posted
Just wandering, around the tunning frequency the cone motion is very little(in a good box) even past the speakers recomended power. the coil moves in and out of the magnetic gap at other frequencys and causes the nonlinear reactance. so it seems at the tunning frequency the impedance would be at a minimum which might suggest you could get a little more clean power out of your amp. But then I dont even know if what I just said is correct. Any thoughts?
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Posts: 1247 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
If you plot impedance vs. frequency response on a graph you will notice that impedance is actually higher at or around fs . There are a few exceptions to this, but for ported boxes, this is alomst always true . As for the statment about the coil moving out of the gap ? , well i havent seen a speaker play again after the voice coil moves out of the gap completly, it does however move within the gap, but just becuse the motion of the coil is small doesnt mean that the impedance will be low .
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Forget the bite, How loud can you bark ?
[This message has been edited by buggsz24 (edited 11-09-99).]
posted
Buggsz24 is right, the impedance goes up at resonance. In some cases the impedance rise is great enough that you could wire more woofers to the same amp safely. I recall a magazine article where the writer had a van with a bunch of 15"dvc's. He had two speakers for each amp wired to a 4 ohm mon load, he measured the impedance at his frequency and it was around 10 ohms. So he wired all the VC's in parallel for around 2.5 ohm mono when using the nominal rating gives you a 1 ohm load.
Because a speaker is an inductor (because it is a coil of wire around a magnet (iron core)) the resistance changes over the operating range, regardless of cone movement. The voice coil does not necessarily always move out of the magnetic gap, especially if the magnetic gap is large and the coil is not (bottomless design with magnetic center towards the rear).
The motor is usually capable of throwing the coil (part, most or all of it) right out of the gap, however. This happens when the speaker gets enough current flowing across the coil and excurts to the point where the throw is longer than the magnetic gap.
The resonance is the point where speaker impedance is highest. But, the output at this point is usually the highest (free-air) because at this point it takes the smallest amount of current to excurt the speaker at this point.
If you look at the ratio of power input to impedance of the sub, you will find that the excursion of the driver is almost constant (in most cases) relative to this ratio. (Check into this, guys)
At the resonance, there is a maxima of impedance. Therefore, that is the point where the driver gets the LEAST current flow. Were one to increase the voltage at that point (by EQ's or something), they could induce more current flow to achieve more excursion, because the driver obviously has flow left, plus the coil has a lot more dissipation ability because of the great reduction in power needed.
For all intents and purposes (going out on a limb here) the resonance is the point where the speaker is the most resisitive, AND the most efficient, of any point on the whole operating range. Therefore, yes, if you can drive more power (by upping the voltage) into the speaker at that point, the amplifier will find it to be the easiest load (speaking simply of impedance). However, amplifiers have a finite limit to their voltage output, meaning that across any given resistance, the total output POWER isn't necessarily the limiting factor.
Example- If an amplifier is rated at 1000x1 at 4 ohm, and outputs a maximum of 100 volts, and a MAXIMUM of 20 amps current, then at 4 ohm it will produce less than 100 volts, and less than 20 amps. If the load has a resonance of 20 ohms, then the amplifier can only generate a peak voltage of 100 v across that load, which only induces 5 amps of current flow, much less than the 20 that the amp could produce, and only 500 watts total. BUT, if you could generate a voltage of 400v, then you could induce the full 20 amps of current, and produce 2000 watts peak...
BUT, the voltage limits the output ability of the amplifier, in the above case. BUT, if the impedance of the load goes DOWN, the current limitation of the amplifier will limit the output power..
Is this fun yet???
BTW, if i've confused anybody.. Don't worry about it :-) Ask another question.
(p.s. I confused myself too. )
ShadowStar
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Computers are a lot like air conditioners.. Open Windows and they become useless..
The day Microsoft makes something that doesn't suck is the day they make vacuums.
Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999
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posted
By the way- The whole point in driving a speaker is to induce as much current across it as possible, without generating so much power that you smoke the voice coil. Current drives any conventional speaker, not power.
ShadowStar
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Computers are a lot like air conditioners.. Open Windows and they become useless..
The day Microsoft makes something that doesn't **** is the day they make vacuums.
[This message has been edited by ShadowStar (edited 11-10-99).]
Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999
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