Acoustic Material

Glassfibre wool?

Yep! That's what I use.

Metal.... all in how you cut and bend the deflection slots.

Seems to be a quandary here...he said "in" the muffler; perhaps he meant "in or on" the muffler? Don't see how stuffing wool inside a muffler will reliably cause quietening other than by limiting or stopping the engine. I would be inclined to agree that it's the exhaust flow path--its length and number of turns, etc--that must be relied on inside the muffler to limit noise emission from tail pipe. On the other hand, outside-surface sound deadening could lower sound emitting from the muffler itself?

Perhaps if you looked at a muffler to see how it was constructed?

Sounds like you don't remember "glass pak" mufflers. We all had them. There were also mufflers packed with steel wool, probably stainless. All these were illegal in Pennsylvania because eventually the packing material would blow out and you would have a loud resonating straight through exhaust.

Hey, I'm old enough to remember those. Cherry Bombs!

They're still around, you can go here & listen to their systems on various vehicles.

Hey! I had a couple of them on my old Mk11 Cortina!

Why? They were irritatingly noisy as they were. They didn't need ant help.

I had them on a V8 Rover SD1. I had a succession of those, on one I fitted a 2½" bore exhaust with a single silencer, that sounded nice.

Ah, yes! The good olde "glasspaks". They made such a neat sounding exhaust, especially if you reved the engine up to a high level and let off the "gas" and bleed the pressure back down.

If I may express my opinion on the matter as I am exhaust sistem manufacturer.

Glass fiber wool is one of the methods, but is usualy result in the wool been blown out through the tale pipe, melted inside the muffler and become a solid ball or plug the perforated pipes inside. It also colect and hold moisture and promote corosion on the muffler.Modern Japanise cars use nothing inside mufler but, perforated tubes guiding exhaust gases in specific way through maze of specialy designed chambers. Each and every diferent vehicle require diferent silencing design. Some European car manufacturers still use the so called "Rock fibre wool" that has much higher temperature melting point.In a few words:Everithing is either very simple either very complicated, it all depend on your desire- to make it good or to make it just

"To do the job"

If you tel me all the info abouth engine you want to silence I may be able to help you fyrther.

My last car spent about a month blowing the glass fibre out of the tail pipe. Every time I parked I would pull off the trail of fibres that was following me. It made no noticeable difference to the sound or performance of the car.

Inconel wool

Inconel is very expensive compared to quartz.

Quartz wool will not melt. It is good to over 1100C. It comes in varying fiber sizes 4 micron to 14 micron. As long as the exhaust temp in the muffler does not exceed about 1050C the quartz will not devitrify and will maintain its properties.

it was used in European diesel studies. There was a company that was able to comply to Euro-5 standards years ago, but the cost was detrimental for mufflers in mass production.

I beleive that regular glass fiber would devitrify due to heat and contamination. This is the reason it would blow out.

You can look at simple models of the transmission loss through a series of pipes and expansion chambers by using the 4-pole method for duct acoustics. The addition of perforated liners and fibrous material makes these models more difficult to develop and you will probably save time by looking for someone elses software designed to do this.

Acoustics of Ducts by Munjal is a good place to start.

Many high performance mufflers have steel baffles inside angled such a way to reflect some of the sound and cause destructive interfearance, reducing the sound output at the tailpipe. Glass packs are still quite common here in the US - I have a set on my 1972 El Camino and despite having a 500 HP 406 cubic inch engine, they do the job nicely.

There are also a number of manufacturers who make mufflers (I think mostly for motorcycles) where you can add or remove baffles (again, steel) and effectively "tune" the sound. I think they go by the name "Super Trap". Go to www.summitracing.com and you can find a variety of exhaust systems for this purpose.