The Frequencies of Music

 

Silver Member
Username: Kbear

Canada

Post Number: 149
Registered: Dec-06
Hey all,

Looking at this chart on the PSB website we can tell at which frequencies certain musical instruments lie.

http://www.psbspeakers.com/audio-topics/The-Frequencies-of-Music

Here's my question: my speakers crossover at 2.8 kHz. It would appear that my tweeter doesn't do a heck of a lot, as only the violin, harp, piano, and piccolo produce frequencies above that range. And not even very many it would seem. The woofer is responsible for practically everything.

Do I have this right? How does one even begin to truly rate how good their tweeter is, driver integration, high frequency roll off, and all that stuff? Maybe 2.8 is a little higher than typical, but even if a lot of speakers cross over at 1.5 kHz or so I'd think you'd really need to listen to a decent amount of classical music to put a tweeter through it's paces.

Thoughts?
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 13709
Registered: May-04
.

"Thoughts?"




Harmonics.




Music is not simple fundamentals, its energy and character falls within the harmonic structure of the instrument(s). If you don't understand harmonics, put the word into a search engine and do some reading. The essence of the term means all frequencies are present in any instrument once a fundamental is struck, plucked, blown or bowed.

In theory the upper range harmonics extend into infinity though they begin to fall off rather rapidly above 50-100kHz (or lower for some instruments) in relation to the fundamental and typically strong second harmonic. It is not uncommon for many musical instruments to have more energy at the second or even third harmonic than at the fundamental itself so that piano that stretches down into the 20Hz range has harmonics of that fundamental that reach well beyond 100kHz. The PSB chart is informative though in providing a visual clue to the repsonsibilities of a speaker system.


Ideally your system should be capable of reproduction into the nether-regions of frequency response at either extreme. This is typically defined as "power bandwidth" in electronics and will typically be many multiples of the simple 20-20kHz frequency response dictated by the FCC in any marketing schpiel or what we accept as the range of normal human hearing. Harman Kardon was one of the first companies (way back in their 1950-60's Citation components) to promote their "wide bandwidth" amplifiers which eventually boasted a power bandwidth with "flat" extension from 4Hz to 120kHz. This sort of response places a strain on the power supply if it is not designed well. HK claimed such a power bandwidth to have benefits in improved rise time and square wave performance. As with any other specification you should decide just how important these "benefits" are to your enjoyment of music.



Many audio designers are of the opinion that if any part of the system cannot reproduce well above the "average" range of human hearing, problems will arise when the harmonics of the signal are truncated or phase shifted against the fundamental. However, this gets you into an area that is ripe for disagreement since the methods involved in extending frequency response in any component bring with them their own set of compromises. In speaker systems electrical phase shift and in room power response anomalies are quite commonly present when extended frequency response is desired. Whether a speaker system needs to reproduce 50kHz is debatable with the current technology that would allow such broad band response. It is, on the other hand, far simpler to get an amplifier to have response well into the 100kHz range and generally considered quite desirable for an amplifier to respond well to extremely high frequency signals.

Digital sources, of course, have their own problems with such broadband response and most systems today probably have a mishmosh of components that have upper and lower limits of response that do not match the component in front or following. One of the so called "advantages" to analog playback is its avoidance of brickwall filters at roughly 22kHz.


Speaker crossovers are the cause of many problems and also great heroics in modern day audio. In general, two way systems have pushed for lowering the crossover point and allowing the high frequency driver more range with the ideal being a crossover that occurs closer to 1kHZ. To the contrary a few designers have taken another tack and placed the crossover much higher than the average 2-3Khz allowing the low frequency driver(s) to run uninterrupted through the midrange where the human ear is most sensitive to errors. As you would expect both approaches have their tradeoffs and their distinct advantages. However, when you consider that the harmonics of any sound are primarily responsible for our definition of "what" (source) is creating the sound it should be obvious tweeters are under considerable strain to get these small signals right or else obviously fail at creating a believable illusion of a piano, voice, violin, etc.



On another issue, your speakers have a stated crossover point at 2.8kHz but that does not mean either the woofer or tweeter cease operation at that frequency. The crossover "point" is generaly stated as the -3dB down point for either driver as they roll out due to either mechanical or electrical filters (or both combined). Depending on the type of crossover filter the speakers utilize the rolloff of the tweeter could be rather shallow (a -6dB per octave 1st order filter) or rather steep (a -24dB 4th order filter) or somewhere in between. If the crossover is shallow (-6db), your 2.8kHz spec would mean the the tweeter is still expected to reproduce signals down into the 1kHz range and do so cleanly without break up or excessive distortion.




One lesson you should learn in audio is that numbers alone do not tell much of a story. You will normally need at least four or five sets of numbers or just simply more information before you can even begin to understand what might be happening with your components. Manufacturers often shy away from giving such details since too few people understand what they might mean and too many people shop catalogs and brochures by looking at specifications to decice what might suit their purposes. And, as always, any chosen path in audio will have its advantages and tradeoffs which will quite frequently have something to do with cost.


.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 13710
Registered: May-04
.

If you don't understand fundamentals and harmonics, place something on the order of "fundamentals+harmonics+music" or "musical instrument harmonics" in a search engine and do some reading.

http://en.wikipedia.org/wiki/Harmonic_series_(music)

Harmonics (and overtones) are what give an instrument or any naturally occurring sound its unique and identifiable timbre.

http://en.wikipedia.org/wiki/Timbre

Without harmonics we wouldn't be able to distinguish a piano from a violin or a flute when all three were playing the same note at the same frequency or provide the difference between two pianos of different make and model. Even in their truncated and tonally artificial form harmonics allow us the ability to identify a familar voice on the telephone. It could certainly be argued that harmonics are the basis for everything we hear and know as natural and real.


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Silver Member
Username: Kbear

Canada

Post Number: 150
Registered: Dec-06
Thanks Jan. I'm going to do some Google searches as you suggested. I kind of have an idea of what you are saying, but it's all very new to me and I think I need to understand the basics first.

I did put my ear up to my drivers while listening today and I heard certain things out of the tweeter that I didn't expect. Some vocals (male), acoustic guitar, and cymbals. Sure the latter isn't a big surprise, but the first two were a bit.
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