I got this from www.AutoRadioStereo.com it’s a shop my friend owns here in Sacramento, CA.
Topic: How come some amplifiers are so cheap and others are so expensive?
Or, how come your 100 watts sounds better than my 500?
Ah, the mystery of amplifiers…
Watts, amps, distortion, impedance, ohms, clipping, voltage – all these wonderful terms that everybody seems to throw about like tissue in a hurricane, yet few really understand, including most salespeople. Installers, on the other hand, better understand these terms, or they have no right installing! In order to understand the answer to this month’s question, we first need to understand, simply, what these terms mean.
Watts – the measurement of how much work an amplifier can actually perform. We’ll come back to this in more detail.
Amperage (measured in amperes or “amps”) – how heavily an amplifier uses energy from the battery. Not to be confused with:
Voltage – the measurement of the amount of power available to a given electrical circuit. A car usually rests at 12 volts and will vary from 11 to 15 with the engine running.
Impedance – measured in Ohms, the load an amplifier “sees” from the speakers. Contrary to popular belief, lower or higher loads don’t necessarily have anything to do with being better or louder.
Distortion – the unpleasant sound generated by an amplifier running under improper conditions (see clipping). Although there are many claims as to amounts of distortion, there are also several types, such as harmonic and intermodulation, virtually all of which are inaudible at normal listening levels.
Clipping – what happens when an amplifier is pushed beyond its capabilities, causing unpleasant sounds as well as damage to speakers.
So, what’s all this mumbo jumbo have to do with how much power your amplifier puts out? Everything! Consider the following formula:
Voltage x Amperage = Watts
Simply put, the more power you have, and the more energy reserve you have, the more work, or wattage, without distortion, you can produce. Period. Some guy named Ohm came up with this and you can ask your favorite installer how it works if you want more details. Anyhow, this allows you to figure out how much power that “Great Deal” amplifier really generates. First, assume the average car generates around 13 volts from a stock alternator. Ever notice those fuses on the side of the amp? Those are not only designed to protect the amplifier in case something goes wrong, but also are usually a great way to gauge how much raw power that amplifier can produce without hurting itself. So, using our equation:
For an amplifier with a 10-amp fuse - 13 Volts x 10 Amps = 130 raw watts
For an amplifier with a 20-amp fuse – 13 Volts x 20 Amps = 260 raw watts
and so on…
And so forth and so on. Simple, huh? So, when you see that e-brand amplifier that says “500W” in big letters and has a 15-amp fuse, you know they’re full of it.
Remember, though, I said raw power, not maximum, peak or RMS. These are a little different. Raw power might also be listed as the Total System Power – a rating I’ve seen used countless times. You see, amplifiers don’t just create power to speakers but, as most of you know, they also create heat. So, while part of that power is going to the speakers, part of it is also just making heat. They have a specification for this, too – it’s called “efficiency”. Simply put, it’s the ratio, stated in percentage, of actual sound to heat, changing our formula to:
Voltage x Amperage x Efficiency = Peak Watts
Since the average amplifier is about 50% efficient, meaning it loses half of all the power it can make to heat, we can calculate for our 780-watt amp:
13 volts x 60 amps x 50% efficiency (.5) = 390 peak watts
Thus that 780-watt amplifier just became a 390-watt amplifier, peak power. A high efficiency amplifier, such as Zapco, can run as high as 80% efficient (624 watts); cheap amplifiers can be as low as 25% (195 watts). All because of heat! There’s no such thing as a 100% efficient amplifier. I wish there was!
But wait, there’s more. Now that you’ve discovered that that “800 watt” bargain basement amplifier is actually less than half of what you thought it was, we can really add insult to injury when we calculate the Root Mean Squared (RMS) power rating. All the fancy calculations aside, what this means to you is how much actual, all day long power your amplifier will generate without distortion or breakage. Fortunately, this also uses what we call a “constant” figure to make our lives easier. This figure is .707, making our new equation:
Voltage x Amperage x Efficiency x .707 = Watts RMS
Thus we can recalculate:
13 volts x 60 amps x 50% efficiency (.5) x .707 = 275.73 watts RMS
Wow, that amplifier, advertised at 800 watts, actually produces about 1/3 of its rated power! If we wanted to actually produce the true 800 watts, that same amplifier, according to our equation, would have to draw nearly 174 amps from you car at 13 volts! Since the average alternator only produces between 80 to 100 amps, this could be a serious problem, requiring hundreds, if not thousands, of dollars in batteries, caps, and electrical upgrades. Numbers never lie, folks. You can lie about the numbers, but the numbers never lie.
