EMD turbo sound question

[RailBus63]

Can someone explain (in layman's terms) why newer EMD turbocharged locomotives (60-series, 70-series, etc.) have a different sound at idle than the earlier 40-series locos? What I'm referring to is how the older locomotives have that constant high-pitched whine when idling. The newer locos are much quieter at idle, and you can hear the turbo whine rev up at the same time as the engine when the throttle is notched out. I was thinking about this today when I was watching a Union Pacific SD70M moving a cut of cars at CSX’s Dewitt Yard.

Jim D.

[MEC407]

This is pure speculation on my part:

* The 710 engine is bigger and newer than the 645, so it's bound to sound different

* There are EPA noise regulations in place now that weren't in place in the days of the 645

And there are probably other reasons as well. But those would be my first guesses as to why they sound different.

[QuietGuy]

The sound you hear is not the turbocharger, it is the radiator fans or fans on the dynamic brakes. These are all electric motor driven and from my experience, that is the loudest sound. Since I've spent time listening to EMD engines in test cells where there are no fans, I'd say you don't really hear the turbochargers on the SD-50's thru 90's, only the fans.

[trainiac]

I'd say you don't really hear the turbochargers on the SD-50's thru 90's, only the fans.

I would have said the opposite. Later EMD's have Q-type fans with 5 unevenly spaced blades, which are significantly quieter than the 8- or 9-blade fans on 40-series units. However, neither type would make much noise (if any) at idle.

Can someone explain (in layman's terms) why newer EMD turbocharged locomotives (60-series, 70-series, etc.) have a different sound at idle than the earlier 40-series locos?

Two possible reasons:
-Later EMD's have exhaust silencers, which most 40-series units don't have.
-The 710 has a normal idle speed of 269 rpm; the 645 has a normal idle speed of 315 rpm.

...Just thought I'd include a bit about EMD whines:

You're right that the whistling/whining sound of the EMD's at idle and during revving up is the turbo. The turbo makes two sounds: a whistle from the individual blades, and a whine from the rotor itself. At higher engine speeds, the turbo whine is less "sharp" and slightly higher-pitched than the fan whine. The whistle is always present but the whine varies in from one unit to the next, and (unlike the fan whine) it isn't in line with the engine speed.

Turbo whine of two run-8 40-series units:
http://trainiax.net/recordings/sample-emd-turbo2.wav

Fan whine from the same train as above, when passing:
http://trainiax.net/recordings/sample-emd-fan.wav

[emd_SD_60]

Here's a GCFX SD40-3, 6062:

http://www.youtube.com/watch?v=QEP2OYAAWEw

Notice as the engine goes by you can hear the whine really well. Mind you, the train was cruising by at about 50 m.p.h. You can barely hear the traling GE's "chugging"!

[mbta1051dan]

Alright, here's my EMD story...

For many years I've lived, during the summertime, near the Conrail, now CSX, Berkshire Sub, better known as the Boston and Albany or the Boston Line. I have always been curious as to what that EMD humming sound was, and now I hear it less than I did in Conrail days. On those warm, summer nights, the combination of the crickets, the highway, and the rumble of the prime movers and honking of the horn, sometimes accompanied by a rather eerie sounding hum, sometimes quite loud. Now, since CSX usually runs their newest power on the B&A, I hear it less.
It is a warm August night, and I have the windows open. In the distance, along with the crickets and the whine of truck tires on I90, I hear the familiar throbbing of the prime movers of 2 new SD70MACs working upgrade, accompanied by an occasional 14L signal from the engineer's K5LA. The easy beat of the two-cycle 710 has always been a rather soothing sound for me, moreso than GE enginesounds (particluarly the GEVOs -- rather eerie sounding!) and so I start to nod off. Suddenly, from out of nowhere, a loud hum slowly starts to rev up. At first, I wonder if its the town fire siren gone wrong...then I realize that one of those gentle sounding 710s has spooled up its turbo--and now it sounds like a screaming beast! Soon, the other unit spools up its turbo -- and the noise is loud enough that I can hear it over the K5LA blowing at crossings! Then, all of a sudden, both turbos spool down, and once again, all I hear is the familiar EMD throb. Then it is silent as it plunges into state-line tunnel. 10 seconds later, they emerge, but the turbos are both enthusiastically spooling back up. When they are both fully spooled, they are unsynchronized, and it sounds like they are having turbo wars! Finally, the train reaches level ground, and the engineer notches back the throttle as he blows for the grade crossings in town. Aside from that, all I hear is the deep sounding idle of the engines plus the rumble of freight cars. Then all is silent for about five minutes until the engineer slaps the throttle into 8 to ascend the grade through Richmond. The turbos spool up, and for five more minutes, the hum is all I can hear, even when I can no longer hear the prime mover. With the lonely sound diminishing, I go back to bed thinking, "hope those things go to the shop tomorrow morning!"

-Dan