"Dipol 08" Baffle Dimension and List of Crossover Parts - Page 2 - diyAudio
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Old 5th November 2010, 08:51 AM   #11
diyAudio Member
 
Join Date: Mar 2008
I do not accept that argument, although you are right
concerning the modal range of the room below
Schröder frequency.

If e.g. a left speaker sounds somewhat "nasal"
due to tolerances compared to the right one, you can
distinguish both when playing from a position nearby
each other. Using white noise e.g. , even auditive
distinction is easy.

But you can also distinguish the speakers when standing
at different positions, distance and angle pointing at the
listener should be the same.

Audibility surely depends on the amount of deviation.

But quality is about controlling deviation, not a about
ignoring it. Sad but true ... all the factors contributing
to further deviation (room ..) can go into compensative
direction but can also worsen the deviation.

A deviation in the direct sound will mostly be audible
above Schröder Frequency and be more audible as
higher you go in frequency towards the presence range.

Using your argumentation, we could even listen with
speakers of different type on the left and the right position
in a stereo setup.

It is a typical "doesn't matter anyhow" argument ...


As a further point a dipole line array is by far more directional than
e.g. a monopole source ... room contribution is much reduced
compared to conventional speakers, which possibly increases the
need for looking at symmetry.

Best
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Last edited by LineArray; 5th November 2010 at 09:12 AM.
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Old 5th November 2010, 09:14 AM   #12
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Location: Örebro, Sweden
Quote:
Originally Posted by LineArray View Post
It is a typical "doesn't matter anyhow" argument ...

Best
It is a to-each-his-own-argument. If u wanna match ur own batch of resistors, go ahead. I aint doing it

Regards /Bo
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Old 5th November 2010, 09:31 AM   #13
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Join Date: Mar 2008
Danerius,

i am giving practical hints here, how to get the best
result when building this particular speaker.

Since i have developed and built it, i should have some
practical experience which i share with other members.

I did not say anything about measuring and matching
the resistors or other crossover components ...
i was talking about the drivers.

And i was talking about a particular driver, which
seemed to have had non optimum consistency in
serial production in the past.

My hints are about handling that - and possibly turning
deviations of the drivers into an advantage ... although
it will also apply to other drivers used in a comparable
configuration.

Building a speaker is not only "building accordingly
to plan", there are also details in execution which
contribute to the quality which can be achieved.

And as there are measures, which i have found to
influence quality and do not even increase cost,
i should mention them to those who are interested.


Kind Regards
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Old 5th November 2010, 10:41 AM   #14
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Since drivers with lower fs will also have lower
efficiency, the bottom position is best for the
lowest fs drivers ... since the bottom position
has the longest effective dipole path length.

If you have a set of slightly varying drivers, there
will be truly a place for everyone ... but this kind
of selection is by far not as important as selection
due to mid to high frequency response.
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Last edited by LineArray; 5th November 2010 at 10:47 AM.
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Old 6th November 2010, 10:37 AM   #15
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Some pics from mounting, here glueing the drivers
to the stone spine ...
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Old 6th November 2010, 10:40 AM   #16
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Wiring of the drivers could be simplified now,
but as the crossover design was not settled
is was easier to have the to connectors of upper
and lower drivers group accessible separately
in the croccover ...
...
Mounting of stand and spine ...
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Last edited by LineArray; 6th November 2010 at 10:48 AM.
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Old 6th November 2010, 10:44 AM   #17
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Left speaker being built,
optional rear muffler,
first crossover tests,
crossover cover closed with
1st version of crossover builtin ...
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www.dipol-audio.de

Last edited by LineArray; 6th November 2010 at 11:03 AM.
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Old 7th November 2010, 01:02 AM   #18
CLS is offline CLS  Taiwan
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Location: Taiwan
Thanks for sharing. All fittings and overall assembly are cleverly and tidily done! How nice I love that wiring method.

-------------

I'm very interested in various line arrays. Some design ideas keep popping in my mind. Besides all the dilemmas and difficulties in designing which have been thoroughly discussed, I'd like to raise another question, about multi-driver.

I have a feeling, when the system is playing quietly and the level gets lower than a point, some details would be gone.

Other than being submerged by the background noises, hearing's sensitivity drop at both ends of spectrum, and possible intrinsic non-linearity of (my) hearing or even the air itself, would it be possible that the speaker driver(s) also hit the non-linear operation zone of the low level side?

I mean, when playing very very quiet, the amplitude is lower than a point, the rise and fall of the signal produced by the voice-coil-cone-assembly might largely fail to track the input because of all kinds of non-linearity in the electrical and mechanical constructions.

For example, maybe small, but there should be a [static friction] in the suspensions of the driver (as physics told us). When the force (by the VC) gets larger than that, then it starts moving. If the force is very small, to a threshold, it might fail to move the cone.

And, there is inevitably some flexibility in voice coil itself and the bonding between VC and cone (not to mention the floppy cone). After all, nothing is perfectly rigid. So, some of the force must be eaten here.

Sorry for the hair-splitting, but I think those are not just (my own) imaginations.

So, I got an impression that smaller, lighter drivers usually behave better at such condition. (or maybe it's the same thing as the term "downward dynamics" brought by Planet10?) OTOH, my 18" woofers are the typical bad example. They are good at playing loud, not quiet.

