually just bad (cheap or badly
engineered) speakers... Or where an installer put a screw threw it or
where the outside (where the cork would be but they dont use cork anymore)
is coming off so badly that the speaker is coming apart from the basket.

The ones where the customer just play the damn things too loud
are typicly burned coils, but we probably see (in the bays) way
more of other types of abuse on the drivers as well....

I see what Liz is saying, and you work in a lab more than a bay so
you may not see what real installers see... But what we see isnt really
what Liz thinks it is (IMO).....

Eddie Runner

  #40   Report Post  
Kevin Murray
 
Posts: n/a
Default Physics of bridging an amplifier - was: Damping Material


"Nousaine" wrote:
snip

If the speaker "bottoms" meaning striking some part of the basket it is often
already damaged.

snip


What do you mean by "striking some part of the basket?" I was referring to the
motor assembly. I'm sure it's possible but I've yet to see a woofer damaged from
a few whacks against the pole piece. I would think that if the diaphragm itself
were to strike the basket, the damage would be assured and catastrophic.


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