I was talking to some people who own large coaxial speakers and they
all said they liked some aspects of them but found certain things
annoying. And the price is insane. I came up with the idea of getting a
tweeter and surrounding it with four mid-woofers-like a D'Appolito but
with four instead of two drivers. Imagine a White Castle burger or a
Liz Taylor Bassman with a tweeter in the center.

Is there some kind of acoustic fundamental flaw with this
configuration? Or how about three in a triangular array, like a Norelco
shaver, and the tweeter in the center?

On 3 Jun 2006 19:33:46 -0700, "RapidRonnie"
wrote:

I was talking to some people who own large coaxial speakers and they
all said they liked some aspects of them but found certain things
annoying. And the price is insane. I came up with the idea of getting a
tweeter and surrounding it with four mid-woofers-like a D'Appolito but
with four instead of two drivers. Imagine a White Castle burger or a
Liz Taylor Bassman with a tweeter in the center.

Is there some kind of acoustic fundamental flaw with this
configuration? Or how about three in a triangular array, like a Norelco
shaver, and the tweeter in the center?

Unlikely to get even radiation in any plane. At least, the vertical
MTM gives decent radiation in the horizontal plane.

Kal

This really depends an lot on the size and proximity of the drivers and the
order and freq of the crossover. The whole point of a coaxial speaker is to
try to emulate a single point in space that has no dimension. Obviously,
that is impossible with dynamic speakers. Dimension of a radiating surface
is connected to the shortest wavelength that the surface can launch into the
air as an omnidirectional wave front. Yes it is possible to get 20KHz out of
an 8 inch speaker. But it will most likely beam right out of the front of it
and have many, unpredictable hot spots and dead zones all around its off
axis radiation. Some designers think that wide, even dispersion is the
ultimate design goal, while other designers believe that a well defined
sweet spot beamed right at the listening chair makes a lot more sense.

James. )


"RapidRonnie" wrote in message
oups.com...
I was talking to some people who own large coaxial speakers and they
all said they liked some aspects of them but found certain things
annoying. And the price is insane. I came up with the idea of getting a
tweeter and surrounding it with four mid-woofers-like a D'Appolito but
with four instead of two drivers. Imagine a White Castle burger or a
Liz Taylor Bassman with a tweeter in the center.

Is there some kind of acoustic fundamental flaw with this
configuration? Or how about three in a triangular array, like a Norelco
shaver, and the tweeter in the center?

In article ,
James Lehman wrote:
This really depends an lot on the size and proximity of the drivers and the
order and freq of the crossover. The whole point of a coaxial speaker is to
try to emulate a single point in space that has no dimension. Obviously,
that is impossible with dynamic speakers. Dimension of a radiating surface
is connected to the shortest wavelength that the surface can launch into the
air as an omnidirectional wave front. Yes it is possible to get 20KHz out of
an 8 inch speaker. But it will most likely beam right out of the front of it
and have many, unpredictable hot spots and dead zones all around its off
axis radiation. Some designers think that wide, even dispersion is the
ultimate design goal, while other designers believe that a well defined
sweet spot beamed right at the listening chair makes a lot more sense.

James. )

You're describing a speaker with a single driver covering the full range, not what I understand to be
a coaxial speaker. The typical coax has a woofer with a centrally mounted tweeter, usually horn-loaded;
some designs have more than one driver mounted concentrically.

The dispersion patterns for a true coaxial or "triaxial" (Jensen's trademark) are pretty good; I don't
hear any real difference between my University 315-C's and the more modern dome tweeter of my AR3a's or
Rogers LS3/5a's in that regard. I'm sure there are measurable differences.

The worst dispersion I've heard from a tweeter was from the small electrostatic arrays sold to be
attached to full-range speakers ca 1965, such as the Janszen 130. I heard one AR1W/130 setup where
the listening chair required lifting by inches in order to hear HF properly.

