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Discussion Starter · #1 ·
Gents,
Just got off the phone with the fella who designed Helmholtz style resonator mufflers on my prior truck. I can attest to how effective they were in effectively reducing highway 'drone' of a true dual v8 exhaust.

Seeing as how one of the potential downsides of an upgraded exhaust install on our Rs is the very same 'drone' at highway speed, and reading that current 'in line' resonators (like Vibrant) only seem to work for a limited time, I couldn't help but wonder if a Helmholtz style res/muffler could be designed for our Rs?

After speaking with this fella & describing parameters of our 'axle back' muffler setup, he said that in order to design a system that would eliminate highway 'drone', he'd first need to know what frequency the actual drone is occurring at. That way, the system can be designed to literally 'tune out' the undesired frequencies. Search & read up on helmholtz resonators for all the juicy scientific mumbo jumbo...

So, this is where you guys come in! If you're at all interested in having a 'drone free' highway ride, I need to ask for some input. Specifically, at what frequency is your R 'droning' at on the highway? In order to know that, the 'drone' frequency must be measured!

There are a bunch of free apps to download that will measure frequency via smartphone mic. So, all ya gotta do is download app and take a highway ride! Then, post up a few specifics:

1. current exhaust setup (factory, what downpipe/catback kit)
2. rpm/cruise speed of loudest 'drone'
3. FREQUENCY

Once this fella has a handle on the frequency range at issue with our Rs, he can move forward & see if there is a viable alternative to designing a helmholtz style system that'd work for our Rs...

Just throwin' this out there as a potential customer & guinea pig. If there's no interest, no worries. But again, I can say that a helmholtz style system IS the way to go to minimize & even eliminate 'drone', once and for all.

Looking forward to your input!
 

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Snabb catless downpipe with factory catback, perfect sound with no drone


Sent from my iPhone using Tapatalk
 

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8-Eight Fab down pipe, NO CAT, vibrant “medium” resonator and the “BIG” Vibrant muffler.

NO DRONE in a 2004 V70R.

You had HUGE DRONE between 2700 and 3000 RPM with the original Borla XR1 muffler.
Swapped to the BIG Vibrant muffler. Still LOUD AS HELL, but no drone.

I did lose some crackle and pop, and a bit of Blue Flame, but it was worth it!!!

80 MPH=2900 RPM, and it’s my DD, so I couldn’t stand it!!!!!!!

Frequency?? Good luck??’nnnnnn


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I have a Re-Volv catted downpipe, ipd exhaust, super annoying drone from about 1800-3000 rpm.

I'm going to measure the space, figure out the best big muffler and replace the stock ipd resonator with something much bigger and longer.
 

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Just measure the length of the original resonator and work backward... You also need to find an R without acoustic glass to get the actual sound profile. Most have laminated windows all around.
 

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Discussion Starter · #6 ·
Just measure the length of the original resonator and work backward... You also need to find an R without acoustic glass to get the actual sound profile. Most have laminated windows all around.
Whatever's measured in cabin will be what your ear perceives as 'drone', so that's what the helmholtz system needs designed around to negate. Even more so if the 'drone' is actually causing cabin resonance, which is completely isolated from any benefit that acoustic glass serves to combat other road related noise...

Fellas said normal 'drone' range is usually between 110-130hz
 

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Gents,
Just got off the phone with the fella who designed Helmholtz style resonator mufflers on my prior truck. I can attest to how effective they were in effectively reducing highway 'drone' of a true dual v8 exhaust.

Seeing as how one of the potential downsides of an upgraded exhaust install on our Rs is the very same 'drone' at highway speed, and reading that current 'in line' resonators (like Vibrant) only seem to work for a limited time, I couldn't help but wonder if a Helmholtz style res/muffler could be designed for our Rs?

After speaking with this fella & describing parameters of our 'axle back' muffler setup, he said that in order to design a system that would eliminate highway 'drone', he'd first need to know what frequency the actual drone is occurring at. That way, the system can be designed to literally 'tune out' the undesired frequencies. Search & read up on helmholtz resonators for all the juicy scientific mumbo jumbo...

So, this is where you guys come in! If you're at all interested in having a 'drone free' highway ride, I need to ask for some input. Specifically, at what frequency is your R 'droning' at on the highway? In order to know that, the 'drone' frequency must be measured!

