The history behind it's design is: I bought aroturbine, installed aroturbine in stock muffler position, then drove to a friendd's house that had a dB meter. It was about 85 dBA @ 2300 rpm inside the cab. Needless to say I was out of $300. 00, and was contemplating putting the stock muffler back on.
The next day I went and purchased donaldsn M90544?? forgot the exact part number, and placed it before aerotb. On my way to the muffler shop it was so loud, that a trucker gave me the air horn salute as I drove past his cab, and I was lighfooted. On went the donaldsn, and per the recommendation of aerotb, the aerotb went in as a tailpiece (huge tip, the guys at the muffler shop were making funny comments).
It was still loud, but tolerable, about 75 dBA (I had now purchased my own meter).
At first I thought that the Donaldsn has only 1 inch restriction, which is less than the airfilter which has about 3-5 or more, so I thought I had it made. Then I discovered it has 1 inch Hg (mercury) or 0. 5 PSI at normal cruising, and 2 inches at full throttle (1 PSI) That's about half of what the stock muffler has, not much better. So I wanted one that will have about 10% of stock, and started designing my own. Long story short, after weeks of research, i made a prototype, and about 2 weeks later had tuned it to where I like it. At first I had the aerotb used as one BIG exhaust tip, but it was noisy at some frequencies, until I switched it the other way around, and instantly found the sound and loudness and negligible back pressure I had sought.