Note: I crosspost to rec.audio.tech in case Mr. Pierce wants to comment
on this .... it is my experience that he knows more about these matters
than I do.

Arny Krueger wrote:

[my comment]

The distortion specs for air are not changed by altering
a bass units suspension,

In a well-designed system, the suspension of the woofer is
the major source of distortion.

I was considering the air in the box and most certainly in the port. I
increased the port area in my @home system as pr. JBL recommendations in
their proprietaty cabinet desiogn software on the advice of
Quali-Service in 1993.

Without that experience I would have agreed that it was correct for home
use, but perhaps not for loudenbooming, with it I say that with a good
loudspeaker unit of sufficient area to avoid extreme excursion the air
is the issue, and not the loudspeaker in terms of LF distortion.

The outcome even at apartment friendly listening levels was a notable
bass quality improvement, much more horn like. No change in the box
tuning mind you, just a doubling of port cross sectional area - from 1
port to 2 longer ports - that I hadn't bothered with in 1980 because one
port was simpler and "surely enough at the modest levels designed for".

Proper high SPL bass bins eliminate most of the loudspeaker suspension
concerns by not letting it have large excursion, and instead horn
loading it as Turbosound does with the example quality bass driver in
this thread.

I have yet to hear a bandbass box or reflex box system sound well in the
bass range at high SPL, they tend to become hard and smallish sounding
instead of just producing moving air as large horns do it. That problem
is however a likely uavoidable compromise between van space requirement
and amplifier wattage needed, it is easier to haul the extra 6 dB of
amplifier power than to haul them big horns.


Kind regards

Peter Larsen

--
*******************************************
* My site is at: http://www.muyiovatki.dk *
*******************************************

That problem
is however a likely uavoidable compromise between van space requirement
and amplifier wattage needed,

No it is the phsics of the design. In order of best transient
response: horn, sealed, vented, bandpass-all things as equal as
possible. Another problem with bandpass designs is the apparant sound
source, the port is rarely as large in area as an 18" driver with it's
associated port. Typically the port in a bandpass design would be very
large if trying to accomplish this, making it impracticle.

Best regards,

John

In article .com, "Servojohn" wrote:
That problem
is however a likely uavoidable compromise between van space requirement
and amplifier wattage needed,

No it is the phsics of the design. In order of best transient
response: horn, sealed, vented, bandpass-all things as equal as
possible. Another problem with bandpass designs is the apparant sound
source, the port is rarely as large in area as an 18" driver with it's
associated port. Typically the port in a bandpass design would be very
large if trying to accomplish this, making it impracticle.

Best regards,

John

The 18's port is what radiating most of the bass energy below
some frequency, and its likely to be no bigger than a typical bandpass
design. Above where the 18's port stops working, there would be area
say200-500 where the sound must come from a different driver, but
no real big problem. For efficiency and bandwidth, the bandpass
must still be a physically large box.

greg

Servojohn wrote:
That problem
is however a likely uavoidable compromise between van space
requirement and amplifier wattage needed,

No it is the phsics of the design. In order of best transient
response: horn, sealed, vented, bandpass-all things as equal as
possible.

Where does transmission line sit in that list?

--
The speaker system brings the sound,
In light effects I'm spinnin round
All the people on the floor they shake their bodies cry for more.
Never let this feeling go and let the music take control.
Forget your problems and be free,
Enjoy this moment, come with me!

"Tim S Kemp" wrote in message

Servojohn wrote:
That problem
is however a likely uavoidable compromise between van
space requirement and amplifier wattage needed,

No it is the phsics of the design. In order of best
transient response: horn, sealed, vented, bandpass-all
things as equal as possible.

Where does transmission line sit in that list?

The list is overly-general, so you can overly-generalize the
transmission line and put it anywhere.

Servojohn wrote:
That problem
is however a likely uavoidable compromise between van space requirement
and amplifier wattage needed,

No it is the phsics of the design. In order of best transient
response: horn, sealed, vented, bandpass-all things as equal as
possible.

If one is to bring in the phsics [sic] of the design, how about
bringing in real physics?

In that case, your list is demonstrably wrong. If "all things are
as equal as possible," then let's actually make those things
can make equal really equal.

Let's, for example, make the bandwidth the same. For a given
bandwidth, considering both high and low end cutoffs, since
they ALL represent band-pass systems, a "bandpass enclosure
has no worse transient response as a sealed box, since both
are a 4th-prder bandpass system. Both sealed and bandpass
have better transient response than both vented and horns,
because vented and horns are higher-order systems, and, all
things being equal, the lower the order of the system, the better
the transient response.

sidebar: there's a pervasive myth that horns, as a general rule,
have better transient response than direct radiator. This myth
was and is widely promulgated by horn advocates and manu-
facturers, but has little basis in physical fact. It ignores the
rather
sharp rollofs resulting from throat and mouth cutoffs imposed
on top of the already multi-pole bandpass function of the basic
driver itself.

