Medium Acute
Speaker.
Objective:
- Bandpass 40Hz... 300Hz.
- Volume 40/50 litres maxi about.
- Conservation of the loudspeaker 8V012DBL.
Calculation:
They are rather quickly done, since I chooses to make a classical
bass-reflex.
Focal advice a volume area for the use of the 8V012DBL in bass-reflex,
and I choose 50llitres.
My calculation software gives me a size of blowhole of Ø10cm
* 26cm.
Calculation Resuls:
- Internal volume of 50l.
- Blowhole of Ø10cm * 26cm, which will be split in 2
blowhole of Ø7cm.
- Speaker Focal 8V012DB, Ø21cm
- Double wooden thickness on the face before
Size of Panels:
After some small counting, I'm choosing 30*32cm of internal section,
with a height of 52cm.
Then, seen that there is always a little loose of volume, I'm using the
principle which I lose 1cm on every dimension.
That give 57.6cm high to us if I want my 50l.
Then I add 10cm more to put the fitrage in a separated accommodation,
therefore there is also 2 or 3cm more thickness for the
additional plate which I puts on from side to side.
I'm going to Jumbo, I'm looking at what they have as plate, then I
takes desire to try a thickness of 27mm in fir 3 coats.
I'm meeting therefore with the following dimensions:
- 1 piece 75.7cm * 25.0cm * 6.5mm (plywood birch 6 coats).
- 2 pieces 2 70.3cm * 30.0 cm * 27mm (fir 3 coats).
- 2 pieces 2 70.3cm * 37.4cm * 27mm (fir 3 coats).
- 1 pieces 30.0cm * 32.0cm * 27mm (fir 3 coats).
- 2 pieces 35.4cm * 37.4cm * 27mm (fir 3 coats).
- 1 pieces 1 75.7cm * 37.4cm * 27mm (fir 3 coats).
- 1 pieces 32.0cm * 30cm * 10mm in MDF.
Making:
Here are some photographs which I made while I constructs this
surrounding wall.
Here are different stages:
Stick on together the front panel with one of the side panel,
with torx screw 5*70mm.
Photo
Then sitck on of the second panel aside, by intercalating a plate which
will act as wrong bottom.
I also use a slim plate in MDF to assure a distance being enough on the
opposite side of the surrounding wall (has right), which will become
the top.
Photo
Then I begin by drawing the site of the loudspeaker, with a blowhole on
each side.
Photo
I start by piercing holes of 30mm with the drill.
This will serve to cross the blade of the jigsaw!
Photo
And Here is the jigsaw with which I makes my 3 holes!
Photo
Result is the following:
Photo
Then I dig a conical clearing opened inwards the wood box with the aid
of a wood saw and a jigsaw.
Photo
Photo
It gives the results:
Photo
Targte is in fact that there is a clearing big enough behind
the loudspeaker so that air can circulate.
Then I nail (momentarily) a plate against the front face, that hides
the holes which I have just made.
Photo
Then we cut up again. First with the aid of the jigsaw, then I finish
with a cutter and chisel:
Photo
This will allow to embed the loudspeaker in the front face.
Then I sand the corners of the front face in a rounded form
with 40mm radius.
Once finishes, it give us this:
Photo
Then we turn the box, and I put the blowhole. I use some " assemblage
glue" FORBO. It is in fact a similar paste than some cement which
allows to fix the blowhole in a final and efficient way in the baffle.
Photo
The blowhole one is momentarily kept with the scotch tape in the slim
plate of MDF which appeared before on photographs.
I pierced a multitude of holes of 30mm to transform it into acoustical
brake. Then I glued it together in both side panels with some
wood glue.
Following stage: I add up the cable of the loudspeaker.
Photo
Then I begin to repatriates the filter since the
ancient box.
Photo
Once all this finishes, I glue together the back panel, the top
panel of the box, and I screw the
back panel. This one will remain not glued together, because I
must be able to achieve the filter regularly.
I enchaine by combing the front face in black:
Photo
A detail about what we see since the speaker
opening : a little wool rigid rock (1cm of thickness) on the
bottom and the top of the box, then a plate of gondron (8mm of
thickness) covered with 1 cm of wool of rigid rock on the back plate of
the surrounding wall.
Photo
The perforated plate, the wool of rigid rock, the plates of
gondron serves to amortize stationary vibrations and wave in
the box.
It is a real potential trouble in the big box!
Then we go to the next stage which consists to cover the wood with
cork. This will act as tackle.
The small needles on this photograph are here, because I have not do it
correctly on the first box.
Photo
Once the vertical tackle of walls makes, I sitck on the tork on the top
and bottom.
Photo
Once this finishes, this give :
Photo
Then I just have to put a coat of lasure on the tork...
Photo
Then I fix the filter, I add boriers...
Photo
Then I nails 4 feet on underside of surrounding walls.
