ABSORPTION: Reverberation time and frequency pattern are governed by the amount of absorption present.
All materials absorb some sound and reflect some; rooms having highly reflective surfaces are said to be reverberant, a
characteristic which is decreased by making all the walls non-parallel. Rooms designed to reflect very little sound are called
|Material||125Hz||250Hz||500Hz||1 kHz||2 kHz||4 kHz||Acoustic Panelling||0.15||0.3||0.75||0.85||0.75||0.4||Acoustic Tiles||0.1||0.35||0.7||0.75||0.65||0.5||Brick||0.024||0.025||0.03||0.04||0.05||0.07||Carpet thin||0.05||0.1||0.2||0.25||0.3||0.35||Carpet thick with underlay||0.15||0.35||0.5||Chair padded dining||1.0||2.5||3.0||Chair upholstered||2.5||3.0||3.0||3.0||3.0||4.0||Concrete||0.01||0.01||0.02||0.02||0.02||0.03||Curtains||0.05||0.12||0.15||0.27||0.37||0.5||Curtains heavy with folds||0.2||0.5||0.8||Door wooden||0.3||0.15||0.05||Fibreglass 1in||0.07||0.23||0.42||0.77||0.73||0.7||Fibreglass 2in||0.19||0.51||0.79||0.92||0.82||0.78||Fibreglass 4in||0.38||0.89||0.96||0.98||0.81||0.87||Floor wood no joints||0.15||0.2||0.1||0.1||0.1||Floor wood blocks||0.05||0.05||0.1||Glass||0.03||0.03||0.03||0.03||0.02||0.02||Person seated||0.18||0.4||0.46||0.46||0.5||0.46||Plasterboard||0.3||0.1||0.04||Plaster on lathe||0.3||0.1||0.04||Plaster on brick||0.024||0.027||0.03||0.037||0.039||0.034||Plywood 3/4in||0.11||0.12||0.1||Plywood 3/16in on 2 batten||0.35||0.25||0.2||0.15||0.05||0.05||Wood 3.4in solid||0.1||0.11||0.1||0.08||0.08||0.11|
Reverberation can be adjusted by the amount and choice of materials to favour low or high frequencies, giving a warmer or brighter effect respectively. A high coefficient means high absorbtion hence low reverberation at the frequency.
ABSORBERS: In extreme cases absorbers can be fitted to walls to control certain frequencies.
Apart from adjusting reverberation time, resonances at specific frequencies can be controlled.
Absorbtion materials will strongly absorb a particular frequency when supported 1/4 of the wavelength from the wall. The percentage absorbtion can be as high as 85% compared to 10% at all other frequencies.
The thickness of materials determine low frequency absorbtion.
|25mm (1-inch)||51mm (2-inch)||76mm (3-inch)||102mm (4-inch)||127mm (5-inch)||152mm (6-inch)||2.2kHz||1.4kHz||800Hz||550Hz||450Hz||400Hz|
Different thicknesses of felt on a solid surface absorb uniformly down to the frequencies shown, below which absorbtion falls off at an approximate rate of 30% per octave.
BALANCED CABLE: A cable consisting of two insulated inner conductors with an outer screen. In an unbalanced system (RCA phono plugs) the screen is connected to the signal return at one end only, so as not to form part of the signal transference system.
BI-WIRING: Facility on some loudspeakers, enabling the connection of a second pair of loudspeaker cables. This allows for a separate cable and crossover for each drive unit. (see Star Earthing).
CAPACITOR: A component made of conducting plates separated by a dielectric. It is impermeable to DC and attenuated the flow of AC as the current frequency drops. They are often categorised by the type of dielectric used- polyester, polypropylene, mica, etc.
COAXIAL CABLE: A cable consisting of a single insulated conductor with an outer screen. The screen is connected at both ends as it carries the signal return.
CROSSOVER NETWORK: A circuit comprising capacitors, inductors and resistors that divides audio frequencies into two or more bands to drive amplifiers (active) or drive units (passive).
DAC (DIGITAL-TO-ANALOGUE CONVERTER): A circuit that reproduces the original analogue waveform from a digital signal. Separating the DAC from the transport is a good way of improving performance.
