Need help with Power Amplifier selection, sifus advice welcomed
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 Sep 27 2009, 10:33 PM
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#1
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Senior Member
9,206 posts Joined: Jun 2006 
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QUOTE(htkaki @ Sep 27 2009, 10:27 PM) I've got an issue with the SVS MTS-01. My puny 4310 can't drive it efficiently. Luckily, help is on hand. My friend happily lend me his Rotel RB-1080 to drive it. Now, sonically better. Forward sounding, punchier bass note and expansive staging. Yet, not to the fullest yet. what;s the rated sensitivity?I suspect it needs something above 250W to make it work above 90%.  |
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Sep 27 2009, 10:53 PM
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#2
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QUOTE(htkaki @ Sep 27 2009, 10:49 PM) 87dB but impedance is 4~6ohms, which is quite pwr sapping even though its power handling is 20-250W. 87 is quite low to begin with.. When I ran my auddysey previously, it detects these as full range speakers. What I knew is that 4310 aint up to the task. Time to scout for beefy power amp liao.  |
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Sep 27 2009, 11:23 PM
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#3
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What is impedance?
Impedance is the extension of the idea of electrical resistance to AC signals (like music). In high school, we all likely learned Ohm's law at some time or another. Whether we remember it or not is another story! Luckily, the refresher course is easy. Resistance is a way of relating voltage and current in a simple DC circuit. An easy way to visualize voltage and current is to think of electricity like flowing water. Voltage is like water pressure: high voltage is akin to high water pressure, with lots of potential energy. Current is like water flow. High current is like a rushing river, low current is like a dribbling faucet. Electrical power (watts) is the voltage times the current. The resistance relates the current to the voltage though Ohm's law, V=I*R (where V is voltage, R is resistance and I is current). When the resistance is high, a high voltage is necessary to result in a given current, and vice versa. This is really all you need for DC circuits. Maybe they're nonlinear (i.e., the resistance depends on the voltage or current), but that's all. For AC signals, the situation is more complicated. The voltage and current are now sinusoidal signals. We need to keep track of both the voltage and the current, but now we need to also keep track of the phase between them. This is where impedance comes in. It is the AC equivalent of resistance, but also keeps track of the phase. We can still write V=I*Z, but now all three of the numbers are "complex" numbers, with a real and imaginary part. The real part of Z is exactly the same as the DC resistance. The imaginary part, called reactance, represents capacitance and inductance. A positive reactance is an inductance; a negative reactance is a capacitance. We can write this down either as a real and imaginary part (i.e. a resistance and a reactance), or as a magnitude and a phase angle. A phase angle of zero means all resistance. A positive phase angle means inductance, a negative phase angle means capacitance. For a speaker, this mathematical complexity is something we care about. An amplifier, or any electronic circfuit, prefers to drive a purely resistive load. The addition of capacitance and/or inductance causes all manner of frequency dependent changes, making a flat frequency response much more difficult to achieve. Unfortunately, speakers have lots of reactance. Most speaker drivers have big coils of wire in the drivers. A coiled wire is an inductor. Tweeters usually look electrically like capacitors. While most amplifiers are designed to deal with reactive loads, speakers that have low reactance will be much more kind to their amplifiers. Also, amplifiers are typically designed to drive speakers with 8 ohms impedance. If the speaker impedance gets too low, the amplifier might not be able to deliver enough current, and will clip. If the speaker impedance is very high, the amplifier might not be able to provide enough voltage gain to play loud enough. interesting read.. |
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