Recording RENFE Alco 321 locomotive

In recent days we have been able to record two Alco locomotives of the 2100 series, 321.054.9 and 321.070.5. There is no doubt that the sound of these engines is spectacular, very similar to 1800 we have also recorded (I’ll upload a small post about this recording very soon) with a very deep and characteristic stroke sound.
The drive system of 2100 locos, with Woodward diesel governor, is different to their 1800 “sisters”, and these characteristic “swings” on some the rev ranges are not present.

321.054.9 dispuesta para ser grabada al aire libre

321.054.9 ready to be recorded in the open air

The 2100 engine is an Alco 251C V12, four-stroke turbocharged, 2180 hp at 1025 rpm. The main engine sound is slightly rough, full of harmonics and prone to soiling and oversaturate. The use of a shotgun microphone of very high quality is essential, and the final sound must be compressed and processed to suit the sound characteristics of the small speaker which will reproduce the sound project.

321.054.9, grabando sonido principal del motor

321.054.9, recording the main engine sound

The turbo sound is very interesting, although not as prominent as in other diesel engines. To get it recorded clearly has not been easy, because the placement of a directional microphone designed to isolate their frequency tends to produce phase cancellation. The solution was to use another highly directional microphone and be very careful calculating its distance from the main microphone. Done this way, it may be mixed with the main engine sound for a balanced outcome and high fidelity.

321.070.5 Grabando sonidos complementarios en taller

321.070.5 recording complementary sounds at the train shed

The horn of 2100 is simply gorgeous. Monotone, very sweet and full of harmonics. It is relatively easy to record sound clearly, and you only must be carefully setting the microphone distance. Since during the recording we were lucky to have a very fortunate acoustic location, we chose to use a cardioid microphone, enabling slight entry of a natural reflected sound. The dynamic brake is subtle, and will be included in the sound project. Its application forces the engine to a certain fixed rpm, and activates an audible fan, not very loud. The video I show below shows the testing levels process to record the sound of the dynamic brake, and it can be appreciated its peculiar sound:

The rest of accessory sounds perfectly complement a very attractive sound project. As always, we have studied their activation times and the response characteristics of each one, to reproduce them on scale with maximum fidelity. We can affirm that Alco engine sounds are some of the most beautiful that can be heard in a diesel locomotive. In short, I will include a sample so you can enjoy them. The sound project for model railways is already in development, applied to sound modules and decoders Doehler und Haass, that are superbly responding  to the demands of diesel projects. The adaptation of the scale locomotives to accommodate the decoders and speaker is, as usual, impeccably performed by Simon Osorio, at

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