by Ron Kurtus

A total of 189 comments and questions have been sent in. They are listed according to date.

## List of next 10 letters

### Country

Sound Echoes Time intervals for an echo India

Sounds with Musical Instruments How do musical instruments make different sounds? USA

Sound Detection Trying to pinpoint source of thumping noises USA

Noise Cancellation Wants to cancel noise around house USA

Sound Amplified Over Water Sound of missing plane crashing Australia

Sound and Acoustics in Buildings Preventing sound from going out a music hall Tanzania

Sound Beats Couldn't hear beat frequencies of sound Canada

Sound and Obstacles Why aren't low pitch sounds blocked by walls? Canada

Noise Cancellation How do I invert a wave? USA

Sound Waves Why can't sound travel through a vacuum? Pakistan

Next 10

First 10 letters

## Time intervals for an echo

Topic: Sound Echoes

### Question

June 4, 2014

Dear Sir ,please help : A student stands between a bell tower and a mountain,distance on either side : 990 m , sound speed - 330 m/sec .Bell rings once but student hears twice, calculate time intervals for first and second time ,thanks and warm regards

manohar - India

25030

The first sound heard by the student will be in 990/330 = 3 seconds. However, the second sound will be heard in (990 + 990 + 990)/330 = 9 seconds. The sound must travel to the mountain (990 m + 990 m) and then back to the student (990 m).

## How do musical instruments make different sounds?

Topic: Sounds with Musical Instruments

### Question

May 29, 2014

my name is audrey h i was wondering if you would help me my question is how do a musical instruments make different sounds

audrey - USA

25002

Musical sounds are created by the vibration of part of the musical instrument. For example, the wire vibrates in a violin, the reed vibrates in a clarinet, and your vocal cords vibrate when you talk.

The thickness of the violin wire and how tight it is strung determines the musical note it will make. Likewise, you can adjust the tension in your vocal cords, as well as the shape of your cheeks to make different sounds when you sing.

## Trying to pinpoint source of thumping noises

Topic: Sound Detection

### Question

May 28, 2014

I am looking for anything that can pinpoint where thump, thump noises that I think I hear in all parts of my house on a regular basis, but not all the time. I hear it in all the rooms as well as in my garage - on a scale of 1-10, it sounds about a 2 to 4 - when I listen hard for it, it increases to about 3 to 5. Please help!

Stanley - USA

24998

Sometimes low frequency sounds from machinery or heavy construction a distance away can be heard in a house. Also, low frequency sounds from loud music can be heard in a house. It goes right through the walls. You've probably heard the boom-boom from music in some cars, even with their windows rolled up.

Another thought is some motor making the noise in your house. We once found a hunk or cardboard stuck to the furnace fan that was making a noise.

Try putting your ear to the walls in various places. Putting you ear to a drinking glass face down on the wall can help hear the sounds. This might help pinpoint the location.

Finally, this time of the year male woodpeckers are known to peck on houses to attract females. But they usually only do that in the early morning.

I hope these ideas help in finding the source of your thumping noises.

## Wants to cancel noise around house

Topic: Noise Cancellation

### Question

April 30, 2014

I am interested in using active noise cancellation to solve noise issues around the house. I'd like to discuss this with you and perhaps you can help or steer me in the right direction (folks working on product ideas, etc.).

Respectfully,

Brant Andrews

Brant - USA

24909

You can't really cancel out noise around the house except by using ANC headsets. Instead, you want to reduce the noise by insulation and buffering.

## Sound of missing plane crashing

Topic: Sound Amplified Over Water

### Question

March 26, 2014

URGENT Hi. My question is: Is it possible for the sound of plane MH370 crashing in the ocean be heard on land? I am asking this as I live in Western Australia near the ocean in a suburb called Ocean Reef.

Two weeks ago whilst I was watching TV at night, I heard an aeroplane flying followed by a huge 'thump'/ explosion noise and then no more flying plane. It scared me as I haven't heard anything like it before.

