Index


Hifi page

    General information

    The purpose of general home audio is to make an enjoyable sound.The "hifi" is short for "high fidelity".The word "fidelity" means the quality or state of being faithful,accuracy in details, exactness and the the degree to which an electronic device (as a record player,radio, or television) accurately reproduces its effect (as sound orpicture). The purpose of hi-fi, however, is fidelity: to make a sound faithful to the original performance. Whether it is enjoyable or not! (quite often very goodplayback system can reveal that the recordings are not ideal).With HiFi-system you get "enjoyable sound" by purchasing enjoyable recordingsthat sound good when accurately reproduced.An "enjoyable sound" comes from having good source material, accuraterecording and reproduction, and a good listening environment. The goal of most "legitimate" recording is topreserve the original as accurately as possible.Sound recording are intended to be heard through a "neutral" reproductionsystem which does not color the sound in any way (such thingdoes not exist, but try to get as close to it as you can).The purpose of a sound recording media and playback deviceis to get the sound to the amplifier as accurately as it can.The purpose of an amplifier and speaker is to provide"The closest approach to the original sound".An idea amplifier is "a straight wire with gain".An high fidelity amplifier must, by definition, reproduce an enlargedversion of the input, with nothing added, nor taken away. Building a resonable amplifier is nowadays quite easy and anycompetent electronics engineer should be able to design a power amplifier,if he or she knows their trade. Speakers is a hard question in any audio system. They are the things which color the sound mostly.You can do a lot of engineering tests on them, but theywill tell if a speaker bad one. Spaker tests won't tell if the speaker is the one that sounds good.For this, you have to trust your ears.A common rule of thumb is to assume consumer output impedance is around 1 kohms, and input impedance is around 10 kohms. Typical consumer equipment transport typically the signal between the system components generally in line level signals (typically 0.1..2V in amplitude).The purpose of interconnection cable is to carry signal betweendevices without altering them (without noise, interference, frequencyresponse problem etc.)Anything that does any more than than becomes a sound effect unit.There are artifical things you can do to several of those links in the chain to make up for deficiencies.Sometimes one makes the sound one wants, so if indeed one likes certain ACCENTS and COLORS in audio, the system components could beselected for this in mind (and not being as accurate as possible).Some people seem to enjoy music played with certain forms of distortion,rather than a more accurate sound (most well know could be "tube distortion").Some audio inteconnect cables have arrows in them to indicate their recommended use direction. The arrows should point from output to input (=the direction of signal). And may or may not have any relevance to anything in the real world.Common cables should not have arrows or make a difference in direction. The direction can make sometimes difference in case of special cables only grounded from one end (to avoid ground loops). The theory on those that the shield should be tied to ground, on the end with the lowest ground noise (usually is not dependent on signal direction, but how equipments on the end are implemented). Sometimes arrows in cables are an indication that the cables are doing the "trendy" attempt atbeing pseudo balanced cables with the shield only connected at one end (usually this kind of pseudo balanced RCA cables work poorly at shielding). The correct way is always the way it works the best. Typical distortion caused by audio equipment are noise and harmonic distortion.Harmonic distortion describes a nonlinear property of systemswhere the output of the system has added energy at frequenciesthat are at integer multiples of the frequencies input to thesystem. To describe what is hardmonic distortion let's say you have a 1kHz signal of 1 volt. If you run this signal throughan amplifier and spectrum analyzer, you will see that there are also some output voltage at 2kHz, 3kHz -- all the harmonics. These should me many tens ofdecibels down from the original in a high quality amplifier. If you sum thevalues of these harmonics the result is "Total Harmonic Distortion".Harmonic distortion is but one manifestation of the non-linearbehavior of systems: it is not a specific "disease" but oneeasily observable symptom of a condition which has multiplesymptoms, also including intermondulation distortion, forexample.