There are a bunch of free apps to download that will measure frequency via smartphone mic. So, all ya gotta do is download app and take a highway ride! Then, post up a few specifics:

1. current exhaust setup (factory, what downpipe/catback kit)
2. rpm/cruise speed of loudest 'drone'
3. FREQUENCY

Once this fella has a handle on the frequency range at issue with our Rs, he can move forward & see if there is a viable alternative to designing a helmholtz style system that'd work for our Rs...

Just throwin' this out there as a potential customer & guinea pig. If there's no interest, no worries. But again, I can say that a helmholtz style system IS the way to go to minimize & even eliminate 'drone', once and for all.

https://www.autoguysland.com/cat-back-exhaust-systems/

Looking forward to your input!
Hi!

What car & engine are you talking aobut?
Do you have a true dual exhaust on it?

Helmholz pipes are good, but do take some space. Not sure you will have that.
Other option is a X-pipe.
 

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My system was drone free until I uncorked the clogged cat...IPD catted downpipe + IPD catback with parallel Borla XR1 muffler out to quad tips. Not a fan of the drone, but it sounds amazing at WOT!
 

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The stock resonator was designed to eliminate drone. Presumably another of the same length would do the same thing. That’s what I was implying.
 

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Discussion Starter · #10 ·
Yes, but you can't correlate resonator length to helmholtz length. A helmholtz resonator is actually 'tuned' to negate a certain frequency. Basically, it is the opposite of tuning a ported/vented subwoofer box to enhance a desired frequency via port size/length/ internal dimension. Rather, a helmholtz is designed/ tuned to frequency wave which effectively cancels the offending frequency range out, thereby silencing it...

I don't propose to know exactly how to do that, but this fella apparently does!
So, if we can get some baseline frequencies to narrow in on, he said he'll run the data against size parameters of our Rs, and see if something is feasible?

Ideally, i'd LOVE to see an 'all in one' muffler/resonator that could directly swap into the current axle back location of our cars. The mufflers on my old truck were just that, muffler & side resonator pipe in one unit. If not, just spitballin' here to see if there's a better alternative to current market resonators that seem to 'blow out' over time. A helmholtz 'tuned' design will not do that. Once its 'tuned' to cancel offending frequency range, it stays that way...
 

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Ideally, i'd LOVE to see an 'all in one' muffler/resonator that could directly swap into the current axle back location of our cars. The mufflers on my old truck were just that, muffler & side resonator pipe in one unit. If not, just spitballin' here to see if there's a better alternative to current market resonators that seem to 'blow out' over time. A helmholtz 'tuned' design will not do that. Once its 'tuned' to cancel offending frequency range, it stays that way...
That would be awesome!!
 

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The stock resonator was designed to eliminate drone. Presumably another of the same length would do the same thing. That’s what I was implying.
I would have to say that the stock system doesn't rely solely upon the factory resonator for eliminating drone. Lots of people remove the factory resonator and replace with straight pipe without incurring massive drone.

The factory muffler plays a large part in managing drone.
 

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Discussion Starter · #14 ·
Yes, yes you can correlate the length (well volume) of the resonator with the frequency it is designed to attenuate...

I took acoustics and know how to use Google...

http://www.ijsdr.org/papers/IJSDR1606008.pdf
Thanks for the link. I actually did my research before purchasing & installing a pair of helmholtz mufflers on my truck, and have seen (heard) how effective they are in real time, over a period of years...

Given that you've been schooled in acoustics, maybe you can share that knowledge & aid with designing something for our cars?
If so, wouldn't you need to determine the offending frequency (range) as Step #1?
Then, wouldn't you use that data to determine dimensions & correlate them with usable/available space to determine viability?
How would you go about designing an iteration of 'all in one' res/muffler?


To digress, all I'm fishin' for here is to get some member feedback on cabin 'drone' frequency, in the hopes passing it along to an interested party, whereby a product might be developed that improves on existing alternatives.

Once I slap in my Snaab downpipe & IPD catback under the car, I'm going to measure this for myself. Just reading along here that others complain about 'drone', and may be interested in a similar product? That, and...the more data points, the better! So...

If not, no big deal. If its too much effort to measure cabin frequency & post up a number (or range), I fully understand. My interest is strictly as (potential) consumer, and would only be happy to share if a better mousetrap were available...
 
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