The nominal input power of a loudspeaker is the continuous power (Watt RMS) that can be absorbed by the speaker without it being damaged, and not a measurement of minimum amplifier power needed to drive it. Naturally the speakers can handle much higher power peaks for small periods of time (a few 1/100s of a second). If a speaker combines high nominal input power with a high sensitivity, then we can generate music and sound at realistic levels without compression or distortion.

No! The input power of a speaker by no means affects its performance. A high quality speaker in general must provide a smooth frequency response both on-axis (in front of the tweeter) and off-axis (at an angle from the tweeter axis), which is done through controlled dispersion, so that it doesn't induce any unwanted colorations in the sound. Furthermore, it must keep distortion at very low levels and at the same time be sensitive enough, without a very low impedance, so that almost all amplifiers can drive it successfully. Although it is a great asset to have high power speakers that can handle that extra boost we need to rock everyone from their seat during a party or movie viewing, the nominal input power is not at all related to the frequency response, dispersion and sensitivity of the speaker.

Every audio component in the world of Hi-Fi and Home Theater is usually accompanied with what is called a “break-in” period. This is usually a period of some days that the audio component is required to operate, before it can perform at its best. Like for ex. in power amplifiers or receivers where the power supply and capacitors “open up” after some hours of operation, the same goes for loudspeakers, where their woofer suspensions become “softer” and more accurate. After the break-in period is complete, the loudspeaker can perform as the manufacturer intended and is ready for critical listening sessions.

Crystal Acoustics loudspeakers will usually require about 100 hours in moderate playback levels before they can perform at their best, although the break-in period continues even after this time frame. It should also be considered that the absolute time of an actual break-in is affected by the speaker type, the amplifier that drives it. the playback level as well as whether the break-in period is performed through continuous or interrupted playback periods.

Tip: In order to perform a quick and effective break-in of your loudspeakers, you can follow this tip.

1. Place your loudspeakers face-to-face, in close distance.
2. Wire the first loudspeaker as indicated and reverse the +/- wiring of the second loudspeaker, thus reversing its phase.
3. Initialize the playback procedure, choosing some rich sounding, full band tracks that equally extend to all frequencies. Because of the out-of-phase setup of the loudspeakers, you will notice that the audio output of the loudspeakers is actually canceled by a great amount. As a result, you can leave your loudspeakers breaking-in without annoying your neighbors, even when you are away from home.

Sensitivity: Sensitivity is a measure of how loudly a speaker will play 2.83 volts, one metre in front of it. Since loudness is measured in decibels of Sound Pressure Level (dB SPL), the sensitivity rating is specified in dB SPL/2.83V/m. Note that 2.83 volts corresponds to one watt when applied to an 8 ohm speaker (P=V2/R, hence 1W=2.832/8). Since modern amplifiers are constant voltage sources across most of their working range, specifying the sensitivity at a specific voltage rather than the older standard of 1W (which translates as a different voltage for speakers that aren’t 8 ohm designs) provides for a much more consistent way of appreciating the sensitivity of speakers.

The sensitivity of a loudspeaker is a very important specification: the greater the sensitivity, the louder the speaker plays, and/or the smaller the amplifier it requires. As a rule, high sensitivity speakers decrease the cost of the required amplifier, offer lower distortion and a greater dynamic range.

Nominal Input Power: The nominal input power of a loudspeaker is the continuous power (Watt RMS) that can be absorbed by the speaker without it being damaged, and not a measurement of minimum amplifier power needed to drive it. Naturally the speakers can handle much higher power peaks for small periods of time (a few 1/100s of a second). If a speaker combines high nominal input power with a high sensitivity, then we can generate music and sound at realistic levels without compression or distortion.

Impedance: The impedance of a loudspeaker is a measure of how difficult a load it is on the amplifier it is connected to. The impedance of a loudspeaker varies significantly depending on the frequency. Most loudspeaker specification sheets provide the nominal impedance, which more-or-less is the average over the full frequency range. Because the impedance is an average, two speakers with the same nominal impedance may have vastly difference actual impedance at given frequencies. Keep in mind that a typical 8 ohm loudspeaker may vary from a minimum of 5 ohm to over 30 Ohm depending on the frequency. A lower loudspeaker impedance causes an amplifier to output more power and to reproduce higher volume levels and places a greater task on it.