    Interconnection cables

    Audio systems have many different kinds of connectors and wirings. On home hifi systems so called "RCA cables" used carry mostly line level audio are the most common. Usually in home Hi Fi systems the colors for audio inputs are red and white. One cables use red and black colors. Here is a quick overview of cable color codes you can find on modern home audio/video systems on RCA connectors:

    • White = Stereo Audio Left
    • Black = Stereo Audio Left
    • Red = Stereo Audio Right
    • Yellow = video

    Typical consumer AV equipment (like VCRs), may have an audio source impedance of 5-20 Kohms (some equipments like some CD players and PC soundcards have lower impedance). The parallel capacitance of a long cable will certainly react with this relatively high source impedance to cause some high frequency rolloff. Ideal interconnection cable forhigh impedance output devices is low capacitance cable (for example RG-59 coaxial cable) that is well shielded. A good quality microphone cable is also usable for consumer hifi equipment interconnections, but it's high capacitance can be problem with some equipments (if equipment output impedance is very high and cable long causes some high frequency loss).

    Audio frequencies aren't much sensitive to the details of the cable construction. All you need is heavy braided shielding and well formed connectors. When you buy a ready made interconnection cable, is is a good idea to avoid the ultra-cheap ones. If you have to happen a long run of cable (many meters)and signal source with high output impedance (few kilo-ohms) then a low capacitance cable is preferred (usually cost quite a bit of more than "basic cables").

    Many people give advice to buy cables with gold planted connectors. Gold plated connecters in theory will not corrode as fast other metals, but they don't sound any better than other connectors if the connecters are kept clean. And anytime you mix two different metals together (including goldinto zinc plated) you are more prone to get corrosion (but I would not worry about it too much unless you live in very warm and wet environment). Usually recious metals aren't needed at all and does not help anything. Gold plating is of questionable value because it corrodes badly at scratches. This means that old plated connectors are great if never subjected to vibration or wear. Once they're scratched, the underlying metal corrodes quickly due to electrolysis. The plain old silver kind are are usually more durable after connectors are subject to movement and many connections/disconnections. The silver colored connectors are plated with nickel,silver, or cadmium along with layers of other metals. The non-gold connecters used in audio interconnections are typically zinc plated (most likely). It makes no difference in sound quality as long as everything is clean and tight-fitting. Gold plating is frequently preferred on input connectors by some people, but it wears out easily through after a few insertions. So with gold planted connectors the quality of the underlying plating is very important important (gold planted bad connector is still bad). And keep in mind that you can find gold colored platings that aren't actually gold.

    A cable in audio applications for carrying microphone and line level signals can be modeled as a low-pas filter. A first-order high-cut (or low-pass) filter is formed by an output's sourceimpedance and the capacitance of the cable. The frequency at which a filter attenuates 3 dB is called its "corner frequency". With short cables (lowcapacitance) and low output impedances, the corner frequency typically occurs well above the audio band. With longer cables and higher output impedances,the corner frequency drops and may drop into the audio band. The formula for the corner frequency is:
    F = 1 / (2 * PI * R * C)
    where F is the corner frequency in Hz, PI is 3.14, R is the source's outputimpedance in Ohms, and C is the cable's total capacitance in Farads. A first-order filter has a slope of 6 dB per octave. This means that beyond the corner frequency, the response will drop 6 dB for each doublingof frequency. Generally it doesn't seem likely that you would get detectable loss even at 20kHz unless you have one or more of these conditions: unusually high source impedance (many kilo-ohms), unusually high capacitance cable or unusually long cable length(tens of meters).

    There's no need to go nuts with speaker wire either. Use high qualitycopper to reduce oxidation at the connections. Super-sizing the guage doesn't help since speakers have at least 3 ohms of their own resistance. Just make sure the total cable resistance is very small in comparison. Generally a 12 gauge (2.5mm^2) zip cord is adequate for most audio speaker interconnection applications. In very long runs (much more than 10 meters) consider using 14 gauge (4mm^2).

