Oh deary me, thanks Cam, my decimal point is most certainly in the wrong place. Poor old Bert will be placing fibres into the silencer one by one with tweezers!
Do I worry about silencer volume - yes, in my day job. Sadly.
Anyway, let's riff a bit more for the fun of it...
The problem with these long-round-thin mufflers is that they actually provide very little silencing volume for manipulating pressure pulses and cannot provide high degrees of transfer loss without putting the gas flow itself though excessive agonies and so creating back pressure. Any damping method will be a compromise within such a shape. Reverse flow, absorption, reflective, disruptive, whatever. Internal chambers can only be small and so only effective over a small frequency range. So we are kinda stuck with small improvements. If the same volume was shorter and fatter it would be more useful, but still not enough.
With a crossover in front we greatly increase the silencer volume available to each pressure pulse, as the ?other? silencer gets to share some of the effort in calming things down.
The tapered lead-in at the front of the silencer is also a lost opportunity - a sudden increase in diameter usefully takes out quite a bit of energy.
So, back to Bert?s problem with noise and his mods. I think Bert will have about 1.65 litres silencing vol per cylinder, less than half what is required to do a decent job. So if we move over to litres (rather than M? which is far too big for our case and causes dimwits to lose sight of where the decimal point should be :
), I would recommend a
lower limit for wool packing in the region of 160g per silencer. It depends on the wool Bert has to hand of course, its fibre diameter and even its strand length (which helps hold it in place structurally). So Bert, weigh out the fibre on the kitchen scales, expand it with your fingers and pop it in and have a look at whether that much can fill the volume decently enough. If not, add some more until the volume is loose (not flopping about) but full. The main reason I am going on about wool weight is not that it is an absolute, but that it will give you a benchmark for any packing changes you do next.
Hag