Dispersion: How widely and evenly a speaker spreads its sound. A speaker with narrow dispersion beams its sound forward like the beam from a flashlight. A wide-dispersion speaker evenly covers the entire listening area with sound. Speakers must have a wide horizontal dispersion for two reasons. Reflections from sidewalls must have as close frequency content as the on axis radiated so that unwanted colorations are minimized. Secondly, wide horizontal dispersion permits all listeners to enjoy music and movies wherever they sit in the room.

Crossover Frequency: The crossover frequency is the frequency at which the signal is split to the different drivers of a multi-way speaker system. In a typical two-way system, the crossover frequency between the woofer and the tweeter will be set around 2500Hz.

Cutoff frequency: The frequency at which the signal falls off by 3dB (the half power point) from its maximum value. Also referred to as the -3dB points, or the corner frequency. The lower it is, the more bass the speaker can reproduce.

An ohm is a measure of resistance (impedance) to the flow of electric current through a device. The impedance rating of a particular speaker varies depending on the frequency of the signal. Different speaker models have different impedance ratings. The nominal impedance that is usually specified for a speaker is an average rating of the impedance over the whole frequency band. Higher impedance speakers are an easier load on the amplifier since there is less current flowing into the speakers.

Therefore the amplifier’s operating temperature is cooler, since it is delivering less power. If a particular amp is designed correctly, as far as heat dissipation is concerned, then a lower impedance speaker can be used to get the most power out of it. Many stereo amps and receivers give a power rating for both 4 and 8 ohm speakers.

Some high-end amplifiers can drive speakers with one ohm impedance! On the other hand, many multi-channel receivers are designed to handle only 8 ohm speakers, since the heat generated by their multiple amplifiers is excessive. It is advised to choose an amplifier that can drive at least 6 ohm speakers. Therefore, you can connect the main speakers with an impedance down to 4 ohm provided that the surrounds are 8 ohm designs.

The sensitivity rating of a speaker is very valuable because indicates how efficient a speaker is. In other words, it tells us how loud the speaker will play when it is fed with a standardized signal.

Years ago, loudspeaker sensitivity was rated as the sound level at a distance of one metre for an input of one watt. Power input is voltage2/resistance. Because loudspeakers do not have the same impedance at all frequencies, a sensitivity rating would apply only at a single frequency (or in a confined frequency range at best). Obviously, rating sensitivity according to power input does not work well. The domination of solid-state amplifiers really provided the solution. These amplifiers are essentially constant-voltage sources, with power rated according to what they can deliver into an 8 ohm resistor. If the load impedance drops to 4 ohm, the power will double; at 2 ohm the power quadruples and so on, until the amplifier cannot deliver any more current or dissipate any more heat. This permits us to define an input voltage, not an input power, to rate the sensitivity.

The sensitivity rating is nowadays given (or should be given!) in number of dB SPL /2.83V /1 meter. For example, a particular speaker may have a sensitivity rating of 92dB SPL/2.83V/metre. This means that when a signal of 2.83V in amplitude is driven to the speaker, the generated sound is 92 decibels when measured at 1 metre from the speaker.

Sound Pressure Level: The three rules to calculation
The following rules are used to calculate the Sound pressure Level (SPL) in the room depending:

- On the distance of speakers and listener:
- Doubling the distance results in a 6dB reduction of the sound level
- At half the distance the sound level is increased by 6dB The sensitivity of our speakers:
- Two speakers deliver 3dB more than one speaker (stereo configuration)
- The power of our amplifier:
- Twice the power (watt) results in a 3dB increase of the SPL (under the assumption that the speakers can handle the extra power without distortion or damage) 

Sensitivity: The sensitivity of a speaker determines the generated Sound Pressure Level. The sensitivity is measured in dB SPL/2.83V/m, depending on the sound pressure level in dB that is generated at a distance of one metre and an input signal of 2.83V (which corresponds to one watt of power when applied to an 8 ohm speaker) from the amplifier. The greater the sensitivity:

- The louder it plays
- The smaller the power amplifier it requires

High sensitivity speakers decrease the cost of the required amplifier and offer low distortion and greater dynamic range.

