On Tue, 30 Nov 2004 17:38:19 -0500, "Arny Krueger"
wrote:

This brings up two factors not yet mentioned. The driver's fundamental
resonance is affected by coupling to a considerable air mass in the
line and by the line air's compliance, making the whole model messy.

The usually stated solution to that is to *properly* damp the line.

Yeah, it's often recommended to use higher stuffing density at the
driver end (which I do with mine) and to taper the bore of the line
(which I don't). They are surprisingly tolerant of my poor
modeling ability, and good thing, too.


For homebrewers, transmission lines have a great advantage. A
perfectly good one can be made from a cardboard tube, like a
concrete pouring form. No wood.

Ditto for ported and unvented enclosures. Seen it done many times.

The best woofers I've heard were made with (corian) tubes. They each
had a fancy 18 inch driver in both ends, a small internal volume to
force fundamental resonance above the operating range, and electronic
correction to F-sub-c of 8 Hz and Q-sub-c of 0.5.

Four of these tubes in a home situation was optimum, and the whole
system only cost a little more than my house. Real nice sound though.

Chris Hornbeck

"William Sommerwerck" wrote:



One of the interesting things about the transmission line
sub is the degree of directionality in the radiation pattern.

Bud has been saying that for decades. Do you have any references?

I will see what I can dig up. I think the point is that the vent is very
far away from the main driver acoustically, and so there are all kinds of
interference things going on between them. My suspicion is that this
results in a pattern that changes wildly with frequency too, but I don't
think I have actually seen measurements. Let me poke around in the file
cabinet for a bit.

One of the theories of TL design is that the rear wave marches down the line
and
disappears, with little or nothing coming out the opening. (I don't like
calling
it a port, because that implies a fourth-order transfer function.) But as
Arny
pointed out, TL design is not well-defined.

If the line is intended to dissipate or absorb the rear radiation of the driver
it would seem that a good one is simply another form of infinite baffle.

My personal subwoofer system uses multiple drivers in a basement loaded IB
system. So when I open the basement door can I call it a Transmission Line?

On 30 Nov 2004 23:58:05 GMT, (Nousaine) wrote:

If the line is intended to dissipate or absorb the rear radiation of the driver
it would seem that a good one is simply another form of infinite baffle.

That's a good point, but there are slight differences. Coupling to the
appreciable air mass within the line lowers sensitivity below
reference sensitivity (free air). And damping by the shorted
quarter wavelength "stub" can potentially reduce Q-sub-c to
below Q-sub-s, not possible in any (passive/ unassisted) IB.

Neither of these are very large effects, so I'd guess that
you're essentially right.

Chris Hornbeck

Chris Hornbeck wrote:

A perfectly good one can be made from a cardboard tube, like a
concrete pouring form.

Yeah, but Bose thought of it and patented it years ago so it's a big
no-no!

Look for their Bose Cannon product.

--
Eric (Dero) Desrochers
http://homepage.mac.com/dero72

Hiroshima 45, Tchernobyl 86, Windows 95

William Sommerwerck wrote:

Agreed. The question is, does a sealed-box overdamped woofer sound the same as a
transmission line? I don't know the answer.

What's overdamped mean technically?

What's a transmission line speaker, again technically?


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

On Tue, 30 Nov 2004 20:50:53 -0800, Bob Cain
wrote:

What's overdamped mean technically?

Total (transfer/ "acoustic") Q lower than Butterworth.

What's a transmission line speaker, again technically?

The name comes from RF, and is really abused in the transfer.
"A damped, shorted-quarter-wavelength line" is both less
and more than a useful model. Works anyway; excellent for
homebrewers; hopeless for modeling-wannabe's like moi.

Maybe you could shed some horsepressure?

I can say that the interesting part may turn out to be in the
fibrous tangle. Chaos enters here, so nobody wants to talk about it.

Good fortune,

Chris Hornbeck

Chris Hornbeck wrote:

On Tue, 30 Nov 2004 20:50:53 -0800, Bob Cain
wrote:

What's overdamped mean technically?

Total (transfer/ "acoustic") Q lower than Butterworth.

What's a transmission line speaker, again technically?

The name comes from RF, and is really abused in the transfer.
"A damped, shorted-quarter-wavelength line" is both less
and more than a useful model. Works anyway; excellent for
homebrewers; hopeless for modeling-wannabe's like moi.

Maybe you could shed some horsepressure?

I can say that the interesting part may turn out to be in the
fibrous tangle. Chaos enters here, so nobody wants to talk about it.

Long haired wool was the fibre of choice IIRC.


Graham

On Wed, 01 Dec 2004 05:43:52 GMT, Chris Hornbeck
wrote:

Maybe you could shed some horsepressure?

Re-reading this reminds me that there are no W. Shakespeare's
alive today. So, rather than trying, probably equally lamely,
to paraphrase myself, please permit me to control-X the above,
and insert:

I wonder if you'd be interested in exerting a little rigor
into the discussion? The existing models lack rigor, but more
importantly lack a fresh viewpoint.

Rock-n-roll,

Chris Hornbeck

On Wed, 01 Dec 2004 05:58:48 +0000, Pooh Bear
wrote:

Long haired wool was the fibre of choice IIRC.

