"Dipol 08" Baffle Dimension and List of Crossover Parts

[LineArray]

Hello,

for DIY'ers who would like to build a "dipol 08" style
speaker for private use, i decided to post some raw
sketches (of the baffle dimensions at least) and a list of
crossover parts as a start.

The baffle should be executed with conical driver cutouts
on the rear and be as rigid but thin and highly damped as
possible. I used a composite with a constraint layer
damper inbetween.

Many variants are possible including "omitted backbone"
for less effort or "reduced size lady edition" ...

Nevertheless, the backbone damper including magnet
mounting of the drivers improves the quality of bass to
midrange reproduction a lot and makes up a good part of
the fascination coming with this speaker.

The backbone is mouted flexibly and damped to the foot
and has a resonance as a "standing pendulum" of approx.
5Hz in my version, when the foot is "clamped" to the
bottom (which is not done usually during operation).

A little shrinking in height, maybe 10%, please do diffraction
simulations first and compare to the original, might be
advantageous for people sitting low and listening close.

If sparkle is missing when listening close and sitting low,
a little tilting forward of the speaker (nearly invisibly) is
also a practical solution (loss in sparkle is only little when
listening "close low"). Listening distances from 1.5m
on upward are recommended. I testet up to 7m listening
distances with very good results in homogeneity and
consistency in the whole listenening room.

I post the files "as they are". Please be understanding,
that i cannot do any consultancy in depth for single
projects and possible variants, as i am occupied with
different projects currently. But i will try to answer
common questions - if any - from time to time.


Remark: A dedicated dipole subwoofer is strongly recommended.
Dipol 08 is easiest crossesd in using a 1. order passive line level filter
("PLLXO") at 80Hz. Fullrange operation is possible, but dynamic headroom
is less. Without subwoofer only some chamber music and few jazz recordings
are enjoyful to my taste ...

---
Since the driver positions are badly readable on the picture
of the handsketch, please refer to the attached text files.




Kind Regards

[matevana]

Thanks for posting Oliver. Can you please give a few details on your layered baffle approach. I agree that the baffle should be as thin and rigid as possible, and would like to know how you appraoced this concept.

Ed

[LineArray]

I used 2 sheets of High Pressure Laminate
(6mm thickness each) with about > 2mm dampening glue
inbetween.

Rear sheet with larger driver cutout .... to make it more
"open" to the rear.

That is not an optimum material, but since the excitation
is very low - achieved by the magnet mounting - it is
OK. Without backbone it would also be too floppy due
to it's height ...

I would try something different in the next one ...


Best

[LineArray]

For those who like to play around using EDGE, here
are 2 files representing the approximate configuration
of "dipol 08" as a starting point.

The file with suffix "HT" includes only the 3 upper
drivers and no mirrored baffle. The other file includes
all 6 drivers and a mirrored baffle, representing the
bottom reflections from the array.

The baffle is rotated by 90 degrees in the sketch,
so the bottom line has to be imagined vertically
in the middle of the sketch, separating the double
height baffle (baffle and bottom mirrored image)
into 2 halves.

This way the image fits better into EDGE's sketch
window ... you cannot handle a tall baffle
including bottom reflections otherwise.

If you make changes, be shure to change the
mirrored baffle accordingly - mirorring is done
manually, it is not an EDGE built in feature ...

File "HT" has better approximation above 2-4Khz,
since the lower drivers are rolled off and floor
reflections are less pronounced.

The third file (without the "mod2" suffix) allows
comparison with an array having equidistant
driver placement.

---
EDGE from Tolvan data:

Home of the Edge

Of course you can also use other diffraction simulators
of your choice. Think of the results as being "tendencies",
not representing what we call "reality".

[matevana]

Here's a theory question for you Oliver. If the drivers were totally supported from the magnet, the baffle could then be built to only consider (1) seperating the rear wave from the front wave, and (2) help encourage desired dispersion characteristics.

In theory the baffle could then be made of an anti-resonant material such as closed cell foam, gypsum or even thin foamboard, since 100% of the support duties would now be releaved. The drivers would not have to physically attach to the baffle, only be placed close enough to simulate a seal.

To me this sounds like an interesting approach to reducing baffle and driver noise, and reduce the speaker's overall weight. Additionally, a "foam" baffle could be shaped to facilitate imgaing and dispersion.

