Advantages of certain rotational speeds??

[jerrylovessirens]

Well, We all know that the chopper speed affects siren performance and decibel output(lower carrying farther), but does how fast one revolves matter??

You see many rotating sirens, like The t-bolt, going at all three different speeds, 2 4 and a very-fast 8, but does it matter at all?

is it for show?--- Fast creating a hectic and chaotic wail---- Or Slow, making for a glowering stare of sound.

Or is there a tecnical aspect too it?

Why would a modern siren like the T-128 bother with speed control and the electronics that go with it, if rotational speed did not matter?

Jerry

[Justin]

Rotational speed is all up to the EM's fantasies. There isn't really a technical aspect to it apart from making attack and fast wail more or less distinguishable. Stopping on wind-down however, helps this cause a little more but the faster the rotational speed, the more likely the signal can become washed out with ambient noise at a distance.

[Shinkansen]

Well it DOES make a difference in the overall sound, yes it does. Take a look at the Leslie Rotating Speakers that go so well with Hammond Organ's. Tall they are really are horns on a rotator. Now compared to the spin rates, I'd say you'd only get a effect from a TBOLT or something at max RPM on the rotator for it to be noticeable but yeah, I'd say it could be used for show.

[Rheems1]

Well it DOES make a difference in the overall sound, yes it does. Take a look at the Leslie Rotating Speakers that go so well with Hammond Organ's. Tall they are really are horns on a rotator. Now compared to the spin rates, I'd say you'd only get a effect from a TBOLT or something at max RPM on the rotator for it to be noticeable but yeah, I'd say it could be used for show.

Ohhh the sound of a Hammond B3 running through a well tuned set of Leslie speakers... I don't care how many electronic versions of this organ they make... they will never be able to replicate the sound of the orignal tone wheel design.

Dave

[Rheems1]

Speaking of the great sound of Hammond, have a listen to Rhoda Scott putting this Hammond B3 (with Leslie single speed rotating speaker) through it's paces on Moanin' (http://youtube.com/watch?v=oIB2ywz3S9o&feature=related. Listen to that pedal bass she is pumping out of there, completely amazing sound and really awesome pedal bass! Ohh.. to bring it back on topic....Thunderbolts that rotate at the 8 rpm setting are louder for shorter amounts of time but they happen quicker.. so it sort of balances itself out.

Dave Fritz

[va_nuke_pe]

The overall effect of siren rotation speed on audibility is zero - there is no difference. The equivalent sound level is the weighted average sound level over a fixed period. If I have two peaks in 1 minute (with a ramp up and ramp down into the background as the siren direction rotates past the listener location) 3 peaks per minute (with a ramp up and ramp down time that is 50% faster), 4 peaks per minute (ramping time 100% faster), etc., the integrated sound level at the ear drum for that minute is exactly the same and the peak is exactly the same, i.e., no change in equivalent sound level.

[JasonC]

Spinning a siren to fast can blur out the attack signal and make it difficult to distinguish between different signals. An old FS planning manual I used to have had a few sentences mention this.