Excellent! And man-made substitutes have a difficult task
substituting. Real chaos is expensive.

Your point emphasizes for me the lack of mathematical modeling
in "transmission-line" speaker boxes. It's too difficult for
schmoes like me, and too arbitrary for lotsa heavy-math folks.

However, I can see an actual model as being possible, even
if requiring an iterative solution. Similar models are needed
for acoustic horn design, incidentally.

Thanks,

Chris Hornbeck

"Pooh Bear"

What's a transmission line speaker, again technically?

The name comes from RF, and is really abused in the transfer.
"A damped, shorted-quarter-wavelength line" is both less
and more than a useful model. Works anyway; excellent for
homebrewers; hopeless for modeling-wannabe's like moi.

Maybe you could shed some horsepressure?

I can say that the interesting part may turn out to be in the
fibrous tangle. Chaos enters here, so nobody wants to talk about it.

Long haired wool was the fibre of choice IIRC.




** It all a load of Baaaaaaaah and humbug if you ask me.




.............. Phil

"William Sommerwerck" wrote:
If the line is intended to dissipate or absorb the rear radiation of the
driver
it would seem that a good one is simply another form of infinite baffle.

True, but I tend to see overdamping as a fundamental element of TL designs,
which is not a part of infinite baffling.

Oh certainly so. Of course, the damping then depends on the Q of the driver but
with an Infinite Baffle the Q of the system is certainly damped as much as it
can be ... with a high Q driver in a stuffed pipe (another word for
transmission line isn't it?) how is this improved?

My personal subwoofer system uses multiple drivers in a basement loaded IB
system. So when I open the basement door can I call it a Transmission Line?

Only if you stuff the basement with damping material!

Good smiley. But is the difference between a 'transmission line' defined by the
exit of the line into the room? Otherwise an infinitely long line would simply
be another another word for infinite baffle.

On 01 Dec 2004 06:42:49 GMT, (Nousaine) wrote:

Good smiley. But is the difference between a 'transmission line' defined by the
exit of the line into the room? Otherwise an infinitely long line would simply
be another another word for infinite baffle.

The name comes from RF practice, but is terribly abused in the
transfer. Imagine sending an impulse "down" a transmission line.

Now imagine the end of the line being reflective. At some time
delay, the reflected impulse will arrive back at the source in
phase opposition, and will attempt to cancel *the next* half-cycle
wave.

This is the the sum-total James Faulkner version of the story, and
I'm sticking to it.

How does this apply to the original impulse? Does this mean that
"transients" can behave differently than "steady-states" ? And
what about Betty Lou?

Enquiring minds...

Chris Hornbeck

Chris Hornbeck wrote:

Now imagine the end of the line being reflective. At some time
delay, the reflected impulse will arrive back at the source in
phase opposition, and will attempt to cancel *the next* half-cycle
wave.

Yeah, we studied acoustic resonance in tubes in high school
physics 45 years ago. Thought it looked sorta familiar.
And rudimentary.

I guess it is equivalent to a reactively terminated
transmission line but what about that is supposed to make it
sound good? You just get a nice comb of resonances. What
am I missing here?



Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

Chris Hornbeck wrote:
On Tue, 30 Nov 2004 20:50:53 -0800, Bob Cain
wrote:


What's overdamped mean technically?


Total (transfer/ "acoustic") Q lower than Butterworth.

Cool. What's the benefit of that?

The name comes from RF, and is really abused in the transfer.
"A damped, shorted-quarter-wavelength line" is both less
and more than a useful model. Works anyway; excellent for
homebrewers; hopeless for modeling-wannabe's like moi.

Maybe you could shed some horsepressure?

Nah, just raw skepticism.

I can say that the interesting part may turn out to be in the
fibrous tangle. Chaos enters here, so nobody wants to talk about it.

That's "fiber bundle". :-)


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

"Paul Stamler" wrote in message
...
But typically a vented box is smaller still for an
equivalent bass response, and easier to build, and lighter to carry.
(Although less well-braced than a TL!)

Just as well braced, if you want it to be though.

TonyP.

I guess it is equivalent to a reactively terminated
transmission line but what about that is supposed
to make it sound good? You just get a nice comb
of resonances. What am I missing here?

That there aren't supposed to be any resonances -- the rear wave of the driver
is (supposedly) absorbed, without reflection.

Chris Hornbeck wrote:
On 01 Dec 2004 06:42:49 GMT, (Nousaine) wrote:

Good smiley. But is the difference between a 'transmission line' defined by the
exit of the line into the room? Otherwise an infinitely long line would simply
be another another word for infinite baffle.

The name comes from RF practice, but is terribly abused in the
transfer. Imagine sending an impulse "down" a transmission line.

Now imagine the end of the line being reflective. At some time
delay, the reflected impulse will arrive back at the source in
phase opposition, and will attempt to cancel *the next* half-cycle
wave.

And, of course, this is just great for a narrowband system (like a lot
of antenna systems, for instance). The problem is that as you deal with
a wider and wider frequency range, the model starts to come apart because
the delay between cycles is of course different.

