The dynamic range of a speaker defines the frequency spectrum over which it can reproduce sounds. Human hearing goes from low bass frequencies of about 20hz through to 20,000Hz (20khz).
Don't automatically expect all speakers to be able to reproduce the entire range. On the contrary, most speakers do not reproduce the full range. Achieving particularly low frequencies requires careful cabinet construction and generally bigger speakers.
Speakers are tweeters for frequencies roughly 2000Hz-20,000Hz, Midrange drivers from 2000Hz down to about 200Hz and woofers and sub woofers handle the bottom few hundred hertz from 200Hz-20Hz.
The number of speakers and the number of frequency bands that the crossovers break the signal up into are described as n-Way speakers, where n is the number of total discrete bands.
Hence a tweeter and a midrange driver would be a 2 Way speaker. Adding a Bass driver would make this a 3 Way speaker. Sometimes speakers are known as 2½ Way when two main drivers are used with overlapping frequency envelopes delivered by the crossovers.
Typically the size of a speaker's cone determines the amount of air the speaker can move and larger speakers are capable of playing louder because of this ability to move more air. Smaller speakers are used where the response rate is extremely high - like in tweeters.
The efficiency measure of a speaker is the loudness of sound produced when 1 watt of power is applied across the frequency range.
As loudness is measured in Decibels dB, the louder a speaker is at the same input power level, the more efficient it is in terms of turning electrical energy into acoustic energy.
The way a speaker becomes more efficient is through clever use of cabinet design, careful choice of electronic components, the shape of the speaker surrounds (eg horn loading), the port designs, and the lightness, responsiveness, size and surface area of the drivers.
As you can see there is a lot of design that goes into efficient speakers.
Since none of us own an acoustically perfect home, speaker placement is always a compromise. Having said that, careful choice of speaker design and placement will make an audible difference to the end result.
There is usually one seat in the house most often occupied for listening or viewing. This position is the prime position or even the "Money seat"
Systems are normally setup around this main seating position with each additional position then receiving consideration.
The reason for this specific selection is that sound wave are long wavelength pressure waves. Midrange and higher frequency sounds are very specifically located by our brains, so ensuring that they arrive in phase at the right point at exactly the right time is critical to ensure the performance is not muddied by phase issues.
Talk to the experts at Audio Junction about your room, bring in a plan view with some measurements and they can make sensible reasonable suggestions to improve your system's sonic performance.
Subwoofers are large speakers specifically designed to produce frequencies typically from 140hz down to below 20hz, the theoretical limit of human hearing.
There are 2 types of subwoofer powered and passive. Powered subs have a built-in amplifier. Passive subs are powered by your amplifier or receiver. Bass frequencies at this level require an awful lot of power, so unless your amplifier is a power house of professional p.a. proportions you need a powered subwoofer.
Below 100hz it is difficult for us to determine the source of these signals. However to create the bass impact one hears at the cinema when there are huge explosions, careful positioning and calibration of the subwoofer is vital.
The wavelengths at these frequencies are particularly long, some as long as 50 feet. Therefore standing waves can become a problem. Standing waves are caused by low frequency waves reflecting off room surfaces and colliding with themselves out of phase to produce a change in amplitude. Large rooms suffer far less than small rooms because the waves are distributed more randomly. Standing waves cause the bass to sound sluggish.
100hz produces a 10 foot frequency wave, logically then the peak of the first wave will be 5 ft away from the subwoofer and then at 10ft increments. To get the full effect of this wave the listener should be positioned 5, 15 or 25 feet away from the subwoofer and so on putting them at the peak of the wave. As the frequency is lowered so the wave gets longer, the reverse is true as the frequency gets higher. This is further complicated by the acoustics of the room. For the 100hz example above, if the room is 25ft long the resulting reflection or standing wave, will match the source wave and cancel the signal out.
The easiest way to find the best spot for the subwoofer is to place it at the listening position, where your favourite armchair would normally be. Then wander around the room until you find the best bass response. Look for a smooth performance rather than the loudest one. Ideally use pink noise as found on test discs, or failing that the test tone on the amplifier although this is not ideal.
It is also necessary to calibrate the sub to the front speakers. This is because there will be some frequency overlap at the low end of the front and centre speaker’s dynamic range and the top end of the subwoofer’s. Subwoofers have a high level frequency cut off, or phase level, dial. Low frequencies can interfere where they overlap and sound boomy. So although it is impossible to have a clean break where sub ends and speakers begin we can set the dial to reduce this effect.
If you are running a THX speaker system simply set the sub’s high frequency cut off at 80hz. This is the standard set by Lucasfilm. THX front and centre speakers are calibrated to have a low frequency cut off at the same point.
With regular speakers check the dynamic range in the instruction manual and set the cut off dial on the sub to meet the low end of the front and centre speakers range.
Finally set the volume level on the subwoofer. This is probably best done by ear unless you have a full frequency range test disc and sound pressure level metre. Do not be fooled into thinking louder is better, start at about the halfway mark and make tiny adjustments accordingly.
Now all that remains is to sit back and enjoy, feel the stomp of T-Rex and the full effect of the Death Star as it explodes!
One could write a book on the methods of setting up speakers, but to a large extent, the method you choose will depend upon the equipment at your disposal. An acoustic engineer for example is going to be able to analyze the entire audible frequency spectrum in your room, looking at node points for reflected sound and all the other buzzwords that echo from the sort of people that carry small firing model cannons around.
For the home enthusiast there are several good rules of thumb to use
Many we speak with are concerned with having "too much" power from their amplifier and this leading to speaker damage. 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 much 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. 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. I am 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.