The following information has been sent to me and gathered from
different sources. There is some conflicting information on Diaphone
types as well as PSI and CFM numbers. In these cases, this info
should serve only as a reference, and not taken as the gospel so
to speak. We would hate to hear of any damage caused to these great
horns, and we in no way accept any responsibility for any damages
that do occur.
types, stator types and diaphone tone/pitch Info
Mike Maderia, President of Maderia Warning
Systems, Garwood NJ says...
made a high tone piston and a low tone piston like you said in your website, but
the difference is that the high tone piston has a extra ring around the bottom
with 42 holes around the ring. This restricts the airflow creating a higher
pitch. The low tone is the same piston but this extra ring would be machined off
in the manufacturing process.”
Mike says that he can make new pistons and copper
projectors for diaphone horns. If anyone is interested please email
me, and I will facilitate the contact.
Close Up Photo - Submitted by Roger Elliott, City
of Orange CA
types, stator types and diaphone tone/pitch Info
researched by Adam Smith.
"I am still working on finding out everything possible about the
variations of the type B, and I'm hoping the folks here who work with
these diaphones can help make som concrete connections between the
configurations and the sound. I have also been consulting Thiessen's
patent for the fog diaphone horns, and it has some information about the
various holes in the stator and piston that I will share here also.
Firstly, here are the known variations of the piston, as documented by
Brett Jones (thanks Brett!). These are all his photos, I've just cut
them out and given them arbitrary designations so that I can refer to
them (A1 and A2 for aluminum, B1 and B2 for the brass variants)."
|Adam Smith - "As you can see, the pistons were made
in two shapes, and each of these in two materials (aluminum and brass).
Piston style 1 has this extra flange with 40-something holes machined in
it, whereas style 2 does not have this ring. So far, what I have heard
on this group regarding these differences are: Mike Maderia tells us
that piston style 1 is the high-tone version, and style 2 is low-tone
(for a given material). I would speculate that the brass pistons are
both lower in pitch that the aluminum ones also, because they are about
3 times the mass, but this is pure speculation. I need to hear from
someone who has compared the sound of the aluminum and brass
"Someone also mentioned a gamewell brochure that suggested two
different "tones" of horn, organ and trombone. At this time,
I'm not certain how this would come about, except perhaps by a different
type of oscillation of the piston, e.g. one more square-wave-like, and
one more sine-wave-like. Perhaps this is due to airflow and
"cushioning" withing the chamber? I do not know. This brings
me though to the question of the 20-rear-holes stator with round intake
holes, vs the 10-rear-hole stator with a slotted intake. Here again is
Brett's comparison photo:"
|"The stator on the right has brass plugs in every
other hole. My presumption is that the entire hole is filled with the
plug, thus this 10-hole stator has half as much vent area connecting the
front of the piston to the rear of the piston. it seems to me that less
connecting vent area would give a more sinusoidal piston movement,
because it would take longer for air to fill in behind the piston and
reverse it. But would this also mean lower pitch? Thoughts? If this
theory is correct about the tone, the 10-rear-holes stator would have
more of a sinsuoidal "organ tone", and the 20-rear-holes
stator would have more high harmonics like a brass instrument. Again,
speculation on my part, I need to hear from observers/operators of known
types. Ideally, it would be great if we had a sound file to match each
combination here on David's site.
Lastly, I'd like to show this diagram again from Thiessen's patent. It's
the diagram for a single-inlet fog diaphone, and it the same pattern
used for Gamewell's horns except that Gamewell's do not have the center
alignment rod (#27) through the piston:"
|"In the patent, the holes in the style 1 piston (#13)
are part of the pathway between the incoming air and the chamber behind
the piston, as are the 10/20 holes in the stator (#21). The patent also
shows that holes #21 must be capped off by the rear cover gasket, so
that they do not vent to the outside. Only the vent holes (#22) are
supposed to connect to the horn's rear vents. Now look at the intake
holes (#3), on the 10-rear-hole horns, these holes connect to slot #4,
as shown. In the 20-rear-hole horns, Gamewell did not just slot #4, they
just drilled the holes right through. I don't know what effect this has
"To sum up, I think the core unanswered questions are these:
1. Is the piston ring with 40 holes to give a different pitch, different
tone, or does it affect both?