DAMPING FACTOR: A speaker cone tends to oscillate for several excursions after the electrical signal has ceased before coming to rest. The coil generates a voltage that produces a current and a magnetic field which opposes the spurious motion and so dampens it. The magnitude of the current, hence damping effect, depends upon the internal resistance of the amplifier output stage through which it must flow. This resistance is much lower than the rated impedance, 0.1 Ohm being typical. The damping factor is the speaker impedance divided by the amplifier source resistance. It ranges from 25 to 1000- the higher the better. Keeping loudspeaker cables as short as possible will help maintain a high damping factor, thereby improving definition
DIELECTRIC: A non-conducting material, an insulator.
DIGITAL INTERCONNECT: Cable connecting a CD Transport to an external DAC. It is important to understand that it is fundamentally different to an analogue interconnect- the tenet, keep your cables as short as possible does not apply, and infact could be detrimental. The smooth transference of a signal between a DAC and Transport requires a perfect 75ohm (110ohm AES/EBU) transmission line (which of course does not exist). Impedance discontinuities occur at junctions, principally the cable/plug, plug/socket and socket/circuit board at both ends. Every time a discontinuity is encountered, some of the signal is reflected back along the cable in the opposite direction (rather like ripples at the waters edge). If any of these reflections get back to the source, they corrupt it. A digital interconnect must be long enough to attenuate (loose within the resistance of the cable) all reflected signals. 1m should be considered a minimum length, and 1.5m optimum.
DIGITAL OUTPUT: Provided on some CD and DAT machines allowing for the connection of an external DAC. They usually take the form of a phono socket, although BNC and XLR connectors may be found. Some units may have digital optical outputs, this type of connection is usually best avoided.
DIN (DEUTCHE INDUSTRIE-NORME): The German industrial standard. In the audio industry governing plugs, sockets and general performance criteria. Din plugs are, thankfully, rare nowadays limited to older equipment. Although they are self cleaning their contact areas are so pitifully small they should be avoided like the plague
DRIVE UNIT: A radiating diaphragm whose motion results in the conversion of electrical energy into sound.
DYNAMIC RANGE: The difference (and hence the range) between the quietest and loudest sounds that can be simultaneously reproduced. Often the reason for an un-dynamic system is noise, which increses the noise floor and thereby reduces dynamic range. RFI is one of the chief sources of noise within a Hi-Fi.
EARTHING: If a piece of Hi-Fi equipment is supplied by a two core mains cable, it is what s know as double insulated. Double insulated components, usually, do not have earthed casings, which means from an RF screening point of view they are less effective at preventing high frequency noise gaining access to the circuitry. Earthing the case can bring about major improvements in low level resolution and clarity. Earthing can be achieved by simply connecting a wire from the case to an earth point in a convenient mains plug.
EMOTION: n. a pleasurable or painful condition of the mind which may accompany our sensations, memories or judgements; the faculty of feeling; a state of excited feeling or agitation. [L. emotio, fr. emovere, to stir]
F.E.P.: Extruded PTFE.
GOLDEN RATIO: If two dimensions are similar (a square room), the resonances will reinforce each other and give a strong emphasis
to all sounds at that frequency. A room that is a cube is even worse. Ideally, room dimensions should be such that all resonances and harmonics
of each are well spaced. The golden ratio to achieve this is 1:1.25:1.6. Any dimension should be a multiple of one or more of these, i.e. 1:2.5:3.2.
Non-parallel walls and bay windows reduce resonace effects and so could be considered desirable.
HARD WIRED: Another name for soldered. Most mains cables are merely mechanically clamped. Hard wired cables exhibit significantly enhanced signal transference and superior aging performance.
HEADPHONE UNIT: Some (usually power) amplifiers lack a 6.35mm jack socket and therefore a headphone facility. The headphone unit runs directly from the 4mm loudspeaker binding terminals and allows safe and very high quality headphone listening. Not suitable for NAIM amplification.
HEARING DAMAGE: The temporary reduction of hearing
sensitivity, as indicated by the increase of hearing threshold level, occurs after exposure to
loud sounds. This can become permanent if the exposure is prolonged. The louder the sound, the
shorter the exposure time to produce permanent impairment. Damage is greater if the sound
contains impulsive components caused by percussive elements in the source.
