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Sounding better - improving the Bachmann 66 sound


eldavo

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First up let me say I am a sceptic when it comes to sound fitted models. Having said that I did purchase a Baccy 66 from my main supplier, Ebay, sometime last year. Well at 90 notes it would have been rude to let somebody else buy it! Here she is on the kitchen table which I have been known to refer to as my "workbench".

 

66022_27Jan09.jpg

 

When I first got the thing I found it very interesting though none too spectacular. I had a bunch of issues with the sound resetting and it generally did not sound very good. The resets and general running were tracked down to over enthusiastic oiling on the part of the previous owner. A good clean up and things improved considerably. Also I took it to my local club and gave it an hours running on our roundy roundy layout which further improved it and all seemed to be working well.

 

Having done all this I was still not that enamoured with it and it went back in the box apart from demonstrating it to a couple of folks. I even refrained from detailing it, fitting my favourite couplers and weathering it as I may well sell it on.

 

Over the last few weeks I've read a bunch of posts on these forums and other places about sound locos and the poor fitting of the systems in various Bachmann models. Being too idle to tackle anything significant yesterday evening I decided to open up my one and only sound loco and see what made it tick. Surprise surprise the speaker fitting in this loco is lousy! There is a single oval speaker clipped into a very small plastic enclosure underneath the cooling array grills. Contrary to all the advice of acoustic engineers and others the fitting is not air tight, in fact there are gaping holes everywhere!

 

So then what to do. Being a cheapskate my first thought was to find some blue tac and seal the speaker into the enclosure and block the holes. So that's exactly what I did. I popped out the speaker, rolled a really thin sausage of blue tac and set it around the edge of the enclosure and blocked the 4 sets of holes in the sides of the enclosure that allow the mounting spring clips to move. Here's the result.

 

Speaker1_27Jan09.jpg

 

You can also see from this picture that there is a whopping great hole where the cables to the speaker enter. The speaker was refitted and the cable hole bunged up with more blue tac. Taking a look at the result there were then 4 more holes where the speaker can be screw mounted! These were duly plugged giving this elegant(!) result.

 

Speaker3_27Jan09.jpg

 

At this point I reassembled the loco and powered it up. My sceptical mind told me I would hear no improvement. After all my ears are over 50 years old, I spent my youth working with speakers the size of telephone boxes trying to get Hi Fi sound and I played for 35 years in brass bands, how could a bit of blue tac improve the sound from a speaker the size of a large postage stamp mounted in a bit of plastic? Well it did and I could hear the difference especially in the horn sounds!

 

Sound is rather subjective so I was still prepared to believe I was deluding myself. Having worked for 8 or 9 years on Fourier transform software and analysing data many years ago I thought a touch of careful measurement might be in order. Before making the modifications I shot a short video clip of the loco sat idling. I framed the shot carefully so the camera would be at a known distance from the sound source. I did the same after the modification, ripped the video from each into a copy of CoolEdit and took a look at the waveforms and frequency analysis. Bear in mind this is using a crappy microphone in a mobile phone so you wouldn't expect great results. I should have used a high quality mic but, as I said before, I'm a cheapskate.

 

The upper traces in this screenshot are the original and the lower the modified. The green trace is the audio waveform, the blue the frequency analysis. They are, very surprisingly, significantly different. The volume level in the modified appears to be greater, and more significantly, there is a distinct shift in the frequencies from high to lower. Some of the "tinny" higher frequencies have been removed and the peaks have become more distinct.

 

Baccy66_sound.jpg

 

I'm now wondering whether the lower frequencies couldn't be further improved with some judicious damping of the plastic body of the loco...

 

Oh, and a nice teak speaker enclosure the size of a phone box!

 

Cheers

Dave

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