Meanwhile, be sure to catch up on the above-linked thread first to get to where we're now at.
Actually, it is my understanding that sine waves are also more efficient on the amps. This is explained very well in the patent for the ACA Allertronic controller (though this was for an ampless controller that I can't believe lasted long). Quite frankly, this is one of the best written patents if you want to understand how electronic sirens work (though its obviously a bit dated given it was filed in 1989).dclarkct wrote:I think square waves are used for amplifier efficiency (keep the heat-sink small). The driver can't reproduce a square wave but it does pass harmonics which give it that attention getting sound. Does anyone know if there are any class "D" or digital amps being used in sirens now?
https://www.google.com/patents/US494533 ... CHcQ6AEwCA
Veering a bit from amps and back to drivers--still relevant to this discussion--is James Biersach's writing on the square wave's effect on the drivers from the above linked patent:
That being said, ATI uses a 1600 watt Class D amplifier in its sirens (hence why its units are offered in increments of 1600 watts). The Class D amplifier is supposed to reduce heat output and increase efficiency (and supposedly reduce activation popping). ATI holds a patent on their Class D amp (and assumedly, any Class D amp to be used for siren applications). That patent can be viewed here:However, the application of this square-wave a.c. energization to the drivers has been the cause of heretofore unrecognized problems and inefficiencies. When a driver is energized with an a.c. of square-wave form, each cycle of that current tends to propel the diaphragm of the driver first in one direction at maximum force and then in the opposite direction at maximum force, with an instantaneous force reversal at each change in phase. In effect, the square-wave current seeks to impose upon the diaphragm an infinite acceleration first in one direction and then in the other, jerking it abruptly back and forth, in contrast to the smooth and gradual accelerations that a sine-wave current tends to produce.
The high and abrupt accelerations of the diaphragm that result from square-wave current energization are obviously stressful and have the effect of shortening its useful life. In fact, failure of drivers is not uncommon, and each of the commercial amplifier modules has a signal light that warns when one of its associated drivers has failed.
Another and very important disadvantage of energizing a driver with a square-wave a.c. is that the driver produces a relatively poor acoustic output. For one thing, the power applied to the driver must be substantially lower than would be feasible with sine-wave energization, to avoid overheating of the driver coil as well as mechanical overstressing of the diaphragm. The driver coil has a high impedance to a square-wave alternating current, inasmuch as a square wave can be regarded as a sine wave of the same frequency that has all of its harmonics added to it, to thus constitute the equivalent of a very high frequency, and the impedance of the driver coil is linearly proportional to the frequency of the a.c. applied to it. In addition, the inherently inefficient abrupt acceleration forces that square-wave energization imposes upon the diaphragm reduce the acoustic output of the driver to a value substantially below what it would be if the same input power were applied to the driver in sine-wave form.
https://www.google.com/patents/US200300 ... CGMQ6AEwBg
However, we know ATI has had such great luck with those doing such a great job outputting audio. ATI uses sine waves, no question about it. Their 1000 hz tone is obvious about it, the 572 hz tone evenmoreso (that's why ATI's tones have that strange muffled quality about them--stick in a 572 hz sine wave into Audacity and it become obvious).
Back to amps now, the ATI amp really is only suitable for a sine wave unless, referencing the Biersach discussion and further discussion in the ATI patent, there were to be major heat problems:
.Still yet another object is the use of sine wave drive versus saturated square wave drive for continuous tone outputs resulting in less stress, lower heating, longer life and higher efficiency of the output acoustical transducers when using such an ultra high power class D audio amplifier in siren applications.
Below is a photograph of an ATI amp (it was pulled from a still-active eBay listing. I've withheld the source link but can post it if given permission to).
- ATI 1600 Watt Class D Amplifier
Today, ASC uses a 400 watt Class C amplifier. User va_nuke_pe commented on that issue in a long ago thread (and was absolutely in a position to know as an installer). When the E-Class first appeared and questions arose about it vs. an ATI, he stated:
Source thread: https://airraidsirens.com/forums/viewtopic.php?t=3350va_nuke_pe wrote:Yes, they are both Kingstar specials. The differences are that the E-Class uses square waves and Class C amplifiers and the HPSS uses sine waves and Class D amplifiers. The HPSS is an excellent outdoor loudspeaker that can be adapted to imitate a siren. The E-Class is not so good as a loudspeaker but is better adapted to imitating a siren.
Meanwhile, I've got no idea what class of amplifier Whelen uses. I do have to say, using one or two 1600 watt amps seems like a horrible idea. The amp goes out and suddenly your whole station is dead. On a Whelen, if one amp goes out, you've got one speaker out. Or on a Federal, one amp out and you have one cell out. The unit still works, just at reduced power. My understanding of how the HPSS works is that if that 1600 watt amp goes out, and you have an HPSS-16, the whole station is toast (btw: lets not turn this into a bash ATI thread; I just am pointing this technicality out).
I hope this proves to be useful information. Anyway, writing this repsonse wore me out! I need a nap now
