991.1 sound symposer in a 996

I want to improve the induction noise in my 996. Various modern vehicles have sound symposers to enhance the induction noise inside the vehicle, including the 991, which I've been lucky enough to drive and think it sounds great. I also don't want to annoy the local people and wildlife any more than I currently do with increased noise externally. Today I've ordered a 991.1 symposer, but it seems to be a rare modification, I can find little info about fitting one to a 996. All I've found via this forum search and Google is a few comments and pictures (and a sound file, sounds great!) by Porschetech3. I don't want to reinvent the wheel if it's been done before so I wondered if anyone had any info on this mod that they could share. Key things are: A) how does it fit to the induction side - if via the silicone hose, is something needed to fit the symposer and silicone hoses together, for example a 1" take-off? B) is there a existing hole that the symposer can go through to get to the cabin? I'm guessing no, in which case where/how is best to make the hole? C) any other care points to consider? Thanks in advance for any help!

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Non-M E85/6 BMWs have a "sound generator"; a ~2" diameter tube that connects to the airbox at one end and plugs into the firewall at the other. It brings intake sounds into the cabin. There are two pieces of foam rubber in the tube, which one can remove to increase the sound to suit one's desire. From the description of of the 991 "symposer" I suspect it may be similar. OP in case you are unaware, the 997.1 3.6 and 3.8 airbox fits a 996 with little modification. Those airboxes have a sound suppressing feature that can be tweaked to stay off all the time, adding to intake sound. Might be simpler than routing a hose from the airbox (or does it come off the intake plenum? doubtful) through to the interior of your car. It's not as simple on a rear-engined car as it it on a front-engined car.

I have the LN engineering performance cat xpipe setup. It tunes up the sound nicely without being obnoxious. Not cheap. Still worth it. Lots of options out there for sure. PSE helps as well.. I'm not a fan of loud, too old too deaf.. The intake side there is a simple heimholts(sp?) eliminator for the intake air box. It takes the intake noise up a notch as well. If your running almost any aftermarket intake your likely losing power somewhere to get sound..

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It is. No speakers involved. It's just a tube that runs from the airbox to the firewall. You have to disconnect it when you remove the airbox.

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Ozone, what have you done up to this point to enhance the induction sound? Ipd comp plenum/GT3 TB, resonator? BMC air filter? It sounds pretty damn good.

Remove some of the sound deadening material under the carpets. You'll hear everything.

Just do it !! You won't regret it !! The sound is addictive .........

Engine sound wise I already have the following: exhaust manifolds, cats and mufflers (already on the car when I bought it) Silicone induction pipe with the resonator blocked The exhaust is already a bit drony 2.6~2.9k rpm, and I've tried to reduce it, so reluctant to remove NVH material, which will let in all engine noise. I suspect an x-pipe will fix it but that's �700+... ​​​ The first car I bought was a Honda Civic, the best mod I ever made was to fit a K&N system. I had an MX5, which I cut a hole in the scuttle and fed the intake through that, it sounded amazing. I've also had an AE86 with ITBs. I love induction noise! I've been fortunate to drive 991.1, 991.2 and 718.1 GT3, they all have great induction noise, so piggybacking off the great engineers in Germany feels like a good move. I'm also an engineer in the automotive industry, so probably have more respect for them than the average owner.

www.carnewal.com in Belgium has a number of mods for our cars which might help. The owner, Gert I believe, is quite knowledgeable and helpful, and might be able to provide additional information. No affiliation; just a satisfied customer.

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FWIW :: if you notice those cars have a relatively low decibel noise from the exhaust, a loud *** exhaust will overshadow the beautiful intake noise... So my advise is to use stock exhaust mufflers for the best Timbre and accentuation of the pleasant intake noise...

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Can you link to the pictures and instructions?

