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Discussion Starter #1
excluding subs, why would you want to give any speaker in your car 150 watts of power?
if, for example, you have a speaker that has an efficiency of 89dB, by the time it hits 150 watts it will be playing just below 111dB at 1 meter

why would you need that much wattage? I already know that I am missing something in my thinking, I just dont know what.

I found a thread yesterday in my searching, where a diyma forum member mentioned that he always gives his mid bass speakers 350 watts, and I could not understand why.
 

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Well one thing to keep in mind is that your speakers are rarely seeing all that power during music, unless you enjoy listening to 0db test tones. ;) So while it might have the potential to play at 111db, it will rarely get that loud during normal listening. There are some here (myself included) who enjoy their music quite loud. That being said, headroom is also nice to have. It keeps your amp from having to work as hard and maintains a clean signal to the speakers. So although someone may have 350w/ea on tap for his mids, it doesn't mean the mids are always seeing that power, or even close to it.
 

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He probably means he utilizes a 350wpc amplifier, but not necessarily that his speaker sees that on a continuous basis.

In the car you also typically have a variety of obstruction and off-axis positioning that results in reduced sensitivity and output as well, not to mention the way alot of people advocate setting their gains at a 1:1 ratio the amplifier is almost certain to never see maximum output.
 

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Discussion Starter #4
what do you mean by setting your gains on a 1:1 ratio? do you mean setting them using a 0dB tone?
 

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Extra watts for power supply current headroom.

Audiograph - Home of the PowerCube

"The PowerCube Measuring System and the "Dynamical Loudspeaker Impedance"


What Makes A Good Amplifier?

Ideally, an amplifier is a perfect voltage generator. In other words; for any given input, the amplifier should maintain a constant output signal, regardless of the connected load.
For example, if an amplifier has a nominal output of 100 watts at 4 ohms, you would expect it to maintain the same output voltage at 2 or 1 ohms as well.

Reducing the impedance to 2 or 1 ohms should produce an output power of 200 and 400 watts respectively, at a constant undistorted output of 20 volts.

An amplifier that does this is of course what we are aiming for. However, the load that we will be connecting, the loudspeaker, is not a simple resistor, and this complicates the amplifier’s task of producing a constant and undistorted output signal.


The Dynamical Loudspeaker Impedance

You are probably aware that a loudspeaker, from an amplifier point of view, does not just act like a resistor. A loudspeaker construction also contains capacitive and inductive components, and the amplifier must be able to handle not only resistive, but also capacitive and inductive loads.

We performed a simple test to illustrate how a complex signal affects the loudspeaker’s behavior:

http://www.audiograph.se/images/oldwebimages/diagram.jpg

The upper graph illustrates the conventional way of measuring the loudspeaker impedance.
The lower graph illustrates the dynamical approach.

We took a commercial ’off-the shelf’ loudspeaker and did a standard impedance plot for it. We swept the frequency from 20 Hz to 20 kHz, measured the input voltage and current, and calculated the impedance.

However, instead of using a sine wave input signal, we used a square wave. The reason for this is that square waves consist of a large amount of sine waves, as does music. The square wave is of course not an equivalent of music, but for this test it was an easy way of showing that a complex signal (not just a simple sine wave signal) may make the load, from the amplifier point of view, very low.

If you study the graph resulting from the test, you will probably agree that not only is it necessary to check the amplifier’s behavior for resistive, capacitive and inductive loads – the amplifier should also be checked for loads with lower impedance than the nominal impedance of the loudspeaker.

This proves to be very important, since a loudspeaker with a nominal impedance of 4 ohms will sometimes have an actual impedance of 1 ohm or less. The PowerCube helps you perform testing of an amplifier, taking all these load attributes into consideration.



AND just as important: The phase angle of the speaker which can move the actual wattage being used from the speaker to the amp. The amp just turns that power to heat and the speaker hardly get any of it.

Phase Angle Vs. Transistor Dissipation
 

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AND just as important: The phase angle of the speaker which can move the actual wattage being used from the speaker to the amp. The amp just turns that power to heat and the speaker hardly get any of it.

Phase Angle Vs. Transistor Dissipation
That was very informative, thanks for the link. I forgot about his site, and will read more later.

But that doesn't really apply to the OP. He isn't designing amps or passive crossovers.
 

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That was very informative, thanks for the link. I forgot about his site, and will read more later.

But that doesn't really apply to the OP. He isn't designing amps or passive crossovers.
It does actually, he was wondering why would you put so much wattage on a speaker. The max wattage typically isn't being used (voltage output wise) but the max power supply current is used, so that would be a reason why bigger amps then needed could be useful.
 

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Discussion Starter #8
so what I have gathered from this so far is that if set the gain on my amp going to my 150 watt rms mid with 0dB tone, I am essentially setting the amp's output to a max of 150 watts, since since 0dB is at the max of the dynamic range of a cd.

does that sound right?

so I would have to set the amp gain at 0dB to a wattage considerably higher to actually have my mid see 150 watts on average.

this to me then begs the question, what is a safe average dB I can assume most music is recorded at these days, taking the loudness war into consideration?
 

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so what I have gathered from this so far is that if set the gain on my amp going to my 150 watt rms mid with 0dB tone, I am essentially setting the amp's output to a max of 150 watts, since since 0dB is at the max of the dynamic range of a cd.

does that sound right?

so I would have to set the amp gain at 0dB to a wattage considerably higher to actually have my mid see 150 watts on average.

this to me then begs the question, what is a safe average dB I can assume most music is recorded at these days, taking the loudness war into consideration?
This question is the very reason nearly everyone on this site sets their gains by ear. Use the loudest CD you have (this one will probably have the least dynamic range) and turn up the gain until you hear clipping, the speaker reaching its limits, or its loud enough for your tastes.

Also the big benefit to high power amps is headroom. If your amp is not operating near its limits it will have lower distortion, better dynamics, and run more reliably.
 

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so what if you have an 800 watt 4 channel amp, and each channel has a 150 watts max mid driver?
wont your amp put out less watts anyways because most speakers are 4 ohm? i still dont understand all this
 

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Why use a huge amp you don't really need?

You can buy a crappy-er amp since you don't need headroom at max output, because you will never max the amp out and near any amp will have 'headroom' if not stressed. (so it does not need to be underrated)

You never have to worry about the amp distorting, because you will not reach that level of output. (I'd say the best reason)

Its cool to have huge amps, cool to say and cool to look at in the car. (can't argue that)

They have multiple use; you can use your huge mid amp to run subs in a pinch.

You don't need to bridge things. (actually bridging can introduce error into the signal, but if you can hear it is another matter)

Will it sound better? I doubt there is much difference due to the actual output capability of the amp if you don't exceed it. A fair quality or better amp should easily amplify the signal correctly below clipping...even most cheap amps.

Setting gains by ear is right, because it does not matter anyway...once you set all your amps to max you will have to go back and turn down the ones that are too loud....only one will be maxed out at your setting unless you somehow matched all your amp sizes perfect and I doubt that is possible. Also remember twice the watts is far from twice as loud.

In a nut shell power use to music is a log scale, that means to go louder you need piles more power. Using a large amp means if you have it loud and hit a peak when you might need that extra power...it will play it true. 99% of the time you will use much less power. Get an amp meter and put it on an amp and play with it, you will find at half volume it hardly draws any power and at 75% and up it starts to eat the power.

Ohms is resistance, the less a speaker has the easier the amp pushes the power through the speaker....and creates more current in the amp that heats up parts and makes the magic smoke come out. In a car you have 12v and a lot of amperage, in a house you have high voltage and don't need as much amperage....thus low ohm car speakers.
 
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