    Nowadays there are also equipment that use digital interconnection cables. For digital interconnections there are two connection options available: optical fiber and coaxial cable. The optical fiber used in digital audio connection carries the digital data as series of light pulses (red light from transmitter LED). The opical fiber used in audio systems is one millimeter thick plastic fiber, that consiss of one millimeter thick round transparent plastic center covered with black plastic. This simple cable can carry the signal nicely for few meters. The fiber optic cable used in audio systems is entirely different than is normally used in computer networking and telecommunications networks (those cables are much thinner and made of glass). The coaxial digital interface in designed to use 75 ohm coaxial cable. Any decent quality 75 ohm coaxial cable works well for this up to around 10 meters. The cable does not need any "magic" properties. In very short interconnections the usually system works also with normal "RCA cables". Bacause the digital interconnection in digital, it means that the signal either gets through the cable without changes or does not get through it. The digital interface has error detection system that mutes the audio for some time output if there are errors are detected. When you hear the audio without interruptions, you know the data gets through right and there are no changes in sound because sound was transported through the cable.

    There are many companies which sell very high priced special cables for hifi people. Most of those cables do not provide any measurable sound quality improvent to the sound system, at least on otherwise properly designed system. Exotic cable vendors typically offer no proof based on acceptable scientific methodologies, but many seem promote these scientific principles while rejecting their provable and measurable implications. Electrical properties of cables are well known and documented from DC up to GHz. Exotic cable psuedo science exists in consumer audio market. Producing cosmetically pleasing cables does carry a considerable manufacturing and materials expense, that's why special cables are expensive. Maybe the manufacturers need to publish psuedo science material so that the buyers would be ready to pay for the high price tag. There seems to be audio cable vendor that are selling you high priced "snake oil". It is true that there are exotic high priced cables that look good and work well, but nothing that would be so good that would justify spending thousands of dollars for interconnection cables (money is better spent when when improving other part of the system, for example amplifier and speakers).

    Do it yourself audio cables

    During this last decade a pletora of special audiophile mains cables have invaded the HiFi market, causing many skeptical reactions among audiophiles. If you want to experiemnt with special cable, you can also do your special cables yourself. Materials for cable building is usually easily available. By building the special cables by yourself, preferably spending almost nothing so that, even if you can't hear any difference at all, the amount of money spent on the experiment is negligible.

    • DIY Cat5 Speaker Cables - This vable is built form vire material taken from CAT5 cable. It is described to have a very low inductance and "Skin-effect" should be negligible.    Rate this link
    • Merlino: DIY mains cable - This is an easy and cheap DIY project. All you need is a shielded mains cable, easily available at any electric/electronic parts store, and suitable mains connectors to the ends od the cable. In addition to this you need to install two ferrite rings (or clamps) at each end of the cable.    Rate this link
    • More practical DIY Interconnect Stuff - article which describes how to build special interconnection cables called X-Cables    Rate this link
    • The TNT Star: DIY speakers cable - Here's something simpler, aimed to the absolute beginners. A speakers cable easy to build and cheap which can be considered the first serious step towards quality connections. The Star is one of the cheapest and easiest to build cables around. All that you need is a shielded four twisted conductors electrical cable (quadripolar copper shielded cable).    Rate this link
    • The TNT Starpower: DIY speakers cable - This is a speaker cable made using a shielded four twisted conductors electrical cable (quadripolar copper shielded cable). The value of this DIY cable is claimed to be comparable with some "HI-FI boutique" cable.    Rate this link