2. Do the 10 vs 20 holes in the stator affect pitch or tone, or both?
3. How much does the mass of the brass piston lower the pitch?
Lastly, if someone could identify the variations in each horn that we
have a sound sample for, that would be of tremendous help. Glen Cove,
Larkspur, Hudson falls, Farmingdale, etc.. all I know so far is what
Northport has, thanks to Brett. I have taken the sound files and
analyzed them, and here's what have for pitch data:
Hudson Falls: 186 Hz
Glen Cove: 162 Hz
Northport: 210Hz falling to 170Hz as air runs out
Larkspur: 210 Hz
Salem, VA: 180Hz
180Hz is the nominal pitch for the type B according to John Pell Northey."
from Airraidsirens.com has been a great source of Diaphone info.
He recently created the following animation and gave a description
to show how the Diaphone works:
says "I made this little animation to show how a single-valve
diaphone operates. I've taken the illustration from Robert Hope-Jones's
patent, and given it motion. In an effort to keep this animation
small, I did not include arrows showing the direction of air
flow, I am showing here only the pressures (darker red = higher
pressure). From this animation, it's easy to see how the sound
is produced. The slots in the moving piston line up periodically
with the slots in the stator, chopping the air stream. What is
more difficult to tell, even with the animation, is how the
vibratory motion comes about. I'll try to describe it as simply
as I can: When high pressure air comes into the horn from the
pipe (from the left in the diagram), it starts to push down
on the rim (ring shaped) of the rear wide part of the piston.
It pushes the piston all the way back, at which point air is
suddenly able to get around to the space behind the piston.
Now, with equally high-pressure air on the front and back of
the piston, it starts to move up again since the back of the
piston has more surface area than the front 'rim'. The piston
moves forward until it reaches the point where the air behind
the piston can escape through the slot in the wide part of the
piston and into the mouth of the horn. Note that the piston
is symmetrical, the diagram shows only the cross section on
the left side, for illustration purposes."
"Pitch of the diaphone is determined by a combination of factors.
Pitch is raised by: Higher pressure air Lighter Piston Shorter
resonator (horn) Smaller air chamber volume behind the piston
Of course, the opposite of any of these things will lower the
pitch. If you listen to the "Dying diaphones" recording on the
sounds page, you'll notice that as the pressure drops, so does
the pitch of the horns. Also, most fog diaphones are 2-valve
types, where the air to the rear "motor" section of the piston
is controlled by a separate feed than the bulk of the air to
the "speaking" front section of the piston. Operation is otherwise
fundamentally the same."
also notes "Variance in sound is a factor of the horn's
condition (how well maintained) and the supply of air. At different
feed pressures, a Gamewell horn will have different pitch and
timbre. At the pressure where the piston's motor frequency and
the horn's natural frequency are the same, the horn is in tune
and has a smooth mellow note like an air horn. It higher pressures,
they have a harsh, more siren-like timbre. With too little air
pressure, the piston frequency drops below the horn's natural
resonance, and it becomes really flabby and inefficient, sounding
like a fart (sorry!). Different sounds come about as the period
of the piston goes in and out of phase with the natural resonant
frequency of the horn projector. The resonating column of air
in the projector exerts a force on the piston that definitely
coerces it towards the horn's natural frequency. But too much
air pressure, and the natural period of the piston's motor section
becomes dominant, at which point the piston alone is setting
the pitch, and the horn is not operating in a resonant condition
anymore. As with any other kind of air horn or whistle, this
is called "overblowing". Some stations have more than one horn,
which is especially common here in Massachusetts, where 2-4
horns per station is typical. In this case, the horns are never
quite in tune with each other, and there is always a strong
'beat frequency' that pulses at a rate which is the difference(s)
in pitch between the two (or more) horns. For example, if one
horn is barking at 400 Hz, and another is 405Hz, there will
be a strong and audible 5Hz throbbing."
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