Balsa Wood Horn

[Chuck]

The first morning glory horn I had and used
with my Edison Standard D machine when I was a kid
was a home made job.

My dad and I made it out of plain cheap art cardboard.
Bristol board.

My dad traced out the shapes of the 10 panels from
memory of what one of those original Edison horns
is supposed to look like. The small tapered end
going down to the reproducer can simply be rolled up.

It was put together using tape and glue. It was
originally white but we then spraypainted it black.
Then we formed up a temporary horn crane for it
because that crane was also missing.

All that was there to go by was the crane foot and
the little bracket with the hole in it sticking out
the front top of the machine.

That large thin cardboard horn sounded good. Of course
being so thin it did not sound as loud and robust as
an actual real sheet metal horn. But it was a whole
lot better than not having any horn!

I would tend to think that using something like
bristol board may be a whole lot easier and cheaper
too than trying to do it with balsa wood.

But hey, if you are set on using balsa, go for it.

Chuck

[winsleydale]

I want it to look legit, lol. Not knockin' your horn or anything.

[phonogfp]

A great deal of horn experimentation had occurred 120 years ago by some very bright people with a lot of experience and who were making a living out of their results. In George Tewksbury's A Complete Manual of the Edison Phonograph (1897), an entire chapter was devoted to horns, and it remains so informative that we included much of it in the horn chapter of our book, Antique Phonograph Gadgets, Gizmos, and Gimmicks. Tewksbury's information on horns is recommended. Another well-informed expert on horns was Russell Hunting: record-maker, recording artist, and Editor of The Phonoscope. Here's an article he wrote and published in the December 1896 issue. Click on the image twice to enlarge it.

George P.

[emgcr]

I remember reading years ago, when I was taking the acoustics course required for the master's in music theory, that the materials of construction made no difference in the resulting acoustical characteristics, that it was all about the dimensions and proportions of the instrument. With my usual skepticism, I was very doubtful of the validity of this assertion, and I remain so. There is a reason (probably many!) why violinists would rather play a Strad than a carbon fiber violin, or an oboist a Lorée rather than a plastic oboe. So I'm very interested in how your balsa-wood horn turns out, winsleydale. Be sure to keep us posted as you develop this project; who knows, you may be the one to discover something useful here!

A fascinating debate indeed and one that can reward hands-on experimentation. Perhaps the following comments based on recent experience might prove helpful ?

In contemporary days EMG and Expert horns were substantially made from paper mainly because that material was found not to propagate, reflect or augment unwanted frequencies---it was acoustically dead or neutral. Production costs were also kept to a minimum due to ease of manufacture and the obvious plentiful availability of cheap paper. The built-up wall thickness was in the region of 3/16" to ¼" for necessary structural reasons, both to enable the horn to support its own weight and to produce a physically stable sound expansion conduit.

The larger EMG horns ("Oversize"---bell mouth diameter 33 ½") are extremely rare and about ten years ago the decision was taken to re-manufacture a batch of 12. Paper could once again have been the chosen material but the alternative of fibre-glass was selected as an experiment being a useful and versatile medium which was not available some 80 years ago.

The results were sufficiently good that, by general consent, the reproduced output is indistinguishable via fibre-glass when directly compared with the identical output via a paper based horn. However, this general finding needs to be qualified in that the surface finish of the inside of the horn proved to be extremely important. In order to produce an acoustically smooth and cosmetically appealing final surface finish, a gel coat of neat resin (up to 0.040" thick) was first laid against the mould which results in a bright glossy appearance. The latter was found to be very counterproductive of first class sound reproduction as unwanted frequencies and reflections became apparent. A simple abrasion to matte totally transformed acoustic quality very much for the better.

Further empirical evidence showed that it was only necessary to build wall thickness sufficient to allow complete structural stability and, being relatively strong fibre-glass, thickness could be reduced to ⅛" to 3/16". Increasing to ¼" made no difference.

The main conclusions seem to be:

1. The exponential design shape and length is critical. EMG and Expert guided by the brilliant Percy Wilson and others in the late nineteen-twenties and early thirties got it right.

2. The material does not appear to be so critical as long as absolute rigidity and structural integrity throughout the entire acoustic horn length---ie right from the soundbox---is achieved.

3. The internal surfaces of the horn (or conduit) should not be reflective and all joints should be airtight.

This is only one brief experiment but good results were achieved and the sound from these large EMG horns is superb. However, it may well be that other materials can produce similar results. Balsa wood could possibly work but wall thickness may have to be considerable to support the special design shape and to gain sufficient rigidity to resist dynamic acoustic forces/frequencies. It may not be easiest thing in the world to form an accurate internal exponential shape in that material but much fun may be had from experimentation.

"Modern gramophones and electrical reproducers" published by P.Wilson and G.W.Webb in 1929 is really the "Bible" for our interest.

The best of luck.

[Mr Grumpy]

A little advice I might offer as I often have similar ideas of building things from scratch.
Make it out of paper or bristol board first in a way that the panels are not attached to each other permanently (use tape).
Then take it apart and use the paper panels as a template for the Balsa. Then, if the Balsa glues together well enough
and you like the end results, you still have the paper template to make another.
Maybe even use wood veneer for your second attempt.

[winsleydale]

A little advice I might offer as I often have similar ideas of building things from scratch.
Make it out of paper or bristol board first in a way that the panels are not attached to each other permanently (use tape).
Then take it apart and use the paper panels as a template for the Balsa. Then, if the Balsa glues together well enough
and you like the end results, you still have the paper template to make another.
Maybe even use wood veneer for your second attempt.

Now, there's an idea!

[RAK402]

You might cover the balsa in something like silkspan (a model airplane covering that is stronger than tissue paper, but still quite light). That would give a bit of additional strength without adding much weight. It can be sealed and finished just like balsa.