Exposure levels and times are regulated in industry. Maximum permissible levels are shown in the following chart;
|NOISE||EXPOSURE TIME||NOISE||EXPOSURE TIME||90dBA||8 hours||102dBA||30 minutes||93dBA||4 hours||105dBA||15 minutes||96dBA||2 hours||108dBA||7.5 minutes||99dBA||1 hours||111dBA||3.75 minutes|
|125dBA||Jet Aircraft taking off||110dBA||Pneumatic drill at 1m, wood working machinery||100dBA||Disco, some bars!||90dBA||Symphony orchestra playing fff||80dBA||P.A system, vacuum cleaner at 1m||65dBA||Speaking voice at 1m||60dBA||General office||55dBA||Whisper at 1m||35dBA||Quiet living room||15dBA||Quiet countryside||0dBA||Threshold of hearing|
HERTZ: A measure of frequency (sound), equal to a specific number of cycles per second. Named after the discoverer of radio waves. Multiples are, Kilohertz (kHz), Megahertz (mHz), etc.
IEC (INTERNATIONAL ELECTROTECHNICAL COMMISSION): An internationally recognised organisation for the establishment of standards for electronic products. Including the standard form 2 and 3 pin mains connector often used in Hi-Fi equipment. As a guide, electric kettles use a 3 pin (hot) IEC connector.
IMPEDANCE: In an AC circuit, the resistance to flow measured in ohms (W). Impedance may vary with the applied AC frequency.
LC-OFC: A very high purity Copper conductor, free of oxygen and possessing a long, linear crystal structure. Oxygen Free Copper has hundreds of crystal boundaries per centimetre. LC-OFC Copper crystals can be several metres long, resulting in a far purer sound quality.
LOW NOISE CABLE: Having a conductive plastic layer to reduce handling noise in operation. Guitar and microphone leads need to be of this type.
NICAM (NEAR INSTANTANEOUS COMPANDING AND MULTIPLEXING): A method of digitally encoding, transmitting and decoding a stereo signal with television pictures.
MAINS SUPPLY: If you are concerned with the quality of your mains, in the UK, you can contact your Regional Electricity Company (the address is on your bill), they have a statutory responsibility to maintain a supply within certain parameters. If you are unhappy with their response you can contact the Office of Electricity Regulation (OFFER) at; Hagley House, Hagley Road, Birmingham, B16 8QG, or Regent Court, 70 West Regent Street, Glasgow, G2 2QZ.
MAINS VOLTAGE: Domestic mains voltage in the UK is being slowly changed (as of 01/01/95) from 240v to 230v, for EC standardisation. Allowable tolerance is also changing from +/-6% to +/-10%.
MUSIC: n. the art of combining sounds or sequences of notes into harmonious patterns pleasing to the ear and satisfying to the emotions; melody. [Gk. musikos, pert to the muses]
PC SOUND CARD: Allows for true 16 bit stereo sound from a Personal Computer (PC). The card is an integral part of a multi-media PC or can be added to the ISA slot on the motherboard. If fed through a Hi-Fi the results can be stunning.
PERSONAL INFORMATION: We have never and will never pass on any customer details to anyone else. If you supply us with your E-mail address we may occasionally send you information.
PURE EARTH: Earth purity and integrity are crucially important if you aspire to a high definition system. A pure or technical earth will give you a significantly more relaxed, less grainy and more consistent performance. All you have to do is connect an additional earth wire from your consumer unit (fuse box), via 120 Amp CONQUEROR~SCL1000 (now available with a green/yellow earth sheathing, upon request, for the price of £4.00/m), or as thick an earth wire as possible to a vertically buried Copper pipe. Ideally the earth wire should be at least 6mm2 (31A) and the Copper pipe at least 30mm in diameter and 1.5m long (the larger the pipe, the more surface area it has, the better the earth- you can use more that one pipe if you wish). Care should be exercised connecting the cable and the Copper pipe, to ensure that the connection prevents the ingress of moisture that would corrode the contact with time. The area around pipe must be kept moist at all times to improve conductivity.There is one very important issue to concider before fitting a seperate earth for your Hi-Fi system, and that is, it is imperative that all equipment connected together share the same earth. This is because, most people have suffered sensitive equipment damage during lightning storms, or know someone who has. On the surface, power surges appear to be the culprit and usually receive the blame for this damage. The power system can carry high voltage surges (lightning), but there is a more likely cause.
