After a hiatus from Rennlist. I'm feeling guilty to get back "in" and contribute to a community that helped me so very much when I first got my 911.

What I'd like to share is the end result from ~100 hours of so of work and futzing with my car to increase the induction sound by successfully installing a 991 sound symposer. What I'll share below is the background and the final result which could be accomplished in just an afternoon.

I have a 2011 GTS Cab which bring a huge smile to my face every day. 53K miles, stage 1-6 DME Rev's (4-6 from a money shift somewhere around 10K miles going from gear 3 to 2 instead of 3 to 4 at 3rd gears redline.)

The car has had the Fabspeed Intake which tremendously increased the sound by creating an intake roar - especially past 5500 RPM.

I still wanted more so I have removed all sound dampening within the "cabin" from underneath the carpet covering the engine bay(except for the portion facing the front of the car as a little sound deadening was good for reducing the heat coming into the cabin, and got rid of some undesirable road noise) I've replaced the portion of the carpet itself that is covering the engine area with a lighter weight garage floor spill mat that lets much more sound through, and allows the convertible to easily slide over it when opening and closing:
http://www.oreillyauto.com/site/c/de...eyword=oil+mat

I've also removed the sound dampening from within the engine bay itself by removing everything that was over the engine. This collectively was awesome. My GTS pretty much roared like a 4.0 RS with no change to the exhaust sounds (except of course I've unplugged the PSE so that it's on all the time- make a big difference in the sound volumes consistency - especially around town.)

Still not enough for me. I wanted more of the engine roar. I started researching the Porsche sound symposer, and Ford Sound Tubes- reading every article and watching every video I could on how they work. This is where the hours really added up. I did ~15 different installs with differing types and lengths of tubes. I know nothing about harmonics or physics and so had to learn by trial and error.

In the end I have leaned that the sound symposer is a membrane encased in a megaphone (which direction-ally matters in its positioning-as you'd expect). The "sound" has nothing to do with piping in sound into the cabin as I'd initially thought. The sound actually comes from the deviation in static air pressure between:
The side of the symposer that's connected to intake (close to the MAF sensor and on the side closer to the filters-not after it!) and the air on the other side of the Symposer which has a tube running into the passenger cabin (through a hole in the rubber gasket on the passenger side of the engine bay that I drilled right above where the wires come through int the engine bay.)
The higher the RPM, the higher the suction coming through, which results in a larger pressure imbalance causing the membrane to vibrate as a result of stopping that suction from the lower pressure on the other side.

Side bar notes:
There is NO SOUND coming through the tube that exits into the vehicle through a small 1" hole that exists at the bottom of the back to the rear passenger side back seat- I put my iphone recording a video right next to it and drove around to test for the sound. As such, other forum articles that are on trying to reduce symposer noise by clogging up that pipe work because of the impact on sound pressure - not because they are plugging the sound waves as one might think. If I were doing this again I'd play with trying to find a differing pressure area within the engin bay area to avoid the drilling and routing into the cabin. (I tried just having the low pressure side not connected into the cabin and it made hardly any sound at all.... perhaps with a big length of tubing just coiled up and off to the side- maybe that would be enough?

Personally I used a Fabspeed metal connector piece that I purchased from them that was in "less than "ideal" intake for the 991 to connect their carbon intake tube to teh sound symposer tube. Any type of connector linking the plastic tubing running to the symposer and the inside of the air box or air tube would work- just make sure its air tight to ensure a great suction. I used hose clamps on all connections to ensure no leakage.

Here are the parts:
From my Porsche dealership - who correctly thought I was crazy:
I ordered the 991 parts
PA991-110-282-03 AS Neck $15
pa991-110-280-03 Sound Membrane $178

From Home Depot: I ended up with ordered bilge pump flexible tubing to connect from the intake to the symposer, and then on the other side from the symposer to the black intake tubing headed through the fire wall and into the cabin.
http://www.homedepot.com/p/Everbilt-...d=841804100011
After several other failed epoxys' this one has worked:
http://www.homedepot.com/p/J-B-Weld-...65-s/100189012 with

I also used a piece of radiator tubing with the correct ID to connect from the black symposer tubing to the little space within the cabin.

