So a few questions if anyone can answer them..
If there is an increase in horsepower via engine boring etc will this increase the 138db 30,000 watts significantly?
I actually had to do some work today, sorry to keep you waiting.
No, that design simply runs an air compressor that feeds rotating blades connected to external horns. Increasing the engine horsepower is equivalent to charging your air reservoir more quickly. If it were a rotational open frame horn, then increasing the power still won't do much except allow you to get up to operating speed faster. The transformation of rotational power to acoustic power is incredibly inefficient. On the order of less than .1% of the engines torque directly contributes to the actual volume of the device. The loudness of the device depends on several factors: One, the tolerance between the rotating blades and the inner surface of the stationary frame has a direct effect on the amount of wasted air that passes through the gap. Also, if the physical distance becomes to great, then the acoustic loading of the rotating blades will create excess drag on the rotor and high pressure zones localized near the holes on the frame can interfere with the production of sound. The output of a rotational siren is maximally limited to the physical air pressure gradients which can be created by slicing the air and causing vibration. If you go too fast, you can exceed the devices ability to slice the air and thus you will have a cavitation effect by creating alternating vacuum and 2atm zones. It is equivalent to overspinning your prop in a boat. Two, the actual pitch of the device and the physical horn design and size need to be synchronized and designed together to ensure that the resonant frequency of your device does not fall outside of the useful frequency cutoff of your horn. The equal-loudness curve dictates that the human ear is much more sensitive at 4000Hz than it is at 400Hz (the frequency of the chrysler siren)... So, if you were aiming to be as loud as possible, you would want to design a horn and siren system that operates at 4khz, then duplicate it as many times as necessary by combining the output of all the smaller horns into a much larger sectoral horn.
I wonder what could be achieved with a 500HP engine. Those 50s engines while awesome as hell aren't quite as powerful as what we have to play with now. How would one change the pitch/tone?
Make the horns smaller and the rotor spin faster.
What would happen if the number of horns was reduced or increased?
More horns= more air capacity needed to drive them=more horsepower needed=more loudness.
What would I need to fabricate to make this work?
My guess is lots of stuff.
I'm guessing from the design that this one doesn't use horns. Would I just have to frame the thing out and mount it so to speak with an air intake "funnel/cone" going in the top?
The funnel is to reduce the impact of stray air going back into the device instead of radiating out into the surrounding area. Plus, it is mildly shaped like a cylindrical wave radiating horn when placed near the ground plane. There could be some small acoustic loading effect from having a horn/funnel shape on the top.
The most current version of this rotating siren is found on 80's firetrucks. The tolerances are so close that the metal on the outside of the rotor actually scrapes the inside of the frame slightly. But they are loud.
Interestingly enough, the creation of loud sound is more easily accomplished by putting a horn in front of a speaker. Large horns attached to very powerful speakers can easily create more sound pressure than this ancient thing. In the 40's, this was probably the only way to generate any sort of tone louder than 120db-- not so nowadays.