Fancy Tech: How to Get Rid of Exhaust Drone, works great!

Nismonerd · 09-13-2016, 01:25 PM

Found this thread while searching for cures for exhaust drone. Gave it a try today and the results are better than I expected. I've got a 2010 NISMO with HFCs and Beluga axle backs. The goal was to reduce the drone between 2500 to 3000rpm. I had the muffler shop install a side branch resonator on each side just before the axle back flanges. Using the formula found in this thread, each branch length is 28in, using 2.25in pipe and capped at the ends. I'm very happy with the results, as the drone at the target rpm range has been reduced by about 80%, and the entire rpm range sounds smoother.

I'm sure others have done this as well as this thread is pretty old. I wasn't aware of this method and just wanted to report that it does work. I know that some aftermarket exhausts come with the resonators, but never thought of fabricating them on exhausts that didn't include them.

The job cost me $125 including parts and labor.

bbermann · 09-24-2016, 08:23 PM

Quote:

Originally Posted by Nismonerd

Found this thread while searching for cures for exhaust drone. Gave it a try today and the results are better than I expected. I've got a 2010 NISMO with HFCs and Beluga axle backs. The goal was to reduce the drone between 2500 to 3000rpm. I had the muffler shop install a side branch resonator on each side just before the axle back flanges. Using the formula found in this thread, each branch length is 28in, using 2.25in pipe and capped at the ends. I'm very happy with the results, as the drone at the target rpm range has been reduced by about 80%, and the entire rpm range sounds smoother.

I'm sure others have done this as well as this thread is pretty old. I wasn't aware of this method and just wanted to report that it does work. I know that some aftermarket exhausts come with the resonators, but never thought of fabricating them on exhausts that didn't include them.

The job cost me $125 including parts and labor.

Good stuff! Wish I saw this before I sold my Top Speed axle back. I had the exact same setup as you and LOVED the sound but cabin noise was too much.

Sold the axle back and got CNT cat back which had the helmholz canisters to eat drone, much like your added pipes. It is now good but your current setup is probably better!

ChopsZ · 09-24-2016, 10:31 PM

Actually, even though the Helmholtz resonators work on reducing drone, the drone isn't really caused by the exhaust.

Drone is caused by the frequency produced at those lower rpms and the natural resonant frequency of the interior air space of the car are tuned to one another, reinforcing those frequencies, making them louder. And if you notice, the drone comes back at double those rpms, around 4000 to 5000. The drone at low rpms is like the first harmonics, the drone at higher rpms are like the second harmonics. This is because the internal air volume of the car interior allows those particular frequencies to propagate - a.k.a. - drone.

Ever notice the drone decreases drastically to almost non-existent when you have the windows rolled down? That's because you just changed the "tuned" resonant frequency of the interior by opening the windows.

Has a trusted friend or family member drive off with your car as you stand outside and listen. I bet you won't hear any drone. I bet the exhaust will sound just about a loud at those low rpms (2000 - 2800) as it does at higher rpms (3000 - 5000).

A very similar thing happens in a room with bass notes on a stereo system. It's called "room gain" and "room modes" which have both peaks and nulls. Different room sizes will have different room modes where different bass frequencies are allowed to propagate near the wall boundaries making them louder or possibly quieter. In certain areas along the walls and within the interior of the room, you'll notice the bass frequencies are louder than normal, typically near the corners (a.k.a. - corner loading).

Anyway, now I'm starting to ramble, so I'll stop there. But my point is this, it's NOT the exhaust system that's droning, it's the enclosed interior of the car that's causing the drone.

Ronin06 · 09-29-2016, 09:08 PM

Quote:

Originally Posted by ChopsZ

Actually, even though the Helmholtz resonators work on reducing drone, the drone isn't really caused by the exhaust.

Drone is caused by the frequency produced at those lower rpms and the natural resonant frequency of the interior air space of the car are tuned to one another, reinforcing those frequencies, making them louder. And if you notice, the drone comes back at double those rpms, around 4000 to 5000. The drone at low rpms is like the first harmonics, the drone at higher rpms are like the second harmonics. This is because the internal air volume of the car interior allows those particular frequencies to propagate - a.k.a. - drone.

Ever notice the drone decreases drastically to almost non-existent when you have the windows rolled down? That's because you just changed the "tuned" resonant frequency of the interior by opening the windows.

Has a trusted friend or family member drive off with your car as you stand outside and listen. I bet you won't hear any drone. I bet the exhaust will sound just about a loud at those low rpms (2000 - 2800) as it does at higher rpms (3000 - 5000).