I'll get some photos and a video up shortly for your reference- In short it was a total success and I could not be happier with the thrill of what is now much more like the 991 GT3RS roar.
There are no ill effects - other than I could have probably just bought a GT3RS and paid someone to turn it into a manual by retrofitting the 911R 6 speed, and then paid someone else to cut off it's magnesium roof and turn it into a cab for far less than my opportunity cost of time was to do all of this.
Oh well!!!!
At least I had fun wrenching and bonding with my 12 year old son...The look on his face at full roar is priceless because we know that WE created it together....now if we can just get our cuts and scrapes all over our hands to heal!
Photo of the device - I mounted as close to my bare firewall was possible
Connection to intake
I removed the vacuum switch that tied into the sport Button activating a butterfly valve inside the tube, and Zio tied it full open.
This is where the intake comes into the cabin and is routed along the firewall to a hole just beneath/ next to rear seat.

 

this

 

Can't wait to hear it John!

 

This is nuts. I want to do it. Need instructions!!

 

Wow ! I have been thinking of something like this too. Do you have before and after videos?

 

Off the stock intake would the effects be the same? Fabspeed sells the cap for the stock airbox which I have. Can't quite stomach $800 for the intake. Might experiment with it.

 

Good idea, definitely worth trying. Consider disabling the helmholtz flapper while you are in there, or at least bypassing the airbox vacuum switch. Or maybe repurpose the flapper as a sound symposer on/off switch.

 

This video below is 2nd gear 5k to redline. It's glorious in real life ! The sound is totally worth the hundreds of hours investsd into it. Top up, windows up, no sport or PSE on- just pure intake sound.


You tube on the site describes the details.

I have a few slight changes to above instructions:
1. Its actually much better to have the sound symposer closer to the deck lid than the rear firewall. ( I could post a video comparing, but you can trust me decibles went up from 105 to 107 max DB by moving the Symposer closer to deck lid.

2. I also learned that it's critical to have an entry into the cabin---- I don't know why but it is. When I close my back seat back up-effectively cutting off the port the max DB drops to 104. Maybe the next user can test trying out other solutions ... but I'm convinced that the tube must go into the cabin for sound pressure. (again no sound comes through the tube).


The next video is just driving onto fwy to give an idea of the sound underway in normal conditions:

I strongly advise anyone looking to make their 997 more awesome to do this !!! Enjoy party people !!!

 

Redline vid missing bro. How hard is it to get the sound deadening material over the engine out if you have a coupe.

Where's this Helmholtz Flapper???????

 

here is the revs video sitting at a stop light

 

its super easy to rip out the sound deadening material. Open your back deck lid and rip out everything that looks like sound deadener stuck to the fire wall above and behind the engine with your hands. I then used goof-off and a firm brush to get rid of the sticky residue on the firewall after ripping off the sound deadening material.

 

I'd give it a try!! You have nothing to lose! Worst case it doesn't create the level of sound you'd like and you then go " nuclear " and buy the fabspeed kit.
The intake make a nice roar, but now 99% of what I hear now is the Symposer

 

Should be 3 videos total. Revs at stop light, 5k to redline and fwy on ramp. Pm me if you need more info- happy to help

 

I misread the description -- how much suspension noise do you hear minus the sound deadened liner? FWIW why not skip the air box all together and put a cone filter basically right on the silicon sleeve and arrange the MAF somehow.

 

There is a vacuum controlled flapper inside the airbox that is opened and closed based on engine rpm to quiet the engine (euro sound regulations like PSE? not sure why).
It's under the small part of the hose going from the airbox to the throttle body - #1 in this picture.




The vacuum line is on the back of the airbox with the solenoid on the right side (passenger's side).
The picture below is showing the backside of the airbox so the solenoid #1 is on the left in the picture.



Many of the aftermarket CAI silicone tubes include a cap to block off the flapper to keep the sound at its loudest.




Perhaps this location could be a good pickup location for a sound symposer retrofit - no drilling the intake manifold, just bypass the solenoid and keep the vacuum constant on, flapper constant closed.
Or change the wiring to the solenoid and run an on/off switch inside the cabin.