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Do you have a 718 GT4/Spyder/GTS 4.0L and are you more sensitive to the amount of cabin drone/resonance in your car, whether it be stock or accentuated by various aftermarket exhaust configurations? You're not alone, and if you've been following our Exhaust Development Thread you might know that Porsche has piped extra sound into your cabin through the firewall right behind your seats via a vibrating diaphragm called a Sound Symposer (and this is not the only car they do this in). Over the past month or so a few Rennlist members and customers of ours have been pursuing DIY modifications of deleting that sound symposer, and have reported significant reduction in drone/resonance in the cabin with different exhaust setups including various manufacturers. Spurred by this feedback, we arranged to have a car stop in to document the process for the Porsche community to reference, and hear the difference for ourselves. A kind local named Jesse volunteered his stock 718 Boxster GTS as tribute as he is particularly sensitive to in-cabin drone due to tinnitus from years of racing (our respect and condolences there).
The whole process was documented with some key photos below and a more in depth Step by Step PDF Guide we made for the process on the 718 Boxster GTS 4.0L. The steps will be much quicker/easier on the Cayman platform where you don't have to mess with the convertible top and cabin carpeting to access the engine cover.
To start, here is a Porsche diagram to show the full scope and functionality of the sound symposer:
With all engine covers removed, here's the symposer as it sits from the factory:
Sound symposer pressure unit plugged with wing nut expansion plug:
Engine side of the cabin port plugged:
Interior side of the cabin port:
Engine bay with sound symposer hose deleted:
The experimental expansion plug we used to remove the sound symposer was a 1" version, so if you were to go out and order a pair for an inexpensive DIY job that is what worked for us and should hold up just fine. However, we won't be sending these particular plugs used in the experiment out to customers as we are working on sourcing non-expansion plugs specifically designed for this type of plastic hose to form essentially a Sound Symposer Delete Kit. If successful the plugs should end up looking similar to the photo below. We also believe that removing and plugging the vacuum line leading to the valve actuator that activates the sound symposer (as seen in the photos) will net most of the benefit of removing the entire unit, if you want to try it that way. You could also try pulling back the carpet behind the seats and plugging it from the cabin side and that may help even though it's still active. That said, we chose to pursue taking the whole thing out...how dare it be there in the first place haha.
RESULTS
The resulting delete is effective in reducing in cabin drone even on a stock 718. Jesse and I went for a drive and noticed immediately less drone/resonance and what we'd call fake sound, which allows you to pick up on more quality and real engine and exhaust sound from outside the car. Jesse reports over the last couple days of driving the difference has continued to be quite noticeable and the car is much more comfortable to drive. This is definitely an underrated mod applicable for all exhaust configurations, and we expect to make more of a difference on cars with exhaust modifications. Spread the word, play around with it yourselves, it works! Sound is subjective, so if you're experiencing drone/resonance in-cabin more than what you're comfortable with this is something you can try to tailor your driving experience.
If you would like to read about the initial trials and feedback from members pursuing this modification, go to our Exhaust Development Thread and start at post #832 with Rennolazine's initial inquiry and start browsing
Best regards,
John Gaydos
Mike Spock
Last edited by Soul Performance; 06-17-2021 at 11:12 PM.
Cool, that should work. Let us know what you think when all back together! My wife doesnt complain as much about the noise level in the cabin... so thats something. Im even now thinking the Kline 200 cell Inconel headers wont be too loud inside....!!!
Well, although not what I would call dramatic the reduction in drone is noticeable... I removed the entire symposer tube and vacuum valve assemblies, plugging both the firewall opening and the chamber at the intake with 1" expansion plugs, my config is with Akra OAP's and JCR silenced Rear sections.
What I note is that any sound that was coming from the symposer is of course now gone, but sound coming into the cabin through chassis resonance remains. I feel that the effort and cost make it a worthwhile exercise but don't expect it to eliminate drone, at least in my opinion if your exhaust configuration drones then it will continue to do so but the symposer will not amplify its effect in the cabin. During top-up drives the cabin drone was better and you could easily tell it was reduced, but lug the engine in a high gear between 2000-2600 RPM and it will drone. What was easier to determine was the frequency change between valves open (higher) and valves closed (lower), but I would say the volume was similar in either setting.
Comparatively a buddy with a GT4 and completely OEM exhaust system felt it was a game changer, what was before tiring and unbearable while cruising was nearly cured by this mod, he said he could have a normal conversation in the car where as before it was not possible.
So at this point your results may vary depending on GT4 versus Spyder (top up/down) and if you exhaust is stock or modified.
Haha patience sir, we just did this on Tuesday and have had mere days to work on getting those plugs. We'll post some updates as we get them : )
Originally Posted by Westcoast
John, so can we assume that the pipe in between is simply removed and saved for future considerations?
Why of course sir. I'm also going to ring Suncoast tomorrow and see how much that assembly we took out cost out of curiosity, in case someone misplaces it or you know....lights it on fire.
Regards,
John
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Sweet mod and very kind of you to share with the community.
I pick up my GT4 tomorrow and will pay particular attention to the sound, but based on my brief test drive last fall I suspect I’ll want the sound symposer disabled. I’ll be following the development!
Cool, and since I will be installing your headers/cats, OPF delete pipes & exhaust tips I may as well get this as well when they become available...nice job, as usual!
Now if only someone could figure out how to control that valve and put an on/off button on the center console. Plenty of blank spots there for the taking.
My understanding is that it’s on all the time (not just when you “floor it” or above certain RPM).
I asked if they could disable it when I ordered the car last year. Kinda forgot about it till now.
The valve to the sound symposer only opens when you press the exhaust button. I have the valve controller, and this is the data I recorded revving out the car to 8k on each setting
Exhaust button on, valve controller disabled: 96DB
Exhaust button on, valve controller enabled: 96 DB
Just turn the exhaust valve off, and the sound symposer is disabled. If the symposer plugged is quieter than just keeping the exhaust button closed, it'll probably be marginal.
06-17-2021, 07:09 PM
SOUL | Drone Reduction Sound Symposer Delete
