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U of MD question of the week

 

Silver Member
Username: Jakeyplaysbass

St. Louis, MO

Post Number: 564
Registered: Jul-05
for my physics class we have to do these questions each week and this weeks has to do with speakers/subs so i thought i would post it to get alot of answers.

http://www.physics.umd.edu/lecdem/outreach/QOTW/active/q242.htm
 

Silver Member
Username: Goatin

U.S.A

Post Number: 300
Registered: Jan-06
I have noo idea.. when you find out ^^bump this thread with the answer I am currious but I am betting on (b).
 

Gold Member
Username: Southernrebel

Monroe, Louisiana USA

Post Number: 2140
Registered: Mar-04

quote:

An audio oscillator/amplifier connected to the loudspeaker is turned on at the resonant frequency of the loudspeaker, about 36 Hz, so that the loudspeaker produces a large sound wave. The input to the speaker is several watts of power, and its efficiency is over ten percent at its resonant frequency, so it is probably putting out nearly one watt of audio.




10%+!!!!!
wow...thats one h3ll of an efficient speaker!
JL 13w6v2's are ~0.33% efficient.

oh yea...i bet the answer is it wont move. cause sound it a wave...not a wind. but sound can create a pressuring effect (SPL)
(dont quote me on that one :-))
 

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11124
Registered: Dec-03
the flame shouldn't really move, since the air is compressed and rarified throughout the volume of the room the speaker is in, assuming the speaker is in a sealed enclosure or infinite baffle.
Now if this were a ported box.. and the speaker were in front of the port it'd be a whole different story.

that's my guess.
 

Silver Member
Username: Redliner

Wilmington, Ma

Post Number: 714
Registered: Jun-05
i was just thinking the same thing marshall but for some reason i dont think that is the answer but I hope it is cause thats what I am going for
D my final answer lol
 

Gold Member
Username: Southernrebel

Monroe, Louisiana USA

Post Number: 2146
Registered: Mar-04
^yea...what glass said :-)

-thats pretty much what i was thinkin
 

Silver Member
Username: Baseball1187

Columbia, SC

Post Number: 577
Registered: Dec-04
if I remember correctly, from doing this in physics... the disturbance created will indeed put out the flame.

it comes from the relatively significant change in pressure that is characteristic of the longitudinal wave. Using a lower frequency tone furthers this, allowing the change in pressure to be more pronounced for a longer period of time.. if you were to plot pressure vs time, it would look like the sine wave on an interval of whatever frequency is being played.

so yes, it will put out the flame...

like Glass said... "that's just my guess"... but i think i'm right.. let us know
 

Silver Member
Username: Baseball1187

Columbia, SC

Post Number: 578
Registered: Dec-04
oh, well perhaps they are assuming the change in ambient pressure wont be significant enough to put the flame out. but it will dance!
 

Silver Member
Username: Jakeyplaysbass

St. Louis, MO

Post Number: 566
Registered: Jul-05
my subs put the flame out but i think its because of all the air from the ported box.
i was actually thinking D as well im hoping my teacher will go somewhat into detail with an answer if so ill make sure to pass it on.
 

Gold Member
Username: Mikechec9

Http://www.cardomain.c...

Post Number: 2139
Registered: May-05
Easy. C

Sound pressure will induce rarefaction, moving the electrons outwards. This, like-wise induces a push also outwards against the flame. The subsequent compression (if wired in phase) will pull the flame in the opposite direction.
At 36 Hz, you are looking at wave lengths in excess of 9.5 meters. So the crest and troughs of the wave won't have any effect on the oscillation of a flame that close to the source. The axis/nature of the wave is thus a moot point. The only factor left is the pressure of the air molecules being moved against those of the flame. Hence, C

(I'm no gambling man, however):-)
 

Gold Member
Username: Chaunb3400

Huntsville, Alabama U.S.

Post Number: 5432
Registered: Jul-05
^^^Teacher,,Hint,Hint...lol
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