Sources such as highway noise or railroad whistles can vary widely depending on the receptor's location. Longer-range diffraction also occurs due to changes in the density of the air.
My experience is that this feature is not recognized by noise mediation experts or local officials. It is more quiet near the wall than away from it. The second is due to the diffraction of sound over the wall.įrom Wikipedia (Wavelengths), "The wavelengths of sound frequencies audible to the human ear (20 Hz–20 kHz) are thus between approximately 17 m and 17 mm, respectively." The low frequency sounds bend over the wall and return to the ground. Enright's answer addresses the first, taught us a lot, and answered the basic question. If we are close to the highway (perhaps a few city blocks) and separated by a cement sound wall, we primarily hear the lower-pitch rumble. So if it sounds like high frequencies travel farther with headphones, it's because headphones are poor at producing low frequencies and your ear is poor at picking them up.Īt some distance from a highway, what do we hear? We hear the lower-pitch rumble enhanced over the higher pitches. Even a good pair of headphones like Sennheiser HD-650 struggle with lower frequencies: For low frequencies subwoofers are large and have a resonating chamber which simply isn't an option with headphones that must produce a large range of sound frequencies in a small space. With loudspeakers you can split the job of producing frequencies among a subwoofer, a midrange speaker, and a tweeter. Headphone sound is doubly compounded by the difficulty of making headphones with good low-frequency response. Even if the low frequencies are reaching your ear, it's harder for you to hear them. All the sound along a curve is of "equal loudness" but as you can see, low frequencies must be much more intense to sound equally as loud as higher frequency sounds.
#Sound diffraction in doorway vs frequency iso
The red lines are the modern ISO 226:2003 data. The curves that show human hearing frequency response are called Fletcher–Munson curves: Instead, the frequency response curve of the human ear plays a big role in perceived loudness. Headphones start off at such low intensities already they don't travel long enough distances for attenuation to be a dominate factor. The above description apply to sounds that travel either through long distances or are otherwise highly attenuated. This is and frequency-based attenuation are why low-frequency sounds are much easier to hear through walls than high frequency ones. High frequencies are better reflected whereas low frequencies are able to pass through the barrier: That graph comes from this extremely detailed article on outdoor sound propagation.Īnother effect that affects sound propagation, especially through walls, headphones, and other relative hard surfaces is reflection. This means low frequencies will travel farther. Here is a graph of the attenuation of sound at difference frequencies (accounting for atmospheric pressure and humidity):Īs you can see, low frequencies are not absorbed as well. See Wikipedia for the technical details and formulas of acoustic attenuation. The attenuation of sound waves is frequency dependent in most materials. Because of this, sound is lost to heating of the medium it is propagating through. Whenever you give molecules a "push" you're going to lose some energy to heat. Remember, sound is a pressure wave vibration of molecules. If it weren't for attenuation (absorption) sound would follow an inverse square law. The reason has to do with what's stopping the sound. I found this rather cute high school experiment online, which seems to conclude that low and high frequencies travel as far, but aren't there laws that physicist wrote centuries ago about this?ĭo low frequencies carry farther than high frequencies? Yes. Perhaps also the low frequencies resonate with the walls of the building? Probably also the medium the sound travels through makes a difference? Or perhaps high frequencies are reflected more by walls than low frequencies? This makes me think that perhaps low frequencies do not carry longer distances, but the very high amplitude of the bass in my neighbor's speakers compensates for that. So with very weak sounds, high frequencies seem to travel further? When I sit next to an unamplified turntable (the disc is spinning but the volume is turned off), I hear high pitched sounds (tchts tchts), not the bass.When I stand near someone who's listening loud music in headphones, it is the high pitched sounds that I hear (tchts tchts), not the bass.Try asking people around, a lot of them believe that low sounds carry longer distances.īut my experience isn't as straightforward. Indeed, the bass is really what you hear when the neighbor plays his HiFi loud (Woom Woom). It is a common belief that low frequencies travel longer distances.
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