Last update: 11 November 2004
My first copy of the Jericho horn was made early 1998, the material of the box is medium density fiber
board, thickness 18 mm.
I found that this gives a considerable amount of vibration of the walls which
leads to coloration of the mid frequencies
which is often called typical for horn enclosures.
Toon is just over 1 year old on this photo and enjoying the music already very much.
Below is a photograph of the second version
under construction, summer 1999, now using birch
plywood of 24 mm for all outer walls. The shape of the horn is made more close to exponential. Wall vibrations
are damped further by "Hawaphon Matte" (obtained from Audiodata
), lead sheets and partial doubling
of front and side walls. The midrange coloration disappeared now to a very large extend but it turned out that
the bass level was lowered unacceptably (too much damping at the first part of the horn?).
Version 3, made in 2000, has again the shape of the original Jericho horn, but it uses the
birch plywood, with sidewalls of 24 mm and additional panels for extra rigidity
at the side of the horn mouth. The Hawaphon matte and the lead sheet are
re-used.
Further I made two changes to the horns. I put much more damping wool in the compression chamber and I increased
its volume. The first change gives more clarity to the high frequencies, probably because internally the high frequencies
have more damping. The second change again gives a little more bass. The photo
below shows how this enlargement is made.
It is quite simple and the value can be chosen to optimise bass performance. From an article written by J. Dinsdale
in Wireless World in 1974 I calculated that the volume of what he calls the throat cavity should be 18 litres to
obtain 30 Hz. This is much larger than commonly used nowadays. I do not recommend this
adaptation in general. It
probably depends strongly on your equipment and room conditions whether it is desirable or not. However if you
use a construction as I did it is easy to change back if it turns out to have a negative impact on the sound. (A
too large volume leads to loss of control at low frequencies. This is probably not what horn builders are after).
This picture shows how the pressure chamber is enlarged and how the side wall is enforced.
A few other improvements have been made during the last winter. The
first was the construction of a wall halfway our living room. This serves two purposes: people in the back room
are not bothered by the music if the door is closed and at the listening position the bass level is increased with
a few dB. The construction, which uses a wooden frame and 6-20-4 double glass filled with SF6, works very well:
it gives a reduction of 33 dB according to the manufacturer. I cannot measure it but I tend to believe this value.
I think that most speaker enclosures gives considerably less damping than this
33 dB. Since the human ear can distinguish details which are 30 dB below the
total sound level one can understand why the enclosure is an important factor in
the sound character of a loudspeaker.
The wall that now separates our living room in a "listening part" and a "working part".
Finally a picture of the complete setup with the Jericho horns.