I told my husband the next morning of what I heard but nothing was said on the news etc until later in the day that flight MH370 disappeared.

When I heard that I was convinced it was the plane I heard. Everyone said its impossible as at that time they thought it was closer to Malaysia. But now that the rubble they have seen is 1,500 miles from Perth; is that possible I could have heard it?? How far can sound travel? Thank you

SOPHIE - Australia

24817

Certainly, it is possible that a plane crashing into the ocean could be heard a distance away, especially if it exploded. However, since sound spreads out with distance, its amplitude diminishes rapidly. Under some conditions, sound can seem amplified when passing over water, but that is usually for short distances, like on a lake.

If MH370 crashed 1,500 miles away, you really couldn't hear it. However, they aren't really sure what path the plane was taking. What you heard was strange. It probably could be a coincidence, but it would be nice to know caused the explosion sound you heard.

## Preventing sound from going out a music hall

Topic: Sound and Acoustics in Buildings

### Question

December 17, 2013

How is it possible for a sound(eg musical sound) to be heard in a certain hall or building but when standing outside of that building can not be heard at all...
Thank you.

Emmanuel - Tanzania

24338

Many music halls have sound-absorbing materials by their walls, as well as thick walls that stop sounds from being transmitted.

However, much of the sound can go out the front doorway. To prevent that, the design of the doorway should be such that sound cannot go directly outside.

## Couldn't hear beat frequencies of sound

Topic: Sound Beats

### Question

October 17, 2013

Hi. Having trouble with the beat frequencies in sound page where it says click on the buttons below to hear the pure tone and the different beat frequencies, there are no buttons below. Would love to be able to see these if you have any help for me that would be great. Thanks.

24108

Thanks for pointing that out to me. For some reason the buttons and tones were deleted. I replaced them at Beat Frequencies in Sound, so they should work fine now.

Sorry for the inconvenience.

## Why aren't low pitch sounds blocked by walls?

Topic: Sound and Obstacles

### Question

September 2, 2013

So I had originally come to this page looking for an explanation as to why lower frequencies seem to travel through obstacles better than higher frequencies, in your article you described how ALL frequencies behaved and then gave what appeared to be arbitrary numbers concerning the percentage of higher frequencies being absorbed and lower frequencies being absorbed without giving any explanation as to why those particular frequencies pentrate better than the others.
Is there a particular reason for low frequencies behaving differently than higher ones or are they simply given larger volumes than the higher frequencies, because our ears detect don't detect lower frequencies as well as higher ones, allowing the bass to propogate through all matter further than the treble because it has more power?

23985

Low frequencies have much longer wavelengths than high frequencies. See Human Perception of Sound Frequencies for a comparison chart.

There is a relationship between the absorption of sound with wavelength and thickness of the material. When the wavelength of the sound is much greater than the thickness of material, very little is absorbed. The wavelength for the highest pitch key on a piano is about 8 cm, while the lowest pitch key is 12.5 meters. Thus, the lower pitch goes through a wall much more readily than the higher pitch sound from the piano.

Note: I will have to add a page on the site to explain this more.

## How do I invert a wave?

Topic: Noise Cancellation

### Question

June 15, 2013

If I have a specific frequency to cancel how do I invert the wave?

David - USA

23776

A pure single frequency would be a sine wave. If you shift the wave 180 degrees, the waveform is inverted, such that they will cancel out when adding together.

However, if the amplitude of the wave varies--as is usually the case--this simple technique may not work well. I'm not sure how the electronic circuitry compensates for changes in amplitude.

## Why can't sound travel through a vacuum?

Topic: Sound Waves

### Question

June 11, 2013

Why a sound cannot travel through vacuum?

irfan - Pakistan

23768

Sound is vibration of air molecules or other matter molecules. A vacuum has no matter to vibrate. Light travels through a vacuum, since it is the vibration of electromagnetic waves.

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