Let's make something else "equal": enclosure size. In that case,
reflex wins, because is is capable of a wider bandwidth, and horns
lose big time, with bandpass and sealed boxes in between.

The problem with your proposition is that it's impossible to make
things "equal enough" to support your assertions.

In such a case, the only way a horn is going to win in the transient
race is if it has a substantially wider bandwodth than any of the other
systems, making the comparison at that point somewhat absurd if,
for no other reaons, than the enromous difference required in
enclosure size.

On Tue, 15 Nov 2005 22:17:38 -0000, "Tim S Kemp"
wrote:

Servojohn wrote:
That problem
is however a likely uavoidable compromise between van space
requirement and amplifier wattage needed,

No it is the phsics of the design. In order of best transient
response: horn, sealed, vented, bandpass-all things as equal as
possible.

Where does transmission line sit in that list?

What is generally referred to as a 'transmission line' is almost
always just an overdamped bass-reflex, the only exception I'm aware of
being the B&W Nautilus.

However, the above list is ludicrous, since the transient response of
the system is tied to it's Qts, and has nothing to do with its basic
form. Horns can be horribly boomy, while bandpass boxes (as
exemplified by some KEF designs) can be really clean and tight.

One can also argue (somewhat inaccurately) that the lower the order of
rolloff, the better the transient response. In that case, the best
result comes from a system which isn't even mentioned above - the
open-baffle dipole.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Stewart Pinkerton" wrote...
Where does transmission line sit in that list?

What is generally referred to as a 'transmission line' is almost
always just an overdamped bass-reflex, the only exception I'm aware of
being the B&W Nautilus.

However, the above list is ludicrous, since the transient response of
the system is tied to it's Qts, and has nothing to do with its basic
form. Horns can be horribly boomy, while bandpass boxes (as
exemplified by some KEF designs) can be really clean and tight.

One can also argue (somewhat inaccurately) that the lower the order of
rolloff, the better the transient response. In that case, the best
result comes from a system which isn't even mentioned above - the
open-baffle dipole.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

The Nautilus is by no means the only TL to be other than an "overdamped
bass-reflex", British speaker manufacturers have been producing TL's for
quite some time, including B&W - I have a pair of early-70's B&W DM2
speakers which feature a folded TL enclosure which still surprise people who
have the chance to hear 'em, even with "dance music" ) One DJ friend of
mine commented that although they didn't go as loud as his 18" subs, they
went "about an octave deeper"... not at all bad for a 30-year old design
with a pathetic 6" driver? When fed with well-recorded organ music they
sound very much like the real thing, which is possibly why my pair started
their life in BBC radio 3's monitoring suite.

A true TL is nothing like a bass-reflex speaker in either design or sound -
it features a line (criticaly damped) tuned to be 1/4 wavelength at the
projected -3dB point - this makes for large cabinets, but not as large as a
horn, bass-reflex or infinite-baffle (sealed box) with equivalent bass
extension. The usual behaviour of the TL is a 6dB per octave rolloff
without the peaks and resonances found in bandpass enclosures (which extend
their bass by placing a second resonant peak below the resonant frequency of
the driver/cabinet coupling by using the reflex port to turn the cab into a
Helmholz resonator).

For some info on these wonderful beasts, particularly for home construction,
take a look at www.t-linespeakers.org, which features TL's old and new.

Dave H.
(The engineer formerly known as Homeless)

On Wed, 16 Nov 2005 22:20:24 GMT, "Dave H."
wrote:


"Stewart Pinkerton" wrote...
Where does transmission line sit in that list?

What is generally referred to as a 'transmission line' is almost
always just an overdamped bass-reflex, the only exception I'm aware of
being the B&W Nautilus.

However, the above list is ludicrous, since the transient response of
the system is tied to it's Qts, and has nothing to do with its basic
form. Horns can be horribly boomy, while bandpass boxes (as
exemplified by some KEF designs) can be really clean and tight.

One can also argue (somewhat inaccurately) that the lower the order of
rolloff, the better the transient response. In that case, the best
result comes from a system which isn't even mentioned above - the
open-baffle dipole.