How does this apply to the original impulse? Does this mean that
"transients" can behave differently than "steady-states" ? And
what about Betty Lou?

I have heard some transmission line systems that actually had excellent
transient response (well, as speakers go). I have seen some others that
were just bloated and out of control too.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Bob Cain wrote:
Chris Hornbeck wrote:
On Tue, 30 Nov 2004 20:50:53 -0800, Bob Cain
wrote:

What's overdamped mean technically?

Total (transfer/ "acoustic") Q lower than Butterworth.

Cool. What's the benefit of that?

Presumably more accurate reproduction of transients.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article ,
William Sommerwerck wrote:
I guess it is equivalent to a reactively terminated
transmission line but what about that is supposed
to make it sound good? You just get a nice comb
of resonances. What am I missing here?

That there aren't supposed to be any resonances -- the rear wave of the driver
is (supposedly) absorbed, without reflection.

The idea being that the damping at the end provides a perfect termination
to the line and therefore there is no reflection.

I should say that a lot of "transmission line" speakers are not designed this
way, and some of them are designed with open air venting at the end of the
transmission line too. These aren't classical TL designs but they are now
probably more common.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

William Sommerwerck wrote:
I guess it is equivalent to a reactively terminated
transmission line but what about that is supposed
to make it sound good? You just get a nice comb
of resonances. What am I missing here?


That there aren't supposed to be any resonances -- the rear wave of the driver
is (supposedly) absorbed, without reflection.

How? Which is the rear wave, the tube end? Achieving
termination in a tube at low frequencies is a really good
trick. Only active termination has worked at all and then
only within the tube itself because the terminating driver
will radiate outside.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

William Sommerwerck wrote:
I guess it is equivalent to a reactively terminated
transmission line but what about that is supposed
to make it sound good? You just get a nice comb
of resonances. What am I missing here?


That there aren't supposed to be any resonances -- the rear wave of the driver
is (supposedly) absorbed, without reflection.

How? Which is the rear wave, the tube end? Achieving
termination in a tube at low frequencies is a really good
trick. Only active termination has worked at all and then
only within the tube itself because the terminating driver
will radiate outside.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

Scott Dorsey wrote:
Bob Cain wrote:

Chris Hornbeck wrote:

On Tue, 30 Nov 2004 20:50:53 -0800, Bob Cain
wrote:


What's overdamped mean technically?

Total (transfer/ "acoustic") Q lower than Butterworth.

Cool. What's the benefit of that?


Presumably more accurate reproduction of transients.

Hmmm. Way back when, I was taught that critically damped
was the most accurate.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

Scott Dorsey wrote:
Bob Cain wrote:

Chris Hornbeck wrote:

On Tue, 30 Nov 2004 20:50:53 -0800, Bob Cain
wrote:


What's overdamped mean technically?

Total (transfer/ "acoustic") Q lower than Butterworth.

Cool. What's the benefit of that?


Presumably more accurate reproduction of transients.

Hmmm. Way back when, I was taught that critically damped
was the most accurate.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

"Bob Cain" wrote in message
...

Scott Dorsey wrote:
Bob Cain wrote:

Chris Hornbeck wrote:

On Tue, 30 Nov 2004 20:50:53 -0800, Bob Cain
wrote:


What's overdamped mean technically?

Total (transfer/ "acoustic") Q lower than Butterworth.

Cool. What's the benefit of that?


Presumably more accurate reproduction of transients.

Hmmm. Way back when, I was taught that critically damped
was the most accurate.

I believe what's usually called "critically damped" has a Q of .577 or so,
lower than the .707 of Butterworth, which is maximally flat. My experience
has also been that a Q between .55 and .58 has the cleanest-sounding bass.

Peace,
Paul

"Bob Cain" wrote in message
...

Scott Dorsey wrote:
Bob Cain wrote:

Chris Hornbeck wrote:

On Tue, 30 Nov 2004 20:50:53 -0800, Bob Cain
wrote:


What's overdamped mean technically?

Total (transfer/ "acoustic") Q lower than Butterworth.

Cool. What's the benefit of that?


Presumably more accurate reproduction of transients.

Hmmm. Way back when, I was taught that critically damped
was the most accurate.

I believe what's usually called "critically damped" has a Q of .577 or so,
lower than the .707 of Butterworth, which is maximally flat. My experience
has also been that a Q between .55 and .58 has the cleanest-sounding bass.

Peace,
Paul

Scott Dorsey wrote:

I have heard some transmission line systems that actually had excellent
transient response (well, as speakers go).

My old TDL's sound pretty good.

Scott Dorsey wrote:

I have heard some transmission line systems that actually had excellent
transient response (well, as speakers go).

My old TDL's sound pretty good.

And speaking of building speakers, John, how did your effort go for
recreating the ServoDrives?

--


Roger W. Norman
SirMusic Studio

"John Halliburton" wrote in message
...

Actually, that is a good question. Why AREN'T the live sound guys using
transmission line subs? It would seem like a good way to get much
deeper
bass, and with some proper vent design even some directionality, out of
small bass cabinets.

They do, it's just a special type, called a horn. ;)

Best regards,

John