    Vinyl records

    There is a group of people who truely apriciate their turntables for the subtle differences in sound compared to the other media.You often hear words like 'warmer' and 'true to the art'and 'more natural'. Many HIFI peoplehave stuck to their vinyl gunsare listening to their turntables through tube ampsVinyl, for all it's charm, is technically terribly flawed and inconsistent a medium it simply cannot even be considered in the same class as properlyexecuted cd technology. Vinyl records have limitations in frequencyresponse, signal to noise ratio and many other things. But in many cases talented people in recording company havesucceeded to get out very pleasing sounds out of this verylimited medium.By all means make or buy the best turntable you can - there's lots of greatmusic not even available on cd, and there were many cd's improperly masteredusing masters intended for LP's. These particular recordings contributed toa bad reputation for cd technology early on, and the LP of same might soundbetter if you don't mind the surface noise, etc.It is true that certain CD recordings were not as true tothe original vinyl versions as some listeners used to thosevinyl versions would like. Sometimes there can bedifferences in loudness and punch with vinyl versions sounding betteror more pleasing.Typical record player cartridge outputs a very low level signal(typically 0..5mV). This signal is typically transported through audio cable (RCA connnectors) to the hifi amplifier which includesa phono input (sometimes separate phono preamplifiers are used instead).Phono input of hifi amplifier (phono preamplifier) is designed to take a up to few millivolt signal from phono pickup and amplify it. The amplifier stage does also some equalization based on standardized RIAA curve. That RIAA equalization is used in the playback to reduce the high pitch noise and maximize bass dynamics in the phono playback. The audio material which is rocorded to the record has been pre-equalized so that the frequency response of the whole chain from the mixing desk to your speaker will give flat frequency response. The RIAA compensation curve was adopted in the mid 1950s, as a way of dramatically improving the fidelity of playback. This curve takes into account the limitations of the mechanican recording system on the record surface. At low frequencies, this amplifier provides 20dB of gain. At medium frequencies it provides no gain, and at high frequencies it provides 20dB of attenuation. So as the result RIAA equalization has an approximate 40 dB variation over the audible range. There have been different kind of picup system in use for phono playback.Pickups embody various mechanical designs, and use differentmeans of translating stylus motion into electrical energy. Thefour basic methods are called "magnetic", "dynamic","piezo-electric" and "capacitance." The first two work by a "constant velocity" response, which means that the power ofthe signal created depends on the speed with which the needlewhips around the wiggles. This is the exact reverse of the processby which the cutting head and stylus cut the record. Piezo-electric (crystal and ceramic) pickups and capacitance pickups have a"constant amplitude" response. Neither method is necessarily superior to theother, but the fact is that a majority of the satisfactory high-fidelitypickups are constant velocity-magnetic or dynamic.Here is overview of technical details of different systems:

    • Moving magnet (MM): This type of cartridge has a moving magnet and a fixed coil. The amplifier input is typically 47 kohms in impedance. Input capacitance recommendations on cartridges and capacitances in amplifiers vary. Bad capacitance matching has effect on high frequencies (problems on both frequency and phase responses).
    • Moving coil (MC): The cartridge has a fixed magnet and moving coil. The amplifier input is typically 100-1000 ohms in impedance and the amplification is typically around 20 dB higher than in MM inputs. When using MC cartridge the electrical matching to amplifier is essentia, and for this reason some preexpensive amplifier have adjustments to set the input resistance and capacitance values.
    • Crystal and ceramic pickups: Crystal and ceramic pickups an electric signal when made to bend. In piezoelectric pickups the head of the stylus is is inserted into the crystal or ceramic (a synthetic crystal). Crystal and ceramic pickups can only be used with with a separate special preamlifier control unit.
    • Capacitive cartridges: Literally hundreds of patent applications have been filed on such designs, and a few such pickups have actually been manufactured. The most successful of them is the Weathers, which is called a "capacitance" pickup. The Weathers pickup cannot be bought alone. You also need the Weathers box with the oscillator which feeds the unmodulated and detects the modulated current.
    Because the low signal levels from record player cartridge, the signalwires from the record player to amplifier can easily pick up noise.Most typical noise is mains frequency humming. The hum usually disappearswhen well shielded cables are uses and a separate ground wire is connected from the phono ground on the receiver to a phono goundingscrew point on the back of the amplifier. The ground wire grounds the tonearm pipe and metal chassis of thephonograph. The cartridge itself is ungrounded by design, with one side tiedto ground at the receiver end. This way the polarity of the cartridge can bereversed, or one channels' phase inverted if required for otherapplications, without losing signal.


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