re: Audiophile/Vinyl Thread - Post Pics, Advice, Questions, Setups, etc.

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AUDIO 101---Volume 2...Not All Watts Are Creates Equal...





So now you are looking for a receiver/power amp to drive your speakers. How much power do you need? How does wattage translate into sound and loudness?

An amplifier has a direct relationship with the speakers it is connected to. It is a two way electrical highway, so to speak, between the two, and the two directly affect each other.


Power in an amplifier's output is expressed in wattage, or watts per channel (WPC). The amplifier's design and circuit topology have a ton to do with how an amp sounds and how it uses it available power.

The real muscle of an amplifier is it transformer, or power supply as it is sometimes called. In many of the mass market receivers, the internal case is so stuffed with boards and decoding chipsets for all the latest Dolby, DTS, Bluetooth, wifi, display panels, and all the other bling that gets people's attention, they leave very little room for a hefty transformer.

THE TRANSFORMER IS THE LIFEBLOOD OF ANY AMPLIFIER!!!

If you have ever been around high end audio and picked up a piece of gear, you will notice just how heavy it is. Half of the weight of a solid powerful amplifier is the power supply--it is what feeds the power stages.

I will say that there is very, very little difference in a 60 WPC and a 120 WPC "Best Buy" receiver because inside the case, they both use the same power supply (not all, but most). It is a marketing ploy. Now, if the power supply is double the size, there may be a difference.

Power ratings and WPC became all the buzz in the '70's because back in this time, speakers were very inefficient and amplifiers just did not have the power we see commonly today. In 1972, a 100 watt amp was a beast!...and expensive. Speakers with an 88dB rating were considered very efficient. It is this reason that many audio manufacturers touted their new models WPC ratings so frequently--very powerful amps were rare and expensive and it took every last bit of power from them to drive the inefficient speakers of the day to consistent high volumes without distorting.

Today, this is not the case, however. I like to parallel it to horsepower in cars. Back in the '70's and '80's, a general family sedan (not a Hemi Cuda guys!), was lucky to get 100HP under the hood. Every last HP was important and made a difference. That is why your dads always asked about HP in a car.
Today, a Toyota Camry is pushing 300HP!--My point is that autos have become more efficient and better built and all accelerate pretty darn well--But the old guys still love to ask about the HP!! --I am not talking about muscle cars and kit cars--just general purpose. Today, in a general utility car, HP talk is not that important to most buyers--they are more attracted to features, not motors.

Same with modern audio. Advancements in amp design make it easy and fairly inexpensive to get 100-200 WPC. BUT, keep in mind, that these WPC ratings can be manipulated to "look good" on a spec sheet.

Most "Best Buy" brands are marketed for the mass public that doesn't understand how this stuff works. They just see that Amp #1 is 80 WPC and Amp #2 is 120 WPC...so Amp #2 must be better and play louder--which is totally false.

An amplifier's spec data is determined from its time spent on the test bench. This is where an electrical "load" is placed on the speaker output terminals to determine power ratings. But, this can be done in different ways, and unless you know what you are reading, it may be deceiving.

Think of it like this...remember when the auto manufacturers used to give MPG ratings in the '80's?...they would drive the car downhill on a windy day with a 90 lb. driver and tires inflated to 50psi. to get unrealistic high numbers--no one back in the day ever got the MPG stated on the sticker (this was finally cracked down on though).

Well, mass market amp/receivers are speced the same way--under perfect, ideal conditions. The WPC spec is attained for an amp that can hold that # for a brief second. Then they can say "look! See here! we did it!"...what they don't like to boast is the high distortion levels and massive heat that built up doing this!

A well built amp will be able to hold those power ratings over the entire audioband (20-20,000Hz) for a sustained duration with very low distortion levels. These amps will have large transformers, and many heat sinks (the metal "fins" on the outside of an amp that dissipate the heat)--and do so without breaking a sweat and without distortion.

A Corolla and a Corvette will both go 100 MPH--one does it with ease, and can do it for hundreds of miles and has even more power to give, the other...you get my point.

When you get into higher end equipment, the power ratings tend to be realistic numbers. A well built 60 WPC amplifier from the likes of NAD, Rotel, Cambridge Audio, Emotiva, etc., will produce 60 watts of power output for hours on end driving a difficult speaker load with very little harmonic and inter modulation distortion.

Now, a 60 WPC Best Buy mass market amp?? No way...there is just not enough cost built in for nicer parts in these to achieve these results. Also, more is spent on "bells and whistles" which the average buyer is looking for, not transformers, heat sinks, silver wiring, thicker boards, etc.


So now---How much power do you need?

The answer to this is " What speakers will they be driving?" As I stated earlier, it is a two way street between the two. The speaker presents a "load" to the amp. How efficient a speaker is or is not, will ultimately determine how much power you will need (and how loud you listen and how big a room to fill with sound how far away you sit--to a lesser degree).

All speaker spec sheets will have an efficiency rating, expressed in dB...around 81 dB on the low end and 102 dB on the high end. Panels (Magneplanar) ribbons, and electrostatic speakers (Martin Logan) tend to be on the lower end of the scale, while single driver (a single full range speaker--like Zu Audio) and horns (think Klipsch here) tend to be on the upper end of the scale. A conventional cone speaker tends to sit right in the middle of the scale.

What does this mean? It means that the speakers on the low end of the scale will need a more powerful amp to achieve the same level output as a speaker in the middle of the scale being driven with an average power amp, and the speakers at the top of the scale will need a less powerful amp to do the same.

What does efficiency mean? What is that dB number?

This means that if you play a 1 kHz sine wave using exactly one watt of power from the amp and place a microphone 1 meter away from the speaker, it will produce ##dB of sound--it is an SPL (sound pressure level) reading. It is usually stated in this manner (ex: 91 dB @1W, 1m). This means the sound will be 91 decibels if you put your ear exactly one meter from the speaker.

A speaker that is less efficient may only put out 85dB of sound with one watt of power one meter away.






............................SEE BELOW FOR PART 2...