Do you see a downside to this?

[LineArray]

Ed, i am with you in most points.

But please do not forget the excitation of the baffle
due to sound pressure, having opposite sign on front
and rear ....

Dipole 08 has kind of purely magnet mounted drivers,
if you knock against the driver baskets from the front,
excitation of the front baffle is close to nothing.

A rather soft, highly damped but dense baffle material
like some rubber granulate e.g. is surely interesting,
but even for pure magnet mounting
("baffle gasket only") you will need at least some
stiffness to withstand deformation due to sound pressure
at low frequencies ....

And we still need that stiffness without the baffle being
extraordinarily thick.

Lead ... is contaminative unfortunately.

Best

[darkmoebius]

Thank you for sharing plans for Dipol-8 starter, Oliver. This is the most interesting project I have come across in a long time.

[LineArray]

Thank you darkmoebius,

and here comes the first correction:

1) The 1st picture (Baffle Sketch) shows the LEFT speaker.
The text said otherwise ... sorry, uploaded a new version.

FR is more balanced - as in almost all OBs - when
the shortest path between drivers an baffle edge points
inwards while listening.

The tweeters are placed accordingly:
Shorter path to the edge inward pointing while listening.


2) Remark: Since there is only one of the tweeters
playing to the top frequencies, its position would
normally be chosen closer to the uppermost fullranger.

I decided to do different, as the more asymmetric
position of the lower tweeter is likely to produce
more unwanted reflections with the backbone.

So it is the upper tweeter, reproducing the
highest frequencies, which can radiate more freely
with the given backbone confguration.


Cheers

[LineArray]

If you build this line array, it will contribute to
best performance if you select your drivers for
symmetry of the left and the right array.

I leave it up to you, whether to rely on measurement
of the drivers solely or prefer an "auditive matching",
which is also possible.

You will notice with most drivers, than none of the
12 will sound the same.

For the upper trio of drivers, which reproduces the
highs predominantly, the candidates which produce
somewhat more "sparkle" but sound balanced and
"unobtrusive" should be selected.

In short: Divide your drivers in a lesser and a better
half due to "presence and sparkle" region and use the
better ones to play in the upper trio.

Some examples for matching the six best for the highs:

- A driver sounding somewhat "beasty" due to being
a little hot (in relation to the others) around 7Khz e.g.
should not play at an elevated position: Best for this
driver is 3rd from above.

- A driver which is unobtrusive but a little more dull
than the others is placed 1st. from above.

- The driver seeming to be the most balanced
one is placed 2nd from above.

For every driver, similar partners should play on the
corresponding positions in the left and right speakers.

---

- Do those selections after a sufficient period of
burning in.

- Have also a look at resonance frequencies and
Rg.

For the 3 lower drivers those are the main
"distinguishing marks" to balance left and right
speaker. The lower the driver's mounting positions
are in the array, the closer the resonances between
left and right "partners" should match.

All in all this is not an "esoterical" approach !
That "balancing and selecting" causes a little effort
but contributes significantly to a simple crossover,
since there is less compensation needed, the speaker
sounds more unobtrusive and balanced because you
simply make the best of the material purchased.

Send drivers with strong deviations back to the dealer !
Same for drivers which have increased noise level !

If the customer does not send back strongly deviating
drivers, the dealers and the manufacturer will not feel
sufficient pain to improve quality. You are in fact helping
them ...

Many manufacturers are pretty good nowadays, but the
CSS FR 125 S were not very homogenous due to
tolerances and quality , as i purchased them in Germany
about 2 years ago.

I hope this has changed by now, since the drivers are
very good by design.

---
Of course fullrangers should always be matched pairs,
no matter which manufacturer.

And as a personal remark:

I seriously wonder why this issue is not being
discussed in here with same enthusiasm like e.g.
"enabling" ... since serial tolerances and quality is
undoubtedly an issue affecting speaker pair symmetry
and speaker quality.


Best Oliver

[danerius]

Originally Posted by LineArray

And as a personal remark:

I seriously wonder why this issue is not being
discussed in here with same enthusiasm like e.g.
"enabling" ... since serial tolerances and quality is
undoubtedly an issue affecting speaker pair symmetry
and speaker quality.


Best Oliver

My thought is that rooms are rarely matched left/right - quite the opposite, and that influences performance more than matching components

Regards /Bo