Mike Squires
--

Mike Squires (mikes at cs.indiana.edu) 317 233 9456 (w) 812 333 6564 (h)
mikes at siralan.org 546 N Park Ridge Rd., Bloomington, IN 47408

"RapidRonnie" wrote in message
oups.com
I was talking to some people who own large coaxial
speakers and they all said they liked some aspects of
them but found certain things annoying. And the price is
insane. I came up with the idea of getting a tweeter and
surrounding it with four mid-woofers-like a D'Appolito
but with four instead of two drivers. Imagine a White
Castle burger or a Liz Taylor Bassman with a tweeter in
the center.

Is there some kind of acoustic fundamental flaw with this
configuration?

Yes. Beleive it or not, even the D'Appolito configuration has some problems,
but the problems increase rapidly with the number of drivers.

Or how about three in a triangular array,
like a Norelco shaver, and the tweeter in the center?

Whenever more than one acoustical source operates in the same frequency
range, and special precautions are *not* taken, there are problems with the
sound fields from the drivers interfering with each other. The D'Appolito
configuration addresses the more severe problem inherently with the spacing
and positioning of the tweeter and the tuning of the crossover. However,
people who want *really* good performance out of a D'Appolito config often
add more complexity to the crossover to address some smaller problems.

As the number of acoustical sources (drivers) operating in the same
frequency range increases, the problems can become more severe. The problems
are called lobing and comb-filtering effects.

I know what a coaxial or triaxial speaker is. And yes, it is supposed to
emulate a single point in space.

The part about "20KHz out of an 8 inch speaker" was to make a point about
radiating surface area and its connection to beaming at higher freqs. This
is relevant to arranging multiple speakers in a baffle that will cover the
same part of the audio range.

OP wanted to know about arranging drivers in a baffle.



"Michael Squires" wrote in message
...
In article ,
James Lehman wrote:
This really depends an lot on the size and proximity of the drivers and
the
order and freq of the crossover. The whole point of a coaxial speaker is
to
try to emulate a single point in space that has no dimension. Obviously,
that is impossible with dynamic speakers. Dimension of a radiating
surface
is connected to the shortest wavelength that the surface can launch into
the
air as an omnidirectional wave front. Yes it is possible to get 20KHz out
of
an 8 inch speaker. But it will most likely beam right out of the front of
it
and have many, unpredictable hot spots and dead zones all around its off
axis radiation. Some designers think that wide, even dispersion is the
ultimate design goal, while other designers believe that a well defined
sweet spot beamed right at the listening chair makes a lot more sense.

James. )

You're describing a speaker with a single driver covering the full range,
not what I understand to be
a coaxial speaker. The typical coax has a woofer with a centrally mounted
tweeter, usually horn-loaded;
some designs have more than one driver mounted concentrically.

The dispersion patterns for a true coaxial or "triaxial" (Jensen's
trademark) are pretty good; I don't
hear any real difference between my University 315-C's and the more modern
dome tweeter of my AR3a's or
Rogers LS3/5a's in that regard. I'm sure there are measurable
differences.

The worst dispersion I've heard from a tweeter was from the small
electrostatic arrays sold to be
attached to full-range speakers ca 1965, such as the Janszen 130. I heard
one AR1W/130 setup where
the listening chair required lifting by inches in order to hear HF
properly.

Mike Squires
--

Mike Squires (mikes at cs.indiana.edu) 317 233 9456 (w) 812 333 6564
(h)
mikes at siralan.org 546 N Park Ridge Rd., Bloomington, IN
47408

check out this website -- http://www.t-linespeakers.org/projects/index.html

btw, D'Appolito is getting bounced around a bit -- not the MTM configuration
per se, but his use of the Augsburger alignment tables for creating the
Thor.

"Michael Squires" wrote in message


The dispersion patterns for a true coaxial or "triaxial"
(Jensen's trademark) are pretty good; I don't hear any
real difference between my University 315-C's and the
more modern dome tweeter of my AR3a's or Rogers LS3/5a's
in that regard. I'm sure there are measurable
differences.

