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Go Back   Blu-ray Forum > Audio > Audio Theory and Discussion


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Old 02-10-2009, 07:58 PM   #1
Beta Man Beta Man is offline
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Default Air-Flow and Standing waves?

Does airflow, such as a ceiling fan, have a significant effect on standing audio waves?

Given the definition of a sound wave...

A sound wave is the pattern of disturbance caused by the movement of energy traveling through a medium (such as air, water, or any other liquid or solid matter) as it propagates away from the source of the sound.
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Old 02-10-2009, 08:19 PM   #2
jeff92k7 jeff92k7 is offline
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Airflow, as with temperature and humidity can have an effect on audio waves but the effect is very minor and typically is not something to worry about until you get into VERY large rooms (arenas). For a typical home theater, or even a full size cinema, airflow is not a concern.

In most cases, airflow from air handling systems or cieling fans is moving at such a slow rate that the audio will pass right "through" it as if it weren't moving at all.
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Old 02-10-2009, 08:39 PM   #3
Audiophile_At_Birth Audiophile_At_Birth is offline
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Quote:
Originally Posted by jeff92k7 View Post
Airflow, as with temperature and humidity can have an effect on audio waves but the effect is very minor and typically is not something to worry about until you get into VERY large rooms (arenas). For a typical home theater, or even a full size cinema, airflow is not a concern.

In most cases, airflow from air handling systems or cieling fans is moving at such a slow rate that the audio will pass right "through" it as if it weren't moving at all.
I beg to differ. Cieling fans do have a significant effect on standing waves or any sound waves for that matter. When I play my Sax in my room with the fan on, I get horrible sonic resonance from the horn and throughout my room.
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Old 02-10-2009, 08:55 PM   #4
jeff92k7 jeff92k7 is offline
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Quote:
Originally Posted by Audiophile_At_Birth View Post
I beg to differ. Cieling fans do have a significant effect on standing waves or any sound waves for that matter. When I play my Sax in my room with the fan on, I get horrible sonic resonance from the horn and throughout my room.
But how much of that is caused by the airflow and how much of that is caused by the sound waves hitting the fan blades themselves. I would argue that what you are hearing is the sound of the sax going up and hitting the fan blade one instant, then all the way up to the ceiling the next, and so on. In that case, it's not the movement of air that is causing what you hear. It is the fact that sound waves are reflecting off of a moving object.

You can hear this effect by speaking into the front or back of a box fan, or any other fan with a safety guard on it. (Never, ever get that close to a moving ceiling fan or any fan without a safety guard on it). In this case, you will note that there is only a very minor difference, if any, in sound between speaking into the front of the fan as opposed to the back. For airflow to have a noticeable effect, there would have to be a noticeable difference between the front and the back since sound is moving in opposite directions on each side.

I should have been more clear and noted that in my first post but since the question was about airflow affecting sound waves and not how the fan blades interact with sound waves, I failed to do so. I stand by my original statement that the moving air will have very little effect on the sound waves - standing or otherwise.

Last edited by jeff92k7; 02-11-2009 at 01:30 PM. Reason: Edit for clarity.
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Old 02-11-2009, 01:17 PM   #5
bluseminole bluseminole is offline
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Quote:
Originally Posted by jeff92k7 View Post
But how much of that is caused by the airflow and how much of that is caused by the sound waves hitting the fan blades themselves. I would argue that what you are hearing is the sound of the sax going up and hitting the fan blade one instant, then all the way up to the ceiling the next, and so on. In that case, it's not the movement of air that is causing what you hear. It is the fact that sound waves are reflecting off of a moving object.

You can hear this effect by speaking into the front or back of a box fan, or any other fan with a safety guard on it. (Never, ever get that close to a moving ceiling fan or any fan without a safety guard on it). In this case, you will note that there is only a very minor difference, if any, in sound between speaking into the front of the fan as opposed to the back. For airflow to have a noticeable effect, there would have to be a noticeable difference between the front and the back since sound is moving in opposite directions on each side.

I should have been more clear and noted that in my first post but since the question was about airflow affecting sound waves and not how the fan blades interact with fan blades, I failed to do so. I stand by my original statement that the moving air will have very little effect on the sound waves - standing or otherwise.
I don't know much about acoustics, but with all respect, I would have to agree that airflow does make a difference. When I play piano (a grand), it doesn't matter whether its open or closed, if the ceiling fan at the other end of the room is on, the sound seems to bounce all over the place and have the kind of "wahWAHwahWAH" effect, similar to the one you get when you talk right into an oscillating fan. It's quite noticeable when the fan is on high; turn the fan on low, and the effect disappears.

I don't know
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Old 02-11-2009, 09:39 PM   #6
hagar852 hagar852 is offline
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It is as Jeff explained it. Airflow doesn't affect the sound. It is the fan blades causing that.
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Old 02-11-2009, 11:50 PM   #7
Sir Terrence Sir Terrence is offline
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Quote:
Originally Posted by Audiophile_At_Birth View Post
I beg to differ. Cieling fans do have a significant effect on standing waves or any sound waves for that matter. When I play my Sax in my room with the fan on, I get horrible sonic resonance from the horn and throughout my room.
Standing waves are room related, and unless the room size is adjusted they re not altered by wind. What you are hearing are reflections from the fans blades, not the effect of standing waves. Your Sax does not go low enough in frequency to even create a standing wave in your room.
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Old 02-11-2009, 11:52 PM   #8
Sir Terrence Sir Terrence is offline
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Originally Posted by bluseminole View Post
I don't know much about acoustics, but with all respect, I would have to agree that airflow does make a difference. When I play piano (a grand), it doesn't matter whether its open or closed, if the ceiling fan at the other end of the room is on, the sound seems to bounce all over the place and have the kind of "wahWAHwahWAH" effect, similar to the one you get when you talk right into an oscillating fan. It's quite noticeable when the fan is on high; turn the fan on low, and the effect disappears.

I don't know
Once again, this a reflection off the fans, not an airflow issue. While wind can assist sound in traveling further if blowing hard enough, a ceiling fan can hardly achieve that.
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Old 02-12-2009, 12:00 AM   #9
hagar852 hagar852 is offline
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in comparison. Current doesn't effect ocean waves. In a room air flow hardly matters at all. The only thing that effects sound is other sound to interfere with it.
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Old 02-12-2009, 02:01 AM   #10
bluseminole bluseminole is offline
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I stand corrected. This is why I hang around forums...
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Old 01-26-2011, 05:28 AM   #11
Chamina002 Chamina002 is offline
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Default Air-Flow and Standing waves?

Hi there
I'm new to the forum. I also have something to add/ask. What about a fan blowing at 90 degrees to the sound wave/source. Will that affect the quality of the sound. We have two fans at the back of our auditorium blowing across the sound waves. Since installing the fans people have been complaining that the sound has become blurry or muffled.
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Old 01-26-2011, 05:51 PM   #12
drummerboy_2002 drummerboy_2002 is offline
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Quote:
Originally Posted by Chamina002 View Post
Hi there
I'm new to the forum. I also have something to add/ask. What about a fan blowing at 90 degrees to the sound wave/source. Will that affect the quality of the sound. We have two fans at the back of our auditorium blowing across the sound waves. Since installing the fans people have been complaining that the sound has become blurry or muffled.
Are the fans audible? Fans introduce white noise into the environment, which is great at masking detail.
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