In a line array, there're many drivers. When playing quiet, each driver is moving even less than the single driver in ordinary speakers. So I'd guess it would hit the "low level threshold" earlier. (such phenomenon might also be non-linear, though...)

So, how does the line array behave in reality when playing very quiet? Would you please share?
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Old 7th November 2010, 07:47 AM   #19
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Quote:
Originally Posted by CLS View Post

...
I mean, when playing very very quiet, the amplitude is lower than a point, the rise and fall of the signal produced by the voice-coil-cone-assembly might largely fail to track the input because of all kinds of non-linearity in the electrical and mechanical constructions.

For example, maybe small, but there should be a [static friction] in the suspensions of the driver (as physics told us). When the force (by the VC) gets larger than that, then it starts moving. If the force is very small, to a threshold, it might fail to move the cone.
...

Hello CLS,

nice to meet you here ...

i observed something - which may point into that
direction - when i was tuning the rear tweeter panel.

I decided for that tweeter panel, because asymmetry
in dispersion of upper presence and brillance region
led to inconsistencies.

When tuning the speaker to have sufficient "sparkle"
to be experienced at all "useful" listening positions it
turned out that it sounded unecessarily sharp or
"beasty" with some music.

The drawback of rear radiation dropping in the highs,
could not be compensated with the front radition.

That was why i made the rear tweeter panel, but
since i did not want it to spoil homogeneity i listened
very carefully while tuning the tweeter panel's
crossover and i also listened at very low levels ...

In that situation the tweeters could also be driven
"fullrange" (mind the L-Pad), so i omitted the
capacitor "C3" for a while.

I experienced, that the subtle effect of the tweeter panel
was improved at low levels, giving slightly more detail
at very quit music passages.

The effect was so subtle, that i normally would not
make a big story of it, but my personal impression
was stable - even though i know that it might be
close to "subliminal".

I suspected the capacitor to cause the loss in detail ...
and tried different types also making it so large that
a change in frequency response caused by presence
of C3 could be excluded.

What i believe finally is, that it was not the
capacitor causing the subtle change, but the low
frequency components causing motion of the tweeters
even at low levels - thereby possibly mitigating those
effects you mention above.

If you observe a cat before jumping, it will not stay
motionless before the jump but preparing to it by
slightly "rocking" herself ... i like to take this as an
analogy.

There must be friction, which causes relatively increased
nonlinearities around the rest position of a vibrational
system. And i think distortion measurements point
towards increased distorsion at very low levels too.

---
In the end i decided to include C3 in a very large and
high quality version as a compromise, for reasons of
durability of the speaker ... most of my speakers will
be used by other persons and not by myself, so
durability and robustness is always a priority.

But i sometimes thought about some part of the
"analog/vinyl magic" experienced by some
audiophiles comes from subsonic vibration
of the speakers, causing a fullranger or a woofer to
oscillate permanently around its rest position, thereby
possibly increasing detail by partly overcoming the
nonlinearities at low excursions.

Maybe some subsonics also causing psychoacoustical
effects ... but that is another story.

---
If so, i could propose a - level adaptive - "rumble"
simulator here, which causes inaudible excursion
of the drivers (and amps!), to increase performance
at low levels.


Compared to all the high end "snake oil" sold, this
could indeed be a real improvement to some systems.
---

In fact is does not solve the problems for the tweeters
in a multiway. A tweeter with impregnated surround,
being the suspension at the same time might suffer
more from that than a fullranger, also excursions are
very small at low levels.

--------
But to answer your initial question, the fullrangers
themselves do not show obvious effects at lower
levels and the whole speaker plays rather "level
consistent" to my ears.

The 80Hz 1st order PLLXO highpass helps increasing
the dynamic headroom and makes the system playing
more "relaxed" at higher levels. That is a major point
concerning dynamics. In that configuration the system
can go very loud - absolutely sufficient for the majority
of listeners in a living room i would say.

Kind Regards
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Old 7th November 2010, 08:45 PM   #20
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These two diagrams show a simulation of the voltage
transfer for the upper and the lower trio of drivers
respectively, to illustrate the concept of the equalizer/crossover.

Loads are assumed as 2.33 Ohms (3 drivers in parallel) and
130 micro Henry VC inductance in series, to represent each group
of drivers.

The real object differs slightly.

The falling slope compensates the rising efficiency
of the OB and also vertical directivity, whereas the
lift in the highs is mainly due to falling energy
response of the fullrangers and the upper trio
getting more dominant in the highs (power tapering).

The frequency dependent voltage shift between the
driver groups is very smooth, so you cannot really
detect which fullranger reproduces which frequency
range from usual listening positions, the array sounds
as being centered subjectively around the 2nd driver
from above as a consequence of the combined effects
of distance weighting and power tapering.

---
For those who already used an FR 125 S, this is a
configuration which makes the driver sound sufficiently
present and gives real sparkle, but is in no way overbright.

As the directivity is less varying than with a single driver
in a monopole box, the insufficient energy radiated in the
highs gets very obvious here and must be compensated for.

Left: Upper driver group
Right: Lower driver group
Attached Images
File Type: png VoltageTransferFunctionUpperTrio.png (28.4 KB, 62 views)
File Type: png VoltageTransferFunctionLowerTrio.png (26.1 KB, 23 views)
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Last edited by LineArray; 7th November 2010 at 09:14 PM.
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