Drone removal is done by a suitcase muffler, a tuned quarter wave resonator, or a hemholtz resonator.

The exhaust pipe is basically an organ pipe with a fundamental frequency and several harmonics depending on its diameter and length. The "Drone" is a combination of the fundamental and harmonics, depending on the frequency of the sound. As an organ pipe, it also transmits the noise from combustion from the exhaust valves to the tailpipe.

At 3000 rpm with a four stroke engine, there is an exhaust frequency of 100 hz for 4 cylinders, 150 hz for 6 cylinders, and 200 hz for 8 cylinders. The exhaust itself will then exhibit fundamental mode vibration at v/4*L, where v = the velocity of the air and L is the length of the exhaust pipe from tip to exhaust valve. The fundamental mode analysis can be done by essentially treating the entire exhaust system as a straight pipe. Note that since exhaust temperature decreases from around 800 degrees celcius to around 120 degrees celcius, the fundamental mode vibration really is somewhat complex. It can still be approximated. Assume a 10 foot long exhaust system, and an average EGT of 500 degrees C, the fundamental mode of the exhaust pipe is about 52hz. This fundamental frequency is also subject to pipe scaling. This has two effects. One, the fundamental mode frequency decreases slightly as a function of exhaust pipe diameter. Two, the exhaust gas velocity increases as the inverse square of diameter. A 5" cylindrical muffler with perforations around a 2.5" tube will decrease the fundamental frequency of the exhaust by 4 times, typically making the fundamental inaudible. This is otherwise known as an "expansion chamber".

An expansion chamber can also serve another purpose. This is by changing the acoustic impedance of the sound wave between the expansion chamber and the exhaust. Mismatching impedance can result in a drastic reduction of acoustic transmission due to the reflected components at Lower Order Mode frequencies.

Now, is an unsuppressed fundamental really what is causing your exhaust "drone"? If your drone is extremely loud, then probably not. You will need an actual muffler to get rid of a "booming" exhaust, or an otherwise loud droning sound. A muffler will need some kind of baffling to maximize dynamic insertion loss. Generally speaking, the DIL of the muffler will increase as its aspect ratio (length to width) increases, so a longer muffler is more effective than a shorter/fatter one.

What might be best is to start by recording the sound of your exhaust drone and performing a basic FFT on the noise to find the high amplitude frequencies involved. Lower frequency noises may best be canceled by expansion chambers, high power middle frequency (50 hz or higher) noise will require some way of diminishing the power of the exhaust pulse - most likely through reflection and baffling.

There is actually a subset of engineers who work on exhaust theory, most of which is centered around the complex interactions between exhaust pulses, exhaust gas interaction, and exhaust shape. There is, strangely enough, a book definition of "sporty sound". I am not an exhaust engineer so I have no idea what that is. This is just an electrical engineer's view of exhaust theory.