Great Western Coffee Shop

Now I accept before I start this the correct place for this post may be trivia.

My question is regarding passing train noise from an HST. Consider this scenario. You are on a train where you can hear the noise of trains passing in the opposite direction. A HST comes the otherway travelling at high speed. You can hear the sound of the train passing...

The sound of the HST passing is almost a constant rhythm until the resturant car passes and then it changes and then reverts to normal. Why is this? I can think of only two reasons. One is the weight distribution of the buffet car is different to the others or it is the change it window pattern which causes a different pattern.

If you know the answer to this question please post or email to i-really-should-get-a-life@.....

Next time you are on a train and a HST passes the other way listen...you know you want to really :)

I'm guessing that this may be the doppler effect.  The air pressure, displaced by the moving train, will allow sound waves to travel at a different speed, thus altering the sound when the train reaches a certain point.  Any one who knows me will appreciate that I am far from being a techie, but I seem to remember a physics teacher droning on years ago and old movies sometimes feature the sound of steam loco whistles altering as they pass at speed.

Thanks MaxwellP but in this case I don't think it is the doppler effect. For example, if you were standing by the side of the road and a car approached you at speed (hopefully with you out of the way) then the pitch of the noise of the car would increase as it approached you until some time as it started moving away from you and then it would start decreasing. My understanding is that is the doppler effect.

Back to the HST. Imagine you are travelling towards london from Reading and an 8 car HST comes at speed in it's normal formation in the other direction. You will first hear the sound of the leading engine and then the 5 births of the standard class carriages. Then the almost "muffled" sound of the buffet/resturant car and then the normal sound of the last two first class coaches. And then at the end of course the training power unit.

It's not that pitch of the buffet changes it is a different sound.

Not sure Ive noticed the change in note when passing another HST but living by the line I'm used to the noise of HSTs passing  at all speeds. Normally it's a roar (loudness depending if it's on power followed by a swish followed by a quiter roar hich fades. At speed the power cars are only  a couple of seconds apart however at slow speed you get the roar then a very quite swish then followed some seconds later by the rear power car. If you get this you you know they are on a single or double yellow and locked down by their ATP.

Wheel flats are another quite noticible noise, times between bangs  depending on speed.

Hmm. Interesting.  I'm guessing that vacman will know as he has diesel rather than blood in his veins.  I will ask  ;D

I don;t know the answer to this question, but would add that I have heard it too.  It isn't the dopler effect, it is just that at close distance (ie on an adjacent line) a buffet car sounds different (quieter) to the other coaches. 

All I can think of it a difference in weight, weight distribution or something like that.  Its not got differently sprung boggies has it?   

I wondered that - I guess it's heavier than other seated coaches?

Could it be due to there being less windows in the buffet car, therefore producing a 'smoother' coach and less wind resistence? **non-techy answer**

Actually, that was one of my original thoughts. Not sure how I would prove this scientifically though!

Could it be less weight, so less downward pressure on the track, creating less of a noise going over the rail?

is there a generator under that coach? i presume the powercars also sound different?

Yes,the sound from the leading and trailing power cars is unmistakable :)

On my journey home tonight I will take more notice than normal but will probably stop short of opening a door window and holding out a recording device...

Do the buffet coaches have a different underside fairing arrangement? That would alter the sound.

Might just be 'straw clutching' as well of course...   ???

Paul

Well, I apologise for letting the thread down but sat on the wrong side of the coach coming home (but I was lucky to sit!) so my scientific analysis will have to wait for another day.

Thanks for all your theories, no matter how weird they may be!

Isn't the Buffet car the heaviest car in the consist...?! I recall FGW trialled removing these some years back to increase acceleration on the Bristol - London corridor? That's why Coach A doesn't have a toilet and Coach H only has 1 toilet - they were used as Stores for Catering Trolleys and Hot Water Urns for hot drinkies :)

Anyone remember that dreaded walk from Coach H - Coach A/B to get a Cup of Coffee at Weekends and having to queue halfway down Coach B to get a drink...? Me thinks FGW did the right thing keeping the Buffet Cars ;D

The Trout, what are your thoughts on the mini buffet, where it appears on the only service i've seen it on, was queueing half way down the coach, and then they ran out of everything except hot drinks on the only service i've seen it on!