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You won’t believe how good they sound . . .
and your friends won’t believe you built them!
“Tiny
Tim”
Horn
Loaded
Speaker
System
This low-cost speaker system
uses a single 4-inch driver to
give surprisingly good bass
and treble response. It is quite
efficient and only needs a
low power amplifier to give
excellent sound levels.
T
his speaker system turns heads,
not only because it looks quite
different from the speaker systems you may be used to but more
importantly because it sounds so
impressive.
It does not use bulky and expensive
eight, ten or twelve-inch drivers and
there are no tweeters or crossovers.
Instead, the single driver in each
box is a four-inch model, which costs
30 Silicon Chip
as little as $25.00. Add some pieces
cut from a sheet of plywood, which
costs perhaps $70, some glue and a
few hours of construction time and
you’ll have a speaker system which
easily competes with much-higherpriced commercial units on the market
today. And yes we know that there are
By Allan Linton-Smith
and Ross Tester
quite a number of tower and minitower speakers on the market right
now, many with multiple drivers and
all sorts of claims. Quite simply, we
believe these are better than anything
we’ve heard recently at anything like
the price!
The secret to such a high-performing
speaker is in the design of the cabinet.
Unlike the simple bass-reflex or other
ported designs you’re used to, these
siliconchip.com.au
are actually rear-loaded horns. They
look difficult to build but providing
you’re accurate with your woodwork
(or you use someone who is!) they are
surprisingly simple to put together.
The drivers
You have a choice of 4-inch drivers
for this design. The cabinets are perfectly matched to – and in fact were
originally specifically designed for
the high-performing Fostex FE103EN
models.
But we tried a couple of locallyavailable drivers: the Altronics C0626
and Jaycar CS-2310 models, which are
significantly cheaper than the Fostex.
And while they might not perform
quite to the level of the Fostex drivers,
most people would be very happy with
the cheaper approach.
Having said that, several of the
SILICON CHIP staff commented that
they thought enclosures fitted with
the Altronics drivers actually sounded
the best!
While the Fostex is a single cone
driver, the Altronics C0626 is a twincone model and the Jaycar is a coaxial
unit with separate miniature tweeter
fed by a bipolar electrolytic capacitor.
The first two speakers have the advantage of simplicity and there is no
problem with phase shift in a crossover network, albeit even the simple
crossover capacitor of the Jaycar unit.
All three drivers have the advantage of using a single driver with its
phase coherency over a wide range of
frequencies. This helps in the realistic
reproduction of voice, instruments or
complex orchestration and in accurate
sound staging or positioning of each
instrument.
Just a note about the Jaycar CS-2310,
it’s intended as a car speaker and its
nominal impedance is 4 so you will
need to make sure your amplifier can
handle this low impedance (fortunately these days, most can). The Fostex
and Altronics drivers are both 8.
So which to choose?
If you’re looking for “most bang for
your buck” the Altronics would be a
good choice because they are the most
efficient (95dB/W <at> 1m) vs 89dB for
the Fostex and 83dB for the Jaycar
unit. Offsetting that lower efficiency
is the fact that the Jaycar driver will
actually receive twice as much power
as the other two (because it has half the
impedance) for a given volume setting
siliconchip.com.au
from the amplifier. This will mean
that the difference in efficiency will
be less apparent than the raw figures
might indicate.
The Altronics and Jaycars are similarly priced, at about $30 pair for the
Altronics vs $25 for the Jaycars but
you’ll pay much more for the Fostex
drivers. You can compare the three
drivers in the spec table below.
The cabinet design
The enclosure design for this
speaker (which you can download
at www.fostexinternational.com/docs/
speaker_components/pdf/FE103En.pdf)
can be regarded as a cross between
a bass reflex vented enclosure and a
horn-loaded enclosure. Horn-loading
can be thought of as an efficient means
of coupling between the relatively
heavy mass of the speaker to the much
lighter mass of air.
Horns have been used for a very
long time. For example, they have
been used for centuries in musical
instruments and as megaphones – the
very first horn speaker. And of course,
all the early wireless sets and gramophones used a horn-loaded speaker. In
all of these early examples, efficiency
was paramount.
The tower speaker we are using
here uses the 4-inch driver as a direct
radiator for the upper frequencies and
a horn radiator for the lower frequencies. The internal construction of the
tower is actually a folded horn with
each section being longer and larger
in cross-section, to approximate the
exponential taper of an ideal horn.
