I have a few thoughts Paul.
First- As a packed baffle they will be too short to be effective. Not enough exposure to the packing. Typical packed baffles are around 10"-12" in length. The inner tube usually needs to fit reasonably tight in the entry part , otherwise the sharp frontal wave of each pulse will rip the packing apart.
Second- the adjustable blocking plate for tuning backpressure needs to be removed if you're going to pack the baffle, otherwise you'll stifle the exhaust with too much back pressure.
Third- The hole design on the baffle is more preferable than the fluted type baffle for a packed baffle, so I don't know what you want to do here.
Options- lengthen the tubes by at least double or more and maintain the hole pattern + remove the inner diverter plate.
Depending on the cost, possibly buy a second set of bafles and weld the smaller ends of the tubes together creating a "dog bone" appearing baffle with no diverter plate, pack the exterior as previously mentioned and install. (Probably the best bet based on your pipe design)
Anyway, I think you know where I'm going with this.
At one point back in my early years, I wanted to build my own headers and bought this book for reference.
For me it was a fascinating read but very heavy on frequencies, resonances and wave motion. 20 years after the original purchase, I went to find the book again and thought I had lost it, so I bought another one. A few years later I found both copies stored in a box during one of my many moves. Guess I liked the book.
There was a whole section dedicated to frequency cancellation and how to design a muffler or resonator to achieve noise cancellation. Hence the reason for mentioning the book.
Indeed a dog bone design would be the best I think as the frontal exhaust wave will encounter a metal plate with a hole in it rather than the edge of some fibreglass, but I don't understand how that design would eliminate sound as the exhaust gases (and presumably the sounds with it) simply go through a smaller hole.... faster...?
Where is the sound deadening happening if it can all go straight thru?
Anyway I only want to take the edge off, not destroy the wonderful sound, or performance...
I will pack these, remove the end plate and insert and see what happens. If not good enough I will get another (smaller and cheaper) set and create a dog bone as you describe.
The "book" would certainly help explain all that's going on here.
First, you elected to run 6 individual pipes instead of merging say 123 together and 456 together which would have had a certain amount of natural cancelation pulses exiting the 2 pipes which would have been more homogenized, or merged all 6 into 1 would have created overlapping pulses with a certain amount of natural noise cancellation. So in effect you have 6 individual pulses every 2 revolutions and now have to try and dampen the pulses individually which is a little more of a problem. It's why a CBX at 10,000 rpm with a 6 in to 1 sounds like a formula 1 car and a Harley with 2 straight pipes sounds like a Massey Ferguson pulling a 3 furrow plow.
So back to your baffles- Preferably make them as long as you can fit in the exhaust tips and if you do the mod and dog bone them, you can try to pack the baffles a little looser to allow the glass matting a chance to "absorb" the sound waves thus neutralizing the sound by changing the sound energy to mechanical energy. The more holes in the baffle tubes, the better the ability of the sound waves to interact with the glass matting.
Something else to think about- different materials of different densities will absorb different frequencies of sound. You could try packing with mineral wool (as an example Rock wool insulation batting material. I can tell you that insulating a room with fiberglass pink and insulating a room with rock wool, the room with the rock wool is silent compared to the same size room with the fiberglass pink. The rock wool is also fire proof to 1900 F.
Another option I was thinking about trying at some point is ceramic cloth as used on header wrap. It too will survive the heat and it also has a different density.
some aftermarket mufflers are packed with an assortment of different materials in order to enhance certain frequencies and diminish other frequencies. I remember reading an article about Honda going through different materials to build mufflers for the CBX 1000 and give it a unique muffled tone for marketing purposes.
Anyway, more for you to chew on.
Paul, the type of muffler you're describing, where a perforated tube is surrounded by packing, is called an absorption, or glass pack muffler. The packing absorbs the higher frequencies, leaving the lower frequencies, which is why they give a deeper sound to the exhaust when fitted. They do a fair job of silencing at lower rpms but the sound basically bypasses the packing at higher rpms. So they're fairly quiet at lower rpms & noisy at higher rpms. I'm with Kawboy, fit the longest perforated tubes with packing that you can. Something like Ebay item no. 163852944021 would be ideal if you could find them cheaper.
Kawboy, I'm currently having some Helmholtz resonators (or J-pipes) made for my car to eliminate drone after a free-er flowing exhaust was fitted, using this handy online calculator I found
Phil wrote: Kawboy, I'm currently having some Helmholtz resonators (or J-pipes) made for my car to eliminate drone after a free-er flowing exhaust was fitted, using this handy online calculator I found
Nice ! Hope the resonance you're trying to eliminate is managed by the Helmholtz resonators. It's all in the math and Physics we learned in school and said at the time " I'll never use this shit" . When I got to the Nuclear plant, I used Trigonometry at least twice a week. Who da thunk ??
Kawboy wrote: First, you elected to run 6 individual pipes instead of merging say 123 together and 456 together which would have had a certain amount of natural cancelation pulses exiting the 2 pipes which would have been more homogenized, or merged all 6 into 1 would have created overlapping pulses with a certain amount of natural noise cancellation.
Nope, 123 go together into a collector and 456 go into another one, then from there three come out each side making in LOOK like it is six-into-six (I am so glad I got you fooled - exactly the effect I was looking for haha!). Colin went as far as calculating the volume of the original collector boxes to make sure there was enough 'room' for the sounds to cancel each other out. ... not sure if that worked... I did ask for him to put one or two baffles in there, but he didn't.
If it is loud when riding I'm not too bothered about, its the idling and pulling away that my neighbour don't like, so thats what I want to reduce.
I have not yet received the wadding. I'll post when I'm done.