What is exhaust drone?

[Rickap7]

New to Broncos I have a 25 Big Bend 2.3l looking for an axle back dual exhaust. and all the videos articles etc. keep saying "drone" what the hell is Drone?

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[DALOLA]

Interior exhaust noise for $1000 Alex!

 

[battering ram]

It’s an annoying sound
I put custom exhaust on a pickup truck. The loud, constant annoying sound. So loud I had to turn the radio up. I removed it the next day and sold it on Craig’s list

It’s a small engine. It’s never going to sound tough. No matter what exhaust it’s got

 

[helifino16]

I have this on my '09 Challenger with an aftermarket Flowmaster cat-back add-on. Really annoying on the Highway (RPMs at about 2000), but around town, it does sound great. If you do ANY highway (constant speed) driving, try to find something without 'Drone'.

 

[SierraBronco]

 

[Bugkillah]

Certain engines at certain rpms give off a particular note at a particular frequency that sounds like a dying sea lion that reverberates through the cabin.

 

[MRTperformance]

What is exhaust system drone?

Drone feels like an uncomfortable noise or vibration you experience while cruising at a particular speed.

The definition of drone is “a monotonous low tone; a humming or buzzing sound”. In physics, resonance is “a phenomenon that occurs when a given system is driven by another vibrating system or external force to oscillate with greater amplitude at a specific preferential frequency”.

Resonance between the exhaust system and the vehicle is what causes drone.

Why does drone occur is some exhaust systems but not others?

Drone is a function of several factors including the vibration of the exhaust system, the ratio of the transmission and rear gearing, the mass of the vehicle, and the engine RPM. The RPM at which the engine turns while cruising at highway speeds is the main factor in drone. When drone occurs, it’s usually between 1800 and 2100 RPM, which is approximately where your engine runs when in a high gear cruising down the highway.

Drone doesn’t occur with a stock exhaust system because a stock exhaust system is very quiet (relative to an after-market performance exhaust system), and is part of the automobile manufacturer’s overall noise, vibration, and harshness (NVH) engineering package.

 

[kr_1315]

Exhaust drone is the effect of replacing the stock exhaust on any Bronco.

 

[HotdogThud]

Exhaust drone is when a DJI Mini 3 flies right up your tailpipe.

 

[Pops]

It’s a pain in the ass for your neighbors.

 

[Whiskey Bizness]

Exhaust drone is when a DJI Mini 3 flies right up your tailpipe.

In some jurisdictions you have to pay extra for that.

 

[swamp2]

What is exhaust system drone?

Drone feels like an uncomfortable noise or vibration you experience while cruising at a particular speed.

The definition of drone is “a monotonous low tone; a humming or buzzing sound”. In physics, resonance is “a phenomenon that occurs when a given system is driven by another vibrating system or external force to oscillate with greater amplitude at a specific preferential frequency”.

Resonance between the exhaust system and the vehicle is what causes drone.

Why does drone occur is some exhaust systems but not others?

Drone is a function of several factors including the vibration of the exhaust system, the ratio of the transmission and rear gearing, the mass of the vehicle, and the engine RPM. The RPM at which the engine turns while cruising at highway speeds is the main factor in drone. When drone occurs, it’s usually between 1800 and 2100 RPM, which is approximately where your engine runs when in a high gear cruising down the highway.

Drone doesn’t occur with a stock exhaust system because a stock exhaust system is very quiet (relative to an after-market performance exhaust system), and is part of the automobile manufacturer’s overall noise, vibration, and harshness (NVH) engineering package.

Some correct, a lot not.

Drone is primarily determined to be present or not (and how loud it is) by the exhaust system itself. It happens when the engine exhaust excitation frequency (output pressure waves exiting the exhaust valves) excites a standing acoustic wave in the exhaust system. And at such a resonance, the volume is much louder relative to nearby rpms.

It looks like this (with the caveat that this is for a net zero flow - same concept applies). Top shows the pressure wave, next graph show particle displacements and last shows the pressure.



The primary variable just being the effective length of the exhaust system. It will happen at an engine rpm when f, the engine frequency

f = rpm/60 * N/2 (N is number of cylinders)

f ≈ c/4L , 3c/4L, 5c/4L, etc.

c = speed of sound in hot exhaust gas
L = effective exhaust pipe length

This is an approximation for a simple, uniform exhaust system with no chambers, resonators or branches.

Straight pipes and large diameters, often done in the pursuit of power are likely to cause or worsen drone.

 

[Ape Factory]

It's very possible to develop a drone-free exhaust. My favorite method is the helmoltz resonator. You can make it variable so less math is involved to achieve a drone-free system without extra power-robbing chambers. It's just a j-shaped extension on the exhaust piping with the extension moving in or out, based on what frequencies need to be cancelled. Think of a trombone, with theextension sliding in or out. Dial it in, set and forget.

 

[CarGuy]

Drone feels like an uncomfortable noise or vibration you experience while cruising at a particular speed.

Also the definition of a nagging passenger

 

[Umichigan1]

New to Broncos I have a 25 Big Bend 2.3l looking for an axle back dual exhaust. and all the videos articles etc. keep saying "drone" what the hell is Drone?

Drone is caused by resonant sound in the exhaust system. It can be "tuned" to have various audible qualities. This tuning process can be done scientifically and with attention to detail (much more necessary with smaller displacement engines to achieve a desired sound) or relatively carelessly (open up the exhaust and let it do whatever it wants). The point of a tuned exhaust system is to improve the efficiency of the engine and enhance performance. With smaller displacement engines, it is less about performance improvement and more about modifying the sound. There is a misconception that only a large engine can sound good. This may be because of the number of aftermarket exhaust companies that do relatively less engineering and analysis, resulting in systems that are only capable of sounding good specifically because they are attached to larger displacement engines. There are some companies that understand both the esthetics and performance issues at play and have produced systems with these variables in mind. MRT in Plymouth, Michigan is one of these companies. It is owned and managed by someone with a clue regarding what people say they want vs. what they really want (everyone is hoping for a system that produces a bad*** sound). To achieve the right sound without producing the relentlessly annoying drone takes more work than just throwing together some pipes and increasing the diameter from stock, and the people at MRT have both the knowledge and understanding to accomplish this potentially daunting series of associated tasks.

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