Originally Posted by LDubz735

Just curious, couldn't you achieve the same results with just plugging up the hole leading into the cabin? Is there a need to plug #1 in the diagram (the pressure unit for the sound symposer throttle valve). I ask mainly bc that's one less plug that could dislodge during driving.

Originally Posted by Soul Performance

Likely close but not as much.

See post #30

"Plugging the vacuum line for the Symposer and or keeping it's valve closed does remove much of the drone as mentioned above. However, even after doing that, the whole plastic tubing apparatus is still physically connected to the engine firewall. Even if plugged, it will still transmit some vibration and sound through into the cabin of the car.

When doing audiology testing on a patients at the doctors office, one can use a tuning fork to help determine a persons level of hearing. The doctor can rap the tuning fork and it will resonate for a while and its sound will slowly decay over time. When you put it near a patient's ear they can hear it for a certain length of time. If you then touch the end of the fork to the patient's mastoid bone just behind the ear, the sound will last a little longer and be a bit louder. This is because the sound is mechanically transmitted to the ear through the vibration of the skull and not just through the sound waves in the air.

So disabling the Symposer valve will help reduce the drone by inhibiting the transmission of the sound waves into the cabin. There will then be a further reduction in the vibration or resonance transmitted into the cabin if the Symposer is physically disconnected and removed. So everyone appears to be correct in their observations, and this should help explain why. So we have a good, better, and best type scenario here."

-Mike

Originally Posted by DIS295

the Rider,

Car has DSC and this mod. Nothing else has been done. John & I are of the opinion that the noise pumped into the cabin contributes to the drone experience. How much it contributes is not known, but I'd guess about 50% or more. All of the frequencies are still being generated by the engine/intake/exhaust, just no longer being piped into the cabin. My norm is Sport plus via individual programming.

Originally Posted by Soul Performance

Pretty much negligible as the pipe itself weighs .266 lbs and the plugs offset that.

-Mike

Originally Posted by iliveoncaffiene

I unplugged the vacuum line to the symposer with Soul's Resonated Race Exhaust - it went from nearly unbearable drone and booming in the 2000-2800rpm range to a pretty livable loudness in the 2200-2600rpm range.
Probably close to 50% reduction just unplugging the line.

Originally Posted by Soul Performance

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.

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

Originally Posted by porscheflat6

Where can I pick up a similar plug like the white one in the photos? Lowes/Home Depot?

Originally Posted by Westcoast

I have been looking, I see them listed as kits on Amazon as they are more of a test plug for plumbing, but nothing listed online at Lowes/Home Depot. Look familiar: Nylon Expansion Pipe Plugs for low pressure applications (cob-industries.com)

If anyone finds them in the wild please share the location.

Originally Posted by porscheflat6

https://www.mcmaster.com/test-plugs/

Here is a better location to find them.

Originally Posted by Westcoast

Thanks for the link, online is likely the best route, but for us Canucks a bit of a pain for an order for 2 plugs...

I might have to resort to making my own...

Originally Posted by Westcoast

Thanks for the link, online is likely the best route, but for us Canucks a bit of a pain for an order for 2 plugs...

I might have to resort to making my own...

Originally Posted by porscheflat6

If I find something local, I can buy extra and send some your direction if you like

Originally Posted by Westcoast

Thanks for the link, online is likely the best route, but for us Canucks a bit of a pain for an order for 2 plugs...

I might have to resort to making my own...