Is it really possible to reproduce low frequency in car?

[Sarong1]

I was reading an article off the internet and came across this interesting one that discusses the possibility of producing low frequency in a car environment.

 

The author argues his theory by using the logic of science and sound behaviour which is interesting and enlightening.

 

To begin, we must first understand that

 

Wavelength=speed of propagation/frequency

 

So, to effectively reproduce freq of 20Hz in a car and by applying the formula above, taking into consideration that audio transverse at 340m per second or 1,122 feet at the temp of 21 deg celcius. We will have:

 

Wavelength=speed of propagation/frequency

20Hz=1122/20

That means Wavelength of 20Hz=56 feet

 

So, in order to reproduce 20Hz, you will need a car length of 56 feet. Where the hell can we find such a long car??? Bus??

 

Now, what about 40Hz then? Applying the same formula, the wavelength is at 28 feet. And at 80Hz???, you will need 14 feet to experience 80Hz!!! Now, that is ridiculous isn't it???

 

But in fact, it is possible. That is because car acoustic actually presents a near vacuum environment. The reason why sub freq range can exist in the car is because of the changes of internal car air pressure that creates what is termed as Transfer Function of Pressure Changes. Now, if the woofer and subwoofer have been installed properly and there are no serious leakages of signal or acoustic cancellation, it is really possible. Adding the fact that if the positioning of the speakers are in harmony with the subwoofer, the pressure in the car will react according to the audio, thus creating what we hear as sub freq, better still seismic (which is the ranges we feel).

 

Of course, a lot will depend on the amplifiers and the crossover point including the db/oct slope which cannot be neglected at all. The vacuum environment at the car boot must also be air-tight which is a determinant of whether your sub ranges can be reproduced effectively.

[Darkness]

Wavelength=speed of propagation/frequency

20Hz=1122/20

That means Wavelength of 20Hz=56 feet

 

Hey bro that is the speed of propogation of sound waves in water (or rather dense medium)...

 

In air it is only about 330 m/s (more or less)... The Human ear can hear from 20Hz onwards...(normal ppl atleast...if x-men then maybe lesser )

 

So thats about 16 feet.

 

40Hz only needs about 8 feet.

 

But of cause since sound is a wave it is present over a space and time. It does not have to travel straight. It can bounce here, bounce there b4 it reaches ur ears...thus u can indeed hear it

 

This is at least based on the property of sound la...in terms of audio in car / home like u say settings and box's tightness etc is important.

[Sarong1]

Bro, 330m/s is only possible if the temperature is at 0 deg celcius and I am talking about dry air and not water. If we are talking about 24 deg celcius which is normal temp in a car, the speed of sound is at 346.0399m/s. What was stated in my post is that the temperature is taken as 21 deg celcius.

 

So, what we can derive here is that we will generally enjoy listening to music at night more than day time. And that is probably why our meetups are usually held at night and into the wee hours.

Edited February 16, 2006 by Sarong1

[Darkness]

Correct at 0 degrees it is about 330. At 100 degrees it is 380 m/s there about hee...

 

i saw ur post refer to the speed at 1000+ oh okie saw it liao...its in feet/s...i took it as meters/s hee hee sorry abt that...

 

but as i had mentioned sound wave need not travel in a straight line so technically u should be able to hear it going by ur hypothesis.

 

But i dont get it, wavelength should not have anything to do with what we can hear in the car (or any enclosed space) rite? I mean if a speaker pushs out 20 Hz and i put my ears beside the speaker i will still hear it rite?

Edited February 16, 2006 by Darkness

[Sarong1]

Not trying to teach science here, but what I really want to share is how sub freq cannot be possible in a car acoustic if we simply apply the scientific laws and how could it be possible that we could hear it in the car after understanding what affects it such that we can hear it. If you read the article again, you will probably understand the phenomenon created in the car. And that is why you will feel trapped or suffocated if you play heavily sub ranges music long enough in the car.

 

Now, to perhaps end the science part and put it in the correct frame, the 1000+ you probably have read is in fact a measurement of speed of sound in FEET.

 

And also, at 100 deg celcius, which is the existence of all life, the speed of sound is in fact at 392.4m/s OR 1287.401 FEET.

 

So you see, the temperature does have effects on the sound (quality as well) that comes to our ear. Generally at home, the ideal temperature is in fact residing somewhere between 24 to 26 deg celcius, the range where you will find comfort in listening for hours without feeling fatigue. Likewise, this can also happen in the car as well. Cheers.

Edited February 16, 2006 by Sarong1

[Darkness]

icic thats interesting well aniway as i had said me not sure about the acoustic part just trying to relate wat i know abt sound with wat u posted.

 

sorry if i have disturbed ur posting

[Sarong1]

Hey, this is what the forum is about, a forum is a "place" where ideas are shared and discuss, no one dominates the forum or thread.

 

In fact, you have helped me opened up more details and led me clear some ambiguous portion to the topic.