While efficiency is a big advantage
of a horn speaker system, they do not
necessarily result in the smoothest bass
response. However, in our case where
we are using tiny drivers, we get a much
more extended bass response than
could normally be expected with their
relatively high free-air cone resonances.
Anyone who is reasonably competent in woodworking and has a selection of suitable tools should be capable
of putting these cabinets together.
In fact, we fully expect these speakers to become the “project of choice”
for many students in their Higher
Fostex
Altronics
C0626
CS-2310
Price per pair ($ approx)
150
34
25
Voice coil dia (mm)
20
-
-
Impedance (ohms)
8
8
4
83
MANUFACTURER'S SPECIFICATIONS
SPL (dB/W<at>1m)
FE103En
Jaycar
89
95
Rated input (W)
5 to 15
8 to 15
15
Magnet
ferrite
ferrite
ferrite
Magnet wt (grams)
193
-
-
Net wt (grams)
580
-
-
Baffle hole dia (mm)
93
93
93
0.005
-
-
7.5
-
122
Cone area (sq m)
Re (ohms)
Free air Resonance (Hz)
83
120
VC inductance (mH)
0.0398
-
-
Qms
2.747
-
4.28
Qes
0.377
-
1.88
Qts
0.33
-
1.31
Mms
2.55g
-
-
Vas (Litres)
5.95
-
3.31
Xmax mm
Frequency response
0.6
-
-
83-22kHz
120-20kHz
90-18kHz
MEASURED RESPONSE
Frequency response ±5dB
60-15kHz
70-15kHz
-
Distortion (THD+N) [1kHz 90dB]
0.45%
0.65%
-
Sound Pressure Level 1kHz 1watt/1m (dB)
92.65
89.97
-
The enclosures are designed for the Fostex FE103En drivers but we’ve found
the much-cheaper Altronics C0626 or Jaycar CS-2310 do an admirable job as
well: in fact, some of our staff members commented they sound better!
October 2013 31
#
#
#
#: ALL 150mm WIDE (+SAW CUT)
50
380 x 150
385 x 150
385 x 150
235
380 x 150
235 x 150
190
190
#
ONE EXTRA
PIECE REQUIRED
840 x 405
4
4
200
200
#
840 x 405
#
7
FIRST CUT
80
810 x 150
#
12
6
810 x 150
13
3
#
13
375 x 150
12
250
180
11
8
20
80
11
375 x 150
6
180
100
19
250
340 x 150
340 x 150
19
7
25
3
10
100
10
25
8
#
17
17
155
C
L
9
155
80
2
93mm
93mm
DIA
DIA
245
80
2
93mm
93mm
DIA
DIA
#
C
L
9
#
32 Silicon Chip
#
#
245
15
1
150
#
250
5
150
18
5
250
16
250
#
18
All dimensions shown
are finished sizes
– allow for saw cut
thickness!
21
21
16 250
14
1
15
400 x 150
14
400 x 150
siliconchip.com.au
#
#
150
#
840 x 405
840 x 405
150
#
Fig.1: it’s a tight fit but all except one
piece (one of the ‘7s’) can be cut from a
sheet of 1220 x 2440 x 15mm ply. This
assumes a saw cut thickness of 2.5mm,
about normal for a kitchen cupboard
maker. Note where the first and second
cuts are made. The lemon coloured
pieces are for box 1, pink for box 2.
#
#
20
Plywood is a must!
The pieces for both boxes can be cut
from one and a half sheets of 15mm
plywood (1220 x 2440mm and 1220
x 1220mm). In fact, with care you’ll
get all bar one small piece (no.7) from
one sheet. See Fig.1: it shows how the
pieces are cut – the first cut needs to
be made where shown.
The missing piece, (235 x 150mm),
could even be cut from scrap as it is
internal and won’t be seen.
Note that this cutting diagram does
assume an “imperial” size sheet; some
suppliers have taken to making their
sheets 2400 x 1200 – this size is not
quite large enough as it cannot make
allowance for the saw cuts. Your supplier should be able to advise you of
the exact size of their sheets. If they
are 2400 x 1200, you’ll definitely need
a second (half) sheet.
We used good quality Aspen Birch
veneer because of its fine grain and
appearance but you can choose the
finish to match your décor. You could
use plain plywood, sand it smooth and
paint or stain it to your tastes.
