Receivers v amplifiers

Power output & Speaker load

Speakers A, B, A+B

Separates

Loudness buttons

Bi-amping

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

- Receivers v amplifiers back to menu

An amplifier is exactly what it says it is. It amplifies a signal by adding current to it and sends it to the speakers.

A receiver is a combination of components in one box. Thos components are at a minimum an amplifier, a pre-amplifier and a tuner.

Receivers have become the norm in Home Theatre applications and have become very common even in the purists world of HiFi stereo.

 

- The Relationship of Voltage, Loudness, Power and Decibelsback to menu

Loudness, to a great degree, is subjective. What is loud to one person is not to another. Thus we need a measure that allows us quantify what we hear. The unit of measure most common is the decibel (dB). Most audiophiles are familiar with the term, but just what does it actually mean? Without getting too technical, the dB is a unit of measure for sound intensity or level. It is a logarithmic scale developed to express wide ranging quantities on a simple scale. Because it is logarithmic, it can be a little bit confusing. As an example, a doubling of volume is not equal to twice the number of dB. The chart below will help you to better understand the dB and how it relates to what you hear, and what is happening throughout your system as volume levels change. But first, we need to look at the other end of the equation.

Power, in this discussion, refers to watts. Power defined is the rate at which energy is converted or dissipated, as in the case of an amplifier driving a loudspeaker. It is important in our discussion in defining the general relationship.

A simple chart will help to understand the relationship of the terms we have introduced:

dB Change Voltage Power Loudness
3 1.4X 2X 1.23X
6 2.0 4.0 1.52
10 3.16 10 2
20 10 100 4
40 100 10,000 16

Looking at the chart, and starting at the left, we can see than an increase of 3dB results in a voltage increase 1.4 times the original, a doubling of power, and yields only a subjective increase in loudness only 1.23 times the original. To get a doubling of loudness, it is important to note that an increase of 10dB is necessary. And to reproduce that volume through our loudspeakers, note that we require ten times more power from the amplifier!

The implications of this comparison in a typical hi-fi system is significant. Let us assume that you are listening to your stereo at a comfortable volume of 8OdB. We will further assume that this level requires 25 peak watts from your amplifier. To just barely increase the volume, we might increase loudness by 3dB. As we can see from the chart, this will require a doubling of power from the amplifier, which will now be churning out 50 peak watts to produce a loudness of 83dB. If we want to double the apparent volume from our original level we will need to create 9OdB of sound pressure, requiring 250 peak watts.

It is obvious from the example above that adequate amplifier power is necessary to provide an accurate portrayal of music. This is especially true when attempting to reproduce realistic levels, or when driving inefficient speakers. However, even small efficient speakers may require copious amounts of power to cleanly reproduce transient peaks. In the final analysis, it is difficult to have too much power. While a small amplifier of only a few watts output can produce surprising average loudness, the dynamic peaks will usually suffer unless the sensitivity of the speaker is very high.

Many we speak with are concerned with having "too much" power. The perception is that an amplifier with an output greater than that recommended by the speaker manufacturer would be likely to damage the speaker. This is not necessarily so. Interestingly, an under powered amplifier is more likely to cause speaker damage! Audio Junction see more speakers (tweeters/midranges) damaged from use with under powered amplifiers than ones that succumbed to being overdriven. Sound strange? Not really, once you understand what is happening.

When an amplifier is over-driven, it "clips" the wave-form. What was a clean sine wave becomes a distorted, almost square, wave. The area under the the sine wave describes the power required, when the power required exceeds that capable of being delivered by the amplifier, the process of "clipping" occurs, whereby the tops and bottoms of the waveform are chopped off as the amp runs out of puff. This results in an almost square waveform being sent to the speakers. A square wave is extremely difficult for a speaker to reproduce, as it requires virtually instantaneous starting and stopping of the diaphragm. At sufficient power levels, the tweeter will simply die trying to reproduce this wave-form. A given tweeter rated to handle 50 watts of clean undistorted sine-wave power, will be capable of handling only a fraction of that amount in square-wave input.

As you can see, clean, undistorted power is the key. A 25 watt amplifier, constantly driven to clipping, is more dangerous than a 250 watt amplifier that is never taxed. Of course, let reason prevail. We are not saying that speakers can handle endless input, they cannot. However, extra power does not mean that speaker damage is bound to occur. If common sense is used, any size amplifier can be employed.

