Whelen Cencom powers one or two speakers from the same terminals. How?

Trebor Cadeau

Member
Jul 22, 2016
21
Colorado
Whelen CenCom
Other sirens have [COM] [100] [200] terminals.
This has only two wires.
One speaker is 11 ohms impedance. Two in parallel create 5.5 ohms impedance.
Does Whelen detect 11 ohms and reduces power to 100 watts? If 5.5 ohms the amplifier produces 200 Watts?
Or is their output really ~125 watts so one speaker is notoover-driven butwo speakerstill work?

Thank you.
 

Trebor Cadeau

Member
Jul 22, 2016
21
Colorado
Yes. But 200 watts powering a 100-watt driver can burn it out.
Sirens had [COM] [100] [200] terminalso that a 100-watt driver is not connected to a 200-watt output.
 

MtnMan

Member
Dec 20, 2012
1,533
Eastern PA
Because physics, lol. The siren amp doesn't need to detect or change anything. The output of the amp (whether it's 100 or 200 W) is a constant square wave of about 33 Vrms. Driving one 11 Ohm speaker, this produces 100 W output, per the equation above. A second speaker, wired in parallel to the same 33 V output, produces an additional 100 W.

To use an analogy, consider a 100 W lamp running on standard 120 VAC receptacle. Plugging another 100 W lamp into the same receptacle doubles the power, without any change in the supply voltage.
 

Trebor Cadeau

Member
Jul 22, 2016
21
Colorado
Thank you. Thanks also for the 33 Vrms. I have not had time to find and connect my oscilloscope.
The issue is if the amplifier puts out 200 Watts into a single 100-watt coil, will it overdrive the coil and burn it out? Otherwise, why have 100 and 200 watterminals?

Two 11-ohm drivers in parallel creates 5.5 ohms impedance.
(Wish that I could see the schematic.)
 

Trebor Cadeau

Member
Jul 22, 2016
21
Colorado
When siren amplifiers have [COM] [100] [200] terminals, is that not a 200 W maximum output?
Fused at 20-amps which would be necessary for 200 watts at 13.8 VDC.
Why does Whelen not reveal the wattage?
Thank you.
 

NPS Ranger

Member
May 21, 2010
1,988
Penn's Woods
So if you're driving at a groundspeed of 60 MPH into a 10 MPH headwind, and your 11 ohm speaker is connected to the 200W terminal but oriented off-axis to the vehicle by 45 degrees, the root mean square of the forward sound pressure will vary with the density altitude. The corollary is that only supersonic vehicles can overdrive their sirens. Whelen doesn't reveal their wattage because the newly promised all electric federal vehicle fleet won't be making enough power with their solar cells, to drive the sirens.

Life was so much simpler when we just had Lafayette Radio & Allied.
 

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