Note that we DO NOT recommend
the more commonly available MDF
because it is 16mm thick – the extra
1mm will decrease the width of the
“horn” by a cumulative 6mm and will
drastically affect performance.
You will note from the photos and
diagrams that the horns are built up by
layers of plywood pieces. It is absolutely
vital that these pieces are very accurately cut to size. If you don’t have either
the equipment or the skills to cut to
close tolerances (to the millimetre!) we
suggest you approach a local kitchen
cabinet maker – most will do it for a
reasonable cost; indeed, many will be
#
#
School Certificate design and technology courses: do the cutting, assembly
and finishing in the woodwork room,
mount the speakers and wire them in
the technology or electronics classes
– and best of all they won’t break the
bank. And after they earn top marks,
they’d have speakers Mum and Dad
would be proud to put in the lounge
room!
6
385
250
C
L
5
15
25
4
80
93
35
2
245
7
190
3
235
1
8
80
2
12
375
150
13
21
250
380
155
340
810
840
21
22
9
10
22
10
180
11
250
200
150
20
240
100
19
18
14
20
17
400
siliconchip.com.au
17
16
14
150
180
Fig.2: looking down on the right side, without the side panels, here’s how all
the pieces glue together to form the loaded horn. The photographs later in this
article will help explain how it all goes together.
able to supply the veneered plywood
as well. Just don’t let them talk you
into MDF (a lot of kitchen cabinets
are made from the stuff these days!).
Incidentally, we investigated a major hardware chain offering a cutting
service and found them unacceptable
for two reasons: first, they guaranteed a
19
18
16
(ALL DIMENSIONS
IN MILLIMETRES)
(13)
50
tolerance of no better than 5mm – useless as far as this project was concerned
and second, they only had “construction grade” 15mm ply.
Now that would be OK if you only
wanted a painted surface but even
then, a fair amount of sanding and
finishing would be required. Also, they
Fig.3: and here’s the front-on view
with the side panels fitted. Piece 13 is
actually the rear panel.
only had full “metric” sheets (2400 x
1200mm) in stock and, as expected,
they tried to talk us into MDF, which
did come in half sheets!
It may be that in time, some of the
kit suppliers will produce a full kit of
parts – keep an eye on their advertisements in SILICON CHIP.
October 2013 33
+15
Frequency Response, C0626 In Cabinet
14/07/13 17:44:51
Another feature of these speakers is their ability to handle
a range of amplifiers. While they’re ideally suited to lowerpower amplifiers (again, that “schoolies” market springs to
mind), they can handle more, with sound output to match.
All three speaker drivers mentioned above are rated at 15W
maximum input so you certainly cannot run them flat out
from a high power amplifier.
We’ve run them from amplifiers as low as 5W output (eg,
“The Champion” from January 2013) and we’ve run them
(judiciously!) from the much higher power Ultra LD MK3
(July-September 2011).
However, even running from The Champion they certainly filled the large SILICON CHIP warehouse with sound!
+10
+5
Relative Power Level (dBr)
+0
-5
-10
In line with driver
In line with horn
-15
-20
-25
-30
-35
-40
20
50
100
200
500
1k
Frequency (Hz)
2k
5k
10k
20k
Fig.4: frequency response plots of the Altronics drivers in
the horn-loaded cabinet. The red trace is the on-axis flat
response and blue trace shows the output from the mouth of
the horn section.
48
Driver Impedance In Folded Horn Cabinet
22/08/13 12:23:36
44
40
Altronics C0626
Fostex FE103N
36
Impedance ( )
32
28
24
20
16
12
8
4
0
20
50
100
200
500
1k
Frequency (Hz)
2k
5k
10k
20k
Fig.5: impedance curves of the Altronics and Fostex drivers,
with multiple peaks resulting from the horn loading. This is
partly a result of the much higher loading to the rear of the
driver’s cone.
100
Driver THD+N In Folded Horn Cabinet
20/07/13 19:00:59
Total Harmonic Distortion Plus Noise (%)
50
Altronics C0626
Fostex FE103N
20
Performance
We tried these with all three speaker drivers mentioned
above. As you might expect, the Fostex drivers gave the
best bass response – but you do pay for it! The others were
surprisingly beefy!
Fig.4 shows two frequency response plots of the Altronics drivers in the horn-loaded cabinet. The red trace was
taken with the microphone on axis and very close to the
tweeter cone of the driver and it shows a reasonably flat
response to 10kHz and rising to a peak at around 18kHz.