Photo
And here it is finish:
Photo
Then the box on the top already existed, I fabricated it some
years ago, in the about in 1995.
This new pair of box, with the small filtering update, with the missing
tools , has me couté 750CHF.
Alors l'enceinte du dessus
existait
déja, je l'ai
fabriqué il y a quelques années, aux environs de
1995.
Cette nouvelle paire de coffrage,
plus les quelques petits changement
de filtrage, plus les outils qui me manquait, m'a couté
750CHF.
Filtration, 4 ways version (December, 2003):
Photo
As long as I am, here is the filter actually used:
Components L1, L3, R2... 5, C16... C21 is established in the
big box (bass).
The rest of components is in the small box wall on the top.
The cutoff frequencies are:
8V012DB: 40Hz...100Hz
7V014DBL: 100Hz...400Hz
5V313: 400Hz...3kHz
T120K: 3kHz...20kHz
Explanation:
- 8V012DBL: It is a loudspeaker doubles spool, that I use as 4
Ω impedance. It uses lowpass filter build with L1 /
C1 C10, located between the 1st and 2nd order. Resistance R2 R3 serves
to amortize the electromechanical resonances. This resonances is owed
for instance to bass-reflex which
generates two resonance (impedance raised) around frequency air hole,
and anti-resonance (low impedance) at frequency chord of the air hole.
This causes some exasperating level varitions if we do not
watch out for it.
- 7V014DBL: It is also a loudspeaker doubles spool, that I use it as
impedance 4 Ω. C16... C21 / L3 constitutes a highpass filter,
and L4 C13 C14 are lowpass filter. They are both in second
order. R4 serves to diminishing the sensitivity a bit to adapt it to
other HP.
- 5V313: C4 C22 constitutes a 1st order highpass filter, R7 serves for
amortizing the effect of the mechanical resonance and L7 restricts the
effect of R7 in low frequency only. L5 and C7+C23 is 2nd order lowpass,
with R8 to amortize resonances. Remain then L6 C6 R6: this allows to
have an answer in phase as close as possible between 5V313 and
T120K around the cutoof frequency. This things is very useful to avoid
the incidents around the cutoff frequency at 3kHz, due to the
low length of sound wave at 3kHz.
- T120K: one classic 3rd order filters with C8 L8 C9. R10
serves for restricting oscillation, and R9 adjusts sensitivity.
Simulation:
With a software that I to create myself 10 years ago, here is what the
simulation of filtration gave me:
Photo
In green, it is the anser curve of every loudspeaker
individually, then in red the full answer.
Conclusion for version 4 ways / 100Hz.
You are going to say to me, but why 4 ways?
At the origin, there was only the small speaker box of the top
on the last photograph, and the 17cm 7V014DBL generate
all bass himself. But this did not admit me. First the cutoff
frequency was higher (around 70-80Hz), and then the bass was not good.
I then decided to add a little bigger loudspeaker of 21cm that are only
in charge of the low register. I am very happy with result, even if
operation was expensive (because I follow it in the 3rd version of the
coffer by serious).
In listening, a first reality appear: with the filtration added on the
21cm, I lost a party of impulse answer that it had at the beginning.
But I would keep this shape 3 months, until March 2004. All the 4 ways
gives a very soft sound and clear enough.
donne un son
très
doux et trpès clair.
Situation is going to evolve when I crash the 17cm (7V014DBL) by
accident. To continue listening to music, I must move the
cutoff frequency of the 8V012DB from 100Hz to about
300Hz. It will be made by diminishing L1 from 6.8mH in 1.5mH, then
augmenting C1 C10 from 100uF in 168uF. It gives us a higher cutoff
frequency, but also more rigid and more frank than the previous.
Result: I recover impulse answer entirely which misses me before, while
keeping a bass light without any aggressivity. What makes that the 21cm
proves to be better than the 17cm on quite a lot of point.
Filtration, version 3 ways (April, 2004):
A
faire...
The final schematics will be put here when everything will be OK.
The bass speaker will be used with Audiom 6WM and T120 TD5, which are
inserted into a separated coffer represented in another HTML page, just
after this one in home page.
Conclusion for 3 ways version / 300Hz (summer, 2004):
Acutally, I'm adjusting this filter again.
I have some worries with resonance of the room. This one are in effect
rather strong between 65Hz and 300Hz. This generates some heaviness in
bass. An idea would consist in diminishing the bass register a bit in
comparison with the medium / acute, what makes some speaker constructor
I believe.
It is besides the first time when I meet to plan to diminish the bass.
I passed in effect some years to searched to increase and
ameliorate the bass register in level and in bandpass!
sizing a speaker - tackle of a speaker - realization of
a bass-reflex speaker - creation of a bass-reflex speaker -
creation of a bass coffer - realization of a bass coffer - alleviation
of internal resonance
Created : 01 june 2004.
Last update : 11 november 2007.