So, let’s put this to the test, shall we? First, let’s examine a Zapco Reference 350, rated at 350 watts, using a 40 amp fuse. Since Zapco amplifiers are generally pretty efficient – usually 70% or better – we can calculate the following:
13 volts x 40 amps x 70% efficiency (.70) x .707 = 257.35 watts RMS
Peak power is 364 watts, real close to what they advertise.
Now, let’s look at that “60w x 4” or 240 watt stereo in your dashboard. If you pull it out, you’ll find at most a 20-amp fuse in the back. Now, assuming that at least 5 amps of that is used to run the CD and tuner, you have a 15 amp circuit, with typical small IC amplifier efficiency of 50% (usually less). Therefore:
13 volts x 15 amps x 50% efficiency (.5) x .707 = 68.9 watts RMS
70 watts, divided by four channels is only about 17 watts per channel, or less than 30% of what you paid for! However, if you don’t perform all the calculations, using only the basic Raw Power equation, you get:
13 Volts x 20 Amps = 260 raw watts
or, about 65 watts per channel.
Let’s try another, shall we? A typical bargain amplifier I know of has “250w x 4” or 1000 watts written right on the box. However, in the amplifier itself are only 50 amps worth of fuses. Once again, if we calculate:
13 volts x 50 amps x 50% efficiency (.5) x .707 = 229.78 watts RMS
Divided by four channels, you get only 57.45 watts, or only 23% of what you think you paid for. No wonder its only $299.99
As if this isn’t enough, add in specifications concerning the type of testing used to confirm the numbers (What voltage? What frequency? With speakers or a dummy load? At what impedance?) and you can see how it’s real easy for the average amplifier builder to sell you one thing while producing something completely different.
What I’ve discovered is, that, for the most part, your better amplifiers run about a buck or more a watt. 300 watts should cost at least $300 – more if you want it to really sound good. Remember that $299 “1000 watt” amplifier? It’s really about 230 watts RMS, or, about $1.30 a watt. That 350 watt Zapco? $429.99, or about $1.22 a watt. It’s actually a better deal! The CD player? Even at a bargain price of $200, it’s about $2.90 a watt, but that also includes your source unit. See? It works!
Now, last but not least, what about that funny “ohms” stuff that everybody spews forth like they know what they’re talking about? Well, let’s put some myths to rest, shall we?
Myth 1: The lower the impedance (fewer ohms) the more power you get. This is only partially true. An amplifier produces what an amplifier can produce. If you take an amplifier with a peak rating of 100 watts at 2 ohms and make it see 1 ohm, it might try to produce 200 watts, but will probably break something, usually itself or a speaker or three, in the attempt. However, the same amplifier at 4 ohms will only produce 50 watts, with tons of clarity and dynamic range. That 100-watt amplifier is still only a 100-watt amplifier, no matter what the guy behind the counter says. So, you ask, what about those “cheater” amplifiers that claim to deliver 50 watts at 4 Ohms and 400 watts at ½ an Ohm? Simple, it’s a 400-watt amplifier built to run at ungodly low impedances. No magic, only physics. Each time you double the impedance you cut the power in half – not the other way around.
400 x ½ = 200 x 1 = 100 x 2 = 50 x 4
Like I said, numbers don’t lie. The only cheating going on here is when you pay $800 for a 400 watt amplifier that doesn’t sound as good as a cheaper “regular” amplifier.
Myth 2: Dual Voice Coil (DVC) speakers are louder because they make your amp work better. Also partially true. If an amplifier is 400 watts at 4 ohms, what configuration that 4 ohms is in is irrelevant. Two 4-ohm DVC’s, one 4 ohm, two 8 ohms, four 16 ohms, whatever, the amplifier still only creates 400 watts. Period. The only thing DVC speakers do is give a good installer more possibilities for system configuration.
Myth 3: A low impedance amplifier is better than a high impedance amplifier. Wrong. Watts are watts. More is always better. If you have 4 ohms in woofers and an expensive ½ ohm amplifier, what good is it doing? Buy a bigger 4-ohm amplifier; you get more power for less cash.
So, the message here? Buy power, not hype. Anybody can say they’re Superman, but can they prove it?