Many factors influence amplifier choice. Some of the more important considerations are: speaker type (efficiency or sensitivity), room size, the type of music you listen to and, most importantly, how loud you like to listen and even how far one sits from the speakers. In an extreme example, one might own an inefficient loudspeaker, have a very large room, and like to listen to pipe organ music at realistic levels. This individual is going to require a tremendous amount of power to satisfy his/her needs. The next listener, with the same speaker, may have a much smaller room, and prefers chamber music at background levels. Here, power requirements might be only one tenth to one-fourth those required in the previous illustration.

Requirements do vary widely. It is wise to take all factors into account before making a decision regarding the amount of power necessary for your situation.

 

- Power output & Speaker load back to menu

From the article above we can see the effect of amplifier power output, but one of the things people regularly try to do themselves without understanding the theory, is to add more speakers to their system in the belief that this will make it sound better or louder.

Simply daisy-chaining additional speakers onto existing speaker cable runs does not have the effect of doubling the loudness of the speakers. The first thing that will happen is the current will preferentially flow through the path of least resistance, so one speaker is going to get more power than the other and therefore try and do more work. Secondly you are altering the  load on the amplifier. This is a good way to pop an inexpensive amplifier without decent protection.

 

- Speakers A, B, A+B back to menu

Many receivers and amplifiers offer two sets of speaker binding posts on the back of the amplifier. These are known as Speaker A and Speaker B outputs. Different brands are wired differently internally so it is a must to speak to the staff at Audio Junction before attempting to use both sets of binding posts. You may find that the speakers you intend to use are to great a load for some amplifiers because of the way they are wired. Some amplifiers may not support a different impedance for the second pair of speakers.

Always be careful when using volume controls on speaker A and B outputs, impedance matching is often required to avoid amplifier damage.

The speaker selector is usually on the front panel of the amp. They usually allow you to select from either set of speakers or both. The maximum volume on both sets of speakers may be lower when using speakers A+B

 

- Separates back to menu

In audio circles the word "Separates" means purity and purposefulness. While for convenience and simplicity many devices have been combined into one to form very powerful and capable receivers for home theatre and HiFi use, there is always acompromise when individual components are made to share, whether it's space inside the skin, or power supply, there is always noise generated. Separates are the purest form of devices. Here you have a separate pre-amplifier, another device is just a power amplifier etc.

With separates each device is the best of it's breed. It has no compromises with power supplies. Each chassis is individually isolated so there is no crosstalk between it's innards.

Finally apart from anything else, there is a certain pride in ownership of a sports car because it's a thoroughbred. The same goes for separate components.

 

- Loudness buttons back to menu

One of the most dangerous buttons known to man. This button should be bright red with yellow and black safety stripes around it.

Here's what it's used for. As you turn down the volume to background listening levels the first thing that drops off is the bass response. Pressing a loudness button gives an increase in SPL mainly driven by an increase in the bass response. Essentially the amplifier is "pumping up" the bottom end so the sound isn't so thin and tinny. This is great if you like that sort of thing and your amp isn't capable of managing the situation itself, but the trouble really starts when you turn the volume back up. Perhaps the kids fiddled with the knob while it was off? Who knows why it happened but somehow the amp got turned right up with the loudness button pressed....then the speakers started to sound rattly and mumbly...sort of muffled like talking through four pairs of socks.

Closer inspection will reveal the speakers have divorced themselves from their surrounds and are waving their tattered cones around. At least there wasn't any acrid smelling smoke issuing from the amplifier....or was there?

 

- Bi-amping back to menu

Bi-amping is the use of multiple power amplifiers to increase the power available to drive a given loudspeaker. While tri-amping is possible, let's stick to bi-amping for the sake of clarity.

In this example the signal output from the pre-amplifier is split and given to two separate power amplifiers. This can be two separate devices or two separate channels within a multichannel power amplifier.

From each amplifier a set of speaker cables is run to the speakers and attached to the two sets of binding posts on the back (bi-wiring technique).

The result of this is usually dramatically improved bass response and a general opening up of the soundstage as well as a noticeable improvement in detail.