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No I abandoned this project well over a decade ago. I built about half dozen custom kits and did the installs for local 996/997 owners and all are still very thrilled over them...they wouldn't take them off for the world, especially on the 3.8 "S" engines... But the concept does't go over well in the general consensus, the majority it seems are more than acceptable to modifying the exhaust sound in any which way possible as almost a "right of passage", but to modify the intake sound is viewed as "immoral" ...smh... There are many ways to modify the intake noise and the Manufactures spend millions of $$$ in R&D to make the right sound...Mann + Hummell is a big OEM of intake systems for Porsche , BMW, Audi, VW , Mercedes ect....who spend Millions on R&D on intake systems and Keet Boone is one of their Engineers whom I have had conversations with.( He actually contacted me about a wireless remote system I was using to turn the symposer On/OFF )..He is the Inventor/Patent holder of the "sound symposer" used by Porsche and also by FOMOCO in the Mustang and others... The "sound symposer" is an easy way to modify the intake sound as compared to redesigning the complete "acoustic stage area" or the whole engine compartment/cabin to get the desired acoustics.. But like I told the OP in a PM,,, Installing the symposer is simple, but difficult... Simple in that you just connect one end of the symposer to the intake rubber connector or air box and the other end to the firewall that separates the cabin from the engine compartment Difficult in that there are numerous ways to do this, and a lot of sourcing for the proper items to do it in the way you want to do it...and whether or not you have the necessary arts/crafts/ fabrication skills to do this type of thing...and the quality of the install/outcome depends strictly on your arts/crafts/fabrication skills. The way I did it was quite elaborate and the "kit" I designed + the install had a total cost of $1k, I did a half dozen of them locally for a net of $6K.. I didn't even bother to figure the gross profit since it was so low and the effort was so high , and the general consensus was that it was just some kid of " gimmick" I just had to abandon it...And I could't sell as a "kit" with instructions since the install required more tools/skills than most owners posses.. But if anyone has the skills to do it I say "go for it" !! Just make it nice and clean looking, you will enjoy the acoustics...Sally still has her "symposer" installed and I still love it.......

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I was having a poke around in the back of the cabin earlier this week. The rearmost vertical trim, just below the rear window, has a load of foam behind it. As an experiment I removed the foam. The next day I drove it to work, there was a small but noticeable improvement in induction noise without any obvious increase in other noise. Not a proper back-to-back but worth people giving it a go as it's cheap, quick and easy to try.

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True. I did the resonator-delete and silicon intake tube, but my Gundo/Fister hack overshadows the intake noise.

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Hey there. I don't belong here, per se, I drive a 2007 Ford Crown Victoria Police. I know that it may be a little awkward, me being here with all you guys driving fancy import sports cars and all, but I was wondering if I could have a few moments of your time. See, I bought this car because it's clean, completely rust free and completely unmolested. Low miles, low hours, was used for a prosecutor to drive to and from work. I know it's underpowered (understressed) but so is the Miata. I had a Focus ST and put $20k into it to make it go fast, but I would pit this ole cop car against that FoST in ANY kind of endurance race scenario. More importantly, though, is the maturity of driving the thing. It's not flashy, it's cool, it's quiet, subtle. I like that a LOT. In my Focus I had a $2000 exhaust installed as a cherry on top, but that cherry must have been sitting around for a while, because it made the whole car taste bad. It was drony, and blaring. Similarly, all the crown vic guys do a muffler "delete" as soon as they get their cars, and I hate that as well. I have had one of these with the muffler delete and the first thing I did was install new mufflers, because not only was it too loud to actually enjoy like a grown up, it lost throttle response, and until I'm deputized to chase down one of you guys, I don't think I enjoy losing throttle response in exchange for something like 5 horsepower in the top end. My man, you know where this is going. I need a sound tube, symposer, whatever. That low pitched growl this engine gives forth when I get on it is the tastiest thing I have ever heard, and I'd like to hear it without dipping below 10 mpg. So what do I do? Just run a tube to the cabin? Point it a certain way? How do I make it not... "whooshy"? The one in the FoST was actually not that bad, how do I recreate it? You can assume two things: 1) I'm cash poor (my wife only let me get this to drive around because I said I wouldn't spend any real money on it, and I've already installed a $4k sound system in it), and 2) I do have some fabrication skills, and can make pretty much anything that doesn't require cnc or the like. Thanks ahead. If this works out maybe I'll swap my Ford badge for a Porsche

Important note: I am fully aware of how different this may be than the same thing on a Porsche engine. I just need to know how to figure it out for myself.

All it consisted of on my Z4 was a tube about 2" in diameter running from the intake airbox, through the firewall, and into the cabin. The tube had a couple of pieces of foam in it that could be removed to add sound. You might get more intake sound simply with a different intake on the car. I'm not a fan of K&N stuff but if they make one for your car it will add intake noise to your experience.

