Frequency Response in Speakers?
Good speakers are the key to getting the best possible audio experience from your sound system. You can put together the best CD or DVD player on the market and the highest-rated AV receiver, but if you don’t have the right speakers, your audio or home theater setup won’t be worth much when it comes to actual sound. Your speakers provide the interface between your audio system’s electronics and the physical world in which sound is actually played. Choosing the right set can make the difference between cramped, muddy audio and crystal-clear concert-hall sound.
You can buy a pair of loudspeakers for $50 or you can spend $50,000 and up. You can buy speakers as small as a baseball or as big as a refrigerator. There are bookshelf-sized speakers costing a few hundred dollars and others the same size that’ll set you back thousands (and are worth every dollar and then some). There are big speakers that sound anemic and tiny ones with sound that will hit you so hard they’ll knock the wind out of you. So, how do you know which type of loudspeaker is appropriate for you?
The concepts of frequency response, frequency range, audible frequencies, how frequency relates to musical notes, etc. are absolutely central and critical to understanding how audio equipment makes, reproduces or records sound and how that sound is related to the live sound produced by singers and instrumentalists.
Of all the loudspeaker specifications, the frequency response is the easiest one to take out of context. The frequency response is used to describe the audible frequency range that a loudspeaker can reproduce. Audio frequencies are measured in Hertz (Hz) and the theoretical range of human hearing is generally regarded as being from about 20 Hz (the very lowest bass tones) through 20 kHz (the very highest treble notes). It may seem logical to presume that a loudspeaker capable of reproducing all or more than the audible frequency range would be best. But this is not the case, so don’t fall into that trap. The range of human hearing is typically about 20 Hz to 20,000 Hz. Frequencies at the lower end of this range are typically referred to as bass, the higher end is called treble, and those in the middle are called mid-range. Ideally, a single speaker would be able to play sounds at all frequencies “equally”, meaning it would not make certain frequencies louder than others. However, this is not the case. Many times speakers are separated into tweeters for playing high frequencies and woofers for playing low frequencies. This has to do with a concept called resonant frequency , sometimes called “natural frequency.” Every mechanical system or object has a natural frequency at which it “likes” to vibrate. In general, smaller, lighter, and stiffer objects like to vibrate faster than bigger, heavier, and softer objects. For example, imagine “pinging” a small metal object (like a ruler or paperclip) by flicking it with your finger. It will vibrate back and forth very quickly—possibly faster than your eye can see. Now, think about much larger objects, like tree branches swaying in the wind; they rock back and forth very slowly. The same concept applies to speakers—smaller, lighter tweeters will vibrate at higher frequencies, while larger, heavier woofers will vibrate at lower frequencies.
A graph of the amplitude of a vibration versus the frequency of the vibration is called a system’s frequency response. A good speaker should have a frequency response that is as “flat” as possible, meaning it reproduces frequencies at the same volume at which they were recorded. Otherwise, large peaks or valleys in the frequency response will result in some frequencies sounding much louder or quieter than others.
The simple description of frequency response of 20 Hz to 20 kHz would seem ideal; however, this is a true statement even if the sound at 20 Hz is 40 dB SPL lower than the sound at 1.2 kHz. This means that the lowest bass frequency is a hundred times less powerful than an average midrange frequency— i.e. the speaker may reproduce all of those frequencies but nowhere near at the same level.
A much more clear method of specifying frequency response involves giving a tolerance, the range within which the speaker produces all of the frequencies within its frequency response range. For example, a frequency response of 20 Hz to 20 kHz +/- 3 dB indicates a much superior speaker to the one mentioned earlier with a bass roll off of 40 dB. Basically, the latter speaker maintains its level all the way into its lowest frequency, while the former just goes away (rolls off) in its lower frequencies. The lowest bass frequency is at most only half of what a typical mid range frequency is reproduced at. Without indicating the tolerance on the specifications, companies can create extremely misleading specifications.
Speaker Test: Full Range (20kHz - 20Hz)
If a speaker company will not indicate a tolerance in their specifications, it raises the question of what they are trying to hide. In addition to indicating how the ends of the frequency spectrum, the tolerance indicates the accuracy of the spectrum. The tolerance indicates that at no point in the spectrum are there extreme spikes or discrepancies that would not show up in a spec without a tolerance reading. Each speaker has its own frequency response that gives it “color,” a speaker’s individual tonal qualities or sound. This characteristic determines how the frequency response shapes the sound to make it better by emphasizing certain frequencies.
Why Frequency Response is important
Frequency response may well be one of the most misunderstood and frequently abused speaker specifications that any consumer has to deal with. It describes the range of frequencies or musical tones a component can reproduce.
Frequency response measures if and how well a particular audio component reproduces all of the audible frequencies and if it makes any changes to the signal on the way through.
By the traditional standards of HiFi, a good audio system is one that takes an input signal and outputs it without changing it at all. This includes components ranging from the source audio file, through to digital processing and components like a DAC, right on out to the amplifier and speakers. Frequency response is just one part of this equation, but one that has a very large impact on how the output sounds.
A speaker with good frequency response is able to play all the low, middle, and high tones correctly—and in the proper proportion to each other—and that is what tell our ears whether or not this is a high-fidelity unit with rich, vibrant sound.
Conclusively, frequency response is the range of range of frequencies that a speaker can play. Some speakers can play between 20Hz to 20 kHz while others can play between 150Hz to 20 kHz. If a source (song/movie) sends a signal for a frequency outside of a speaker’s frequency response, the speaker simply won’t be able to play it. The frequency response of a speaker is how loud a speaker plays at the tones that you can hear. It is usually given as a range of tones or frequencies and the variation of volume either greater or less than the nominal level.