RADIO FREQUENCY INTERFERENCE (RFI): High frequency noise picked up by cabling supplying your Hi-Fi system (both mains and signal, inside and out side your home). Its effect is often insidious, only being noticed by its absence. Effectively filtering RFI, removes graininess and improves focus and dynamics.
RESONANCE: The tendency for a mechanical or electrical device to vibrate at a particular frequency, governed by its mass and stiffness.
RGB (RED/GREEN/BLUE): The three separate colour signals that make up a TV picture. When connecting a video to a TV, RGB SCART will give the best picture quality.
SCART CONNECTOR: A 21 pin universal connecting cable/socket system used for audio/video components in Europe, to transmit RGB, composite video, S-VHS, mono and stereo sound. Also known as PERITEL or Euroconnector.
SCHUKO PLUG: European mains plug (DIN49441/CEE7). Two pins with two scrapping earth points. Nickel plated. N.B. this is the plug used in Europe instead of a UK 3 pin mains plug.
SCREEN: Electrical barrier composed of a conducting layer between signal carrying conductors. Prevents the transference of electromagnetic energy.
SPIKE: A high mains voltage surge of very short duration. Caused by many common occurrences such as the switching on or off of thermostats, or other current hungry equipment, load switching by the power companies and local lightning strikes. They cause short term power supply saturation, premature component ageing and in extreme cases, equipment failure (see VDR).
STAR EARTHING: The process whereby every component, in for instance a loudspeaker crossover, has a discrete signal return path back to the source. Bi-wiring (running two cables to each loudspeaker) is a rudimentary form of this, where the signal and signal return paths are separated for each drive unit crossover. Obviously to correctly star earth something with many components is difficult, but worthwhile. When properly executed, star earthing improves dynamics and openness and reveals another layer or two of resolution.
STP: Standard temperature and pressure. Meaning normal ambient temperatures and sea level pressure.
SURGES: Mains borne over-voltages lasting more than one cycle. Causes include the switching off or stopping of voltage hungry devices and load switching at substations. Lasting for several cycles they rob a system of both dynamics and detail, they cause general and progressive degradation and can lead to component failure (see VDR).
SKIN EFFECT: Describes the process whereby inductance increases with depth through a conductor, reaching a peak at its centre. Consequently, resistance is greatest at the centre resulting in a concentration of current flow at the surface. Expressed as a ratio of AC resistance to DC (Rac/Rdc), it is dependant upon frequency and conductor diameter and can be calculated thus;Rac 4d f Rdc
Where d is the diameter of the conductor in mm; and f is the frequency in mHz.
TELEFUNKEN (FIGURE8) PLUG: Also known as a shaver plug, a two pin connector is often found on CD players, especially those derived from Philips/Marantz designs.
TRANSPORT: The motor and laser assembly in a CD player. In a two box player, the Transport is usually separate from the DAC.
VOLTAGE DEPENDENT RESISTOR (VDR): A device whose resistance decreases with increasing voltage. Fitted across the Live and Neutral pins in a mains plug, it has an extremely high resistance at 240v and is therefore invisible. When a voltage spike or surge is encountered the VDRs resistance drops rapidly, thereby helping to maintain a more constant voltage.
WIRING: Below is a guide to the wiring configurations of various plug and socket arrangements;
|Pin 3||Right/Out of phase|
|5 PIN DIN|
|Pin 1||Not connected|
|Pin 3||Left/channel 1|
|Pin 4||Not connected|
|Pin 5||Right/channel 2|
|Pin 1||Right audio out|
|Pin 2||Right audio in|
|Pin 3||Left audio out|
|Pin 4||Earth audio|
|Pin 5||Blue ground|
|Pin 6||Left audio in|
|Pin 7||Blue video|
|Pin 8||Switching composite video/luma/chroma|
|Pin 9||Green ground|
|Pin 10||Intercom data line|
|Pin 11||Green video|
|Pin 12||Intercom data line|
|Pin 13||Red ground|
|Pin 14||Intercom data line|
|Pin 15||Red video|
|Pin 17||Composite video/luma/chroma ground|
|Pin 18||Blanking ground|
|Pin 19||Composite video/luma/chroma out|
|Pin 20||Composite video/luma/chroma in|
|Pin 21||Casting/socket Ground|
XLR PLUG: Plug and socket design used primarily in professional audio. The 3 pin version is slowly finding its way into domestic Hi-Fi equipment.