A very similar thing happens in a room with bass notes on a stereo system. It's called "room gain" and "room modes" which have both peaks and nulls. Different room sizes will have different room modes where different bass frequencies are allowed to propagate near the wall boundaries making them louder or possibly quieter. In certain areas along the walls and within the interior of the room, you'll notice the bass frequencies are louder than normal, typically near the corners (a.k.a. - corner loading).

Anyway, now I'm starting to ramble, so I'll stop there. But my point is this, it's NOT the exhaust system that's droning, it's the enclosed interior of the car that's causing the drone.

I agree with you right up to the point it's not the exhaust causing it. If so, then why does the drone stop when the engine is off or you change exhaust?

ChopsZ · 09-30-2016, 07:33 AM

Quote:

Originally Posted by Ronin06

I agree with you right up to the point it's not the exhaust causing it. If so, then why does the drone stop when the engine is off or you change exhaust?

Please re-read my post. It's explained in there.

JARblue · 09-30-2016, 07:48 AM

Quote:

Originally Posted by ChopsZ

... the drone isn't really caused by the exhaust.

Quote:

Originally Posted by ChopsZ

Please re-read my post. It's explained in there.

Based on your understanding, I do not think you mean to suggest that different exhausts do not produce different frequencies. The exhaust is most certainly a key variable of the drone. Not that there aren't other factors like you explain. But to suggest that the exhaust is irrelevant to drone is wrong.

09-13-2016, 01:25 PM	#1 (permalink)
Nismonerd Base Member Join Date: Jan 2016 Location: North Alabama Posts: 37 Drives: 2010 370z Nismo Rep Power: 11	Found this thread while searching for cures for exhaust drone. Gave it a try today and the results are better than I expected. I've got a 2010 NISMO with HFCs and Beluga axle backs. The goal was to reduce the drone between 2500 to 3000rpm. I had the muffler shop install a side branch resonator on each side just before the axle back flanges. Using the formula found in this thread, each branch length is 28in, using 2.25in pipe and capped at the ends. I'm very happy with the results, as the drone at the target rpm range has been reduced by about 80%, and the entire rpm range sounds smoother. I'm sure others have done this as well as this thread is pretty old. I wasn't aware of this method and just wanted to report that it does work. I know that some aftermarket exhausts come with the resonators, but never thought of fabricating them on exhausts that didn't include them. The job cost me $125 including parts and labor. bbermann likes this.

09-24-2016, 10:31 PM	#3 (permalink)
ChopsZ Track Member Join Date: May 2016 Location: Central Florida Age: 50 Posts: 965 Drives: 2016 370Z GM 6MT Rep Power: 2302	Actually, even though the Helmholtz resonators work on reducing drone, the drone isn't really caused by the exhaust. Drone is caused by the frequency produced at those lower rpms and the natural resonant frequency of the interior air space of the car are tuned to one another, reinforcing those frequencies, making them louder. And if you notice, the drone comes back at double those rpms, around 4000 to 5000. The drone at low rpms is like the first harmonics, the drone at higher rpms are like the second harmonics. This is because the internal air volume of the car interior allows those particular frequencies to propagate - a.k.a. - drone. Ever notice the drone decreases drastically to almost non-existent when you have the windows rolled down? That's because you just changed the "tuned" resonant frequency of the interior by opening the windows. Has a trusted friend or family member drive off with your car as you stand outside and listen. I bet you won't hear any drone. I bet the exhaust will sound just about a loud at those low rpms (2000 - 2800) as it does at higher rpms (3000 - 5000). A very similar thing happens in a room with bass notes on a stereo system. It's called "room gain" and "room modes" which have both peaks and nulls. Different room sizes will have different room modes where different bass frequencies are allowed to propagate near the wall boundaries making them louder or possibly quieter. In certain areas along the walls and within the interior of the room, you'll notice the bass frequencies are louder than normal, typically near the corners (a.k.a. - corner loading). Anyway, now I'm starting to ramble, so I'll stop there. But my point is this, it's NOT the exhaust system that's droning, it's the enclosed interior of the car that's causing the drone. __________________ She's For Sale! PERFORMANCE: Aero Workz \| Akebono \| BC Racing \| EcuTek \| HKS \| MaxBore \| Motordyne \| Nismo \| RJM \| SPL \| StopTech \| Z1 AUDIO: Arc Audio \| Bazooka \| Helix \| Pioneer \| Stereo Integrity

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