posted
how does more wattage increase the SPL? like i know it will increase excursion but is that the only way it makes it louders is having more power to push the sub further and increase excursion?
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When the sub moves farther, it displaces more air in the same amount of time, therefore creating a bigger difference in pressure from compression to rarefaction. This difference is your SPL.
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posted
If you take a 20hz tone and a 40hz tone, in the same second the 40hz moves the sub twice as much. That's what I've always heard.
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Spl is a measure of the rarifaction and evacuation of the air molecules on the leading edge and trailing edge of the sound wave respectively.
Increasing the power will cause the sub to respond more quickly further compressing the front edge of the wave and further decompress the air behind the wave. I personally think this is why you see a change not the excursion deal...
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posted
Ya I meant goina from a 20hz tone to a 40hz tone. Doesn't that move the sub twice as much in one second.
-------------------- Hello, my name is Danny and I am addicted to slurpies. Hey, wanna check out my sounddomain site? http://members.sounddomain.com/tocooldrw2 Posts: 425 | From: Port Orchard Wa | Registered: Jun 2003
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quote:Originally posted by tocooldrw: Ya I meant goina from a 20hz tone to a 40hz tone. Doesn't that move the sub twice as much in one second.
I see what you are talking about now, I think...
You are asking if the frequency of 40hz has the sub moving in and out 2x faster than at 20hz? The answer is yes, that is what frequency is, cycles per second. At 20hz the sub will move from rest, to excusion, back to rest, to incursion, and back to rest. That is one cycle. If the sub does it 20times/second it's playing 20hz. If the sub does it 40times/second it's playing 40hz.
Now if you mean "moves more" in refrence to excursion, then no. Say for instance a sub produces 150db @ 40hz. To do the same score (150db) at a lower frequency, say 20hz, the cone must excurt and incur 4x more than it did when playing the higher note.
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posted
SPL is a measure not only of sound pressure but also of immediate sound energy (notice it converts directly into sound intensity, which over time measures sound energy.) To impart the same amount of energy overall into a sound wave of frequency X which is half frequency Y, it takes approximately four times as much displacement to create the same intensity, thus imparting the same amount of energy over time.
Which means that the lower the frequency goes, the amount of excursion necessary goes WAY up.
ShadowStar
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posted
i guess the reason the sub moves more at 20 hz over 40 is because the sub doesnt have enough time to hit full excursion at 40 hz because its traveling back and fouth faster then the driver can allow for full excursion, when it slows down to 20 hz it gives the driver more time to move, i guess the port tuning could have something to do with this also. and i guess with more wattage there is more force on what the cone moves so just because it may not be moving at much it might have more power behind it, thats just what im guessing.
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quote:Originally posted by ShadowStar: Which means that the lower the frequency goes, the amount of excursion necessary goes WAY up.
ShadowStar
This would also explain why tweeters have such small excursions with such high frequencies. We all know this is because you cant move and control a large cone that fast without huge amounts of power and loss of sq. But I guess part of it also is that because a tweeter cone is moving so many friekin times per second, those small movements really add up, and equal the slower, larger displacements.
If a cone moves 1 inch (basically producing X displacement of air depending on cone size), 40 times in a second, it produces 40 inches of SPL in that second, lets say 150dB. A cone moving that same 1 inch, 20 times in a second, it only produces 20 inches worth of SPL, let say 100dB. So to get the 20hz tone up to 150dB, you have to either increase the length of the inches (longer excursion) or the amount of single inches (frequency - but that would change the tone).
Am I on the right track?
So where does this take place? Is the source wave all the same level and the amp lowers the amount of power as the freq goes up? Or is power constant and the source level goes down as freq goes up (like it's recorded that way?)
I would think everything evens out in the end, or else we would use 2000 watts for lows and 10 watts for highs.
Just my 2cents.
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quote:Originally posted by BrainBandAid: So where does this take place? Is the source wave all the same level and the amp lowers the amount of power as the freq goes up? Or is power constant and the source level goes down as freq goes up (like it's recorded that way?)
From reading thru this post I would have to say neither, they both stay the same (source level and power level). The reason the SPL goes down as hz decreases is because there is less rarification and evacuation of the sound wave (compression/decompression), thus creating less sound energy which is why excursion must increase to acheive the same level with a lower hz. With the longer waves there is less energy (intensity?) than with the shorter waves (not as much compression/decompression happening with the longer waves).
Also, one thing I remember is that watts aren't everything. JUST FOR AN EXAMPLE, NO MATH WAS DONE TO CHECK FOR # ACCURACY: Increasing your power from, say, 1000w to 3000w at say a 2ohm load to increase SPL may actually work against you because the increase in wattage also increases the heat, thus changing the impedence of your sub and again decreasing the power you just added. Say with the excess power your new impedence is 6ohm which causes your power to drop back down to 1000w and that money you just spent was worthless.
Hope this helps and anyone corrects my inaccuracies!!
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