|20th November 2010, 03:41 PM||#31|
Join Date: May 2003
The Golomb ruler seems interesting.
Now I'm thinking about Bessel arrays. They should be not too far from your ("statistic") array in a conseptual sense. Did you simulate a Bessel array for a comparison?
I simulated Bessels in several occasions in the past, but I never build one yet. Simulations showed quite good and uniform performance. However, the main blockage for me not to build one is that from an array I want the maximum directivity possible! Thus I use a straigh line array, no tapering of any kind. If I want less directivity I decided to use some other consepts.
|20th November 2010, 04:47 PM||#32|
Join Date: Mar 2008
i kind of agree with your estimation that bessel arrays
have something in common ...
I attended a demonstration of a bessel array in
different configurations - not only line array -
at a local university here and had some exchange
of experience with the designer too some years ago.
Dipol 08 is more directional in the vertical
plane than a 5 or 7 driver bessel array would be ...
In a dipole line array using a frequency independent
voltage distribution according to a bessel function,
would not allow for the same lower frequency limit
and dynamic headroom in the bass, if you were to
use the same drivers ...
In a dipole line array you have to make the best of the
mechanical limits of your drivers, which implies to have
the same excursion for all drivers in the bass and make
use of the total amount of volume displacement possible.
Also think of distorsion ... a chain is as strong as it's
weakest link, or the most burdened driver(s).
Driver load in dipol 08 is equal in the bass for all drivers.
I can rely on that smallish drivers only because
the FR 125 S driver has large excursion and a special
motor, which makes the driving force nearly as constant
within sane excursion limits as if it would be an
underhung voice coil design, it is a double magnetic
gap design in fact.
You can forget that design using equally small
Fostex drivers e.g. ...
Dipol 08 is designed to work in combination with a
monophonic subwoofer - if necessary - and be able
to "standalone" above 80-100 Hz, giving a smooth
overlap with the woofer.
Using a bessel array you will need more or larger drivers
or you have to go up significantly with the crossover
In that case you will need stereo subwoofers, which
have to be placed somewhere near(er) to the arrays.
Using a wider baffle would be possible also to increase
the dipole path length and reduce excursion, but then you
have to consider side lobing of the array.
Having all that in mind, the dipol 08 design is very
conciously chosen ... and driven to the edge of sane
mechanical limits using small drivers and a narrow baffle.
The subwoofer covers the range which is typically
affected by room gain (<80 Hz) and can be placed
for optimum balanced mode excitation in a fairly
wide area ... adjusting its level accounts for specific
room gain rather well, so the system is easy to adjust
for different rooms:
- Place the satellites for best stereo imaging
- Place the subwoofer for balanced low frequency
mode excitation rather independently
- Fine adjust subwoofer level properly for seamless
integration according to room specific gain.
Ready means: No fumbling with the crossover frequency,
no fumbling with the slopes of the satellites.
Last edited by LineArray; 20th November 2010 at 05:04 PM.
|2nd March 2012, 05:56 PM||#34|
Join Date: Mar 2008
using stereo subs is obligatory then, yes.
The principle will work, but you will have to re-
align all the crossover stuff and also the baffle
dimensions (width about 2 .. 2.2 X cone diameter etc.)
Maybe you can also shrink the height a bit.
One interesting feature in 'Dipol 08' is having noticeable
vertical directivity in the transition region of the room.
You may loose that a bit, but especially when using dipole
subs i would say 'yes it can work if implemented carefully'.
Last edited by LineArray; 2nd March 2012 at 05:59 PM.
|3rd March 2012, 08:24 AM||#35|
what do you mean by 'transition region of the room' schroeder freq?
btw. how did you model the freq response? is there a software i can use for simulation?
|3rd March 2012, 10:02 AM||#36|
Join Date: Mar 2008
yes transition region means the frequency range
where the room goes from modal (resonant) bahaviour
to statistical (reverberant) behaviour.
That is the range around Schroeder frequency (and
often above). Fs is often around 120Hz dependent
on the room's size and furniture.
But many roms lack diffusivity even up to the lower
For gross simulation of the baffle diffraction you can
use e.g. EDGE from Tolvan Data.
But this won't help you aligning the drivers "correction
network" since that software uses idealized drivers.
You will need some experience and measurement tools
to make a new version work.
E.g. exact knowledge of the driver's voice coil inductance
will help in simulating passive crossover/equalisation
networks using appropriate software.
So in my view it will lead into a
cycle to refine your system ...
You can start using a test baffle without eq network, all
the drivers in series-parallel circuit to aquire first data and
listening impression. But that will be just the start of your
Last edited by LineArray; 3rd March 2012 at 10:10 AM.
|3rd March 2012, 11:25 AM||#37|
measurement and crossovers are no problem for me (I use digital filtering, so I'm sure I can fine-tune easily)
I should have said - what kind of simulation did you use to find the driver layout on the baffle - to minimize comb filtering? is edge useful here?
anyway, if I decide to try your design I will post results. thanks for your support!
|3rd March 2012, 12:09 PM||#38|
Join Date: Mar 2008
Of course, EDGE is useful here. For low frequency behaviour you may use
it in a 'creative' manner and simulate also the bottom reflections from the
line array by mirroring the baffle at the "bottom line".
For LF behaviour that mirrored configuration using all drivers may serve
as a starting point, while for HF the upper 3 drivers are more in the focus.
Unfortunately you cannot simulate crossing over or drivers having different
input voltages in EDGE AFAIK.
To make the bottom-mirrored baffle (double height) fit into the sketch
window of EDGE you can turn it by 90 degrees ....
So you are just turning the space and moving the virtual mic up and down
on the screen resembles moving it sideways "in reality" ...
Because of said drawbacks i would not call it "simulation", but used
wisely and "with a grain of salt" it will yield some orientation in design.
You cannot simulate the cone breakup either ... so it might be usefull to
"do as if" the cones would be somewhat smaller at HF.
But that should not affect "good distances/ratios" that much, you will find
out quickly that some "rulers" will work rather "well behaved" at likely
listening positions while others will not.
It is also beneficial to look at larger (even vertical) off axis angles
(yes, where is the "axis", you have to define your own in a practical way
.. use a certain height or "2nd driver from above", which makes
intermediate results more comparable IMO)
Sure ... looking forward.
Last edited by LineArray; 3rd March 2012 at 12:24 PM.
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