The Siren Board

The 3V8-H-B is now available. It's rated at 116 dB at 100 feet and has an effective range of 3,400 feet. It's driven by a 4HP motor that runs on 48VDC as opposed to the normal 72V that the other models use.

Introduction
Link To The Siren On Sentry's Website
Link To Cutsheet

Man, this is what I like about Sentry. Little efficient powerful sirens. All that a siren should be. And they keep pumping out new models like crazy!

This siren has great stats for today's standards especially for a 4HP motor

This is what I love about Sentry. Their sirens are built to last, are virtually maintenance-free, and produce HUGE sound outputs for their size. And, their new models never fail to impress.

Is this another 8-port siren like the regular 3V8?

How does this get 7 more Decibels than the regular 3v8-H? Isn't this just a battery powered version? Not to mention the motor is 1 less HP than the regular 3V8-H. This is so.. weird. Maybe redesigned chopper, or.. I don't even know.

On another note, its amazing how fast Sentry is just releasing sirens. It wasn't too long ago that the 14v was shown off, with a video on the Sirens for Cities Facebook page.

Is Sentry messing with their dB ratings yet again?

IDK

The specifications posted by Sentry do not give the siren's average decibel rating at 100 feet. Instead they show the peak rating: the absolute maximum sound any siren will give. Peak ratings are not consistent because no two sirens are machined identically at the factory: some sirens have finer tolerances while others are sloppier and produce less sound.

"Tolerance"

The tolerance is the fine space between the fan ("rotor") and drum ("stator"). The less space between fan and drum, the more sound is produced. Naturally each maker tries to make the tolerances as fine as they can get, but it's not always possible during mass production. Mass producing a siren is very hard work. The fan must be balanced on a lathe to ensure it is balanced. An unbalanced fan will explode at high speeds. Then one must ensure there are no other defects with the fan or drum after casting. One small defect leads to several big problems later on. Finally, this is all done under rigid scheduling - there's no room for delays and mishaps. It's all tough work and the result is some sirens will turn out less refined than others.

While it is nice to see Sentry try out a more competitive DC battery backup siren, their methods of measuring specifications and subsequent advertisement of specifications leave something to be desired.

As far as AVERAGE goes, every single Sentry siren is db tested. Some produce more than rated but the db rating is the MINIMUM users can expect.

I'm sure the folks at Sentry will be responding to this.

Peak ratings are not consistent because no two sirens are machined identically at the factory: some sirens have finer tolerances while others are sloppier and produce less sound.

I can't imagine a situation where they would be changing their tolerances all the time during production.
The part drawings will have tolerances on them and if production is run right all the parts will be within those tolerances and will fit.

The rotor has a certain tolerance on outer diameter and the stator has a certain tolerance on inner diameter that should stay the same on all drawings and parts if they are built correctly. If they aren't built correctly then they won't fit together and they will be rejected and returned to who machined them to be reworked or rebuilt.

Just throwing some numbers up for an example...
The rotor might be dimensioned at 16.00 inches in diameter with a tolerance that is plus 0.0 and minus something say .03". That way the rotor diameter isn't built over 16.00 inches in diameter but could be as small at 15.970" in diameter (if QC is doing their jobs and the machine operators are doing their jobs).

The stator may have a dimension of 16.03" inner diameter with tolerance of minus 0 and plus say .020".
That way the stators in production will all have an inner diameter of no smaller than 16.03" and no larger that 16.05"

If you have parts that are run on their dimensions you would have a rotor that is it's LARGEST diameter and a stator that is run at it's SMALLEST diameter which during assembly they will always fit.
For example; you would have a 16.00" diameter rotor inside a 16.03" diameter stator. That's .015" of clearance between (around) the rotor and stator when the siren is put together.
If you have a rotor and stator set that is run at the limit of it's tolerances (which would be it's biggest gap) then you would have a 15.970" rotor inside of a 16.05" diameter stator which would be a .040" clearance between (around) the rotor and stator when the siren is assembled. Still pretty close and I guess would result in less output but I really wonder how much.

I guess my point is that if you make 100 rotors this way and 100 stators this way and have two piles of parts then you can pull any parts and they will fit and they are all manufactured to the same "refinement" or tolerances.