The blue trace was taken with a microphone adjacent to
the horn section and it measures the augmenting effect of
the horn loading.
As you can see, the response is quite well maintained
to below 60Hz (quite similar to the much more expensive
Fostex drivers). Generally speaking, at distances of over
2m, the response will be a combination of the two cuves.
Fig.5 shows the impedance curves of the Altronics and
Fostex drivers. These are quite different to the equivalent
curves you would see with the drivers in a bass reflex enclosure which normally shows two impedance peaks in the
low frequency region. The horn loading results in multiple
peaks and this is partly a result of the much higher loading
to the rear of the driver’s cone. It also results in better bass,
as shown by Fig.4.
Fig.6 shows the harmonic distortion of the Altronics
and Fostex drivers and again the cheaper Altronics driver
gives a good account of itself. Note that the distortion is
quite low over much of the audible range but rises at the
low end, partly as result of the horn loading and also the
fact that the fundamental output drops markedly at very
low frequencies.
Building the speakers
10
5
2
1
0.5
0.2
0.1
The amplifier
20
50
100
200
500
1k
Frequency (Hz)
2k
5k
10k
20k
Fig.6: harmonic distortion of the Altronics and Fostex
drivers. Note that the distortion of both drivers is quite low
over much of the audible range but rises at the low end,
partly as result of the horn loading.
34 Silicon Chip
We have simplified each step so you shouldn’t have any
problems. Build one speaker box at a time otherwise mistakes are much more likely; do not rush things and make
sure you understand each step before diving in!
Again, we must emphasise the need for accuracy in
cutting out the panels. Using a hand-held saw of any description will usually result in errors and out-of-square
cuts which will inevitably lead to air leaks or malfitting
panels. The panels are butt-glued so squareness is next to
Godliness! To this end, wipe up any glue excess as you go.
And to ensure perfect alignment, the enclosures need to
be assembled on a completely flat surface – a work bench
is fine if it is flat and stable; otherwise a (say) concrete floor
with some single newspaper sheets spread on it.
siliconchip.com.au
Putting them together
Step i: We are assuming you already have all your pieces accurately cut out. Number each piece as shown on the diagram – use
“Post-It Notes” or similar to avoid leaving glue – in any case stick them to the “bad” side of the plywood (ie, not the face side).
Step ii: Using the diagram (Fig.2) as a guide, on one of the side panels (piece 1) use a pencil on the “bad” side to mark out where all
the pieces are going to go.
Step iii: Take pieces 2 and 3 and first check their dimensions to make sure you have the right ones – we’re about to glue them together
and once stuck, you won’t be able to get them apart. Use 2 or 3 small nails or panel pins to tack them together, then prise them
apart without bending the nails and run a 3mm bead of glue* along the join. Push the nails back into the holes and gently tap them
with a hammer until you are happy with the fit. Wipe off any excess glue with a damp rag.
If for some reason they haven’t ended up where they should, light tapping with the hammer should get them right. You have about
10 minutes to move things around before the glue sets.
Clamps or a vice should be used to hold the pieces together to give a really good bond – the glued pieces should be ready to remove
after about half an hour.
Take the completed pieces and place them on the side panel where they will go – but don’t glue them in place just yet.
* We used a caulking gun and “Parfix Maxi Nails Fast” water-based construction adhesive, which will bond wood to just about anything. It’s cheap ($3.95 for a caulking gun tube at our local hardware store), it sets quickly (about 20 minutes) but gives up to 10
minutes or so of “fiddle time” before the glue gets too tacky. This glue (or several other bonding adhesives) are available from
most hardware outlets. NOTE: PVA wood glue is not recommended.
Lay out all the pieces on a flat surface so you understand
how they all go together. Note the identifying “post-it” notes.
siliconchip.com.au
Now we’ve glued all the pieces together and when dry,
have then glued them in position on the left-side panel.
October 2013 35
Step iv: Repeat step iii for pieces 4 and 5.
Step v: Glue pieces 2 & 3, and 4 & 5, together
Step vi: Glue pieces 21, 22 & 10 together, using a square to ensure that the end is perfectly flat. Allow them to set for an hour or so,
then glue them to the pieces you made in step v. (They glue to piece 3).
