Drone is a low, steady note that fills the cabin at cruising throttle and refuses to go away. It is not the same thing as volume. A system can be loud at full throttle and quiet at a cruise, or moderate everywhere and still drone badly at one road speed. The difference is that drone is a resonance: a combination of engine speed, exhaust pulses and cabin cavity happens to line up, and the result is a note stronger than the engine's other harmonics.
Because it depends on lining up, drone is speed-specific. That is the clue that separates it from simple loudness. Enthusiasts notice it most on a highway, because that is where a constant load and a constant engine speed let the resonance sit still long enough to become tiring.
The cabin is a box with windows and panels that flex. Every enclosed space reinforces some notes and cancels others. When the exhaust produces energy at a note the cabin already favours, the two add rather than cancel, and the driver hears far more inside the car than a bystander hears outside it. That is why a system can sound modest at the tailpipe and still be unpleasant from the driver's seat.
Panels and trim also buzz in sympathy, which adds a drier, higher noise on top of the low note. Dealing with the resonance often removes the buzz as well, because the panel no longer has anything to follow.
A muffler is a chamber with an inlet, an outlet and internal paths between them. The volume of that chamber, the size and arrangement of the perforated tube, the packing material and the way the gas is routed all set which notes the muffler absorbs and which it passes.
Packing matters as much as geometry. Material that fills the chamber and stays put absorbs energy and takes the edge off the note; material that blows out or settles leaves the chamber empty, and the sound changes over time, usually getting harsher. The stainless steel exhaust mufflers made here are closed welded assemblies for exactly this reason: the internal arrangement is fixed and cannot shift.
Exhaust gas does not flow smoothly; it leaves the engine in pulses. Those pulses travel down the pipe, meet junctions, changes in diameter and finally the atmosphere, and reflect back. Where a reflected pulse meets an incoming one they can add together instead of cancelling. Pipe length sets the timing of that meeting, which is why a short system and a long system can drone differently even when they share the same muffler.
Junctions and changes of section do the same job as a change in length. Every place where two pipes meet, or where the diameter steps up or down, reflects some of the pulse energy. A system with several such points has more opportunities for a standing wave to form, and moving one junction along the run can shift the note enough to matter.
The reliable routes are a larger muffler volume, a change of internal routing, added packing, or an extra resonator placed where the standing wave is strongest. A well-placed resonator is often more effective than making the whole system bigger, because it targets the band that is causing trouble without adding restriction everywhere else.
Changing the material or the wall thickness of the tube shifts the note as well, since a stiffer pipe vibrates less and radiates differently. Working within a complete stainless steel exhaust system gives a fabricator room to place a resonator where the geometry actually needs it, rather than where a bolt-on part happens to allow.
Adding a tip, changing the air filter or fitting a different clamp will not address a resonance, however much they change the sound outside the car. Neither will driving around the problem, since the same road speed returns. A device that simply blocks flow will quieten the system by making it work worse, which trades one problem for another.
The honest approach is to identify the note, find the load and road speed where it appears, and change the part of the system responsible for it. That is a design question rather than a volume question, and it can be answered with the geometry in front of you.
