High pitched buzz on Meridians

[oliverp]

Hi all,

Been lurking about for a while but only just posting now. Just a reasonably enthusiastic passenger rather than rail staff!

My question to you is...what is the high pitched buzzing sound that (appears) to come from the speakers of EMT Meridians when the train is coasting/braking. It's not particularly loud but it is quite irritating and if it's coming from the PA system surely it can be stopped?

Thanks all.

 

[westcoaster]

Ive wondered this, and have put it down to breaking, it's more prevalent during leave fall season.

 

[222001]

It's the Rheostatic braking system. The brakes work by running electricity through resistors mounted on the roof (the noise your hear), which creates electrical resistance on the traction motors to slow the train down. It's quite fundamental to the operation of the train, so it can't be stopped really.

 

[Crossover]

I guess the same applies for Voyagers too?

 

[Pumbaa]

Yes you can hear it on both (Super) Voyagers/Meridians.

 

[Crossover]

Now you mention it, I can think of the noise you mean, but to be honest, I've never found it particularly intrusive

 

[mallard]

Despite numerous travels on Meridians and their Voyager cousins, I can't say I've ever noticed this noise... I'll have to listen out for it next time I'm on one!

 

[MCR247]

It isn't even loud.....?

 

[TGV]

Are the rheo resistors force-cooled on the Meridians? If so, presumably you can hear a fan at the same time?

 

[Mojo]

I don't often travel on 222s (and haven't been on a Vomit in ages but used to use them very frequently) and I know exactly what the sound is and have wondered in the past. It is an awful sound and I don't like it!

I wasn't aware it was coming from above though; I thought it was from the cabinets at the ends of the coaches.

 

[cyclebytrain]

It's also the only noise I've ever found that my noise cancelling headphones amplify instead of cancelling...

 

[oliverp]

Thanks for the replies.

Glad I'm not the only one who has noticed it!! I think in a crowded/noisy carriage you wouldn't notice it but in a quiet one it would be more noticeable.

 

[asylumxl]

I don't really find it at all loud, nor do I think it's a horrible sound. I'd also say that it's far, far, far quieter than discs or pneumatic systems.

 

[Bomber]

Ii's caused by induction from the rheostatic system being picked up in the wiring to the speakers. The same thing happens in some Mk2 stock when travelling under OHEL that comes close to the minimum clearance to the coach roof.

 

[TGV]

Is it force cooled by fans as well on these units?

 

[Hydro]

Speaking of irritating braking noises, anyone else noticed that "squeak" on Electrostars when the brake first goes in? I don't know why, but it gets on my tits.

 

[Pumbaa]

That drives me crazy. And I'm not the only one - take a rush hour service from West of Chichester, by the time you've cleared the Arundel the whole train will clawing at the windows to get out.

 

[MCR247]

Don't loads of trains do it? Desiro's do it, 222s do it as well if its the one I'm thinking of....

 

[ChrisCooper]

Do you mean the high pitched squeek you get when braking first starts, or the whine that carries on throughout braking, lowering in tone as speed falls. The latter is coming from the motors, and is the same sound you will get when accelerating, although it's harder to hear on DEMUs over the sound of the engines. The other sound, no idea. Could be pnumatic, could be electronic. Presumably something to do with setting up the braking.

 

[Hydro]

It's when the braking first starts. I think it's just the braking being activated, via whatever means.

 

[ChrisCooper]

I'm not sure how exactly the braking works on modern EMUs and DEMUs. I know on London Underground stock the tread brakes are initially applied and then released as the rheostatic comes in, then held lightly against the wheels until applying again as the rheo fades off. It's because the rheostatic takes a few seconds to work properly (if it does at all), and holding the brakes lightly on allows smoother blending in and quicker response if the rheo fades (such as loss of power). A similar thing to this could be the cause of the squeek when braking starts, the rapid application or release or the disk brakes. Like I said it's got a fairly pnumatic sound to it.