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Sound Channeling Material? Polymer or Other?

  1. Oct 9, 2012 #1
    Hey Guys,

    Been a while since my last visit, as ive been away for a well earnt break..

    But recently i've been set a challenge and its baffling me some what, and i wonder if anyone can help pleaseeee:biggrin:

    Basically long and short of it, a Car Manufacturer has been struggling in enhance the "Feel & Experience" of driving there cars, customers have mentioned they'd like more sound and acoustic feeling when accelerating.

    Now i've been asked to design a conceptual to that enhances the sound characteristics of the engine, NOT USING the exhaust... and NOT USING ARTIFICIAL EQUIPMENT..(Basically Aston Martin and a few other manufacturers actually use small microphones placed in the engine bay and after a certain rev band is accessed, play those noises under the dashboard to enhance the drivers experience..

    So am thinking of making some sort of cover for the engine to manipulate and channel the sound of the engines tones towards the cabin..

    Anybody know of any materials thats properties would assist me?
    Or any technology you may suggest i look into to help me as am relatively stumped...

  2. jcsd
  3. Oct 9, 2012 #2
    I don't think they are avaliable commercially.
  4. Oct 10, 2012 #3
    Many materials conduct sound well enough. The true challenges are
    - Avoid lengthy reflections at the channel's ends
    - Control all propagation modes to avoid metallic sound
    - Pass the sound efficiently from air to solid to air, typically with a membrane.
  5. Oct 11, 2012 #4
    Assume you want this to be 100% passive.

    Imagine an auditorium (in fact read about auditorium design). Geometry is going to be the factor for optimal focusing. Then you want to design whatever you do to have a resonance frequency near the Frequency of sound of the engine so it reverbs with the sound thus magnifying it.

    So the project has two parts.
    1. directing the sound - some sort of casing / funnel design potentially, maybe some sort of parabolic or semi-parabolic focuser
    2. amplifying the sound - some for of harmonic oscillator with resonance near the tone you want to amplify (probably the deep rev).

    hm ... I'm imagining a parabolic collector near the engine that focuses onto a harmonic oscillator near the resonance frequency of the tone that is in a partial parabolic dish focused towards the driver with focal point near the drivers head.
    Last edited: Oct 11, 2012
  6. Oct 11, 2012 #5
    The sound of an engine is not a single frequency but rather a noise (although there might be a predominant one), so that you would need a number of oscillators.
  7. Oct 11, 2012 #6
    I give you my car for one of yours, mine makes too much noise for my taste. In my case the reason is in the engine rather than in the materials the rest of the car is made of. This particular engine operates at higher revolutions than other engines do. If you can't change your engine, then you can not do much more than drill a hole to communicate the interior of the car with the underhood space. But, if you don't like having engine fluids getting around you then you can close the hole with a membrane, as if it were a drum.
  8. Oct 11, 2012 #7
    Getting engine sound into the passenger compartment is as easy as removing acoustic insulation. The real issue here I think is getting the engine sound in while excluding road noise and other undesirable sound.

    You might explore the idea of skipping the air phase of the sound conduction from the engine to your channeling device. Why not collect the sound directly from the engine block. The engine is going to be supported by several engine mounts. Usually these mounts are attached to sub-frame but suppose 1 mount were attached to the firewall, Voilà, engine sound is transfered to the firewall in proportion to the hardness of the rubber used in the mount and there is very little effect on other sound insulation. If you wanted to get fancy about it you could use a hydraulic mount with magnetorheological fluid so that a module could control sound transfer rates.
  9. Oct 14, 2012 #8
    Guys thanks for your input some great stuff here...

    Right let me respond to some of the replies :)
    Firstly yes directing the sound will be a vital part of this project, the focus will be majorly focused towards enhancing the drivers experience, when applying medium to full throttle... therefore the product would need to be almost silent when engines at low speed ( for arguments sake below 3,000 rpm) then be activated once a threshold has been breeched for example (3200rpm)
    -I totally agree the 1 stage is going to be some sort of channeled casing.. the semi-parabolic focuser sounds very intriguing it is something i will certain look into with more detail..

    Secondly - This is where i see the stumbling block, yea i am going to have to somehow isolate the frequency or frequencies that are lets say defined as desirable by drivers, and design a resonator system that amplifies those frequencies through some kind of diaphragm system focused towards the driver.

    Since my post i have had a meeting with the manufacturers development department:
    maybe this information can shed some light on things:

    -Yes it has to be an engine cover so to speak, or an above engine piece that enhances the drivers experience.

    -Preference is leaning towards, using mechanisms and sound manipulation (through resonator technology) rather than artificial means, speakers microphones etc etc...

    Now i have researched a few other manufacturers have attempted similar systems: for example Audi /Volkswagon, had a system that using air flow from the air intake passing through a resonator chamber above the engine, vibrated a diaphragm to amplify the engine tone...

    But this was apparently scraped after testing as it sounded more like a "woodpecker" pecking at the bulkhead...

    Please bare in mind this is going to be used and tested on a V8 and possibly a V12 engine so please dont confuse the required engine tone, that of one from a small 4 four cylinder daily round around...

    Thanks very much for your input guys, massively appreciated.

    Thanks, any questions fire away
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