Here is one of the installs I did back in 2012 on a 997 3.8 "S", notice the Sound Symposer just below the oil fill cap..This Sound Symposer has a vacuum controlled On/OFF and is the version used on 991, the one for the Mustang and others is the same without the ON/OFF valve....Cheyenne GTS also uses them as most other priemium models.. The Sound Symposer has a membrane inside like a drum ( not a snare drum), the membrane is tuned to 400HZ and when struck by the intake pulses puts out an amplified tone on the other side that is channeled to the passenger compartment via a corrugated plastic tube...The Inventor/Patent holder is Keet Boone , an engineer for Mann+Hummell in the Intake Developement Dept. He contacted me after seeing my "wireless remote" I incorporated into my version of a Retrofit Kit to install the Sound Symposer on earlier models... I told Keet that they were welcome to use my wireless remote system, just break me off a piece of the $$$ ...lol....of cource they never did... Like I said, I abandoned the project due to a very low profit margins since the main cost is labor/fabrication. I had the MAF housing made by a machine shop in Michigan to my specs, and I fabricated the Lexan see-through heat shield to direct cool air to the Open Cone Air Filter while the car is moving ...But the largest cost and complication was the time to install, had to cut an outlet hole in the hat-rack and install a small 2 inch "speaker grill" . This proved more difficult than the average Porsche DIY'er could do so the project was abandoned.. The Helmholtz delete and the open cone type air filters do enhance the intake sound very much, but the Sound Symposer just adds another level of sound and tone/timbre to the intake music, but like I mentioned before, to fully enjoy the Intake music, you HAVE to keep the exhaust DB level down to a factory level..loud *** exhaust will not do... Edit :: BTW, I named my retrofit kit, "The Banshee Stethoscope" because it makes a sound like a Banshee Scream at high RPM, and functions like a stethoscope in that it "listens" to the intake and produces an enhanced/amplified sound to your ears...

BTW , here is a pic of the Porsche 991 Sound Symposer with the vacuum controlled On/OFF valve. It is much more expensive than the one used on Mustang GT, Carmarro SS, McLaren MP4-12C and others that don't have the ON/OFF valve.... they are the same otherwise... You can figure out how to fabricate and connect to the intake pulses and route to passenger cabin. Many hot rodders like to modify thier cars, but most do it the easiest/cheapest way, Kuddo's for going the "Path less Traveled" to obtain the utmost in acoustics quality for oral pleasure...I find the older I get, the less I like loudness/Decibles over quality in tone/timbre..

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I assume your Crown Vic has a decent size v8 or v6? Here�s what you need: Buy two AutoZone FlowMaster mufflers, attach each of them to the exhaust headers or manifolds coming right off the collector, and then don�t run any exhaust pipe after the mufflers. The mufflers will sit under the floor boards and the sound inside the cabin will be glorious. And it won�t be too loud because you have mufflers, but it will be much louder than stock, especially inside the cabin.

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It's true that the Flow Masters sound better on the FoMoCo 5.0 and 4.6 MOD engines than any other, for some reason. But if the poster wants that sound like the old Rochester Quadrajet on the T/A 455 Super Duty Ram Air, the Sound Symposer will do that...

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I tend to like the idea of being hard to hear from a distance too, though

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Yeah, exactly. I'm an audio engineer by trade, actually, or at least I was. Lived and worked in Memphis, and my taste for good sound got, and remains, a little obsessive. Like I said, first thing I did was install a stereo in the thing that probably could have bought me another car, but I just have to. I love cars, always have, and I spend about 10 hours a day driving my cars in and out of town for my courier company. So, whatever I do to this car has to not just be enjoyable for a drag down the strip, it has to not get old 10 hours a day, six days a week. So, it's basically a drum, NOT direct airflow. I suppose I can just order one of these, and not make one from scratch. Would make things much easier, if that doesn't compromise the results. I'm not really sure how I would tune the membrane to 400hz... unless, you mean it's literally tuned the same way a drum skin is tuned??

Yes, the Air Flow does NOT go through the Sound Symposer. It "listens" on the right side ( that has the shut-off valve), and enhances the sound on the left that is carried to the cabin... When the intake valves slams shut under load, a pressure wave is sent back up the intake tract towards the air filter. This pressure wave "beats" on the membrane ( drum) and creates an enhanced sound out the other side...The membrane is already "tuned" to 400HZ, well actually it's tuned from 250HZ to 400HZ and will equate to 5k RPM to 8K rpm on 6 cyl engines and 3750 RPM to 6K RPM on 8 cyl engines...But it does make some sound below these HZ, and the "Banshee Scream" on the M96 really starts to sing at 5k ,and whails at 7K rpm... If you don't want to turn it off and on. ( I wouldn't bother, you will NOT want to turn it off, ever ) just get the one for Mustang, it will be the least expensive. Just make the install nice and neat, something to be proud of..

Another less acoustic option is to install the hardest/stiffest Function First transmission mount. It will add sound to the interior.

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I'll bet it will !! I just reserected a 1989 F250 that my ex-father-in- law left behind . It had been sitting dormant for 10 years (the brakes were locking up after they got a little heat )... It is all oringinal 460ci FI engine with "grand maw" 4 speed and overdrive....3/4 ton chassis...It has amazingly the worst NVH I have ever heard. The "grandmaw" 4 speed has no vibration dampening or DMF and makes a hideos sound when pulling below 2k RPM.....It's a greeat heavy duty truck with only 70K miles, but man is the NVH so difffernt from modern trucks...