Those are classic examples from the distant past, but coaxial and triaxial
speaker technology is still alive and well. A ton of them are being sold for
car sound use - I have both 2-ways and 3-ways in my cars. KEF is still
selling "Uni-Q" series speakers which are based on a 6.5" coax. The classic
Tannoy 2-ways from the 60s have been updated and are still highly thought
of.

"Michael Squires" wrote in message


The dispersion patterns for a true coaxial or "triaxial"
(Jensen's trademark) are pretty good; I don't hear any
real difference between my University 315-C's and the
more modern dome tweeter of my AR3a's or Rogers LS3/5a's
in that regard. I'm sure there are measurable
differences.

More modern is certainly relative with those examples. ;-)

Kal

There is a significant difference between a true studio monitor style
coaxial and a car speaker. For one thing, a real coax usually has an
inverted dome driving a sectoral horn and the voice coils of both the woofer
and the tweeter are extremely well time aligned. This is not the same as
mounting a tweeter in front of a woofer to save space in the cut out of the
rear deck of your car.




"Kalman Rubinson" wrote in message
...

"Michael Squires" wrote in message


The dispersion patterns for a true coaxial or "triaxial"
(Jensen's trademark) are pretty good; I don't hear any
real difference between my University 315-C's and the
more modern dome tweeter of my AR3a's or Rogers LS3/5a's
in that regard. I'm sure there are measurable
differences.

More modern is certainly relative with those examples. ;-)

Kal

In article , "James Lehman" wrote:
There is a significant difference between a true studio monitor style
coaxial and a car speaker. For one thing, a real coax usually has an
inverted dome driving a sectoral horn and the voice coils of both the woofer
and the tweeter are extremely well time aligned. This is not the same as
mounting a tweeter in front of a woofer to save space in the cut out of the
rear deck of your car.

Not only are they out of position but those simple crossovers are
not well planned. One could probably use an electronic crossover with
delay, and by biamping get the alignment and levels right.

greg



"Kalman Rubinson" wrote in message
.. .

"Michael Squires" wrote in message


The dispersion patterns for a true coaxial or "triaxial"
(Jensen's trademark) are pretty good; I don't hear any
real difference between my University 315-C's and the
more modern dome tweeter of my AR3a's or Rogers LS3/5a's
in that regard. I'm sure there are measurable
differences.

More modern is certainly relative with those examples. ;-)

Kal

"James Lehman" wrote in message


There is a significant difference between a true studio
monitor style coaxial and a car speaker.

Yeah, today the difference is measured in $1,000's. ;-)

For one thing, a
real coax usually has an inverted dome driving a sectoral
horn and the voice coils of both the woofer and the
tweeter are extremely well time aligned.

While I object to the use of the word "real", I agree that the inherent
time-alignment can be a very good thing.

This is not the
same as mounting a tweeter in front of a woofer to save
space in the cut out of the rear deck of your car.

In the days of speakers like University 315-C's and the AR3a's or Rogers
LS3/5a's there were many speakers that were widely considered to be coaxes,
but did not use a horn tweeter.

OK, they were mostly cheap. ;-)

BTW, my recollection is that the 315-C was a triax. Were both upper range
drivers horns?

IIRC I've seen double concentric horn drivers. The center is more like a
super tweeter.




"Arny Krueger" wrote in message
...
"James Lehman" wrote in message


There is a significant difference between a true studio
monitor style coaxial and a car speaker.

Yeah, today the difference is measured in $1,000's. ;-)

For one thing, a
real coax usually has an inverted dome driving a sectoral
horn and the voice coils of both the woofer and the
tweeter are extremely well time aligned.

While I object to the use of the word "real", I agree that the inherent
time-alignment can be a very good thing.

This is not the
same as mounting a tweeter in front of a woofer to save
space in the cut out of the rear deck of your car.

In the days of speakers like University 315-C's and the AR3a's or Rogers
LS3/5a's there were many speakers that were widely considered to be
coaxes,
but did not use a horn tweeter.

OK, they were mostly cheap. ;-)

BTW, my recollection is that the 315-C was a triax. Were both upper range
drivers horns?