Sound Generator Modification

[daveg]

it is a feed directly from the air intake ducting, that passed a oneway valve (i think that's what it is ) and then leads into the cockpit, behind the glovebox (on RHD versions).

To me it sounds like it's coming from behind my head which is great as it sounds like a sporty exhaust.

I presume under hard acceleration air is being sucked into the intake from the cabin?

 

[acerboo]

just sounds an odd thing for a firm like bmw to do, more nissan.

 

[jwa1]

When I was a university we studied acoustics a little. Sound generation in cars was a topic during a lecture one day. Ok BMW have it to enhance the sound of the engine, but they also do it to get rid of the noise (unwanted sound). I was under the impression that this was the main reason for doing it.

TO REMOVE UNWANTED SOUND
Microphones pick up a sound waveform and then subsequently the inverse of that waveform is outputted through the speakers to cancel out that sound. So to ellaborate, say at a given point in time the amplitude of a sound wave is -1. A value of zero means no sound so therefore the speakers will output +1 to make 0. This analasys is done tens of thousands of times per second because the frequency and amplitude of the waveform changes over time and also because the human ear samples at up to 20,000 times a second (20 kHz).

The system will have been programmed to let certain frequencies through (thrashy engine sounds etc) but not frequencies associated with road noise (lower ones).

By the way - Noise Cancelling Headphone do exactly the same thing!

 

[sk93]

I presume under hard acceleration air is being sucked into the intake from the cabin?

nope, there's a one-way valve by the looks of things.

 

[sk93]

When I was a university we studied acoustics a little. Sound generation in cars was a topic during a lecture one day. Ok BMW have it to enhance the sound of the engine, but they also do it to get rid of the noise (unwanted sound). I was under the impression that this was the main reason for doing it.

TO REMOVE UNWANTED SOUND
Microphones pick up a sound waveform and then subsequently the inverse of that waveform is outputted through the speakers to cancel out that sound. So to ellaborate, say at a given point in time the amplitude of a sound wave is -1. A value of zero means no sound so therefore the speakers will output +1 to make 0. This analasys is done tens of thousands of times per second because the frequency and amplitude of the waveform changes over time and also because the human ear samples at up to 20,000 times a second (20 kHz).

The system will have been programmed to let certain frequencies through (thrashy engine sounds etc) but not frequencies associated with road noise (lower ones).

By the way - Noise Cancelling Headphone do exactly the same thing!

this is also acheieved by a resonator isn't it? well.. the same affect I think?
My ZX6R has two of them under the cowel... removal of them makes one hell of a racket!

 

[jwa1]

Exactly - resonators are a non electrical way of doing things. Basically sound goes in to a cavity / chamber and is reflected out as an inverse wave form that cancels out the noise! Really simple. Another application is in theatres too - they cut out echo and low pitched (talking) frequencies too. (The size and shape of a resonator dictates which sounds come out of it as this dictates the resonators resonant frequency - I won't bother to explain on here but google if you're interested!).

 

[daveg]

Is there an active/electronic acoustic cancellation system in use in the BMW?

If there is a one way valve that closes and stops air from the cabin being sucked into the air intake why does it get louder when I acccelerate? Surely when the valve closes it would go quiet?

 

[sk93]

AFAIK, there is no electronic noise cancellation system in the Zed...


To be honest, I've no idea.. nor am I 100% it is a 1-way valve.
It's in the big section that clamps onto the block and without wanting to play around with it much, I could only make a guestimate at what it was by looking at it..

You have, however, got me interested in knowing what it actually is
it's part number is: 13747514863

 

[sk93]

Wow Guys,
Thanks for the fascinating how to. Now I have a weekend project. Very informative and great recipe style directions I may be able to do it without screwing anything up. But that remains to be seen
great presentation

Hey Johnnybwaiting, Welcome to the forum!
Thank's for the comments and feedback! Let us know how you get on.

 

[Incompatible]

The sound generator assembly uses a diaphragm to both seal off the intake so as not to have a massive air leak while also magnafying the selected frequencies and tunneling them into the passenger cabin to enhance the "ultimate driving experience." The post facelift (3.0Si) cars have a more complex sound conditioning system then the pre-facelift cars. Both use a diaphragm. The post facelift cars have an intake tube which has two large resonance chambers attached (glued) to the tube body, pre cars have a simpler intake tube without the resonance chambers.

 

[The Moo]

Since moving up from my old 2.8 Z3 to Z4 the only aural pleasure I have had has been provided by my wife (in the form of her Mondeo V6, which sounds georgeous under acceleration)

Just read this how to and have removed just the sponge from the bulkhead end which is literally a 2 min job no tools required. and have been for a blast up the bypass and wow :evil: Car now sounds superb under brisk acceleration and remains quiet cruising at a constant speed. Sponge is safely inside glove box but I don't think I will rush to put it back on!!

As mentioned by others I think there might be an increase in fuel consumption and I seem to have relearned how to double declutch as taught by my old man just to remind me how good it sounds!!!

One happy teddy. :driving: Excellent How too SK93

 

[Rudd]

hey guys, just a quick one that has probably been answered before.

does the sound generator come as standard on an 03/53 3.0litre? there is one in the scrappy just down the road from me and il go along and get it.


how much would you expect to pay for a second hand one of a car from a scrappy?

 

[sk93]

yeah.. it comes in the 03 3.0 litre, cos that's what I've got

they're £60 from the dealer brand spanking new, so I'd go and offer £15.. maybe £20.. and at a push, £30...

gl.

 

[Rudd]

i take it they are easy to locate/recognise in the engine bay, i just dont want to look a fool when i go down

and do you know if it will fit straight to a 53 2.5i?

great writeup btw

 

[sk93]

afaik, they'll fit straight in.

and you can't miss it

if you look on the right-side of the engine, you'll find this big lump of plastic attached to the back right side.
if you look at my pictures earlier in the howto, you should be able to work out what you're looking for.


EDIT: Here's a guide for what you want

 

[Rudd]

ok cheers, so its just the pipe, generator box jobby thingy and nothing else. or do i need to take something from the firewall i.e number 7 or 8 in your diagram?

 

[sk93]

I'd grab no7 as well if it's there.

you'd also need the modified air intake pipe that this all connects to.
I cant find it on realOEM at the moment to give you a picture, but you'll know what I'm on about if you have a look see.

i can give you my mobile number if you like, so if you get there and aren't sure, you can give me a bell?

 

[sk93]

ok.. found it

it's part number 5. the left end of part 1 in the original document, will be plugged into this part, at the point where it says "6" on this diagram



in all, you should end up with this lot:

 

[Rudd]

Cheers for all of the help, thats geat!


i think i would be able to handle it from all of the info you have given, ill basically take everything from the intake pipe back. and ill print off some of the bits and bobs on here.

i just need to decide how much foam i want in or out now

ill stick an update up on how i get on


thanks again!!!!

 

[sk93]

pleasure.
good luck