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New composite-material helmholtz resonator delete...
(or: Why I stuffed some old microfiber towels into my airbox)
After watching years of watching folks silicon tube / orange cap / transom plug / third-party upgrade their stock airboxes, I wanted to see what would happen if I eliminated/reduced the Helmholtz effect.
Some of what we refer to as exhaust drone is due to the interaction of the exhaust note and the harmonics/resonance of the Helmholtz resonator. Reducing the ability of the medium in the chamber to expand and contract (one of the Helmholtz resources I came across refers to this as the "springiness" of the air in the resonator, which is a strange adjective to use for air, but I digress).
Since no air gets sucked through the resonator, there isn't really a concern about the stuffing getting "sucked" into the intake; even so, it's tightly packed to prevent anything from moving around.
The car certainly isn't any louder - which was an important development. The combination of Fisters and IPD plenum makes plenty of noise), but at the point in the RPM range where my car was sounding a little bit droney (only a little - I don't want to suggest that either the Fisters plus the plenum are too loud/droney for daily driving), it still sounds mean without any annoying undertones.
I didn't bother with before-and-after clips; this was a quick first try to see if it made any difference. Since it appears to make some difference, I'll find a location where the effect is most noticeable and post before and after clips. I can also sample sound pressures at various frequencies to see if peak levels in/around the engine bay change noticeably.
The resonator is sealed; it's a completely separate volume within the airbox, so it's less likely than a lot of other parts to catch fire.
Assuming this works as expected, we can try stuffing Gonzo's resonance chamber (with shop towels, sicko) to see if there is a corresponding decrease in volume.
- WildBilly32 to buy a bushel of deceased mice & overnight FedEx to Kalash
- Gonzo to finally get his 'rat *****' tattoo
- Kalash to deposit mice into Gonzo's airbox, then beat him in tennis
For clarification, Gonzo's resonance chamber is not part of his car. Your action items are fine as-is; I just wanted to bring this up now to avoid confusion later.
Refer to this photo of the Gonzo household last holiday season if you're still unclear:
Cheers, I have been reading many forums and blogs on this concept of by passing or removing the Helmholtz resonator (HR). One stated that removing the HR from the box gives you move air flow in the box due to the amount of room that the HR takes. According to this more air volume is a good thing. With that said, I have a Tiptronic with a breather line that is connected to the main air feed "Y" tube so the straight pipe is not suggested. I am curious about when stuffing the HR box did you reconnect the original air flow pipe back, if so what were the sound results.
I am wanting to remove the HR and add a upriser in its place and replace the OEM air hose. This will give me more air draw and air volume in the box (I am thinking). How did your experiment end up with just plugging the HR.
Thanks
(or: Why I stuffed some old microfiber towels into my airbox)
After watching years of watching folks silicon tube / orange cap / transom plug / third-party upgrade their stock airboxes, I wanted to see what would happen if I eliminated/reduced the Helmholtz effect.
Some of what we refer to as exhaust drone is due to the interaction of the exhaust note and the harmonics/resonance of the Helmholtz resonator. Reducing the ability of the medium in the chamber to expand and contract (one of the Helmholtz resources I came across refers to this as the "springiness" of the air in the resonator, which is a strange adjective to use for air, but I digress).
Since no air gets sucked through the resonator, there isn't really a concern about the stuffing getting "sucked" into the intake; even so, it's tightly packed to prevent anything from moving around.
The car certainly isn't any louder - which was an important development. The combination of Fisters and IPD plenum makes plenty of noise), but at the point in the RPM range where my car was sounding a little bit droney (only a little - I don't want to suggest that either the Fisters plus the plenum are too loud/droney for daily driving), it still sounds mean without any annoying undertones.
I didn't bother with before-and-after clips; this was a quick first try to see if it made any difference. Since it appears to make some difference, I'll find a location where the effect is most noticeable and post before and after clips. I can also sample sound pressures at various frequencies to see if peak levels in/around the engine bay change noticeably.
The resonator is sealed; it's a completely separate volume within the airbox, so it's less likely than a lot of other parts to catch fire.
While there is no suction or air flow on the Helmholtz resonator, there is air pulses/vibration that could eventually dislodge these stuffers/sound absorbers. I would secure them in some fashion.
I am defiantly not in favor of the sound reduction of the Helmholtz resonator,in fact, I went the opposite way to amplify the intake sound using the not-so-favorable Sound Symposer of the 991 to amplify the sound that the Helmholtz resonator muffles !!
Sound clip of my 99 996 with stock mufflers, my Banshee intake system with a 991 sound symposer.This design has three levels of sound enhancement over stock intake. 1. The Helmholtz reduces sound in the 260hz at 5000-6000 range, removing it increases sound in the 260hz range at 5k-6k rpm. 2. Removing the enclosed air filter box, and replacing with open K&N style increases total overall intake sound over the entire range. 3. Installing the 991 Sound Symposer amplifies the sounds in the 200hz -450hz at the 5500-7000 range.. https://rennlist.com/forums/attachme...d-symposer.mp3
Last edited by Porschetech3; 12-19-2018 at 08:29 PM.
07-20-2017, 01:40 PM
New composite-material helmholtz resonator delete...