The Nautilus is by no means the only TL to be other than an "overdamped
bass-reflex", British speaker manufacturers have been producing TL's for
quite some time, including B&W - I have a pair of early-70's B&W DM2
speakers which feature a folded TL enclosure which still surprise people who
have the chance to hear 'em, even with "dance music" ) One DJ friend of
mine commented that although they didn't go as loud as his 18" subs, they
went "about an octave deeper"... not at all bad for a 30-year old design
with a pathetic 6" driver? When fed with well-recorded organ music they
sound very much like the real thing, which is possibly why my pair started
their life in BBC radio 3's monitoring suite.

These are a perfect example of the overdamped bass-reflex. The clue is
in the open end..........

A true TL is nothing like a bass-reflex speaker in either design or sound -
it features a line (criticaly damped) tuned to be 1/4 wavelength at the
projected -3dB point - this makes for large cabinets, but not as large as a
horn, bass-reflex or infinite-baffle (sealed box) with equivalent bass
extension.

Actually, a *true* transmission line is quite different from a 1/4
wave line, as the back wave is entirely absorbed in a real TL, such as
the Nautilus.

The usual behaviour of the TL is a 6dB per octave rolloff
without the peaks and resonances found in bandpass enclosures (which extend
their bass by placing a second resonant peak below the resonant frequency of
the driver/cabinet coupling by using the reflex port to turn the cab into a
Helmholz resonator).

The 1/4 wave reinforcement of the common commercial 'TL' speaker is
equally a device for using the resonant frequency of the pipe to
refinforce the direct radiation by plaqcing a resonant peak below the
resonant frequency of the driver.

For some info on these wonderful beasts, particularly for home construction,
take a look at www.t-linespeakers.org, which features TL's old and new.

Which, so far as I can see, are all just 1/4 wave reinforcement
designs, not true TLs............
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Dave H. wrote:
A true TL is nothing like a bass-reflex speaker in either design or sound -

Well, in a sense, you're right, but not like you'd prefer to think.
It's not like a conventional bass reflex in that it has an
exceptionally
high and lossy port inertance and a very low and somewhat lossy
enclosure compliance.

When you model the system this way, the response predicted by the
very closely matches that actual measured response.

If it quacks like a lossy reflex, it's a lossy reflex.

it features a line (criticaly damped) tuned to be 1/4 wavelength at the
projected -3dB point - this makes for large cabinets, but not as large as a
horn, bass-reflex or infinite-baffle (sealed box) with equivalent bass
extension.

Utterly false, and I would challenge you to produce repeatable
measurements to back up this claim.

The usual behaviour of the TL is a 6dB per octave rolloff

Not in this universe, it isn't. This is a persistant claim on TL
enthusiasts
that has no basis in physical fact. ALL systems that use real drivers
MUST
have a minimum asymtotic rolloff rate of 12 dB/octave: that's imposed
by
the simple mechanical rolloff rate of a second order mechanical
resonant
system. There exists NO means by which a second order system can
be transormed into a first order system. None. Zilch. Nada. I don't
care
WHAT some web site claims, I don't care what nonsense Bud Fried has
spouted for however many decades, it doesn't happen.

At the VERY best, a seriously overdamped line will becahse as a third
order system: what essentially happens is the open line imposes a
zero in the response at DC, leading to an symptotic roloff rate of 18
dB per octave: 12 dB from the mechanical properties of the driver
and 6 dB due to the cancellation of the zero at DC.

without the peaks and resonances found in bandpass enclosures
(which extend their bass by placing a second resonant peak below
the resonant frequency of the driver/cabinet coupling by using the
reflex port to turn the cab into a Helmholz resonator).

It would seem you know as much about bandpass enclosures as you
do transmission lines, because your description of how they work is
quite flawed. Let's look at the simplest case: a 4th order bandpass
enclosure.

An enclosure-port, or "helmholtz resonator) is a low-pass filter,
simple
as that: a second-order low-pass filter to be exact. A driver, i.e. a
mass
(the cone) and a compliance (the combination of the suspension
compliance and enclopsure compliance) used as an acoustic radiator
act as a high-pass filter, a second-order high-pass filter, to be
exact.

Put the enclosure port between the driver and the final radiation load,
and you take a second-order high-pass function (the driver and its
enclosure) and impose the second-order low-pass filter of the port
and enclosure and end up with, magically, a 4th order bandpass
transfer function. That's ALL there is to it. The driver, its moving
mass
and the combined compliance of its suspension and its enclosure
and it's electrical and mechanical losses determine the frequency
and response function of the high-pass cutoff, and the front enclosure
and port and its losses determine the frequency and response function
of the low-ass cutoff. Tune the latter above the former, you have a
viable
bandpass system.


For some info on these wonderful beasts, particularly for home construction,
take a look at www.t-linespeakers.org, which features TL's old and new.

Dave H.
(The engineer formerly known as Homeless)