When buying the equipment, it is important not to be deceived by the specifications.
To define the ideal power according to the size of the room or considering other home theater devices is not an easy task. This theme is among the champions of questions from all users. After all, what unit should have higher power: the receiver or the speakers? Can you rely on the specs published by the manufacturers? What is the relationship between the power amplifier and the sensitivity of the speakers? And what is the acceptable level of distortion?
The truth is that when it comes to power, values count for little. The fact that two devices are specified with the same power does not mean that both have the same output. There are a number of factors that weigh in the final result. Depends largely on how the power was measured and the recorded distortion. Remember: the higher the distortion, the greater the listening fatigue and worse the system performance. There are, for example, receivers and amplifiers that are capable of working with higher flow of electrical current and, therefore, can even exceed the performance of other who have higher power output. Therefore, always be suspicious of the numbers.
Power vs room size
When choosing the equipment, this question always comes up. The power can be measured in several ways. The most accepted standard is Watts RMS. Get away from other types of measurements, such as the so-called “peak power” (PMPO), very common in minisystems specifications and integrated systems in the past. Reason: showed high numbers, creating a false sense of quality.
Another problem encountered, mainly in integrated home theater, is the disclosure of the total power of the set only, not the power of each channel. Of course, when we sum power of all channels, the final number is used as bait to impress the consumers. Do not be fooled! Try to discover the power of each channel, information can be found in instruction manuals, usually available on the websites of some manufacturers.
In the case of receivers and amplifiers, check whether the measurement refers to the power got with only two front channels, or with all channels working together. Prefer the second option: the first will also result in higher numbers, but in home theater all channels are used simultaneously.
There are devices for all room sizes. In general, integrated home theater systems are designed for installation in rooms up to 15m2. But most receivers releases enough power to comfortably fill up rooms of 25m2. In larger spaces, the suggestion is to opt for a receiver to ouput from 120W per channel; the result will be even better if the amplifier(s) and the processor are separated devices, followed by speakers at the same level.
How the power should be specified
Receiver x integrated systems
It is an unfair competition. As much as they have developed in recent years, the home theater-in-a-box sets (HTBs) can not reach the performance of systems with separated receiver and speakers.
But is there a difference between a receiver and an integrated system with the same power? In practice, yes. It all starts in the design of each unit. Good receivers manufacturers use more sophisticated circuits and components that enable significant gains in performance (if the speakers are in the same pattern). And in general, products are built to last many years, also therefore are more expensive. As for the HTBs are mass products, manufactured in large quantities and where the cost factor is crucial. Usually they have a core module that performs multiple functions.
Furthermore, it is common that the HTBs manufacturers just specify the “peak power” of the product, based on the peak levels during a short time. It is more accurate to advertise the continuous power in watts RMS, as the most manufacturers of amplifiers and receivers do. In this case, the final value is a measure of performance of the device over a longer period of time (at least 5 minutes). Therefore, the specifications published in the integrated systems can not be taken “literally”. And that also applies to models with class D amplification (more efficient and less energy consumption).
Most HTBs offers passive subwoofer (no internal amplifier). Such subwoofers “steals” power of the central module, resulting in less bass impact and greater distortion. Thanks to its own amplification and the use of selected components, active subwoofers are the best option for those who want to enhance the reproduction of low frequencies.
Main differences between audio systems
|AMPLIFIER||PROCESSOR (PREAMP)||RECEIVER||INTEGRATED SYSTEM|
|Receives signals from the processor and uses the strength of electrical current to amplify them and send them to the speakers.||Receives signals from the sources (player, microphone, etc..) and sends them to the amplifier.||Amplifier and processor are together on the same device, which performs two functions simultaneously.||Includes receiver and also the player (DVD or Blu-ray), thus performing several functions at once.|
Power: Receiver x speakers
It is the main question for consumers: the power released by the receiver (or amplifier) should be higher or lower than that specified for the speaker? There is no consensus among market professionals. The majority suggests that the consumer should choose speakers which outputs the same power released by the receiver in each channel of the system (or at least approximate). This way, we avoid that one of the devices work above its capacities, which can cause flaws or even damage them. But some technicians advise that the receiver should offer a bit more power than the speakers can handle. Is that in this case, the consumer does not need to raise the volume to very high levels to get good sound pressure, which would force the receiver to operate above capacity.
In the opposite situation (with the power of the receiver far below that recommended for the speaker), there is a great risk of distortion and – even worse – the burning of the speakers.
Power x sensitivity
Calculated in dB/w/m (decibels per watt per meter), sensitivity indicates the sound pressure produced by a speaker receiving 1W of power and placed at 1m distance from the measuring microphone. Most speakers for sale have a sensitivity (or efficiency) of 86dB to 92dB. The higher this number, the less power is required of the amplifier or receiver. In theory, each 3dB over the sensitivity of the speaker corresponds to half the power required to obtain the same volume.
Power x impedance
The receiver and the speakers should also match the impedance, which is the resistance to the passage of electrical signal. If you connect a speaker with an impedance higher than the receiver, there will be a loss of power. But, if the impedance of the speaker is lower than the receiver, this will need to release more power than normal. The natural tendency in this case is greatly increase the volume, which can burn the speakers. In almost all projects, this is hardly an obstacle. Much of the speakers has nominal impedance of 6 to 8 ohms, values compatible with most receivers (8 ohms). But there are also 4 ohms speakers (usually in high-end models), requiring receivers with compatible setting.
Power x distortion
To analyze on what level of distortion the power of the equipment was measured makes all the difference in audio. The most widely used parameter is the Total Harmonic Distortion (THD), which shows (in percentage) the degree of distortion introduced in the original signal by the circuitry of the device. The ideal is at most 1% in measurements related to the frequency of 1kHz or up to 0.08% for the entire frequency range (20Hz to 20kHz). It is useless the device to carry a superlative value of Watts RMS power if this specification is measured at a level of distortion of 10%, for example. Some manufacturers even advertise the Intermodulation Distortion (IM) for receivers and amplifiers. It should be noted this type of distortion when a frequency band begins to disrupt the hearing of another, creating an uncomfortable overlap of signals that cause ear fatigue. Tip: search appliances that IM does not exceed 0.08% (in the range of 20Hz to 20kHz).
- When comparing the power of different receivers, verify if the specifications (in RMS) consider the same frequency band. There are measurements that refer only to the frequency of 1 kHz, and others that cover the entire audible range (20Hz to 20kHz). The latter is the most reliable.
- Despite having modest numbers, some receivers work with electrical current high loads. In practice, they have a power reserve, which is used when the unit is longer required (for example: a movie with sound effects or music with lots of heavy bass). The result is a performance equivalent to other models with higher power.
- Remember: twice the power (an increase of 3 dB) does not mean twice the volume. The variation can be up to 10x. To listen to twice the volume obtained with a 100W amplifier, you will need a 1000W amp! So if you’re thinking of replacing a 70W receiver with other of 100W just to get volume, forget it: the final difference will be little.