But what is the real gain of 3dB? A speaker with 3dB higher sensitivity requires half the amplifier power to produce the same sound level. For example, a speaker with 94dB sensitivity requires half the wattage of a speaker rated at 91dB sensitivity to produce the same sound level. Thus, if the first speaker requires 100 watts to produce a certain sound level, a 91dB speaker will need 200 watts and a 88dB speaker 400 watts!

- How much more money do you need in order to buy a 400 watt amplifier and a speaker that can handle 400 watts?

In addition, the distortion of a speaker with a 400 watt input is greater than a 94dB sensitivity speaker with only a 100 watt input

Since the very first days of speaker design and evaluation there has been a big debate on what measurements tell us about the speaker: how they correlate with our listening experience; to what extent the designer can rely on them; and how accurate and repeatable they are. Of course, these are questions that are the subject of specific fields of acoustics, such as psychoacoustics, and it would be impossible to cover everything here. However, we can give some useful insights to the user that wants to know more about the scientific aspect of acoustics as opposed to the hocus pocus that often surrounds speakers!

The main measurement a designer cares for is the frequency response of the speaker as measured at a specific distance (one or two metres from the speaker) from the driver and exactly on the axis of it (on-axis). This shows the response of the speaker for all frequencies of the audible band. Whatever you may hear and read about, 'flat' is unquestionably the best response. It is the only reference one can rely on, and it is what designers should thrive for. A flat response means that the speaker reproduces all sounds without emphasizing or reducing specific frequencies that would result in a sonic coloration.

Now watch out because there is a big problem here. Room acoustics truly define the lower frequency response of a speaker. In order to have accurate and repeatable measurement in many places for bass, we either must have a huge room, so that sound reflections don't influence the measurement, or we must employ a technique called Near-Field measurement. In this technique, the low frequency response of the speaker (and port(s) if any) is measured with the measurement microphone almost touching the cone, thus eliminating the contribution of all reflections whose magnitude is much smaller than the original signal. This measurement is then spliced with the on-axis measurement at a certain frequency, to give a very good approximation of the speaker’s response in an open space, with no physical boundaries nearby.

The interesting point of the accurate near-field response is the frequency where the Sound Pressure Level of the speaker falls by 3dB compared to its average value. This is referred to as the f3 and is a measure of the ability of the speaker to reproduce low frequencies. Of course when evaluated in a realistic room the speaker's bass will be quite different due to the standing waves (room modes). However, the flatter the response up to the f3 frequency means the easier it will be to find an optimum place for it in the room that gives a smooth result.

Then we have the frequency measurements performed at angles off-axis. These depict phenomena as the summation issues introduced by the phase shifts of crossover networks, etc. Again here we want to be as close to the on-axis response (which should be the flattest it gets!) as possible. In this way we are pretty sure that the reflected sound from the ceiling, floor and sidewalls will have the same sonic character as the direct signal. We need to confirm as well that the crossover network used does not cause a big response deviation off-axis.

Another important measurement is the impedance versus frequency graph. This depicts the overall impedance of the speaker (including the resistance of the coil, its inductance along with the effect of the air and the enclosure interacting with the driver) from 20Hz to 20kHz and shows where the minimum impedance occurs and what is its value. Normally we want the minimum impedance to be higher than 3-4 ohm, so that pretty much any amplifier can drive the speaker. In high-end speakers however values of minimum impedance down to even one ohm are not unusual. The frequency at which the lowest impedance is observed is also important. If the frequency of lowest impedance is high, the load is easier on the amplifier, because in this area the power of audio information is small. If the lowest impedance frequency is in the mid or low range, then the speaker is considered a difficult load, since there is a great percentage of the audio power in this range.