Step vii: Now glue pieces 11 & 12 together, allow to set for an hour, then glue those to the pieces in step vi (they glue to piece 10).
Step viii: Glue pieces 7, 8 & 9 together and set aside to dry.
Step ix: Fit the input (banana) binding posts to piece 13 – drill two 3.5mm holes 50mm down from the top and 25mm apart.
Step x: Now glue pieces 16, 17, 18, 19 & 20 together.
Step xi: Glue pieces 6 & 13 together, using the side panel to keep them square while they set.
Step xii: Glue pieces 13 & 14 together, again using the side panel to keep them square while they set.
Step xiii: Now glue all the pieces together from step x, to pieces 13 and 14.
Step xiv: Once all of the glue has set, you now should have everything ready to be glued to the side panel. Place all pieces accurately
in position on the side panel.
Here’s the completed speaker box once the glue has dried.
All that remains is a bit of tidying up, finishing the veneer
with your desired stain or paint and then fitting the 4-inch
speaker.
Use small panel pins and clamps to hold your speakers
together while the glue is setting. Any blemishes can be
smoothed over later.
36 Silicon Chip
And here it is with a clear polyurethane finish. This shot of
the rear of the speaker (from the top) also shows the input
terminals in place. You can see how the rear panel and top
are inset 5mm from the rear edge of the side panels.
siliconchip.com.au
Step xv: Glue all those pieces in place. By now you should have a pretty good idea how much glue is used so you shouldn’t have too
much excess. If you do, don’t waste time wiping it away - remember, you only have about 10-20 minutes before the glue sets so
you need to work fairly fast.
Step xvi: When everything is in place, take the other side panel (piece 15) and without applying any glue, place it on top of the whole
assembly with some weights on top. If you have worked fast enough, the glue should still be wet enough so that you can move any
pieces that need to be adjusted so they are flush with the side panel. It’s most important that the front of the cabinet is flush to the
side because that’s the part that you see. Adjust it first, then the back if you have time (you won’t see the back!).
Step xvii: When the glue has dried, solder a 300mm length of figure-8 cable to the input terminals. Remember which is to the red and
which is to the black (normally, stripe goes to – or black). Hang the other end of this wire out the front speaker hole.
Step xviii: It’s time to complete the enclosure. Add a bead of glue to all the edges and place the side panel in place, adjusting it again
so that the front is aligned to the sides. Put the weights back on and wait until it dries.
Hopefully, you will have done it all correctly. . . now you get to do it all again with the second enclosure!
Finishing off
You can now carefully sand off any rough edges or dags
of glue then stain, coat or paint your enclosures as you
desire. We simply applied a coat of clear polyurethane to
the timber as the Aspen Birch veneer really shines with
this treatment.
But remember that paint hides a multitude of sins if you
have made any “oopses” along the way.
When the cabinets are completely dry, cut two 150mm
x 245mm pieces of cellulose wool (often sold under the
brand-name “Innerbond”) and place them loosely behind
the speaker area – but do not block the entry to the horn.
We found that any packing in the horn reduced the bass
by half (6dB) but the little packing behind the speaker had
no effect on the bass. However, it did reduce the “hollow”
sound at mid frequencies, caused by standing waves and
reflections.
Fit the speaker drivers to the boxes, making sure you
get the phasing (ie + and – connections) the same on both
boxes. As a final check, briefly connect a 1.5V battery to
the input terminals (+ to red, – to black) and watch the
cone. Both speakers should move the same direction when
connected the same way.
The drivers should have some form of gasket between
them and the woodwork to ensure a seal. We wouldn’t use
silicone sealant – it works really well but makes the speaker
incredibly difficult to remove intact if you have to remove
it for any reason. A large “O” ring is ideal; at a pinch you
could even use a large elastic band. Just make sure it seals
all the way around as you tighten the four screws.‑
If you use the Jaycar drivers, fit the grilles over the front
of each speaker. Of course, you can buy grilles to fit the
Altronics or Fostex speakers. Grilles are almost mandatory
if you have young people with prying fingers around: that
speaker height is just about perfect.
Training the speakers
What’s this? Training speakers? Believe it or not, all
speaker drivers “straight out of the box” are a little stiff and
benefit from being “run in”. We allowed about two hours
of continual music at reasonable volume before we were
satisfied that ours were nice and mellow. You will certainly
note a significant improvement over time, particularly in
the bass response.
SC
siliconchip.com.au
October 2013 37
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