Some BMW's (the first gen 528?) had a little flap that opened into the engine bay which was linked to the gas pedal.

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My Race Car from the 80's had a flap on the firewall ( SOHC T-88 series 2.0T) .but it was used to extract the camshaft out of the back of the head... I could change cams in 30 min at the Track...

Progress has been made! I've installed the symposer via the standard air box, it runs down the RHS of the engine. See pics below. How does it sound? It's not a massive difference but does make the engine sound more pleasant, more of a roar than before. I've recorded a 2nd gear pull before fitting, after with the valve closed and valve open, and asked a colleague in the NVH department at work to compare them (without telling him which is which), so I'll know if it's placebo or an actual objective difference on my car. He did come out in the car with me to help diagnose a 2.5krpm boom and said my exhaust is very loud (verses production cars he usually works on), so this is likely masking some of the improvement from the symposer. (As mentioned in a previous post it works best with a quiet exhaust). If you are interested in the the function of these devices you can read the following patents: US 8,634,574 B2 US 6,600,408 B1

I never updated this. My NVH engineer friend could see a difference between before and after, and with the valve open and closed, albeit the difference wasn't very big - the overall volume was the same, but there was some small changes to the balance of the frequencies which he said were more 'sporty' with the symposer fitted and the valve open. I've seen another thread recently that inspired me to relocate the take-off from the airbox to the induction pipe. https://rennlist.com/forums/996-foru...r-install.html I've not made any measurements yet but subjectively the induction noise is much louder now, without being too loud, and is noticeable between the valve open and closed. I'll try at some point to record the new induction sound and post some objective results here.

I finally managed to get out in the car with my son so I could record the sound with the valve open (symposer active) and closed (symposer output blocked). Bad news is that the roads around me have recently been cheaply resurfaced (tar and stone chips) so there is a lot of background noise but mostly it hasn't effected the objective analysis. Test was performed as a full throttle 2nd gear pull from low down to just short of 7krpm. The waterfall chart is shown below: - y axis is engine rpm - x axis is sound frequnecy - colour is sound magnitude, related to dB - the top plot is with the valve closed, the bottom plot is with the valve open As you can see with the valve open the volume is louder in a number of areas, notably around 500hz. There appears to be a resonance just over 100hz in both cases (I suspect likely to be related to the exhaust, as I've previously recorded a 130hz boom when cruising). A number of the diagonal lines (which relate to the various engine modes) are clearer and louder. I'm not sure why there is a lot of 'noise' above 6.5krpm with the valve open, it looks like some error/artifact in the recording. Further graphs: In both graphs Red is with the valve closed, Green is with the valve open. The top graph shows the 3rd order engine mode magnitude, which in a 6-cylinder 4-stroke aligns with the firing order. As you can see, from 3krpm upwards it is louder with the valve open (I forgot to include it but it is a similar result for overall volume). The bottom graph is an interesting one, it shows sound modulation. It is difficult to explain (for me anyway), but in this context the greater the magnitude, the more 'sporty' or powerful the sound is subjectively. As you can see pretty much across the board it is better with the valve open. (Ignore the values below 2.5krpm, the engine rpm 'signal' wasn't strong enough to generate suitable results in that range). I may try to repeat the measurement on a smoother road, which will improve the noise-to-signal but the expected trend would be the same.

Nice work on the sound graphs !! I can "see" what i "hear" in my application of the Sound Symposer .. My car still has the stock 99 mufflers which were the quietest of all 996 OEM mufflers...To get the full oral pleasure you need the same balance of the exhaust note to the intake note to get the right "mix".. Keet Boon who is the Inventor/Patent Holder along with Mann+ Hummell contacted me back in 2012 when I published by Retofiting Application of the Sound Symposer here on Rennlist...He sent me some Sound Symposer Prototypes he was working on and some Mustang GT Sound Symposers..He also presented my Retrofit Application to the higher-ups at Mann+ Hummell for consideration... The low frequencies/notes are easy to get from engines and are not that appealing to me..so I particularly dislike them in higher decibels/loudness... But the higher frequencies you hear from V10's , v12's, or Two-Strokes that fire every stoke so a 10k RPM 2-stroke has the frequency of a 20k rpm 4 stroke... And when you ballance the pulses of the exhaust note to the pulses of the intake note you get double the frequency.. and can be in a low decibel/loudness...To me the Intake note/timbre alone is glorious...