[Darkness]

[K2000]

haha, exactly same article i saw few months ago, the world is round

 

anyway i dont understand

[Sarong1]

Hope I didn't duplicate any threads here though. I didn't remember seeing threads of this sort, so, just wanted to share and deepen our knowledge lor...

 

But I definitely like it this way, we discuss , we throw in more ingredients and meat to the threads, that will make the forum attractive and not the reverse .

 

As mentioned by one of our members, we MAKE LOVE, NOT WAR

[K2000]

This article i not saw from this forum, probably other ICE forum not in SG. so surprise

[Hyun]

i dun really understand this part of physics any more but let me just ask this:

 

what u're assuming is that the space available for the wavelength MUST be present in the car, whether it is in a straight line, or in a bounce.

 

a WAVElength is the distance required for the sound to complete one wave. a sound traveling to your ear can complete the wave over TIME. whether there is enough space in between your speaker and your ear or not, first, the speaker will push the air from the zero line to the apex of the wave, back to zero, then back to the other apex below zero. that wave travels to your ear, pushing your eardrum and you hear it. whether there is 1 foot or 10 feet between the speaker and your ear, the sound wave is pushed in the same manner by the speaker driver, and arrives at your ear doing that exact same wave pattern. the wave pattern (e.g. sine wave) has been reproduced at your eardrum OVER TIME. your ear drum starts from 0, goes to maximum excursion at the apex, returns back to zero, goes to negative excursion.

 

when u listen to a high frequency wave, your eardrum just vibrates to that high frequency. each waveform completes its cycle in a very short time. low frequencies just take a bit longer. either way, your eardrum moves over TIME with the air pushed out by the driver.

 

the confusion seems to lie in the concept about the length / size of the enclosed listening area (the car cabin). again, i've forgotten this part of physics, but what u are referring to here seems to be the resonant frequency of a container. a large container would have a different resonant frequency compared to a small container. dun think this applies to the ear hearing a sound wave emitted from a speaker, all while enclosed in the cabin.

 

pls correct me if i'm wrong.

[Sarong1]

Let me try to put it in a simpler manner. We know that sound behaves in the same characteristics as light, in that, they travel in a straight line. But sound propagates and each freq displays different wavelength, which is represented by Hertz.

 

So, how can a 20Hz freq be reproduced in a car that lacks the length for it to effectively completes a cycle? And how come we at times claim that sub can actually performs and we hearing it at that range? Well, the article has explained it though.

 

There is no confusion at all if you understand why the arguement was put forth. The article above has already explained in clear the condition and length at which the lower freq transverse. The article was citing audio within a car acoustic, but of course, acoustic in a container will be another different calculation afterall.

[Hyun]

hi sarong, yup i got ur message. the formula isn't wrong but i think the application of it isn't quite right in this setting. as i attempted to allude in the previous post, my main contention is that the "wavelength" variable in the equation is *not* referring to the space required to reproduce a sound.

 

as i tried to graphically describe, sound produced at a point, travels to the next point thru a medium like air, going through its waveform changes, and completes the cycle over time. e.g. a 20 hz wave completes 20 cycles in 1 second. as the air reaches your ears, it makes ur eardrum vibrate 20 times within one second, that means it completes its cycle in 1/20 of a second.

 

it can complete its cycle *despite* having not travelled its entire wavelength! that is the contention. it does so because this wavelength minimum distance is in fact not a pre-requisite. check out that "example" i mentioned, try to imagine it ..

 

and correct me if i'm wrong again.

 

______________

just thought of another analogy.

think of the Kallang wave at the stadium.

wavelength is the distance a person can walk while doing the Kallang wave while walking.

however, to feel the kallang wave (listen to it) u dun have to walk. u sit beside one person who's doing the wave, he stands up and down doing the wave, and u can feel it. even though the wavelength is longer than the distance btw your body and his (the emission point), the wave is transmitted irrespective of the distance travelled. you FEEL the increase and decrease in amplitude of his wave.

Edited February 17, 2006 by Hyun

[Wankie]

cheem man

[Hyun]

i like physics, and i like all these for fun discussions. but i've been out of touch with physics for a long time. based on what i remember, this is the idea lor, but whoever's more up to date please correct us ...

 

the idea about wave propagation is that the air particle itself is not flying the entire distance. it's vibrating due to the vibrations of the neighbour particle. the vibrations have an amplitude (the extent of movement from its original position) and to generate a wavefrom, all it needs to do is go through the sine wave form of its frequency, without needing to move through any distance. therefore the air is stationary. any distance doesn't matter. a 20 hz wave just means it's a slow wave and the air moves thru its amplitudes slower than high freqs.

[Wankie]

sorry boss, i arts student, my physics all give back teacher liao not that i was paying attention anyway in physics class since teacher not

Edited February 17, 2006 by Wankie

[Jeffteng]

WAH RAO bro , i read the second sentence only and see so many tech specs and details i headache liao~~~ kekeke